UK ISSN 0032–1400
PLATINUM METALS REVIEW
A Quarterly Survey of Research on the Platinum Metals and
of Developments in their Application in Industry
www.matthey.com and www.platinum.matthey.com
VOL. 48 APRIL 2004 NO. 2
Contents
Platinum Metals Review: E-Journal
46
By C. R. N. Clark; Editorial
The Transition Layer in Platinum-Alumina
47
By Peter Panfilov, Alexander Bochegov and Alexander Yermakov
Manufacture of Platinum Fibre and Fabric
56
By Kenya Mori
Iridium Oxide Sensors for Industrial Lubricants
Surface Finishing of the Precious Metals
58
59
A book review by A. S. Pratt
Building the Bridge to Hydrogen Cars
60
By Philip D. Chizek
Scotland’s First Fuel Cell Battery Powered Electric Vehicles
61
By Sinclair Gair
Palladium Colloids Stabilised in Polymer
62
By Bénédicte Thiébaut
The Most Commonly Used Platinum Group Metal Salts
63
By J. E. Gourd
Expanded Coordination Chemistry
64
A book review by Ann K. Keep
Palladium Oxide Sensitiser for LPG Detector
The Minting of Platinum Roubles: Part I
65
66
By Professor Christoph J. Raub
6th European Congress on Catalysis
70
By Reza Torbati
Light-Driven Alkane Oxygenation by Ruthenium(II)
The Minting of Platinum Roubles: Part II
71
72
By David F. Lupton
Abstracts
New Patents
Final Analysis: Safeguarding Thermocouple Performance
79
84
88
By R. Wilkinson
Communications should be addressed to: The Editor, Susan V. Ashton, Platinum Metals Review, [email protected]
Johnson Matthey Public Limited Company, Hatton Garden, London EC1N 8EE
Platinum Metals Review: E-Journal
www.platinummetalsreview.com
This edition of Platinum Metals Review is the
last one to appear in hard copy. From now on
the Journal will be published online. I am
pleased to mark this progressive change by paying a small tribute to what has already been a
long and illustrious history.
Since its inception in 1957 the Journal has
been unswerving in its commitment to the promotion of research into the platinum group
metals and the encouragement of authors all
over the world to write on this subject.
There is no question that this Journal is the
standard work on platinum group metals
research and development, and the very signifi-
cant growth in the platinum industry over these
past nearly 50 years is evidence of the success of
Platinum Metals Review.
When I joined Johnson Matthey, Platinum
Metals Review was just 5 years old. I published
some small articles in the sixties and have been
a fan ever since. Whereas I retire from Johnson
Matthey this year, I am sure Platinum Metals
Review can look forward to another 50 years with
total confidence. I wish it well.
C. R. N. CLARK
Dear Readers
We are now forging ahead with the new website for Platinum Metals Review. The centre piece
will be our E-journal, Platinum Metals Review,
with the papers and articles that you, our readers, communicate about your work. Indeed, you
and your research are our reason for being here.
As with the printed journal, the E-journal will
appear four times each year. The papers, the
website and the information under our control
will be all freely available.
We hope that over the years you have found
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The website will develop as new features are
progressively added. Features will aim to inform
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data resource, demonstrate the link between
bench and industrial process, discuss intellectual
property, good practice and common sense.
There will be links to where useful information
can be found and to sites advising on equipment
and procedures. This is all directed towards creating a resource for platinum metals users
Hatton Garden, London, April 2004
worldwide. We would encourage you to visit the
website, and we aim to provide an environment
that will persuade you to return. As our readers
are, by their natures, highly communicative, we
anticipate and welcome your comments. Indeed,
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Finally, it is a privilege to be associated with
this Journal. With my colleagues, Pavla White
and Keith White, I look forward to welcoming
you to our new website in the summer.
With our best wishes
Susan V. Ashton, Editor
Platinum Metals Review, Electronic ISSN: 1471–0676
Platinum Metals Rev., 2004, 48, (2), 46
Chris Clark is the Chief Executive of Johnson Matthey PLC. He
has been with Johnson Matthey for 42 years, much of this time
being involved with the platinum industry. He will be retiring
from Johnson Matthey at the end of July this year.
46
The Transition Layer in Platinum-Alumina
THE MORPHOLOGY AND PROPERTIES OF THE LAYER IN CRUCIBLES BETWEEN METAL AND CERAMIC
By Peter Panfilov
Urals State University, 620083 Ekaterinburg, Russia; E-mail: [email protected]
Alexander Bochegov and Alexander Yermakov
Ekaterinburg Non-Ferrous Metals Processing Plant, Lenin Avenue 8, 620014 Ekaterinburg, Russia
Platinum-based composites are potential materials to substitute for platinum in some
applications, for example, for containers in which to grow single crystal oxides. Ceramic
coated platinum is the best material for crucibles as: first, the cylindrical geometry is suitable
for coating with ceramic; second, the ceramic coating carries the basic mechanical loading,
with the platinum acting both as the heater and anticorrosive coating; and third, refining
this secondary platinum for recycling is neither a complicated nor expensive procedure. Plasma
evaporation of alumina onto platinum is a technology that can be successfully applied to
manufacturing commercial composite containers. In this paper the problem of cohesive strength
between Pt and Al2O3, and the morphology and properties of the transition layer between
the metallic matrix and the ceramic will be discussed.
As a container material for growing single crystals, platinum has to perform three functions:
[a] it must be inert to the scrap materials from
crystal making;
[b] as the metallic cylinder it must serve as the
heater during induction melting; and
[c] as the container material it must retain its optimal shape (generally cylindrical).
Experience has shown that it is the third function (retaining the optimal shape to determine the
mechanical strength of the container) which
requires the maximum amount of platinum. The
container wall thickness is not important for func-
tions [a] and [b], especially for [a] (1).
This paper describes how the mechanical
strength of the containers can be increased – not
by increasing the thickness of the platinum – but
by using platinum-based composites as the structural material (2, 3). Ceramic-coated platinum is a
potential high-temperature material for this use, as
it allows crucibles to be manufactured with less
platinum, but in similar sizes and with improved
properties (4, 5).
The evaporation of ceramic onto metal by
plasma methods may be considered an appropriate
commercial technology due to its simplicity and
Fig. 1 Composite
Pt-Al2 O3 crucibles; these are
manufactured by direct
plasma evaporation of the
ceramic onto the metallic
substrate.
The crucibles can have a
diameter up to 170 mm with
either a flat or spherical
base
Platinum Metals Rev., 2004, 48, (2), 47–55
47
Table I
Vicker’s Microhardness of the “Platinum” Side Opposite to the “Transition Layer” Side in the Initial State
and after Mechanical Testing of Metallic Samples Cut from Workpieces of Platinum-Alumina Crucibles at
Different Stages of Manufacture
Material,
state
tested
Pt
Ptsanded
Pt+Cer
Pt+Cer+An
Initial
state,
Tension
at 20ºC,
Creep at 1300ºC,
s = 50 MPa
MPa
MPa
grip, MPa
7.4
7.4
9.7
6.9
8.7
8.9
9.7
8.9
5.6
5.6
5.9
6.1
fracture, MPa grip, MPa
5.6
6.6
5.0
6.3
resulting lower costs (6). The composite crucibles,
shown in Figure 1, can be produced by a process
that includes four steps (7):
• The first step is the manufacture of platinum
crucibles that serve as the substrates for the evaporation of ceramic. A crucible is fabricated from
rolled platinum (Pt) sheet and can be up to 170
mm in diameter with a flat or spherical base.
• The second step is to process the crucible using
alumina particles under pressure or “sanding”
(Ptsanded). This forms a deep relief on the platinum
surface.
• In the third step the ceramic (Cer) (in this case
Al2O3) is applied to the crucible surface by plasma
evaporation (Pt+Cer).
• The final step is a stabilising anneal (An) of the
alumina coating at 1250ºC for 2 hours in air
(Pt+Cer+An).
Contrary to expectations, the cohesive strength
of such a platinum-alumina join is very strong. The
coating does not separate from the platinum even,
for instance, after using a composite crucible for
7000 hours to grow PbWO4 single crystals. Also,
the appearance of cracks in the ceramic did not
lead to separation of the coating from the substrate.
Using plasma technology therefore provides a
join of high cohesive strength, but the reason for
this high cohesive strength is not yet understood,
and the nature of the cohesion mechanism
between the Pt and Al2O3 is not clear. In this paper
the morphology of the transition layer at the interface between the metallic matrix and the ceramic
Platinum Metals Rev., 2004, 48, (2)
Creep at 1300ºC,
s = 70 MPa
5.6
7.1
5.2
6.1
Creep at 1300ºC,
s = 90 MPa
fracture, MPa grip, MPa
5.6
5.9
5.5
7.4
5.6
6.9
6.1
7.1
fracture, MPa
5.6
7.4
7.0
7.4
coating, and the effects of this layer on the
mechanical properties of platinum will be considered.
Experimental Procedure
It is well known that the adhesion characteristics of plasma coatings depend strongly on the
geometry of evaporation (or shape of the metallic
substrate) (6). In addition, the stress state of a
cylindrical surface is different to that of a layered
parallelpiped of comparable width and thickness
(8). Hence, data obtained from ceramic coated flat
samples would not explain the behaviour of a composite cylindrical container. Therefore, such
laboratory samples of Pt-Al2O3 composite were
not made for testing. Instead, test samples were cut
from the platinum substrate of composite containers (wall thickness 0.5 mm) taken during the four
stages of manufacture: Pt, Ptsanded, Pt+Cer and
Pt+Cer+An. These samples had a standard “double spoon” shape with a working area of 20 ´ 3
mm2. The ceramic layer (3 mm thick) was separated from the metallic matrix prior to cutting the
samples, as it was impossible to cut samples from
a ‘metal-ceramic’ crucible. Similar metallic samples
were also taken from containers which failed in
use. Both the back surfaces of the samples (“platinum” and “transition layer” sides) were studied in
detail in their initial states by optical and scanning
electron microscopes (SEM). Tensile tests were
carried out in a regime of semi-creep when the traverse rate was very slow: 0.1–1 mm h–1 (applied
stresses of 50, 70 and 90 MPa) at 1300ºC in air,
48
while some of the samples were stretched at room
temperature (at a traverse rate of 1 mm min–1 ).
After that, their back and fracture surfaces were
again studied.
Clearly, the information obtained cannot
directly characterise the mechanical behaviour of
a Pt-Al2O3 composite container, but it can allow
an understanding of the adhesive mechanism
between the platinum and the alumina coating.
(a)
Morphology of the Transition Layer
between Pt and Al2O3
As the platinum crucible has been pressed out
of rolled sheet without intermediate recrystallisation annealing, the platinum substrate is in a
deformed state, see Table I. Treating this platinum
surface with alumina particles (~ 300 µm in size)
leads to the appearance of a relief consisting of
approximately flat areas oriented to the substrate
plane at arbitrary angles. The shapes and sizes of
these regions are similar to those of the alumina
particles used for sanding the platinum. The depth
of the relief (~ 30 µm) also correlates with the particle size, as long as the work-hardening of the
platinum, which prevents the alumina particles
from penetrating into the metallic matrix, is taken
into account. There are two kinds of alumina
inclusions in the sanded platinum: large and small.
On SEM images, they appear as dark regions, see
Figure 2(a). The dimensions of the large inclusions, ~ 20–30 µm, correspond to the pyramidal
ends of alumina particles used for sanding.
Therefore, the large inclusions may be considered
to be the sharp tips of particles which have been
stuck into the metallic matrix.
The average size of the small inclusions is ~ 1
µm. Large and small inclusions are uniformly distributed on the surface; their positions are not
connected with the distribution of surface defects
caused by preliminary processing of the surface.
Despite the appearance of the relief, sanding does
not influence the microhardness of the “platinum”
side of the samples because of the considerable
thickness of the crucible walls (Table I).
After the evaporation of alumina and the separation of ceramic from the substrate, particles of
Al2O3 are observed on the platinum surface. The
Platinum Metals Rev., 2004, 48, (2)
(b)
(c)
Fig. 2 Surface of the transition layer between Pt and
Al2 O3 at different stages in the manufacture of composite
containers:
(a) Ptsanded sample
(b) Pt + Cer sample
(c) Pt+Cer+An sample
Black areas are Al2 O3 particles inserted into platinum
average size of the large inclusions has increased to
~ 50 µm, see Figure 2(b), although their quantity
per unit area of surface remains the same. By contrast, the dimensions and concentration of the
49
Fig. 3 The coarse grained structure of the platinum
surface in a composite crucible after a stabilising anneal
(1250ºC for 2 hours, in air) at the Pt-Cer-An stage
Fig. 4 Scrap (PbWO4) areas in the transition layer
between Pt and Al2 O3 of a damaged composite crucible
small inclusions have not changed. The microhardness of the “platinum” side in the Pt+Cer
samples has considerably increased, see Table I.
The stabilising anneal of the ceramic has no
influence on the size of both kinds of alumina
inclusions or their distribution on the surface, but
“jogs” on the surface becomes round or fused, see
Figure 2(c). However, the microhardness of the
“platinum” side has decreased in comparison with
the Pt and Ptsanded samples (Table I). A coarse
grained structure, in which all the crystallites are in
the deformed state, appears on the “platinum”
side, see Figure 3, while features of recrystallisation, such as grain boundaries or a new kind of
relief, do not appear on the rough “transition
layer” side. After evaporation of the ceramic and
its stabilising anneal, the character of the distribution of the alumina inclusions on the surface
remains the same.
Platinum Metals Rev., 2004, 48, (2)
The results obtained are important for understanding the cohesion mechanism between
platinum and alumina in composite crucibles manufactured by plasma technology. The main feature
is the “point”, “fragmentary” or “discontinuous”
contact of the Al2O3 with the transition layer (9).
Because of such a join, both the environment and
the melted scrap could percolate between the
metal wall and the ceramic coating, see Figure 4.
However, this circumstance does not affect the
usefulness of the containers. Indeed, the scrap
never chemically reacts with the walls of the crucible, and the level of mechanical stress due to
scrap percolation between wall and coating is not
sufficient to break the cohesion of the join.
Moreover, experience has shown that separating
the ceramic from the platinum in used crucibles
requires as much effort as in new ones, and the
number and size of the large alumina inclusions in
the platinum is the same in both cases. It should be
particularly noted that small inclusions of alumina
are absent on the samples.
The alumina particles either do not chemically
react with platinum, or, if reactions do occur then
the region where it happens is so thin that it cannot be detected by conventional SEM or X-ray
techniques. Therefore, the join between the platinum and alumina may be considered as
(a)
(b)
Fig. 5 The back surfaces (“platinum” side) of samples
after tension at 20ºC: no necking is observed:
(a) Pt sample; (b) Pt+Cer+An sample
50
“mechanical” when the sharp ends of the ceramic
particles penetrate into and remain in the metallic
matrix. The large inclusions serve as anchors for
the ceramic coating which “glues” to them during
plasma evaporation. No joining of alumina to platinum is revealed in other places, although the
ceramic replicates in detail the surface of the transition layer. The increase in size of the large
inclusions, the preservation of their numbers and
character of distribution on the surface after evaporation of the ceramic agree with this supposition.
On the other hand, small inclusions can play the
role of second phase particles which increase the
yield stress of the metallic matrix by blocking dislocation motion as it takes place in dispersion
strengthened metals.
(a)
(b)
Mechanical Properties of Platinum
with a Transition Layer on the Surface
Identical mechanical behaviour is inherent in all
the materials: Pt, Ptsanded, Pt+Cer, Pt+Cer+An at
room temperature (10). Samples fail after ~ 3–5%
elongation, and no necking is observed on their
back surfaces, see Figure 5. Localisation of plastic
deformation takes place near fracture surfaces, but
happens in a very narrow region, see Figure 6. This
is very unusual behaviour for a pure f.c.c. metal,
which should have high plasticity (11). On the
other hand, analysis of fracture surfaces (where
necking to a line occurs even in the most strength-
Fig. 6 Back surfaces near the fracture place of the
samples after tension at 20ºC:
(a) Pt sample; (b) Pt+Cer+An sample (“transition layer”
side)
ened material, such as Pt+Cer, see Figure 7) shows
that all the samples are in a ductile state. The
results for the Pt samples (Table II) confirm metallographic observations and measurements of
Fig. 7 Fracture
surface of a
Pt+Cer sample
after tension at
20ºC.
This sample
shows the
material is in a
ductile state –
as analysis of
all the fracture
surfaces has
shown
Platinum Metals Rev., 2004, 48, (2)
51
Table II
Mechanical Properties of the Platinum Matrix at Different Stages of Preparation of “Pt-Al2O3” Composite
Material
Pt
Ptsanded
Pt+Cer
Pt+Cer+An
Yield stress (s0.2)
at 20ºC,
MPa
Strength (sB)
at 20ºC,
MPa
Creep-rupture life
at 1300ºC,
s = 50 MPa,
hours
Creep-rupture life
at 1300ºC,
s = 70 MPa,
hours
Creep-rupture life
at 1300ºC,
s = 90 MPa,
hours
55
100
130
65
155
170
235
160
18
18
10
13
4
4
1.5
3
1.5
2
1
1.5
microhardness, indicating that the metallic matrix
had been hardened before test: yield stress is 55
MPa.
Sanding the platinum increases the yield stress
by a factor of two (100 MPa), but has practically no
effect on the strength and microhardness of the
Ptsanded samples (170 MPa and 8.9 MPa, Table II
and Table I, respectively) in comparison with Pt
samples. This is normal behaviour for f.c.c. metals,
as the volume of a sample generally determines its
strength, while the surface makes a significant contribution to the yield stress of a metallic sample. In
practice, the sanded surface does not change its
morphology up to the fracture area, and the alumina inclusions disappear only in the vicinity of the
fracture surface because of local plastic flow of the
material, see Figure 6(b). Evaporation of ceramic
(a)
(b)
Platinum Metals Rev., 2004, 48, (2)
causes a big rise in the microhardness (9.7 MPa,
Table I) and yield stress (130 MPa, Table II) in the
Pt+Cer samples, and in doing so the strength of
the material increases by ~ 100 MPa, as in the Pt
samples and the Ptsanded samples, while the microhardness of their “platinum side” after mechanical
test remains the same (9.7 MPa, Table I). A stabilising anneal decreases the initial microhardness
and yield stress for Pt+Cer+An samples (6.9 MPa
and 65 MPa, respectively). After tensile testing, this
parameter becomes 8.9 MPa and the strength
reaches 160 MPa, respectively. Despite differences
in some mechanical properties (s0.2, sB and HV), the
morphology of the fracture and back surfaces of the
Pt+Cer and Pt+Cer+An samples does not change.
Observation of the behaviour of the samples at
1300ºC in air has shown that they are typical of
f.c.c. metals at high
temperatures: the
applied stress and
roughness of the
back surface determine the creeprupture life (tlife) of
the sample under
load (11). In practice, at high stress
(90 MPa), the tlife
and the morphology of the back
Fig. 8 The back surfaces
surface near the
(“platinum” side) of
samples after the creep test
fracture zone do
at 1300ºC, s = 90 MPa:
not depend on the
(a) Ptsanded sample
(b) Pt+Cer+An sample
type of material
52
(a)
(b)
Fig. 9 The back surfaces near the fracture place after creep tests at 1300ºC, s = 90 MPa: (a) Ptsanded sample
(b) Pt+Cer+An sample
(Table II, and Figures 8 and 9). Lowering the
applied stress increases the sensitivity of tlife to the
state of the surface layer (Figures 10 and 11). For
example, the size and number of neck regions in
the samples start to grow at middle and low
applied stresses. This causes an increase in the area
(a)
Fig. 10 The back
surfaces (“platinum”
side) of Pt samples
with transition layer
after the creep test at
1300ºC, s = 70 MPa:
(a) Ptsanded sample
(b) Pt+Cer+An
sample
(b)
(a)
(b)
Fig. 11 The back surfaces near the fracture place after creep test at 1300ºC, s = 70 MPa: (a) Ptsanded sample;
(b) Pt+Cer+An sample
Platinum Metals Rev., 2004, 48, (2)
53
Fig. 12 The fracture surface of dispersion
strengthened platinum-alumina wire (creep
test in air at 1300ºC).
At this elevated temperature dispersion
strengthened platinum shows necking on
the back surface but transcrystalline
cleavage on the fracture surface.
(The black mark, lower left on the
specimen is detritus)
near the fracture zones where alumina inclusions
are absent. The tlife for Pt at 70 MPa and 50 MPa
(4 and 18 MPa, respectively) are more than 1.5–2
times greater than for Pt+Cer and Pt+Cer+An
samples though are the same as the Ptsanded samples
which also have rough surfaces with implanted alumina particles.
Thus, the geometrical characteristics of the surface relief and the distribution of alumina
inclusions are the same in all three cases. This
effect is connected with the structure of the surface layer in the samples, where the deep relief and
the second phase inclusions (here, Al2O3 particles)
induce the fracture process, including the localised
plastic deformation in the platinum matrix. The
difference between Pt+Cer, Pt+Cer+An and
Ptsanded samples may be explained by the fact that
in the first two materials (Pt+Cer and Pt+Cer+An)
the transition layer is dispersion strengthened platinum, which displays high strength and semi-brittle
fracture mode at high temperatures, see Figure 12,
whereas in the Ptsanded material the surface layer
only contains mechanically penetrated alumina
particles. Indeed, the regime of heating the platinum substrate during evaporation of alumina is
similar to that of the temperature treatment of
platinum strengthened by oxide particles. Despite
this, the fracture surfaces of all the samples investigated at high temperature have the same
morphology attested earlier as necking to a line.
Platinum Metals Rev., 2004, 48, (2)
Discussion
These experiments have shown that the transition layer between the platinum and the alumina
coating (30 µm in depth) is formed in stages by
sanding and plasma evaporation of ceramics. The
transition layer contains small (~ 1 µm) and large
(~ 20–50 µm) alumina inclusions and possesses a
rough surface on the ceramic side. The Al2O3 particles have penetrated into the platinum matrix
during the sanding stage, but this treatment has not
changed the mechanical behaviour of the platinum
either at room or elevated temperatures.
Differences begin to show only after the evaporation of alumina, when the sanded surface has
been heated to a temperature close to the alumina
melting point then cooled very quickly to
300–400ºC. Performing a stabilising anneal is
important for the mechanical properties of the alumina coating. However, its influence on the
morphology and properties of the transition layer
is negligible. In performing a stabilising anneal it
should be noted that the surface layer, enriched by
oxide particles, causes plastic deformation in the
recrystallised grains of platinum.
Dispersion Strengthened Platinum
An assumption that the transition layer is a thin
film of dispersion strengthened platinum can
explain the results. Indeed, the properties of dispersion strengthened metals do not depend on
54
annealing after oxide particles have been formed
(2, 3), and the inclusions are permanent sources of
thermomechanical stress, which induce plastic
deformation in the metallic matrix. The thermal
stability and high strength of the dispersion
strengthened surface layer also become apparent
under middle and low tensile stresses at high temperature. Due to these, the lifetimes of the Pt+Cer
and Pt+Cer+An samples decrease compared to
the sanded platinum.
The thin film of dispersion strengthened platinum, between the metallic matrix and the ceramic
coating, with its rough surface containing large
Al2O3 inclusions, can explain the high cohesive
strength of the join between the platinum and alumina. The evaporated ceramic layer “glues” to
these inclusions, while in other places it only covers the metal (without adhesion).
When the crucible is cooled, after a crystalforming procedure has been completed, gaps
appear in places between the ceramic and the
metallic matrix; this is due to the difference in
thermal expansivity for these materials: as the thermal expansivity for dispersion strengthened
platinum is less than that for the pure metal.
However, these gaps close during heating, when
the container is being used, and the relief on the
transition layer should facilitate the lowering of the
cleaving stresses at the boundary between metal
and ceramic (8).
As a result, the thermomechanical stresses are
effectively suppressed due to the morphology of
the transition layer, which forms simultaneously
with plasma evaporation of the ceramic. Using
these Pt-Al2O3 composite containers has shown
that such a metal-ceramic join is very resistant to
the action of thermomechanical stress. However,
it should be noted that growing single crystals is a
process where the level of fatigue stress is minimal. Perhaps, this is a third reason for high
cohesive strength in this join. An alumina coating
would not be considered as suitable corrosion protection for a metallic substrate. However, this does
not affect the service characteristics of these composite containers, as platinum, due to its high
chemical inertness, does not need protection from
either molten scrap or air.
Platinum Metals Rev., 2004, 48, (2)
Acknowledgements
We would like to thank Vladimir Cheremnykh and
Alexander Mazaletskii for their help in this work. The Russian
Foundation for Basic Research supported part of this project.
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p. 162 (in Russian)
10 P. Panfilov, A. Yermakov and A. Bochegov, in
“Proc. Second Int. Conf. Fracture and Monitoring
of the Mechanical Properties of Metals”,
Ekaterinburg, 26–30 May, 2003, CD-ROM (in
Russian); http://www.imach.uran.ru/conf/metall
11 R. W. K. Honeycombe, “The Plastic Deformation
of Metals”, Edward Arnold, London, 1968, p. 408
The Authors
Peter Panfilov is a Senior Scientist in the Institute of Physics and
Applied Mathematics of the Urals State University at Ekaterinburg
(Russia). His scientific interests are the mechanisms of plastic
deformation and crack growth in solids. Since 1986 he has been
collaborating with scientists and technologists at the Ekaterinburg
Non-Ferrous Metals Processing Plant on the problem of brittle
fracture and processing of refractory platinum group metals and
platinum base materials.
http://www2.usu.ru/physics/conden_state/
Alexander Bochegov is a Development Project Manager in the
Ekaterinburg Non-Ferrous Metals Processing Plant (Russia). The
fields of his research activities are protective coatings on metallic
materials and the manufacture of ceramic crucibles for melting.
Alexander Yermakov is the Director for Research and Development
of the Ekaterinburg Non-Ferrous Metals Processing Plant
(Russia). His scientific interests are metallurgy and the
processing of platinum group metals.
55
Manufacture of Platinum Fibre and Fabric
A TECHNICAL NOTE ON AN INTERESTING MATERIAL, SOME PROPERTIES AND USES
By Kenya Mori
Technical Administration Department, Tanaka Kikinzoku Kogyo K.K., Technical Center, 2-73 Shinmachi, Hiratsuka,
Kanagawa 254-0076, Japan; E-mail: [email protected]
Since 1996, Tanaka Kikinzoku Kogyo K.K. has been producing flocculate platinum fibre and
non-woven fabric made from this fibre. The background to the production of this material is
briefly described. Flocculate platinum fibre and fabric are currently used as filtering materials
in filtering applications that require both heat and chemical resistance. The platinum fibre
and fabric are also finding application as electrically conductive fillers for porcelain enamel.
Like gold, silver, and copper, platinum can be
reshaped mechanically, without thermal treatment.
Taking advantage of this characteristic, fine platinum fibre has been produced by repeated
multi-core wire drawing processing using a combination of platinum wire with copper pipe. This has
resulted in the formation of fibre – fine wire – having diameters of up to 0.1 mm (1). Figure 1 shows
platinum wire pieces from which the copper has
been removed.
Platinum Fabric Made from
Platinum Fibre
A length of multi-core wire combining platinum and copper was cut into pieces 1 mm in
length. The copper was then removed to produce
short platinum fibres having a diameter of 0.1 mm.
These fibres were then dispersed in water and filtered to form a non-woven “fabric”. The nonwoven platinum “fabric”, made from the 0.1 mm
Fig. 1 Multi-core drawn platinum wire approximately
1 mm in diameter. As an indication of the scale, one of
the dashes that make up the dotted white line at the
bottom of the micrograph is 10 mm long
Platinum Metals Rev., 2004, 48, (2), 56–58
fibre, was then heat-treated at 650ºC to strengthen
it – platinum begins to melt at 700ºC. Figures 2
and 3 show heat-treated platinum fibres. Despite
the classification of the filter components as heatresistant materials, the micrographs suggest that
the maximum working temperature for the filter is
600°C.
The separation characteristics of a non-woven
fabric filter composed of platinum fibres 0.1 mm in
diameter was assessed at the Matsumoto
Laboratory, Division of Materials Science and
Chemical Engineering, Faculty of Engineering,
Yokohama National University. Test samples had
specifications: basis weight (weight per unit area of
filter) of 210 to 830 g m–2; thickness of 0.09 to 0.34
mm; and porosity of 88 to 90%. The Table gives
specifications of the fibre in detail.
The following results were found:
[i] The effects of basis weight on the maximum
fine pore diameter, and the results of measuring
the maximum fine pore diameter by the bubble
point method, indicated that the maximum fine
pore diameter was ~ 1 mm. The maximum fine
pore diameter varied between 1 and 2 mm with low
basis weights.
[ii] The effects of the basis weight on the mean
fine pore diameter, and the results of measuring
the mean fine pore diameter by the transmission
method, indicated that the mean fine pore diameter was ~ 0.35 mm, regardless of the basis weight.
[iii] The variations in filtration pressure and the
percentage of particles rejected over time: the filtration experiment involved using ultrapure water
56
Parameters of Platinum Fabric Made from Platinum Fibre
Sample number
Thickness, mm
1
2
3
4
5
6
7
8
9
10
0.1
0.1
0.35
0.35
0.17
0.17
0.16
0.17
0.15
0.18
with suspended particle contaminants from the
environment. In the dispersion media, particles
having diameters of 0.1, 0.15, 0.2, 0.3 and 0.5 mm
were counted with a particle counter. Over time,
more than 95% of particles having a diameter
greater than 0.1 mm were filtered and removed
from the water. Nevertheless, the filtration pressure remained virtually constant, and no
significant increase in filtration pressure (considered to indicate a transition from depth-type
filtration to cake filtration) was observed. This
may be due to the high porosity (88 to 90%) of the
filter and thick depth-type filtration material.
These results were compared with those of
other material filters. The porosity of materials
that have a mean fine pore diameter of less than 1
mm and which are widely used, was 30% or less,
while the porosity of the 0.1 mm diameter platinum
fibre filters reached 90%, as described above. Such
high porosity for the platinum fibre filter may be
due to a combination of factors: low filtration
pressure loss, less-pronounced pressure increase,
and superior filter characteristics. In addition,
despite a maximum working temperature of
600ºC, the filter is significantly resistant to heat
and exhibits the corrosion resistance that is
expected of platinum materials. However, due to
high cost, this filter is currently used only in special analyses, and in minute quantities.
The potential application as electrically conductive fillers for porcelain enamel was suggested by a
porcelain enamel manufacturer (2). In this application, platinum fibre is described as being used in
Platinum Metals Rev., 2004, 48, (2)
Porosity, %
90.2
90.2
88.8
88.9
88.5
88.4
87.8
88.5
89.1
89.0
Basis weight, g m–2
210
210
837
832
418
423
418
420
348
423
glass-lining materials, which are utilised as insulating material for glass-lined devices used by the
chemical, pharmaceutical and food industries.
Fig. 2 Heat-treated platinum fibre of diameter 0.087 mm.
The fibre has been heated at 650ºC for 30 minutes in air;
melting only occurred at places where the fibres touched.
Scale: one of the dashes that make up the dotted white
line at the bottom of the micrograph is 1 mm long
Fig. 3 Heat-treated platinum fibre of diameter 0.087 mm.
The fibre was heated for 30 minutes at 700°C in air;
melting occurred.
Scale: one of the dashes that make up the dotted white
line at the bottom of the micrograph is 1 mm long
57
These materials have volume resistivity of 1 ´ 1013
to 1 ´ 1014 W cm. Thus, agitation in nonaqueous
solutions containing organic substances results in a
significant buildup of excess electric charge over
leak charge. This can result in static charges of several tens of thousand or hundreds of thousand
volts that could lead eventually to damage or
explosion of the glass-lining materials, even if the
glass-lined devices are electrically earthed. It is
standard practice to embed or wind platinum or
tantalum wires in or around the glass lining materials, but such treatment primarily has a local effect
and is inadequate.
An example in (2) describes how the addition of
0.5 wt.% of platinum fibre of diameter 0.5 mm and
length 2 mm to porcelain enamel reduced the volume resistivity to 1.3 ´ 103 W cm. This can
effectively prevent electrostatic buildup. If, howev-
er, platinum powder is used, 20 wt.% of platinum
powder must be added to achieve a volume resistivity of 4.7 ´ 103 W cm.
A container that had to be glass-lined every
three months to repair damage caused by static discharge was replaced with a container made of
electrically conductive enamel, using the said
method. After five years, the container remains
serviceable and exhibits no problems.
References
1
2
S. Shimizu, K. Mori and E. Sakuma, Japanese Appl.
11-226,627; 1999
Y. Iizawa and M. Akazawa, Japanese Appl. 10081,544; 1998
The Author
Kenya Mori is a Chief Researcher at TKK’s Technical Center in
Kanagawa. His main professional interests are in developing
precious metals for industrial materials.
Iridium Oxide Sensors for Industrial Lubricants
Engine oil lubricates and protects engines against
wear. Engine oils comprise a base oil and additives (1)
to improve the performance and long term stability of
the oil, such as antioxidants, antiwear and corrosion
inhibitors, detergents (surfactants), dispersants and
viscosity modifiers. The working life of any engine oil
or industrial lubricant may depend on its base oil formulation and the additives, and the engine size and its
operating conditions.
In use, engine oils change chemically due to oxidation and contamination by ethylene glycol, fuel,
soot, water, worn metal, etc. Industrial lubricant is
degraded by exposure to high temperature, air, alcohols, glycol, NOx and water. The additives interact
with both the oil contaminants and oxidative byproducts of oil degradation to render them harmless.
However, continuous monitoring of the chemical
condition and degradation of the oils, by an online
sensor to indicate the necessary oil changes, could
make engines more efficient and safer. Engine oil
breakdown is closely related to the level of acidity:
increase in total acid number (TAN) (oxidative degradation), and level of basicity: decrease in total base
number (TBN) (degradation of antioxidants, dispersants and detergents), in the oil.
Acidity/basicity measurements by potentiometric testing is standard practice and iridium oxide
(IrO2) shows promise for measuring pH range and
sensitivity, ion and redox interference, and hysteresis effects. Now, a team from Case Western Reserve
University and the Lubrizol Corp., U.S.A., have run
Platinum Metals Rev., 2004, 48, (2)
tests with chronopotentiometric (CP) sensors having
IrO2 as working electrode, and have detected TAN
and TBN in a diesel oil (2). The sensors were both
conventional (a macro-scale) and miniaturised
(microelectromechanical system (MEMS)) devices.
In diesel oil drains the sensors showed good correlation between the TBN and TAN numbers and
their individual voltage outputs. Conventional IrOx
sensors displayed greater sensitivity to changes in
TAN and TBN than the MEMS sensors.
A CP sensor (a “melt Ir oxide sensor”) consisting
of an Ir wire electrode, oxidised in a Li2CO3 melt to
form a LixIrOy film on its surface, had a large increase
in sensitivity due to the LixIrOy responding to carboxylic acids, and also to esters through a second
surface reaction catalysed by Li.
The sputter-formed CP sensor gave a better
response to oxidative degradation of oil due to its
higher sensitivity to ketones and carboxylic acids. The
differences in reaction mechanisms between the Ir
oxide and the components of the solution gave opposite responses to changes in basicity in aqueous and
non-aqueous systems. However, as long term stability and durability is a problem it is concluded that
work is needed to improve design and fabrication.
References
1
2
A. J. J. Wilkins, Platinum Metals Rev., 2003, 47, (3),
140
M. F. Smiechowski and V. F. Lvovich, Sens. Actuators
B: Chem., 2003, 96, (1–2), 261
58
Surface Finishing of the Precious Metals
ELECTRODEPOSITION OF THE PRECIOUS METALS: OSMIUM, IRIDIUM, RHODIUM, RHENIUM, RUTHENIUM
BY TERRY JONES, Finishing Publications Limited, Stevenage, U.K., 2003, 165 pages,
ISBN 0-904477-22-4, £30, U.S.$ 60; post & packaging free in the U.K., £10 Rest of the World
This compilation of review papers written by
Terry Jones describes the electrodeposition and
electroless deposition of the metals: rhodium (Rh),
ruthenium (Ru), iridium (Ir), osmium (Os) and rhenium, from liquid media (primarily aqueous and
molten salt). The book is divided into six chapters,
with Chapter 1 being an “Introduction to Plating
of the Rarer Precious Metals”. Each metal has a
chapter which begins with a brief account of its
plating history. Only the four platinum group metals are highlighted in this review.
The longest chapter, Chapter 2, deals with Rh
plating which only began commercially in the late
1920s, possibly due to the high cost and the many
processes available. Rh coatings became more
popular for industrial and decorative use in the
1930s and 1940s, for instance, silver-plated searchlight mirrors were Rh plated. Rh electrodeposits
are hard, tarnish-free, wear and corrosion resistant
and Rh has a very high melting point. All the metals share these properties to varying degrees.
Rhodium is very resistant to acidic attack, being
insoluble in aqua regia, in hot concentrated HCl and
in HNO3. It only dissolves in hot concentrated
H2SO4 and in fused KHSO4. On heating, it decomposes readily to finely divided metallic Rh sponge,
“Rh black”, which is a starting material for many
Rh compounds.
Modern Rh plating solutions are based on sulfate and phosphate electrolyte. Rh sulfate concentrate is prepared from Rh black. Rh phosphate
concentrate is produced from Rh hydroxide.
Plating bath performance depends on the preparation sequence. The quality of Rh electrodeposits
can be greatly improved by including certain additives in the electrolytes; for example, sulfonic acids
improve brightness; selenium works as an antistress agent; and crack-free deposits have been
obtained by adding a mixture of H2SO4, sulfamic
acid, thallium nitrate and various sulfonic acids.
Data on the properties of the coatings are given.
Platinum Metals Rev., 2004, 48, (2), 59
Chapter 3 deals with Ru electrolytes, which are
generally derived from RuCl3. Ru electrolytes are
acidic and are operated at high temperature so will
corrode most substrates before electrodeposition
begins. Thus, substrates should be pretreated, for
example, by a gold flash prior to Ru plating.
Chapter 4 relates to electrolytes for Ir plating. Ir
has a number of industrial applications, most
notably being as a hardening constituent in Pt. PtIr alloys (for jewellery use) are harder and stiffer
than pure Pt. Ir is used in Pt-10%Ir thermocouple
junctions, and as anode coatings. Processes for the
aqueous electrodeposition of Pt-Ir, fused salt electrolyte plating of Ir and Pt-Ir deposits and nonaqueous Ir coating of graphite are described. Metal
treatments prior to Ir plating are given.
Osmium is not thought of as an electroplating
material. However, Chapter 6, describes Os electrodeposits as very hard and very wear resistant.
With the highest work function known and a high
melting point, Os was used in thermionic valves. It
has high resistance to chemical attack by strong
acids, but dissolves in aqua regia, molten alkalis and
oxidising fluxes. Electroplating processes with Os
sulfamate electrolyte, Os hexachloro-osmate and
Os nitrosyl complex/sulfamate are reviewed.
The author has spent many years in the metal
finishing industry. In his book he provides practical information on many processes and lists the
optimum conditions to obtain successful deposits
for various plating processes. He gives extensive
details of the properties of the deposits. The book
is well supported by tables, figures, and by
literature and patent references. Supplementary literature has been added at the end of each chapter
A. S. PRATT
for up-to-date reading.
The Author
Allin Pratt is a Principal Scientist in the Innovation Group at the
Johnson Matthey Technology Centre. His main interests are the
application of metallurgy and materials science to new areas of
research as well as conventional applications in materials,
catalysis, biomedical applications, and renewable energy systems.
59
Building the Bridge to Hydrogen Cars
By Philip D. Chizek
Ford Motor Company, Fuel Cells and Hydrogen Vehicle Programs, Research & Advanced Engineering, SMT Lab I,
15050 Commerce Drive North, Dearborn, MI 48120, U.S.A.; E-mail: [email protected]
Ford is working on a project to link the technology of its current gasoline- and diesel-fuelled fleets
to evolving hydrogen technology. Project concepts
of energy, mobility and the future are represented
by the vehicles described below. The technologies
build off each other, combining efforts to produce
environmentally-sound vehicles for the future.
Escape Hybrid – Energy
The Escape Hybrid is Ford’s first full hybrid
vehicle. It can run on either its gasoline engine or
its electric battery – or both together – depending
on the driving situation. It has an acceleration performance similar to a V-6 engine and achieves
significant fuel economy and a range increase over
the current gasoline-powered Escape. It is Ford’s
cornerstone vehicle to bridge from traditional
vehicles to future hydrogen vehicles.
Hydrogen Hybrid Research Vehicle (H2RV)
– Mobility
Using technology from the hybrid vehicle and
combining an internal combustion engine powered
by hydrogen and boosted by a supercharger, the
H2RV stands next in line as Ford works toward
replacing gasoline vehicles. Ford are the only car
manufacturer to have successfully developed the
powertrain combination of hydrogen and electric
charge, along with the patented Modular Hybrid
Transmission System, in a car (1).
Focus Fuel Cell Vehicle (FCV) – The Future
In combining the improved range and performance of hybrid technology with the overall benefits
of a hydrogen fuel cell, the Focus FCV completes
the vehicles in development that look towards the
next decade. The fuel cell engine converts chemical energy into electrical energy via hydrogen and
oxygen to power the electric drive motor. This
results in a Zero Emissions Vehicle (ZEV). Water
and heat are the only tailpipe emissions.
Reference
1
Ford, U.S. Patents 6,176,808; 2001, 6,655,989; 2003,
and 6,585,066; 2003. U.S. Patents related to controls:
6,364,807; 2002, and 6,600,980; 2003
The Author
Dr Chizek is the Marketing Manager for Fuel Cells and Hydrogen
Vehicle Programs within the Ford Motor Company. His main
professional interests lie in the advancement of the hydrogen
economy through the development of hydrogen-based vehicles’
programs at Ford. He began working on advanced planning of the
Hybrid Electric and Fuel Cells projects in early 1999. He is fully
involved in strategic planning and customer insight development
for the next generation of hydrogen vehicles.
The Focus Fuel Cell Vehicle (FCV)
This Ford vehicle combines the
improved range and performance of
hybrid technology with the overall
benefits of a hydrogen fuel cell (it has
up to two to three times the fuel
economy of a ‘normal’ gasoline
engined vehicle). The Ballard Mark
900 series PEM fuel cell provides the
electrical power for the electric drive
motor. This ZEV (Zero Emissions
Vehicle) produces only water and
heat as tailpipe emissions
Platinum Metals Rev., 2004, 48, (2), 60
60
Scotland’s First Fuel Cell Battery Powered
Electric Vehicles
By Sinclair Gair
Scottish Fuel Cell Consortium, University of Strathclyde, Glasgow, Scotland; E-mail: [email protected]
In December 2000 the Scottish Fuel Cell
Consortium (SFCC) was formed as a partnership
between the Scottish Enterprise Energy Team,
industry and academia. It draws upon the engineering expertise of the University of Strathclyde
(Centre for Economic and Renewable Power
Delivery); Products of Technology Ltd; ASCO plc;
the Grampian Primary Care NHS Trust; PowerGen
Renewables; and fuel cell manufacturers.
SFCC is focused on using fuel cells in vehicles.
To aid this at Strathclyde, there are projects on
clean hydrogen production using electricity from
renewable energy devices (wind or wave turbines
to power electrolyser units). This clean hydrogen
production and utilisation is one of Scotland’s
efforts towards a sustainable hydrogen economy.
Hybrid Fuel Cell Vehicles
As part of this effort, SFCC has developed
Scotland’s first fuel cell battery hybrid powered
electric car. The vehicle is equipped with an alkaline fuel cell range extender, compressed hydrogen
gas storage, a lead acid battery pack, and a watercooled induction motor drive system. The prototype fuel cell vehicle is a Mark 1 drivetrain demon-
stration unit with the lowest possible cost configuration achievable with standard production items.
This hybrid drivetrain and system configuration is
also being applied to a small delivery van, retrofitted to take a fuel cell/battery electric drive, and an
18-seat battery-powered bus with a fuel cell range
extender for inner city transport use. Other units
for transport fleet application customers are in
development.
SFCC also has expertise in higher specification
items in the hybrid drivetrain layout, including:
• PEM or alkaline fuel cell systems, using onboard
hydrogen storage systems;
• high efficiency, permanent magnet brushless
DC, axial field, direct drive traction motors with
oscillating rotor capability; and
• customised power electronic controllers.
Advanced software modelling tools allow fast custom
design of the drivetrain for any vehicle duty cycle.
The Author
Professor Sinclair Gair is a director of the Scottish Fuel Cell
Consortium and works in the Institute for Energy and Environment
at the University of Strathclyde. His research interests are in fuel
cells for vehicular and stationary applications, and the design of
electric traction drive motors and power electronic controllers.
www.scottishfuelcellconsortium.org.uk
The fuel cell battery hybrid
drivetrain has been packaged
into the space frame of an AC
Cobra sports car. The range
which the vehicle can achieve
is a function of the amount of
hydrogen stored onboard
which, in this case, doubles the
range available from the lead
acid battery pack
Platinum Metals Rev., 2004, 48, (2), 61
61
Palladium Colloids Stabilised in Polymer
By Bénédicte Thiébaut
Johnson Matthey Technology Centre, Blounts Court, Sonning Common, Reading RG4 9NH, U.K.; E-mail: [email protected]
Colloids have been known about for centuries,
and studied since the nineteenth century, but
recent developments in technology have allowed
for improved and more versatile systems. For
instance, the stability of colloids is now achieved
through surface functionality. The high value of
the surface area to volume ratio of metal colloids
makes them highly attractive for catalysis applications and the surface functionality prevents their
aggregation. Surface functionality can be achieved
using ligands, surfactants and polymers with specific donor atoms or chemical groupings (1). In
this article the preparation of palladium (Pd) colloids stabilised with a non-ionic polymer,
polyvinylpyrrolidone (PVP), see Figure 1, will be
discussed (2). The Pd precursor usually forms a
complex with the PVP before reduction is carried
out. The colloid is then stabilised by hydrophobic
interactions between hydrophobic segments of the
polymer and the surface of the metal colloid, see
Figure 2.
Various preparative routes may be used to
synthesise Pd colloids in the PVP matrix. One of
the simplest ways is by alcoholic reduction in aqueous solution in the presence of PVP and gentle
heating. The use of alcohol as a reducing agent
offers the advantage that the residues are simple
organic compounds, unlike the residues of other
reducing agents such as borane types.
Although this preparative path is simple, a
N
*
CHCH2
O
*
n
Fig. 1 Polyvinylpyrrolidone (PVP)
Platinum Metals Rev., 2004, 48, (2), 62–63
Fig. 2 A colloidal Pd particle stabilised in a polymer
matrix
number of variables and parameters may influence
the characteristics of the end product. These
include reaction conditions (for instance, reaction
temperature and time), the quantity and molecular
weight of the PVP, the polymer to metals ratios, as
well as the metal precursors or pH of the initial
solution. These parameters will affect mainly the
particle size of the Pd colloid and its distribution
within the polymer, see Figure 3.
A range of Pd precursors is available and it was
found that solubility of a precursor in the reaction
mixture is not a prerequisite. For instance,
Pd(CH3CO2)2 showed partial solubility in a 50/50
EtOH/H2O solution at room temperature. Upon
heating, subsequent dissolution and reaction yielded colloidal Pd. Some literature preparations (2, 3)
used H2PdCl4 as the precursor in specific concentrations, and the pH of the reaction mixture was
changed by addition of NaOH (2). It was noted
that the particle size distribution of the colloidal
solution decreased with increasing pH. A suitable
amount of base in the reducing system produced
an increase in the reduction rate, thus leading to
smaller particle size colloids.
The metal to PVP ratio influences the size and
particle size distribution of the colloidal species.
The general trend shows that a low ratio (large
quantities of PVP) gives rise to a monodispersed
62
Fig. 3 A typical distribution (1–10 nm) of a Pd colloid
in a polymer matrix
colloidal species while a high ratio yields a wider
particle size distribution, that is, small particles are
present as well as larger ones.
A wide range of short chain alcohols may be
used for such experiments. As their boiling points
will influence their reducing abilities it is difficult
to rationalise their effects. However, for a given
alcohol and concentration, an increase in temperature will induce crystal growth and result in the
formation of larger particles (2, 3).
It is interesting to note that the reverse effect is
observed when Ru(III) salts are reacted in polyols
in the presence of PVP. This study showed that
more nuclei are formed at higher temperatures and
in a short period of time, and in turn the growth in
size of the particles is hindered (4). The long alkyl
chain of the polyol may have an important effect
on the rate of the reaction as well as on the heating rate, since, in another study, the reduction of
Pd in the presence of PVP with ethylene glycol
showed that an increase in temperature yielded
more sintered particles (3(b)). Other factors, such
as the heating rate, will have a large effect on the
resulting colloid; for instance, a study on a wide
range of metals, including Pd, showed that
microwave heating yielded smaller sized particles
compared with oil bath heating (slower heating
rate) (5).
These Pd colloidal materials ought clearly to
find use in catalysis. Indeed, a number of papers
reporting their activities in a range of reactions
have been reported (6). However, in order to optimise activity and selectivity of these colloidal
material as catalysts, further work is needed to
manipulate and control the size and the morphology of these colloids and understand the relationship between their characteristics and activity.
References
1
2
3
4
5
6
(a) M. T. Reetz and W. Helbig, J. Am. Chem. Soc.,
1994, 116, (16), 7401; (b) G. Schmid, V. Maihack, F.
Lantermann and S. Peschel, J. Chem. Soc., Dalton
Trans., 1996, (5), 589; (c) H. Bönneman, G. Braun,
W. Brijoux, R. Brinkmann, A. Schulze Tilling, K.
Seevogel and K. Siepen, J. Organomet. Chem., 1996,
520, (1–2), 143
W. Yu, M. Lui, H. Liu and J. Zheng, J. Colloid Interface
Sci., 1999, 210, (1), 218
(a) H. P. Choo, K. Y. Liew and H. Lui, J. Mater.
Chem., 2002, 12, (4), 934; (b) F. Bonet, V. Delmas, S.
Grugeon, R. Herrera Urbina, P.-Y. Silvert and K.
Tekaia-Elhsissen, Nanostruct. Mater., 1999, 11, (8),
1277
X. Yan, H. Liu and K. Y. Liew, J. Mater. Chem., 2001,
11, (12), 3387
W. Tu and H. Liu, J. Mater. Chem., 2000, 10, (9), 2207
(a) A. B. R. Mayer and J. E. Mark, Mol. Cryst. Liq.
Cryst., 2000, 354, 221; (b) A. M. Venezia, L. F. Liotta,
G. Pantaleo, V. La Parola, G. Deganello, A. Beck,
Zs. Koppány, K. Frey, D. Horváth and L. Guczi,
Appl. Catal. A: Gen., 2003, 251, (2), 359; (c) B. Wan,
S. Liao and D. Yu, React. Funct. Polym., 2000, 45, (1),
55; (d) Y. Gao, F. Wang, S. Liao, D. Yu and N. Sun,
React. Funct. Polym., 2000, 44, (1), 65
The Author
Bénédicte Thiébaut is a Senior Scientist in the Chemical Group at
the Johnson Matthey Technology Centre. She is interested in a
wide range of colloidal materials for catalysis and catalytic
applications.
The Most Commonly Used Platinum Group Metal Salts
The most commercially used pgm salts are generally their chlorides. Their main uses are: chloroplatinic
acid – as a precursor for loading platinum onto substrates for heterogeneous catalysts; palladium chloride
– for electronic plating; rhodium trichloride – for plating applications and catalyst loading; chloroiridic acid
– for plating, especially for anode coatings for chlor-
Platinum Metals Rev., 2004, 48, (2)
alkali use; osmium tetroxide – in electron microscopy;
and ruthenium trichloride – for plating, especially for
anode coatings for chloralkali use.
J. E. GOURD
John E. Gourd, is the Commercial Manager - Products, Precious
Metal Refining and Products, Johnson Matthey, Royston. U.K. His
main professional interests are the supply of precious metal salts and
compounds. E-mail: [email protected]
63
Expanded Coordination Chemistry
COMPREHENSIVE COORDINATION CHEMISTRY II. FROM BIOLOGY TO NANOTECHNOLOGY
Volume 6 TRANSITION METAL GROUPS 9–12
EDITED BY D. E. FENTON; EDITORS-IN CHIEF, JON A. MCCLEVERTY AND THOMAS J. MEYER, Elsevier, Amsterdam, 2003, 1321 pages,
ISBN 0-08-0443281 (Volume 6); ISBN 0-08-0437486 (Set), U.S.$ 5975,
The original “Comprehensive Coordination
Chemistry” was published in 1987 and since then
the field has expanded massively. This new edition
covers developments since 1982. There is now so
much literature that a comprehensive review is not
possible, so particular areas of interest have been
selected. As with the first edition, in these volumes
organometallic compounds have been excluded.
These are defined as compounds where metal-carbon bonds are greater than half the coordination
number of the metal. Such organometallic compounds are covered in a companion work,
“Comprehensive Organometallic Chemistry”.
Altogether there are 10 volumes in the set, with
the last one comprising indexes. Volumes dealing
with the platinum group metals will be reviewed.
Volume 6 aims to be nearly comprehensive in
its coverage. The coordination chemistry of the
elements: Co, Ir, Ni, Pd, Pt, Cu, Ag, Au, Cd and
Hg is covered. Rhodium, unfortunately, is not covered due to factors beyond the Editors’ control. In
most chapters, the chemistry is ordered by the
metal oxidation state and then by the ligand donor
atom. Applications are only briefly described as
they are covered in more detail in Volume 9.
P. V. Bernhardt and G. A. Lawrance review
cobalt chemistry, referring to secondary references
as there are 18,000 primary references for the period covered. The biological chemistry of cobalt and
its applications are discussed, including cobalamins
and non-corrin proteins. A table of ligand lability
rates is included. Industrial applications for organic transformations such as oxidation, carbonylation,
hydroformylation and cycloadditions, and cobalt in
electrocatalysis and analytical sensors are reviewed.
Iridium chemistry is discussed by L. J.
Yellowlees and K. G. Macnamara. The majority of
the coordination chemistry concerns iridium(III).
There is an emphasis on structural data. Biological
complexes of iridium(III) and iridium(I) are dis
Platinum Metals Rev., 2004, 48, (2), 64–65
6274 per Set
cussed and there is a short section on the catalytic
activity of iridium(III) complexes and a detailed
table of iridium(I) catalytic systems.
F. Meyer and H. Kozlowski contribute a noncomprehensive review of nickel coordination
chemistry, with sections on bioinorganic and materials chemistry. There are many nickel-dependent
enzymes and complexes with macrocycle and porphyrin ligands. Structural features of nickel(II)
complexes are discussed and data on the electronic absorption spectra and electrochemical data of
nickel(II) macrocycles is tabulated. Complexes
with bioligands: models for the carcinogenic properties of nickel, are covered. Structural data on
nickel(0) phosphine complexes are provided.
The chemistry of palladium is reviewed by N.
M. Kostic¢ and L.-M. Dutca.. In some places, the
text of this chapter is rather difficult to understand.
There is a useful survey of review articles on palladium. Applications of palladium chemistry that are
mentioned include the use of palladium acetylacetonates for thin film deposition, the use of
palladium phosphine complexes in catalysis and
the use of palladium(II) complexes for peptide
hydrolysis. Dendrimers, polynuclear systems and
palladium nanoparticles are all discussed.
L. M. Rendina and T. W. Hambley review the
chemistry of platinum. As in other chapters, the
authors have not attempted a comprehensive survey because of the size of the field. However they
provide a flavour of the current state of platinum
chemistry. There is a section on oxidative addition
reactions to platinum(0) which are models for catalytic reactions such as hydrosilation. Reactions of
ligands coordinated to platinum(IV) are discussed,
as are the kinetics and mechanism of platinum(IV)
reduction.
R. Mukherjee reviews major developments in
copper chemistry, focusing on structural aspects
and magnetic behaviour. Structural data is tabulatÚ
64
ed by ligand type. There is emphasis on the modelling of biological systems.
M. C. Gimeno and A. Laguna review silver and
gold chemistry – separately although combined in
one chapter. There is a discussion of the chemical
differences between silver and gold. The chemistry
of gold mainly concerns oxidation states (III) and
(I). A number of gold complexes have interesting
luminescence properties and some show biological
activity. Gold(I) thiolates in particular have antitumour, antiarthritic and antimicrobial activity.
They are also used to make gold films.
An overview of key results in zinc chemistry, by
S. J. Archibald, has an emphasis on X-ray structural data. As zinc(II) is the only significant oxidation
state, the review is subdivided by ligand type.
Many complexes serve as models of biologically
active zinc systems, for example, complexes with
mixed donor ligands are models for liver alcohol
dehydrogenases. Zinc macrocycle complexes are
in a separate section. Applications in pharmaceuticals, catalysis and the fluorescent detection of zinc
in cellular systems are discussed and there is a section on the biological chemistry of zinc.
D. K. Breitinger reviews cadmium and mercury,
including methods used to study their coordination
chemistry. Their complexes, in particular inclusion
complexes such as Cd(CN)2, are reviewed. As the
chapter contains a lot of structural description, I
felt more diagrams would have been helpful.
Reading Volume 6 gives an overview of the
vast area of coordination chemistry and could be a
useful source of ideas for the synthetic inorganic
chemist. The enormous amount of literature generated in the past 25 years means that the authors
had a very challenging task. In a work of this size,
a few typographical errors are inevitable and they
do occur. The colour diagrams are helpful
although they are segregated on pages in the middle of the book. Some of the diagrams, such as
X-ray structures, are a little fuzzy. The number of
potentially explosive perchlorate counterions still
being used in synthesis is a cause for concern.
With modern search techniques, it is often easier to search for a substructure rather than consult
a book of this size. However, computer searches
can never capture the richness and diversity of
coordination chemistry in the way that this volume
ANN K. KEEP
does.
The Author
Dr Keep is Principal Development Chemist in Johnson Matthey
Catalysts in Royston, U.K. Her main professional interests are
the synthesis of precious metal compounds and their use as
homogeneous catalysts.
Palladium Oxide Sensitiser for LPG Detector
Liquid petroleum gas (LPG): butane, propane
or their mixture, is used as a fuel particularly in
regions and activities where the usual utilities are
missing. It is used commercially and domestically
for space and water heating, cooking, lighting, and
as an automotive fuel. It is sold and stored in refillable cylinders as a pressurised liquid. It is a clean
versatile fuel (producing lower green house emissions than alternatives), but its flammability
requires awareness and vigilant leak detection.
Zinc oxide (ZnO) or tin dioxide are common
gas sensing materials usually with a thin layer of a
noble metal (palladium (Pd) or platinum) to
increase their catalytic activities and response times
(1). Various methods are used to apply the catalyst
layer to the substrate: salt decomposition, spraying,
impregnation by salt solution, and CVD by sputtering or evaporation. Substrates have also been
dipped into salt solution followed by evaporation.
Optimisation of the noble metal catalyst layer and
Platinum Metals Rev., 2004, 48, (2)
its properties is critical to the success of a detector.
Now, scientists in India have found some optimum values for catalyst layers in a wet-chemical
process where a Pd oxide sensitiser layer was
formed on a thin ZnO film for LPG detection (2).
They found a sensitised film with stable resistance was formed after 15 to 20 dippings of a ZnO
film into a PdCl2 suspension. The room temperature resistance was a function of the amount of Pd
loading. Stable sensors were fabricated with optimised Pd loading, with a suitable operating temperature ~ 250ºC. A sensitivity of 88% was observed for 1.6 vol.% LPG in air with a 15 s response
and 60 s recovery. The fast response and quick
recovery provides a useful domestic LPG alarm.
References
1
2
Platinum Metals Rev., 1999, 43, (4), 165
P. Mitra and H. S. Maiti, Sens. Actuators B: Chem.,
2004, 97, (1), 49
65
The Minting of Platinum Roubles
PART I: HISTORY AND CURRENT INVESTIGATIONS
By Professor Christoph J. Raub
Waldsiedlung 17, D-73525 Schwäbisch-Gmünd, Germany; E-mail: [email protected]
Nineteenth century Russian roubles are collectors items, but because of their history, there
is a question over each one whether it is a genuine Russian rouble or a forgery. There has
been some prior research and analysis on the platinum used to make these roubles and on
their method of manufacture. As W. C. Heraeus and Johnson Matthey both hold small collections
of roubles never before investigated, it was decided to see what could be found out about them
and what this could tell us about their origins. This is the first of a three part series and begins
with some of the background history to the work. Part II appears later in this issue and Part
III will be published in July.
Although there had been rumours in the early
1800s that platinum was to be found in Russia (1),
it was not until 1819 that small pieces of white
metal, “panned” with gold and other minerals of
high density, in the gold fields in the Urals, south
of the city of Ekaterinburg, were noticed by the
authorities and taken for examination to laboratories in Ekaterinburg. (Alluvial platinum nuggets
had been found earlier in Colombia, and later
examples have been found in other regions, for
example, in the Far East. Even in the river Rhine
nuggets of platinum and platinum group metals
have been reported.)
By 1825 large quantities of the native metal had
been collected from several areas around
Ekaterinburg and sent to St. Petersburg. The
increased volume of metal was noticed by the
Imperial Russian Government and resulted in
them declaring a State Monopoly on all platinum
dealings – except under licence – with no export of
native metal being allowed. The poor administration of this Monopoly in the remoter areas of the
country promoted smuggling and this distorted the
published statistics for Russian output of platinum,
even after the State Monopoly had ceased (1).
Early Platinum Refining in Russia
On analysis, the samples of platinum from the
Ekaterinburg region were also found to contain
iridium, osmium, iron, gold, sometimes osmiridium, and sometimes copper and rhodium. These
Platinum Metals Rev., 2004, 48, (2), 66–69
samples were refined by Janety’s process and by a
process developed in 1827 by Peter G. Sobolevsky.
Sobolevsky’s process involved boiling the native
metal with four times its weight of aqua regia.
Malleable platinum was produced from the calcined chloroplatinate. In the final stages, the
platinum sponge was cold pressed, then heated to
whiteness and further compressed. The granular
structure became dense and malleable by this final
compression (1). The malleable metal was hammered for fabrications. Platinum was thus available
in pieces of any required size. The platinum was
made into medals, wires, dishes, crucibles, ingots
and other artifacts (1).
As there seemed to be plentiful amounts of
platinum, Count Egor F. Kankrin, Minister of
Finances to Tsar Nicholas I, and Head of the
Department of Mining, suggested its use as
coinage. Kankrin brushed aside words of caution
from the German naturalist and traveller,
Alexander von Humboldt, who had travelled in
Colombia and was knowledgeable about Colombian
platinum. He had advised that as Colombian platinum was available there would be difficulty in
controlling the platinum price sufficiently to prevent depreciation and counterfeiting. In spite of
this in 1828 Kankrin issued first 3 rouble platinum
coins, and later 6 and 12 rouble platinum coins.
In 1846, due to the falling price of platinum
outside Russia, “cessation of coining and withdrawal of the whole platinum currency” was
66
Coin
Inscription
3 rouble
6 rouble
12 rouble
2 zol. 41 dol.
4 zol. 82 dol.
9 zol. 68 dol.
1 zol. » 4.26 g
1 dol. » 0.044 g
ordered. In fact, the platinum price had fallen to a
lower level than the exchange value of the Russian
platinum coins (1).
All the coins that were minted bore, curiously,
the same inscription on the reverse. In the centre
of the face was the denomination, the date, and
the mint mark: SPB for St. Petersburg. Around the
edge was the mass of pure Urals platinum in zolotnik (zol.) and dolya (dol.).
The coins, minted for eighteen years, numbered in total: 1,373,691 3-rouble; 14,847 6-rouble;
and 3474 12-rouble. The total weight of platinum
used in their production was 485,505 troy ounces
(1, 2).
The Purity of the Platinum
It was soon realised that the native platinum
was rather impure, so samples were sent to the
famous chemists of the time: Berthelot, Berzelius
and Döbereiner, asking for help with analysis and
refining. While the Russian efforts and achievements in platinum chemistry at that time have
been extensively discussed, the contemporary
work of Berzelius in Stockholm, Döbereiner
Senior in Jena, and Osann, Klaus and Döbereiner
Junior in Dorpat has been neglected (1).
Johann Wolfgang Döbereiner (Senior) was the
towering figure in chemistry at the beginning of
the 19th century, issuing final verdicts on the work
of his contemporaries (3). He confirmed the discoveries of other platinum group materials: pluran
(Platina + Ural) platinum, polin (probably iridium
oxide) by Gottfried Wilhelm Osann, and ruthen
(ruthenium) by Karl Klaus in the residues of the
St. Petersburg platinum refinery.
Johann Wolfgang Döbereiner
Döbereiner’s connections with the platinum
industry were arranged by Maria Pavlovna, a
daughter of Tsar Paul I, who had married Carl
Platinum Metals Rev., 2004, 48, (2)
Friedrich von Weimar in 1804. She financed much
of the scientific work in Jena, not only that of
Döbereiner but also, for instance, work by J. W.
Goethe on mining in Thüringen. Indeed, she may
be considered to have provided the venture capital
for the upcoming German chemical (catalysis) and
optical (Zeiss/Schott/Abbe – glass) industries.
Maria Pavlovna believed that by cooperation with
Döbereiner the work of Count Kankrin and
Sobolevsky in St. Petersburg might advance faster.
However, Döbereiner had no wish to leave
Jena for St. Petersburg and instead sent his son,
Franz. On his way to St. Petersburg Franz stayed
for a while in Dorpat, in the laboratory of Osann
where he and a Dr F. Weiss worked on the platinum problem (1).
In 1836, F. Wöhler’s translation of J. J.
Berzelius’ “Lehrbuch der Chemie” appeared in its
4th Edition, extensively discussing the state of
knowledge of the platinum group metals based on
work on Russian platinum (4). Wöhler, the
favourite pupil and collaborator of Berzelius, was
the discoverer of aluminium. On the cover sheet
of this first chemistry textbook in Swedish/
German he proudly states: “translated from the
Swedish handwriting of the author” (4). He mentions that Alexander von Humboldt brought back
from America a nugget of 1080.6 “gram” weight
and that in Tagilsk in the Urals, a nugget of 10 and
another of 3.5 “Pfund” weight were found. These
platinum nuggets contained mostly platinum and
iron, less copper, palladium, rhodium and nearly
always some iridium. Wöhler states that:
...some of these nuggets contain so much iron, that
the greater part of it can be dissolved in nitric acid
and one can consider the iron as present in elementary form. Many of the smaller platinum grains are
attracted by a magnet... The most iron-rich platinum occurs near Nischne-Tagilsk. It is dark grey
and has between 11 and 13% iron. Some grains
are not attracted by a magnet. This is caused less by
a lower iron content but more by a higher iridium
concentration. The platinum in Goroblagodat in
the Urals is, more than others, free of iridium in the
state in which it is co-dissolved (with platinum).
Therefore this ore produces the purest platinum.
67
In the book, Berzelius/Wöhler discusses details of
the raffination of the nuggets. Basically it is the
classical method used before the introduction of
the liquid-liquid extraction processes. The precipitate was called by Berzelius/Wöhler “Platinsalmiak”
(4). Later is mentioned:
...if one does not care much for the purity of platinum it can be precipitated with ‘Salmiak’ (ammonium chloride) immediately after dissolution... (most
platinum is currently produced this way). It
therefore contains iridium in all cases...
He then describes compacting and sintering of
platinum sponge and states:
If it (platinum) is free of iridium it can be drawn
into fine wire, like gold and silver.
From the work of Berzelius we must conclude that
the main impurities to look for in Russian platinum
coins will be iridium and iron. However, it will be
difficult to discern between the use of a natural
high-grade alluvial platinum powder with low iridium and iron content and a well refined one, due to
the large variations in the contents of their ore.
Forged Russian Coins by
‘Novodel’ Mintings
Russian platinum roubles are now collectors’
items (5). After the coinage was withdrawn, additional mintings took place (‘Novodel’ mintings)
until 1890, and for a while after that other forgeries
were made. The original coins were made from
natural platinum alloys containing ~ 75 wt.% platinum. This was refined to obtain a technically pure
platinum powder for forging and minting. This
powder also contained additional material, such as
gold- and copper-rich inclusions.
However, one ‘Novodel’ coin, dated 1828, has
been shown to consist of technically pure platinum, and was probably struck at the end of the
19th century (5, 6). In a textbook on chemical technology published in 1900 (7), the impurity
concentration of platinum for crucibles was listed
as Ir 2.56%, Rh 0.20%, Pd (trace), Ru 0.02% and
Fe 0.20%. It is thought that some of the coins may
have been ‘mechanically’ diluted by inclusions of
natural platinum alloys, containing gold. Genuine
Platinum Metals Rev., 2004, 48, (2)
Russian roubles contain iron impurities up to 4
weight percent. In fact, a compilation of the composition of the platinum from Russian placer
deposits shows that the iron content varies
between 2.3 and 18.9% and iridium between traces
and 5.32%. Coins analysed so far contain iron: 0.5
to 1.4%, and iridium: undetected to 0.85 to 1.06%
(6, 8 ). (XRF-surface analyses) confirm Berzelius’
remark on iridium.
It is interesting to note that metallography
shows that one coin (6) has a surface area rich in
platinum. This might indicate the use of better
grade platinum for the surface than for the centre
of the coin. This would not be a problem for the
sintering method used for the coins. However, the
use of chemical/electrochemical enrichment, “platinising”, by pickling in acids must be excluded for
platinum and its alloys.
Depending on the process parameters of the
sintering process, the coins will:
[a] have a density less than that of platinum produced by the melt-solidification process. This is
caused by “rest porosity” (voids, bubbles, pores,
defects between sintered grains, etc.). Impurities
may also reduce the density;
[b] possess a certain striated structure seen in
microsections;
[c] and, depending on their sintering, show a
“snake skin” surface structure (irregularities in the
surface). This is observed on the surface of pieces,
sintered, annealed and deformed from powders.
A microsection of one coin confirmed the sintered structure. Surface irregularities of coins
typical for sintered and deformed metals (‘snake
skin’) were observed (6, 8).
The densities of the roubles investigated until
now vary between 20.7 and 20.03 to 21.32 g cm–3
(4, 6, 8), all less than the currently accepted value
for the density of platinum of 21.45 g cm–3. Values
for the density for platinum known at that time
were (in g cm–3 ): Wollaston 21.53; Berzelius 21.45
(J. R. Bréant, Paris); and Klaproth 21.47.
First Indications of Ferromagnetism
The ferromagnetism of platinum nuggets and
coins was noted very early. Berzelius attributed it
to the presence of metallic iron (4). Platinum
68
nuggets display ferromagnetism at room temperature, irrespective of their origins. Recently the
(B´H) (magnetic energy product) was measured
semiquantitatively (6).
Magnetic measurements on synthetic platinumiron alloys, in thermodynamic equilibrium, are
somewhat inconclusive (9, 10). Platinum-rich
alloys (above 90% Pt) in disordered f.c.c. solid
solution are not ferromagnetic at room temperature. The ordered Pt3Fe phase seems to be
antiferromagnetic. Cold-working disorders the
phase and generates strong ferromagnetism as
does ion beam irradiation (11).
However, neither the effects of heat treatment
nor of cold working on the magnetic properties
have been properly investigated. Cabri and Feather
have proposed a partial phase diagram in the
regions Fe-PtFe (10). They postulate “that the
composition has a greater effect on their crystal
structure (assuming no cold-working effects) than
their annealing histories ...”. It may therefore be
assumed that in coins that have regions which
contain ~ 12 wt.% Fe (30 at.%) or a little less, iron,
at least to some extent, may be in the form of partially disordered Pt3Fe.
Lattice constant measurements were used to try
to decide if the iron was in solid solution with platinum, but the method was insensitive and the
conclusions not convincing as the authors did not
observe any ordering, only line shifts in their X-ray
patterns from their ferromagnetic coins (6).
Furthermore, true disordered f.c.c. solid solutions
at low iron concentrations, even if cold deformed,
are not ferromagnetic. This might support the
chemical observation of Berzelius that iron, at
least to some extent, is present in elementary form.
We have to expect changes in the magnetic
properties of the coins compared with the starting
powder. These will be due, for example, to composition changes, disorder-order phenomena by
heat treatment and/or deformation during sintering. Indeed, it has not been established how
nuggets and/or coins are in thermodynamic equilibrium, as synthetic alloys are.
After the cessation of circulation the platinum
coins, together with native platinum, were sent for
refining to European refineries, such as Johnson
Platinum Metals Rev., 2004, 48, (2)
Matthey, W. C. Heraeus, Hanau, and W. Sieber,
Hanau, Frankfurt (later Degussa, now Umicore).
The Sieber coins were investigated some short
while ago (8). The coins investigated in (6) came
from private collections. Experimental results of
investigations on coins in the possession of W. C.
Heraeus (Hanau) are published later in this Journal
and results on Johnson Matthey’s roubles will be
published in the July issue.
Acknowledgement
The investigations would be impossible without the generous support of the companies W. C. Heraeus, Hanau, Germany,
and Johnson Matthey, Sonning Common, Reading, U.K.
References
1 D. McDonald and L. B. Hunt, “A History of
Platinum and its Allied Metals”, Johnson Matthey,
London, 1982, pp. 239, 241–247, 280
2 E. K. Fritsman, Ann. Inst. Platine, 1927, 5, 23–74
3 G. B. Kauffman, Platinum Metals Rev., 1999, 43, (3),
122–128
4 J. J. Berzelius, “Lehrbuch der Chemie”, aus der
schwedischen Handschrift des Verfassers übersetzt
von F. Wöhler, 4 verbesserte original-Auflage, 3 und
4. Band Dresden und Leipzig, in der Arnoldischen
Buchhandlung, 1836
5 K. Janssens, G. Vittiglio, I. Deraedt, A. Aerts, B.
Vekemans, L. Vincze, F. Wei, I. De Ryck, O.
Schalm, F. Adams, A. Rindby, A. Knöchel, A.
Simionovici and A. Snigirev, X-Ray Spectrom., 2000, 29,
73
6 E. Auer, Th. Rehren, A. von Bohlen, D. Kirchner
and R. Klockenkämper, ‘Über die Hertstellung und
Zusammensetzung der ersten Platinmünzen in
Russland’, Metalla (Bochum), 1998, 5.2, 71–90
7 F. Fischer, “Handbuch der chemischen
Technologie”, Leipzig, Verlag von Otto Wigand, 15.
umgearbeitete Auflage, 1900, 787 Seiten, S. 305
8 H.-G. Bachmann and H. Renner, ‘Nineteenth
Century Platinum Coins’, Platinum Metals Rev., 1984,
28, (3), 126–131
9 M. Hansen and K. Anderko, “Constitution of
Binary Alloys”, 2nd Edn., McGraw-Hill Book Co.
Inc., New York, 1958
10 L. J. Cabri and C. E. Feather, ‘Platinum-iron alloys:
a nomenclature based on a study of natural and synthetic alloys’, Can. Miner., 1975, 13, 117–126
11 S. Maat, A. J. Dellock, D. Weiler, J. E. E. Baglin and
E. E. Fullerton, J. Magn. Magn. Mater., 2003, 265, (1),
1–6
The Author
Professor Raub is retired from the Forschungsinstitut für
Edelmetalle und Metallchemie, Schwäbisch Gmünd where for
many years he was its Director. He is now interested in the history
of precious metals, especially of the platinum group metals, and
their geology, and in iron smelting in southern Germany.
69
6th European Congress on Catalysis
COMPREHENSIVE COVERAGE OF HETEROGENEOUS CATALYSIS AND SURFACE SCIENCE FROM
FUNDAMENTALS TO INDUSTRIAL USES
By Reza Torbati
Johnson Matthey Technology Centre, Blounts Court, Sonning Common, Reading RG4 9NH, U.K.; E-mail: [email protected]
The 6th European Congress on Catalysis
(EuropaCat-VI) took place in Innsbruck, Austria,
from the 31st August to 4th September 2003, and
was attended by more than 1000 participants.
Many aspects of homogeneous and heterogeneous
catalysis were covered, with four oral sessions running simultaneously. Three poster sessions
contained a large number of presentations. This
selective review covers aspects of the presented
heterogeneous work featuring the platinum group
metals.
Sir John Meurig Thomas (The Royal
Institution, U.K.) opened the conference by giving
a plenary lecture, emphasising the importance of
pursuing in situ studies at pressures and temperatures which simulate real conditions, that is,
atmospheric pressure and temperatures greater
than 500°C, in order to understand the mechanisms of chemical reactions that need to be
catalysed under the conditions of industrial use.
The lecture highlighted a number of specific examples where deployment of two or more parallel in
situ techniques, such as X-ray absorption spectroscopy, X-ray diffraction and chemical analysis
(by gas chromatography/mass spectrometry
(GC/MS)), shed considerable light on the nature
of both the short- and long-range structures of an
active catalyst. Such studies describe some of the
chemical modifications that could be implemented
in the vicinity of active centres in order to boost
catalytic performance.
In a keynote lecture, Professor Robbie Burch
(Queen’s University Belfast) talked about the use
of transient techniques to understand and control
catalytic reactions, especially when used in conjunction with in situ spectroscopy such as FTIR. In
his talk he gave several examples of catalytic reactions where the reaction rate can be significantly
enhanced by periodic perturbation of the reactant
Platinum Metals Rev., 2004, 48, (2), 70–71
composition. He also discussed the use of transient
techniques to investigate detailed catalytic reaction
mechanisms. An example given was the reduction
of nitric oxide (NO) over 0.3% Pt/Al2O3 under
lean-burn conditions using octane as reductant.
Below a critical temperature (< 185°C) the steady
state activity is very unstable and self-poisoning of
the catalyst rapidly leads to deactivation. However,
it was demonstrated that periodic perturbation of
the surface state of a catalyst can result in a dramatic change in its steady state activity. Professor
Burch showed that the low temperature activity for
NO reduction can be maintained indefinitely by
creating short temperature spikes on the Pt surface
by addition of pulses of methanol as a fuel.
Lean DeNOx Catalysis
In the symposium on lean deNOx catalysis,
Professor Angelos M. Efstathiou (University of
Cyprus) described the use of Pt/Mg-Ce-O as a
novel stable, active and selective catalyst for the
reduction of NO to nitrogen (N2) with the use of
hydrogen in the presence of excess oxygen. The
Pt/Mg-Ce-O catalyst gave the highest N2 production yield ever reported in the open literature for
the NO/H2/O2 reaction. The catalyst operates
extremely well in the 100–400°C temperature range
and shows excellent stability in the presence of 5%
H2O and 20 ppm SO2 in the reaction feed stream.
Poster Display
There were also a large number of posters on
display. A poster by S. Morandi (University of
Bologna, Italy) tackled the removal of NOx from
lean-burn gasoline and diesel engines. This
requires the development of alternative catalysts to
the conventional three-way catalysts (TWC) which
are inactive in converting NOx under lean exhaust
conditions, that is in excess oxygen. A potential
70
solution was represented by Toyota-type NOx
storage-reduction (NSR) catalysts, containing Pt
and Ba supported on alumina – NOx are adsorbed
and stored in the catalyst under lean driving conditions, and then released and reduced to N2 during
rich operation. The main drawbacks of the NSR
catalysts are low resistance to sulfur, low activity at
temperatures < 200°C and low resistance towards
hydrothermal treatment. NSR catalyst containing
1 wt.% Pt and Pt-Cu (1 wt.% Pt and 4 wt.% Cu)
supported on calcined Mg/Al hydrotalcite-type
(HT) compounds were shown to have higher
activity than Pt-BaO/Al2O3 systems at temperatures below 300°C and better resistance to sulfur
poisoning. Also for the Pt-Cu catalysts, higher
resistance to hydrothermal treatment was observed
compared to the Pt-BaO/Al2O3 sample.
In a separate study, the effect of the addition of
a solid solution of ceria-zirconia on the PtBaO/Al2O3 matrix was investigated by C.
Manfredotti (University of Torino, Italy). The
presence of the ceria-zirconia solid solution
enhances both the metal dispersion and the Pt surface area accessible to reactant gases with respect
to a NSR catalyst. The barium-containing phase
favours reducibility of the Pt particles and generation of more electron-rich metallic sites compared
to Pt/Ce0.6Zr0.4O2/Al2O3. Furthermore, the sample was shown to have higher sulfur resistance of
the NOx storage capacity than the corresponding
Pt-BaO/Al2O3 system, probably due to ceriazirconia acting as a trap for SOx.
R. Villa (Politecnico di Milano, Italy) looked at
the effect of calcination and ageing treatment on
the activity and stability of alumina and zirconia
supported PdO for methane combustion. Alumina
supported systems, calcined at low temperature (~
600°C), showed the best activity. However, calcination treatments at high temperature (> 900°C)
caused PdO decomposition to Pd. This had a
strong negative impact on the catalytic activity and
stability. The study demonstrated that using ZrO2based supports strongly increases the stability of
the catalytic system upon high temperature calcination and ageing treatments. It was proposed that
zirconia-type supports significantly narrow the
hysteresis of the PdO-Pd redox by facilitating the
onset of Pd reoxidation during cooling.
Concluding Remarks
In summary, four parallel oral sessions, together with the large number of posters meant that
only a few of the many papers and posters presented could be attended and reviewed. The
Congress, held in the beautiful city of Innsbruck,
did, however, cover all the main aspects of heterogeneous catalysis from fundamental catalysis and
surface science to industrial catalysis.
The EuropaCat website is: www.europacat.org
The Author
Reza Torbati is a Research Scientist in the Automotive Catalyst
Technology Group at the Johnson Matthey Technology Centre.
His main interests are in the development of catalysts for diesel
applications.
Light-Driven Alkane Oxygenation by Ruthenium(II)
Photocatalysts can activate unreactive C-H bonds
of complex saturated hydrocarbons, such as alkanes,
to functionalise them: an important reaction in organic chemistry. The dissociation of a ligand often starts
the reaction, catalysed by a transition metal complex.
Ru(II) polypyridyl complexes take part in photosubstitution reactions, probably by excitation in the metal to
ligand charge transfer (MLCT) region by dissociation.
Now, researchers from the Tokyo Metropolitan
University, Japan, have developed, under visible light
irradiation (> 385 nm), stereospecific and photoregulated catalytic alkane oxidation reactions using
chloro(Me2SO)Ru(II) complexes with tris(2-pyridylmethyl)amine or its derivative in the presence of
Platinum Metals Rev., 2004, 48, (2)
2,6-dichloropyridine N-oxide (M. Yamaguchi, T.
Kumano, D. Masui and T. Yamagishi, Chem. Commun.,
2004, (7), 798–799). Excitation in the MLCT band
selectively substituted the S-bound Me2SO ligand by a
solvent molecule.
When adamantane, the most stable C10H16 isomer,
was catalytically oxidised, 1-adamantanol and adamantane-1,3-diol were selectively formed in good
yields. The Ru complex and irradiation were both
necessary for oxidation to proceed; without irradiation the reaction diminished, but irradiation restored
it. Thus the reaction is photoassisted, not photoinitiated. Irradiation may initiate the catalytic reaction and
generate the active species for alkane oxidation.
71
The Minting of Platinum Roubles
PART II: THE PLATINUM ROUBLES OF HERAEUS
By David F. Lupton
Engineered Materials Division, W. C. Heraeus GmbH & Co KG, Heraeusstrasse 12–14, D-63450 Hanau, Germany
E-mail: [email protected]
Heraeus has in its possession four platinum rouble coins and one commemorative platinum
medallion minted between 1826 and 1844. In order to determine their composition and to
learn a little more about the methods used in their manufacture, they have been subjected to
various techniques of non-destructive examination. These have included a developmental
SQUID microscope specifically used to look at magnetic effects due to the iron content.
In order to find out more about the methods of
manufacture of Russian platinum roubles and to
investigate the magnetic effects of iron on platinum, Christoph Raub suggested some studies on
the platinum roubles owned by Heraeus. The platinum used in nineteenth century Russian roubles is
known to contain small amounts of iron. Various
non-destructive tests, including the use of a developmental SQUID microscope, were therefore
undertaken into the structure and purity of the
coins and medallion. The samples are:
· 2 coins of 3 roubles minted in 1842 and 1844,
· 1 coin of 6 roubles minted in 1830,
· 1 coin of 12 roubles minted in 1832, and
· a medallion minted to commemorate the coronation of Tsar Nicholas I in 1826.
Experimental Techniques
After initial optical photography and determination of the mass and dimensions, the density of the
coins was measured using the Archimedes tech-
nique of immersion in water. The obverse faces of
the coins and the medallion were then examined in
the scanning electron microscope (SEM) and two
areas on each were subjected to energy dispersive
X-ray analysis (EDX). To obtain a more representative overview of the impurity contents, the coins
and medallion were examined by energy dispersive
X-ray fluorescence analysis (ED-XRF) over essentially the complete surface area (the maximum
diameter analysed = 29 mm). The ED-XRF analyses can only be regarded as semi-quantitative
because of the uneven surface of the coins. The
average error of the measurements is estimated to
be 10% of the value.
In view of the significance of iron as an impurity in the platinum, the 12 rouble coin of 1832 and
the coronation medallion were also investigated
using a superconducting quantum interference
device (SQUID) microscope. This instrument was
operated in the direct current mode, permitting the
magnetic properties to be determined throughout
Table I
Density and Dimensions of the Heraeus Platinum Coins
Mass,
g
3 rouble / 1842
3 rouble / 1844
6 rouble / 1830
12 rouble / 1832
Coronation / 1826
10.27
10.37
20.64
41.34
11.58
Density, g cm–3
(Archimedes)
20.78
20.40
21.18
20.26
20.42
Thickness, mm
min.
max.
1.41
1.37
1.83*
2.36*
1.97* 1.50**
1.45
1.40
1.99*
2.46*
1.98*
Diameter, mm
min.
max.
23.38
23.55
28.49
35.77
22.16
23.43
23.59
28.65
35.82
22.22
* rim; ** inside
Platinum Metals Rev., 2004, 48, (2), 72–78
72
Fig. 1 3 rouble coin minted in
1842
3 rouble coin minted in 1844
6 rouble coin minted in 1830
12 rouble coin minted in 1832
Platinum medallion
commemorating the coronation
of Tsar Nicholas I, minted in
1826
Platinum Metals Rev., 2004, 48, (2)
73
the thickness of the material. The SQUID was
being developed in the Institute of Applied Physics
at the University of Giessen in collaboration with
Heraeus (1). This device permits the imaging of the
magnetic properties of the sample over a relatively
small area (areas of approx. 20 ´ 20 mm and 7 ´ 7
mm were examined).
Results and Discussion
Table I contains a summary of the mass, density and dimensions of the coins and medallion. In
all cases the density is considerably lower than that
of pure platinum (21.45 g cm–3 ), the highest value
being 21.18 g cm–3 for the 6 rouble/1830 coin.
Optical Macrographs
Figure 1 shows optical macrographs of the
obverse and reverse of the four coins and the
medallion. Most of the coins show a streaky surface structure which is unrelated to the stamping
on the coin face. Particularly in the case of the 12
rouble/1832 coin and the coronation medallion it
can be seen that the striations on the obverse are
essentially a mirror image of those on the reverse.
It can therefore be assumed that they relate to
material inhomogeneities which are present
throughout the thickness of the coin. The fact that
the large striation on the obverse of the coronation
medallion cannot be seen where it crosses the
raised portion of the “H” demonstrates that it is
not a superficial scratch caused after minting.
SEM Micrographs
A number of SEM micrographs of the coins
and the medallion are shown in Figure 2. In many
areas, a mottled structure can be seen (for instance,
around the crown on the obverse of the 6 rouble/1830 coin, Figure 2(a)). The surface striations
are less obviously visible than in the optical macrographs because of the lower contrast in the SEM.
However, they can be clearly seen on the obverse
of the coronation medallion, especially above the
2(a)
2(b)
2(c)
2(d)
Fig. 2(a) SEM, obverse of the 6 rouble coin
Fig. 2(c) SEM, obverse of the coronation medallion
Platinum Metals Rev., 2004, 48, (2)
Fig. 2(b) SEM, obverse of the coronation medallion
Fig. 2(d) SEM, obverse of the coronation medallion
74
Table II
Heraeus Platinum Roubles, EDX Analysis in Scanning Electron Microscope
Element
Cr
Mn
Fe
Cu
Ir
Au
Rh
Pd
Ni
Pt
3 rouble
1842
3 rouble
1844
6 rouble
1830
12 rouble
1832
Coronation
1826
0
0
0.2
0
2.1
1.6
0.3
0
0
95.9
0.1
0
0.9
2.2
1.8
11.8
1.3
0.7
0
81.2
0.1
0
0.4
0.3
1.7
1.2
0
0.2
0
96.2
0.1
0.4
1.1
0
1.6
0.1
0.2
0.4
0.1
96.0
0
0
2.0
0.4
3.3
0.9
0.4
0
0
92.9
0.1
0
0.3
0
2.2
1.0
0.6
0
0.1
95.7
0
0
0.3
0.6
1.0
3.5
2.7
0.2
0.2
91.6
0.2
0
0.3
0
1.2
0.7
0
0
0
97.6
0
0
0.4
0
2.1
1.8
0
0.1
0
95.6
0
0.4
1.8
0.8
1.4
0
0
0
0.4
95.2
2 measurements on each surface (wt.%)
“H” to the left of the crown, Figures 2(b) to 2(d).
The 12 rouble/1832 coin has a distinctly scaly
surface appearance, see Figures 2(e) and 2(f). The
structure of these areas is shown at higher magni-
fication in Figures 2(g) and 2(h). The black spots
marked “A1” in Figure 2(h) were analysed by EDX
and found to consist of almost pure iron, possibly
resulting from the tooling used in stamping the
2(e)
2(f)
2(g)
2(h)
Fig. 2(e) SEM, scaly surface of obverse (12 rouble coin)
Fig. 2(g) SEM, high magnification (12 rouble coin)
Platinum Metals Rev., 2004, 48, (2)
Fig. 2(f) SEM, scaly surface of obverse (12 rouble coin)
Fig 2(h) SEM, high magnification (12 rouble coin)
75
Fig. 2(i) SEM micrograph; high magnification of
the 12 rouble coin shows the high quality of the
stamping on this coin. A superficial scratch is
visible
coin. Figure 2(i) shows the high quality of the
stamping on this coin, in contrast to the striations
described above, and also a superficial scratch.
During examination in the SEM, EDX analyses
were carried out on two areas on each coin (Table
II). The main impurities found at various levels in
all coins are iron, iridium, gold and rhodium. The
values of the individual elements vary significantly
within one coin. The most substantial impurity is
gold in one area of the 3 rouble/1844 coin which
is also associated with relatively high values for
copper. This coin also contains an unusually high
level of rhodium.
Table III gives the results of the semi-quantitative ED-XRF analyses which can be regarded as
integral measurements over the whole surface area.
For the major impurities there is a reasonable
degree of correspondence with the SEM-EDX
analyses. The relatively high levels of copper, gold
and rhodium in the 3 rouble/1844 coin and of iron
and iridium in the coronation medallion are essentially confirmed. The largest discrepancy is to be
seen in the impurities in the 6 rouble/1830 coin
where the ED-XRF analysis indicates a higher concentration of iron but lower concentrations of gold
and iridium than SEM-EDX. This is probably a
result of the considerable inhomogeneities in the
material.
The SEM and ED-XRF studies had revealed
significant quantities of iron in the coins. Berzelius
(2) reported relatively high levels of iron in native
platinum ore which was magnetic in some cases.
Besides the Fe-rich solid solution, disordered FePt3
Platinum Metals Rev., 2004, 48, (2)
is reported to be ferromagnetic in Massalski
(3) after Kren et al. (4, 5). Also, Auer et al. (6)
found platinum coins to be ferromagnetic in
varying degrees. The expectation of ferromagnetism in the Heraeus platinum coins
was the main reason for then turning to the
developmental SQUID microscope to
obtain more information on the internal structure
of the coins.
SQUID Microscope
The reverse and obverse of the coronation
medallion were examined at low magnification
over an area of 20 ´ 20 mm or 20 ´ 17 mm
(Figures 3(a)–3(c); Figures 3(a) and 3(b) show the
same area with different false colours to highlight
the contrast features). The area in the centre of the
obverse was then examined at higher magnification over an area of 7 ´ 7 mm (Figures 3(d)). An
area 7 ´ 7 mm of the 12 rouble/1832 coin which
had the distinctly scaly appearance was also examined (Figure 3(e)).
A comparison of Figures 3(a)–3(c) shows that
substantial magnetic inhomogeneities are present
which are elongated across the diameter of the
medallion. The orientation on the obverse (Figure
3(c)) is essentially a mirror image of that on the
reverse (Figures 3(a) and 3(b)), corresponding to
the optical macrographs in Figure 1. This demonstrates conclusively that the superficially visible
defects on both faces of the medallion are associated with inhomogeneities in the bulk of the
material. The correspondence of the inhomogeneities on the obverse (Figures 3(c) and 3(d))
with the optical image is particularly striking.
The 12 rouble/1832 coin also demonstrated
substantial magnetic inhomogeneities, Figure 3(e).
Unfortunately, however, the coin became so
strongly magnetised that magnetic saturation was
reached after the first measurement and no further
76
Fig. 3(a) (left) and 3(b)
(right) SQUID microscope
images of the coronation
medallion of 1826 (reverse)
showing ferromagnetic
inhomogeneities. Different
false colours are being used.
Area = 20 ´ 20 mm
Fig. 3(c) (left) SQUID
microscope image of the obverse
of the coronation medallion.
Area = 20 ´ 17 mm
Fig. 3(d-micro) (right) SQUID
microscope image of enlarged
detail from Figure 3(c) (obverse)
corresponding to the area marked
in the macrograph below.
Area = 7 ´ 7 mm
Fig. 3(d-macro) Macrograph of the coronation medallion with
an area marked for enlargement and shown in the SQUID image
in Figure 3(d-micro) above
Fig. 3(e) (left) SQUID
microscope image of
the 12 rouble/1832
coin. The detail shows
ferromagnetic
inhomogeneities in the
12 rouble coin of 1832
Fig. 3(f) (right) The
area marked in the
macrograph shows the
area examined by the
SQUID image on the
left.
Area = 7 ´ 7 mm
Platinum Metals Rev., 2004, 48, (2)
77
Table III
Heraeus Platinum Roubles, Semi-Quantitative Energy Dispersive X-Ray Fluorescence Analysis
Element
3 rouble
1842
3 rouble
1844
6 rouble
1830
12 rouble
1832
Cr
Mn
Fe
Cu
Ir
Au
Rh
Pd
0.4
< 0.05
0.3
£ 0.1
1.7
< 0.5
0.1
0.1
< 0.05
< 0.05
0.4
1.0
< 0.05
1.8
2.5–3
1.0
< 0.05
< 0.05
1.8
< 0.1
0.5
< 0.5
< 0.05
< 0.05
< 0.05
< 0.05
0.6
0.3
1.0
< 0.5
0.1
0.1
Coronation
1826
< 0.05
< 0.05
1.2
0.2
2.0
< 0.5
0.3
0.1
Integral measurements over an area of max. 29 mm diameter (wt.%)
measurements could be made. The above results
are compatible with a powder metallurgical production route using grains of partially purified
native platinum.
Auer et al. (6) described techniques used in St.
Petersburg for purifying platinum. Also described
is a method used for compacting sponge (from a
fully dissolved phase) and manufacturing sheet by
forging and rolling. In their earlier paper on 19th
century platinum coins, Bachmann and Renner (7)
quoted work by Kieffer (8) who reported that platinum sponge was compressed under high pressure
to circular blanks which were sintered, again compressed, heated and struck into coins. The
presence of the surface striations and the oriented,
scaly appearance of the surfaces observed in the
present investigations indicated that the manufacturing route for the coins is more compatible with
the method described by Auer et al. (6) than that of
Kieffer (8), that is, the metal was forged and rolled,
before being struck into coins.
Conclusions
The results of our investigations, in particular
the SQUID microscope examination of the 1826
coronation medallion, indicate strongly that the
manufacturing route was one described by Auer et
al. (6) where partially purified platinum grains were
pressed to a block, sintered and then forged and
rolled to a sheet or strip, thus causing the residual
inhomogeneities to become elongated. Blanks were
then punched from the sheet and struck to coins.
Platinum Metals Rev., 2004, 48, (2)
Acknowledgements
Sincere thanks are due to Dr Michael Mück and the late
Professor Christoph Heiden, Institute of Applied Physics,
University of Giessen for the investigations with the SQUID
microscope. I also thank my colleagues Klaus Belendorff,
Wolfgang Hartmann, Margarete Hoss, Ronald Röhr, Hanne
Schneider and Friedhold Schölz for their invaluable assistance in
the work reported.
References
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3
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6
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8
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The Author
Dr David Lupton is the Development Manager for the Engineered
Materials Division of W. C. Heraeus in Hanau. His main interests
are the processing and applications of the platinum group metals
and refractory metals.
Improvements to the Microstructure and
Physical Properties of Pd-Cu-Ag Alloys
On page 10, right column, of the paper by A. Yu.
Volkov, in the January 2004 issue of Platinum Metals
Review the text should be d2r/dt2 = 0, not dr/d(t) = 0.
78
ABSTRACTS
of current literature on the platinum metals and their alloys
PROPERTIES
The Stabilization of Pt3Al Phase with L12 Structure
in Pt–Al–Ir–Nb and Pt–Al–Nb Alloys
C. HUANG, Y. YAMABE-MITARAI and H. HARADA, J. Alloys
Compd., 2004, 366, (1–2), 217–221
Gas-Phase Studies on the Reactivity of the
Azido(diethylenetriamine)platinum(II) Cation and
Derived Species
S. WEE, J. M. WHITE, W. D. McFADYEN and R. A. J. O’HAIR, Aust.
J. Chem., 2003, 56, (12), 1201–1207
The structure of the Pt3Al phase in the title alloys
was investigated using SEM, XRD, DTA and TEM
techniques. The alloys were prepared using pure
metal powders by an arc-melting method in an Ar
atmosphere. The structure form was determined to
be cubic L12. The stabilisation of the L12-Pt3Al structure at room temperature was due to the effect of Nb.
Collision-induced dissociation and ion–molecule
reactions of [Pt(dien)N]+ (1) were carried out in the
gas phase. Labelling studies ( 15N and 2H labelling of
the dien ligand) were also employed. The H atoms of
both the amino groups and the C backbone of the
dien ligand are involved in loss of NH3 from (1). The
crystal structure of [Pt(dien)3]+ was also determined.
Phase Transformation and Magnetic Anisotropy of
an Iron–Palladium Ferromagnetic Shape-Memory
Alloy
Coordination of Amines to Palladium(II)
Complexes of N 21,N 22-Bridged Porphyrins
J. CUI, T. W. SHIELD and R. D. JAMES,
(1), 35–47
Acta Mater., 2004, 52,
The f.c.c.-f.c.t. transformation in Fe7Pd3 is a weak
first-order thermoelastic transition. The latent heat of
the f.c.c.-f.c.t. transformation is 10.79 ± 0.01 J cm–3.
Magnetic measurements indicate the tetragonal martensitic phase has easy axes in the [1 0 0] and [0 1 0] (a-axes)
directions while [0 0 1] (c-axis) is the hard direction.
Microstructure and Mechanical Properties of
Ru–Al–Mo Alloys
T. D. REYNOLDS and D. R. JOHNSON,
(2), 157–164
Intermetallics, 2004, 12,
Alloys in the Ru-Al-Mo system were produced by
arc-melting and a cold crucible Czochralski technique. One set of alloys consisted of eutectic
microstructures between RuAl and a b.c.c. (Mo, Ru)
solid solution. The other set of alloys consisted of
RuAl and a h.c.p. (Ru, Mo) solid solution; a change
from eutectic to peritectic solidification occurs as the
Mo concentration increases. The RuAl-h.c.p. (Ru,
Mo) eutectic microstructure was found to consist of
RuAl fibres embedded in a (Ru, Mo) matrix.
Synthesis, Structure, and Reactivity of Arylfluoro
Platinum(II) Complexes
2003, 22, (25), 5235–5242
Organometallics,
trans-[PtPhFL2] (L = PPh3 (1) and PMe2Ph (2)) were
synthesised and then (1) was characterised by X-ray
crystallography. The equilibrium constant for the substitution of F– trans to phenyl in (1) by Cl– and I– was
determined. The Pt has preference for the halide: I >
Cl > F. (1) and (2) reacted with Me3SnPh within 2–15
min. (1) gave trans-[PtPhMe(PPh3)2], whereas (2) gave
trans-[PtPhMe(PMe2Ph)2] and trans-[PtPh2(PMe2Ph)2].
Platinum Metals Rev., 2004, 48, (2), 79–83
Pyridine and ethylenediamine (en) reacted with the
title Pd(II) porphyrins to give mixed-ligand Pd(II)
complexes. The splitting pattern in the Soret region
of their UV-vis spectra was dependent on whether
the porphyrinato Pd(II) was coordinated by neutral
ligands or anionic ligands. In the 1H NMR spectra of
en complexes of porphyrinato Pd(II), signal broadening of porphyrin b-pyrrole protons and a chemical
shift change of en protons were seen in the dichloride
in comparison with the bis(perchlorate).
Synthesis and Reactivity of Bucky Ruthenocene
h5-C5H5)
h5-C60Me5)(h
Ru(h
Y. MATSUO, Y. KUNINOBU, S. ITO and E. NAKAMURA,
Lett., 2004, 33, (1), 68–69
Chem.
Metathetical coupling of Ru(h -C60Me5)Cl(CO)2 and
CpNa resulted in a molecular hybrid of ruthenocene
and fullerene: Ru(h5-C60Me5)(h5-C5H5) (1). In (1), the
bonding between the Ru atom and the C60Me5 ligand
as well as between the metal atom and the Cp group
is very different from that of known ferrocene and
ruthenocene compounds. (1) is quite reactive compared to the rather stable bucky ferrocene compound.
5
Specific Heat of Sr4Ru3O10
CHEMICAL COMPOUNDS
P. NILSSON, F. PLAMPER and O. F. WENDT,
Y. TAKAO, T. TAKEDA and J. SETSUNE, Bull. Chem. Soc. Jpn.,
2003, 76, (8), 1549–1553
X. N. LIN, V. A. BONDARENKO, G. CAO and J. W. BRILL,
Commun., 2004, 130, (3–4), 151–154
Solid
A flux grown (FG) sample of Sr4Ru3O10 (1) had a
sharp mean-field-like anomaly at the onset of magnetic order, TC = 102 K, but a much broader anomaly,
indicative of residual heterogeneity, was observed for
an image furnace grown sample. Even for the FG
sample, however, the anomaly was at least an order of
magnitude smaller than would be expected for complete ordering of the spins. Neither sample exhibited
an anomaly at TM ~ 50 K. Anomalous behaviour was
observed at low temperatures for both samples,
indicative of the unusual magnetic order in (1).
79
ELECTROCHEMISTRY
IrO2/SnO2 Electrodes: Prepared by Sol–Gel
Process and Their Electrocatalytic for Pyrocatechol
Y. LIU, Z. LI and J. LI,
Acta Mater., 2004, 52, (3), 721–727
IrO2/SnO2 (10%:90%, molar ratio) electrodes (1)
were prepared by the sol-gel method. Oxide films
prepared at low temperature were in an amorphous
state, while hydrous IrO2 crystal and cassiterite phase
SnO2 were formed at 300ºC or even to 500ºC. (1)
with the highest electroactivity were formed at 400ºC.
For the electrocatalysis of pyrocatechol on (1), a
quasi-reversible process occurred. The detection limit
of pyrocatechol was 5 × 10–3 mM.
NiO-Based Composite Electrode with RuO2 for
Electrochemical Capacitors
X. M. LIU and X. G. ZHANG,
229–232
Electrochim. Acta, 2004, 49, (2),
NiO/RuO2 composite materials were prepared by
the coprecipitation method followed by heat treatment. XRD spectra indicated that the Ru oxide
particles were coated by NiO particles. RuO2 partly
introduced into NiO-based electrodes improved their
electrochemical performance and capacitive properties. A maximum specific capacitance of 210 F g–1 was
achieved for a NiO-based composite electrode with
10 wt.% RuO2 at –0.4 to 0.5 V in 1 mol l–1 KOH solution. Chemically modified composite electrodes had
more stable cycling properties than those of physically
modified electrodes.
PHOTOCONVERSION
The Photohydrochlorination of Platinum(IV)
Chloride in Chloroform
P. E. HOGGARD, A. J. BRIDGEMAN, H. KUNKELY and A. VOGLER,
Inorg. Chim. Acta., 2004, 357, (3), 639–643
When irradiated by light at 240 nm, PtCl4 in CHCl3
was converted to H2PtCl6, via a Pt(V) intermediate.
When irradiated by light at > 265 nm, PtCl4 was converted to H2PtCl4 and H2PtCl6 in equal amounts. At >
265 nm, the reaction may proceed by Cl dissociation
from a LMCT excited state of Pt(IV), through a
Pt(III) intermediate.
Multicolored Electrogenerated Chemiluminescence
from Ortho-Metalated Iridium(III) Systems
B. D. MUEGGE and M. M. RICHTER, Anal. Chem., 2004, 76, (1),
73–77
Bis(3,5-difluoro-2-(2-pyridyl)phenyl-(2-carboxypyridyl))-Ir(III), F(Ir)pic, is a blue emitter (lECL ~ 470 nm)
and bis[2,(2¢-benzothienyl)pyridinato-N,C3¢](acetylacetonate)Ir(III), (btp)2Ir(acac), emits in the red (lECL
~ 600 nm). The ECL solution spectrum of each complex is identical to its photoluminescence spectrum,
indicating the same metal-to-ligand excited states.
The oxidative reductive coreactant tri-n-propylamine
was used. ECL intensity increased in the presence of
Triton X-100 surfactant: up to 6-fold for F(Ir)pic and
up to 20-fold for (btp)2Ir(acac).
Platinum Metals Rev., 2004, 48, (2)
Enhanced Electrochemiluminescence from
Os(phen)2(dppene)2+ (phen = 1,10-phenanthroline
and dppene = bis(diphenylphosphino)ethene) in
the Presence of Triton X-100 (Polyethylene Glycol
tert-Octylphenyl Ether)
J. WALWORTH, K. J. BREWER and M. M. RICHTER,
Acta, 2004, 503, (2), 241–245
Anal. Chim.
The anodic oxidation of Os(phen)2(dppene)2+ produced electrochemiluminescence (ECL) in the
presence of tri-n-propylamine (TPrA) in aqueous surfactant solution. Increases in ECL efficiency (³
3-fold) and TPrA oxidation current (³ 2-fold) were
observed in Triton X-100 surfactant media.
Experiments indicated adsorption of surfactant on
the electrode surface.
Can Clay Emit Light? Ru(bpy)32+-Modified Clay
Colloids and Their Application in the Detection of
Glucose
P. Y. LIANG, P. W. CHANG and C. M. WANG, J. Electroanal. Chem.,
2003, 560, (2), 151–159
Electrochemical-quartz-crystal-microbalance techniques showed that Ru(bpy)33+ can be adsorbed by
montmorillonite K10 clay colloids. The resulting clay
particles (1) emitted light (lem = 610 nm) when they
were fabricated as thin films sandwiched by two conductive ITO electrodes with opposite biases. A
glucose optrode was fabricated using (1) and glucose
oxidase. The electrochemiluminescence signals behaved
as a function of [glucose]: 0.1–10 mM at pH 10. At
this pH, the detection limit reached 0.1 mM.
Photoelectrochemical Properties of
Supramolecular Species Containing Porphyrin
and Ruthenium Complexes on TiO2 Films
A. F. NOGUEIRA, A. L. B. FORMIGA, H. WINNISCHOFER,
M. NAKAMURA, F. M. ENGELMANN, K. ARAKI and H. E. TOMA,
Photochem. Photobiol. Sci., 2004, 3, (1), 56–62
Supramolecular species based on porphyrin and
Ru(II) polypyridyl complexes were used as sensitisers
on mesoporous TiO2. The peripheral Ru complexes
act as an antenna system by transferring electronic
charge to the porphyrin ring. meso-Tetrapyridylporphyrin coordinated to two Ru complexes converted
21% of the incident photons into current after excitation at the Soret band.
Photosensitization of Nanocrystalline SnO2 Films
with a tris (2,2¢-Bipyridine) Ruthenium(II)Fullerene Dyad
C. NASR, D. M. GULDI, M. MAGGINI, F. PAOLUCCI and S.
HOTCHANDANI, Fullerenes, Nanotubes, Carbon Nanostruct.,
2003, 11, (2), 121–133
A photoelectrochemical study of a tris(2,2¢-bipyridine)ruthenium(II)-C60 donor–acceptor dyad adsorbed on nanocrystalline semiconductor SnO2 electrodes was carried out. The results showed that the
incident photon-to-current conversion efficiency of
the dyad-based photoelectrochemical cells is ~ 10%.
80
Novel and Efficient Organic Liquid Electrolytes for
Dye-Sensitized Solar Cells Based on a Ru(II)
Terpyridyl Complex Photosensitizer
K. HARA, T. NISHIKAWA, K. SAYAMA, K. AIKA and H. ARAKAWA,
Renewable Hydrogen from Ethanol by Autothermal
Reforming
G. A. DELUGA, J. R. SALGE, L. D. SCHMIDT and X. E. VERYKIOS,
Science, 2004, 303, (5660), 993–997
Chem. Lett., 2003, 32, (11), 1014–1015
EtOH and EtOH-H2O were found to be converted directly into H2 with ~ 100% selectivity and >
95% conversion, with a residence time on a Rh/CeO2
catalyst of < 10 ms. The reactions run at ~ 700ºC,
but as the process is exothermic, the starting mixture
only needs to be heated to ~ 140ºC. The mixture is
then cooled to 400ºC and passed over a Pt/CeO2 catalyst, where any CO reacts with hot H2O to give CO2
and H2. Onboard reforming of liquid fuel into H2
provides an alternative to storing H2 for fuel cells.
APPARATUS AND TECHNIQUE
Transient Studies of Direct N2O Decomposition
over Pt–Rh Gauze Catalyst. Mechanistic and
Kinetic Aspects of Oxygen Formation
An electrolyte composed of 1-ethyl-3-methylimidazolium iodide, I2 and MeCN solvent has been
developed for a nanocrystalline TiO2 solar cell sensitised with a Ru(II) terpyridyl complex (1).
Trithiocyanato 4,4¢,4²-tricarboxy-2,2¢:6¢,2²-terpyridine Ru(II) (black dye) was used as (1). Under AM 1.5
irradiation (100 mW cm–2 ), a solar energy-to-electricity
conversion efficiency of 8.0% was achieved.
Thin Film Dissolved Oxygen Sensor Based on
Platinum Octaethylporphyrin Encapsulated in an
Elastic Fluorinated Polymer
R. N. GILLANDERS, M. C. TEDFORD, P. J. CRILLY
R. T. BAILEY, Anal. Chim. Acta, 2004, 502, (1), 1–6
and
The title sensor (1) was fabricated by encapsulating
Pt octaethylporphyrin in an O2 permeable elastic fluorinated copolymer matrix. Phosphorescence, which
was partially quenched by dissolved O2, was observed
by (1) when (1) was immersed in H2O. At elevated
temperatures the dye aggregated. (1) exhibits good
sensitivity, rapid response and photostability.
Carbonate-Melt Oxidized Iridium Wire for pH
Sensing
M. WANG and
1606–1615
S. YAO,
Electroanalysis, 2003, 15, (20),
A thick, uniform and dense ceramic oxide layer was
grown by oxidation on the surface of an Ir wire in
molten Li carbonate. After treatment in acid solution,
the hydrated oxide layer was characterised as
Li0.86IrO2.34(OH)0.76·0.39H2O (1). An electrode made
with a film of (1) exhibited good pH sensitivity and
stability, even in strong acid/base solutions. The electrode has excellent long term stability over 2.5 years.
HETEROGENEOUS CATALYSIS
The Influence of Ir and Pt Addition on the
Synthesis of Fullerenes at Atmospheric Pressure
G. N. CHURILOV, R. B. WEISMAN, N. V. BULINA, N. G. VNUKOVA,
A. P. PUZIR, L. A. SOLOVYOV, S. M. BACHILO, D. A. TSYBOULSKI
and G. A. GLUSHENKO, Fullerenes, Nanotubes, Carbon
Nanostruct., 2003, 11, (4), 371–382
The addition of metallic Pt and Ir to a fullereneforming atmospheric-pressure plasma reactor
influenced the generation of carbonaceous products.
The added metals were efficiently dispersed into the
plasma. The addition of Pt increased the proportion
of C60 oxides and decreased the proportion of higher
fullerenes, whereas Ir caused a noticeable shift in the
fullerene distribution towards C60. The Ir also caused
a reduction of the soot particle size and the formation
of a large quantity of C nanotubes.
Platinum Metals Rev., 2004, 48, (2)
E. V. KONDRATENKO and J. PÉREZ-RAMÍREZ,
2003, 91, (3–4), 211–216
Catal. Lett.,
Transient experiments were carried out in a temporal analysis of products (TAP) reactor by pulsing
N216O over 18O-pretreated Pt-Rh gauze catalyst at
1073–1273 K. From isotopic studies and fitting of
transient data from N2O, N2 and O2, two separate
routes for O2 formation during catalytic N2O decomposition were identified. These are: (a) interaction of
N2O with adsorbed O species formed from N2O, and
(b) recombination of adsorbed O species on the catalyst surface. The relative contributions of (a) and (b)
depend on the reaction temperature.
Microwave-Assisted Catalytic Transfer
Hydrogenation of Safflower Oil
B. L. A. PRABHAVATHI DEVI, M. S. L. KARUNA, K. NARASIMHA
RAO, P. S. SAIPRASAD and R. B. N. PRASAD, JAOCS, 2003,
80, (10), 1003–1005
Catalytic transfer hydrogenation (CTH) of safflower oil using aqueous ammonium formate as H
donor and Pd/C as catalyst was carried out in a
closed vessel under controlled microwave irradiation
conditions. Good selectivity in the complete reduction of linoleic acid to mono-unsaturated acid was
achieved with a slight increase in stearic acid, compared to other reported CTH methods. No emulsifier
or high ratios of H2O to oil were required.
Improvement of Catalyst Durability by Deposition
of Rh on TiO2 in Photooxidation of Aromatic
Compounds
H. EINAGA, T. IBUSUKI and S. FUTAMURA, Environ. Sci. Technol.,
2004, 38, (1), 285–289
The deposition of Rh onto TiO2 improved the TiO2
catalyst durability in benzene photooxidation. The
role of Rh0 was to reduce the amount of intermediates and byproducts on the catalyst surface. A Rh
loading of 0.5–1.0 wt.% produced the highest reaction rate. The deactivation of Rh/TiO2 was
prevented by heat treatment in a flow of H2 or N2
after the photoirradiation in humidified air.
81
HOMOGENEOUS CATALYSIS
Rhodium Catalysed Coupling Reaction of Myrcene
with Ethyl Acetoacetate in the Ionic Liquid
1-Ethyl-3-methylimidazolium Triflimide
Process Development and Pilot Plant Scale
Synthesis of Spiro[3.5]nonane-6,8-dione
Org. Process Res.
K. DHANALAKSHMI and M. VAULTIER, Tetrahedron, 2003, 59,
A two step pilot plant process for the production of
spiro[3.5]nonane-6,8-dione has been developed. The
first step is the epoxidation of spiro[3.5]non-7-en-6one mediated by sodium perborate. The resulting
crude epoxide afforded spiro[3.5]nonane-6,8-dione
in 26% overall yield via a Pd-catalysed rearrangement.
Pd(PPh3)4 was generated in situ from Pd(OAc)2 and
PPh3 in the presence of triethylamine as the reducing
agent. Pd(PPh3)4 formed the active catalytic species
upon reaction with rac-BINAP.
[RhCl(COD)]2/TPPMS (triphenylphosphinemonosulfonate sodium salt) can be used for the coupling
reaction of myrcene with ethyl acetoacetate in the
title ionic liquid [emim][NTf2]. The coupling product
was obtained in 93% isolated yield without formation
of side product. The catalytic system could not be
recycled due to its deactivation.
Palladium-Catalyzed Aryl-Amidation. Synthesis of
Non-Racemic N-Aryl Lactams
B. BREIT and E. FUCHS, Chem. Commun., 2004, (6), 694–695
T. E. LEHMANN, O. KUHN and J. KRÜGER,
Dev., 2003, 7, (6), 913–916
R. G. BROWNING, V. BADARINARAYANA, H. MAHMUD
C. J. LOVELY, Tetrahedron, 2004, 60, (2), 359–365
and
The Buchwald-Hartwig aryl amination method was
used to obtain a series of chiral, non-racemic N-aryl
pyrrolidinones from a common pyrrolidinone precursor and the corresponding aryl bromide. The
Buchwald catalyst/ligand system was Pd2 dba3/
Xantphos. The stereochemical integrity of the N-aryl
lactam after cross-coupling was proven by synthesis
of the racemic compounds and comparison by 1H
NMR spectroscopy using Pirkle’s chiral solvating
agent.
Palladium Catalyzed Reaction in Aqueous DMF:
Synthesis of 3-Alkynyl Substituted Flavones in the
Presence of Prolinol
M. PAL, V. SUBRAMANIAN, K. PARASURAMAN and K. R.
YELESWARAPU, Tetrahedron, 2003, 59, (48), 9563–9570
(S)-Prolinol facilitated the coupling reaction of terminal alkynes with 3-iodoflavone using (PPh3)2PdCl2
as catalyst and CuI as cocatalyst in aqueous DMF. No
significant side reactions such as dimerisation of terminal alkynes or opening of the flavone occur. This
is a mild and convenient method for the synthesis of
3-alkynyl substituted flavones of potential biological
interest.
Cationic Rhodium(I)/PPh3 Complex-Catalyzed
Dehydrogenation of Alkanethiols to Disulfides
under Inert Atmosphere
K. TANAKA and K. AJIKI, Tetrahedron Lett., 2004, 45, (1), 25–27
[Rh(cod)2]BF4/PPh3 was an effective catalyst system for the dehydrogenation of primary or secondary
alkanethiols to symmetrical disulfides under an inert
atmosphere of Ar with CH2Cl2 as the solvent. The
highest yield of disulfides was achieved at 4ºC for 1
h. A longer reaction time (16 h) for the reaction of a
primary alkanethiol at the same temperature
decreased the yield of disulfides. This dehydrogenation reaction is reversible and the formation of
disulfide is a kinetically favourable process.
Platinum Metals Rev., 2004, 48, (2)
(50), 9907–9911
Phosphabarrelene-Rhodium Complexes as Highly
Active Catalysts for Isomerization Free
Hydroformylation of Internal Alkenes
Phosphabarrelene-Rh complexes (1) were shown to
be extremely active hydroformylation catalysts.
Turnover frequencies £ 12,000 h–1 were observed for
the hydroformylation of internal cyclic olefins. (1)
can enable a position-selective hydroformylation of
an internal double bond (C=C) essentially free of
alkene isomerisation to occur.
Numerical Modeling of Differential Kinetics in the
Asymmetric Hydrogenation of Acetophenone by
Noyori’s Catalyst
R. HARTMANN and P. CHEN,
(12), 1353–1359
Adv. Synth. Catal., 2003, 345,
An analysis of the catalytic cycle by which transRuCl2[(S)-binap][ (S, S )-dpen] asymmetrically hydrogenates acetophenone combines numerical integration of the rate equations and experimental
measurement of the time dependence of rates, rather
than concentrations. The method yields rate constants for activation, dihydrogen cleavage, and
hydride transfer. The turnover-limiting step changes
from dihydrogen cleavage to hydride transfer if H2
pressure is increased, and this also occurs during the
acetophenone hydrogenation under typical conditions.
FUEL CELLS
The Role of the WOx Ad-Component to Pt and
PtRu Catalysts in the Electrochemical CH3OH
Oxidation Reaction
L. X. YANG, C. BOCK, B. MacDOUGALL and J. PARK,
Electrochem., 2004, 34, (4), 427–438
J. Appl.
High surface area catalysts, Pt/C, PtWOx/C,
PtRu/C and PtRuWOx/C, were prepared via a chemical reduction route using single metal precursor salts.
The addition of Ru decreased the particle size. The
Ru was found to be partly incorporated into the f.c.c.
lattice of Pt and to form a single Ru catalyst component. The PtRuWOx/C catalyst has a high degree of
catalyst particle agglomeration. Both Ru containing
catalysts showed significantly higher activities for the
CH3OH oxidation reaction.
82
Homogeneous and Controllable Pt Particles
Deposited on Multi-Wall Carbon Nanotubes as
Cathode Catalyst for Direct Methanol Fuel Cells
Carbon-Supported Pt–Fe Alloy as a MethanolResistant Oxygen-Reduction Catalyst for Direct
Methanol Fuel Cells
W. LI, C. LIANG, W. ZHOU, J. QUI, H. LI, G. SUN
A. K. SHUKLA, R. K. RAMAN, N. A. CHOUDHURY, K. R. PRIOLKAR,
P. R. SARODE, S. EMURA and R. KUMASHIRO, J. Electroanal.
Carbon, 2004, 42, (2), 436–439
and Q. XIN,
The size of deposited Pt particles on multi-wall
nanotubes (MWNTs) was controlled by using different concentrations of ethylene glycol-deionised (DI)
H2O. The Pt loading was ~ 10 wt.% for all the samples. The Pt/MWNTs produced using ethylene
glycol-5% DI H2O exhibit higher O reduction reaction activity and superior cell performance in DMFC
tests, than those from 0%, 40% and 70% DI H2O.
Mechanism of Preparation Process and
Characterization of Highly Dispersed Pt/C Cathode
Electrocatalyst for Direct Methanol Fuel Cells
Z. ZHOU, W. ZHOU, L. JIANG, S. WANG, G. WANG, G. SUN and
Q. XIN, Chin. J. Catal., 2004, 25, (1), 65–69
A modified polyol process was used to prepare 40%
Pt/C (1) for DMFCs. Highly dispersed Pt nanoparticles with narrow size distribution (mean size of 2.9
nm) supported on C were obtained. DMFC tests
indicated that (1) had better electrocatalytic activity
and stability for the O reduction reaction in DMFCs
than its commercial equivalent. The redox reaction
between PtCl62– and ethylene glycol was confirmed to
take place via a single-step reaction path.
Analysis of the High-Temperature Methanol
Oxidation Behaviour at Carbon-Supported Pt–Ru
Catalysts
A. S. ARICÒ, V. BAGLIO, A. DI BLASI, E. MODICA, P. L.
ANTONUCCI and V. ANTONUCCI, J. Electroanal. Chem., 2003,
557, 167–176
MeOH oxidation (1) at three Pt–Ru catalysts varying by the concentration of active phase on the C
support was investigated at 80–130ºC. When the catalyst had intrinsically high catalytic activity the fuel
cell performance was enhanced, but the MeOH reaction rate was less influenced by an increase in
coverage of active species. Catalysts with a higher
degree of alloying and metallic behaviour on the surface are more active towards (1).
Preparation of Pt–Ru Bimetallic Anodes by
Galvanostatic Pulse Electrodeposition:
Characterization and Application to the Direct
Methanol Fuel Cell
C. COUTANCEAU, A. F. RAKOTONDRAINIBÉ, A. LIMA,
E. GARNIER, S. PRONIER, J.-M. LÉGER and C. LAMY, J. Appl.
Electrochem., 2004, 34, (1), 61–66
Using a galvanostatic pulse electrodeposition technique, Pt and Ru were electrodeposited on C
electrodes to prepare DMFC anodes (1) with different Pt:Ru atomic ratios. Most of (1) consisted of 2 mg
cm–2 of Pt-Ru alloy particles with the desired composition and with particle sizes of 5–8 nm.
Electrochemical tests in a single DMFC found that
the best Pt:Ru atomic ratio at 50–110ºC was 80:20.
Platinum Metals Rev., 2004, 48, (2)
Chem., 2004, 563, (2), 181–190
The electrocatalyst Pt-Fe/C crystallises in an
ordered f.c.t. crystal structure with higher proportions of active Pt sites than Pt/C. Pt-Fe/C exhibits
significantly high O reduction activity in the presence
of MeOH, while Pt/C shows a MeOH poisoning
effect under similar conditions.
ELECTRICAL AND ELECTRONIC
ENGINEERING
Molecule-Independent Electrical Switching in
Pt/Organic Monolayer/Ti Devices
D. R. STEWART, D. A. A. OHLBERG, P. A. BECK, Y. CHEN,
R. STANLEY WILLIAMS, J. O. JEPPESEN, K. A. NIELSEN and
J. FRASER STODDART, Nano Lett., 2004, 4, (1), 133–136
Electronic devices (1) comprising a LangmuirBlodgett molecular layer sandwiched between planar
Pt and Ti metal electrodes were shown to function as
switches and tunable resistors over a 102–105 W range
under current or voltage control. Reversible hysteretic switching and resistance tuning was
qualitatively similar for the very different molecular
species: Cd eicosanoate salt, an amphiphilic [2]rotaxane (R) and the dumbell-only component of R.
Structural and Morphological Characterization by
Energy Dispersive X-ray Diffractometry and
Reflectometry Measurements of Cr/Pt Bilayer
Films
B. PACI, A. GENEROSI, V. R. ALBERTINI, E. AGOSTINELLI,
G. VARVARO and D. FIORANI, Chem. Mater., 2004, 16, (2),
292–298
Double-layer Cr/Pt thin films were deposited by
pulsed laser deposition at room temperature to
600ºC, both on crystalline (Si and MgO) and on
amorphous (SiO2) substrates. Epitaxial films with a
very good texture and a very smooth surface were
obtained. With the excimer laser at an energy fluence
of 5 J cm–2, the Pt/Cr multilayer shows a high crystalline quality independent of deposition temperature.
Ballistic Transport in Metallic Nanotubes with
Reliable Pd Ohmic Contacts
D. MANN, A. JAVEY, J. KONG, Q. WANG and H. DAI, Nano Lett.,
2003, 3, (11), 1541–1544
Contacting metallic single-walled C nanotubes by
Pd gave highly reproducible ohmic contacts, which
were used for an examination of ballistic transport in
metallic nanotubes. The Pd ohmic contacts were
more reliable than previously used Ti ohmic contacts.
Pt gave non-ohmic contacts to metallic nanotubes.
The length of the nanotube under the metal contact
area is electrically turned off; transport occurs from
metal to nanotube at the edge of the contacts.
83
NEW PATENTS
ELECTROCHEMISTRY
Durable Electrode for Electrolysis
ISHIFUKU MET. IND. CO LTD
Japanese Appl. 2003-293,196
An electrode (1) is provided with: (a) a substrate of
Ti or a Ti alloy; (b) an intermediate layer of: a Ti-Ta
alloy layer, a porous Ta layer, and a layer of mixed Ir
oxide and Ta oxide; and (c) an external layer of 50–98
mol% Ir oxide and 2–50 mol% Ta oxide. (1) has sufficient durability even when used as an anode for high
speed plating of metal at high current density.
Photovoltaic Cell Interconnection
U.S. Patent 6,706,963
A photovoltaic module (1) with improved cell
interconnections comprises a photosensitising agent
of a Ru- or Os-complex, and an Fe complex. (1)
includes a plurality of photovoltaic cells each having
a photosensitised nanomatrix layer and a charge carrier “media”. Preferably, the cells further include a
catalytic “media” layer of Pt. The photovoltaic cells
are disposed between two electrical connection layers.
KONARKA TECHNOL. INC
Fructose Concentration Sensor
ELECTRODEPOSITION AND SURFACE
COATINGS
Palladium Plating Solution
European Appl. 1,396,559
A Pd plating solution (1) contains: 0.1–40.0 g l–1 Pd;
pyridine carboxylic acid and/or soluble Fe, Zn, Th,
Se and/or Te salts; an amine derivative of pyridine
carboxylic acid; an aldehydebenzoic acid derivative;
and an anionic surfactant or an ampholytic surfactant. (1) can form high-purity stable Pd film deposits,
thickness of 5 µm, which are free from cracks.
KOJIMA CHEM. CO LTD
Electroless Platinum-Rhodium Alloy Plating
U.S. Patent 6,706,420
An electroless plating composition comprises an
aqueous solution consisting essentially of: (a) a water
soluble Pt nitrite salt or Pt ammine-nitrite salt; (b) a
water soluble Rh nitrite salt or Rh ammine-nitrite salt;
(c) ammonium hydroxide; and (d) hydrazine hydrate.
A uniform coating of a Pt-Rh alloy can be deposited
on virtually any substrate and material, including
fibres and powders, of any geometrical shape.
HONEYWELL INT. INC
APPARATUS AND TECHNIQUE
Detection of Oxygen Concentration in Exhaust Gas
ROBERT BOSCH GmbH
World Appl. 03/106,989
A sensor element is claimed for determining the O2
concentration in the exhaust gas of ICEs, in particular for a broadband lambda probe. It comprises: a
solid electrolyte, which forms a pump cell; and a catalyst comprising two electrically connected electrodes,
of Pt, Rh, Pd and/or their alloys, in an antichamber
in the electrolyte. Measuring inaccuracies even with
very high quantities of hydrocarbons are prevented.
Preparation of Noble Metal Nanotubes
World Appl. 04/005,182
A nanotube (1) has a skeleton comprising: a single
metal element (Pt, Pd, Rh, Ir, Au or Ag) or a mixture
of two or more in an arbitrary ratio, with Ru or a base
metal. (1) has an outer and an inner diameter, of ~
5–7 nm and ~ 2–4 nm, respectively; a thickness of ~
1–2 nm and a length of ³ 10 nm. (1) are formed by
admixing nonionic or ionic surfactants of different
sizes, and then reducing the metal.
JAPAN SCI. TECHNOL. CORP
Platinum Metals Rev., 2004, 48, (2), 84–87
Japanese Appl. 2003-227,811
A fructose concentration sensor comprises a Au
electrode where fructose dehydrogenases is immobilised by a combination of Au and cysteamine, a Pt
counter electrode, a Co phenanthroline complex (1)
solution, and a Ag/AgCl reference electrode. (1) can
be easily adjusted and reversible oxidation reduction
can occur at relatively low potential. The sensor has
high selectivity and sensitivity.
TAMA TLO KK
Oxygen Sensor Element
Japanese Appl. 2003-315,303
An oxygen sensor element (1) comprises: a sensor
section with a reference- and a measuring-electrode(s) made of Pt formed on opposing surfaces of
a long ZrO2 solid electrolyte plate; and a heater section with a heating element embedded in a ceramic
insulating layer. (1) has excellent gas responsiveness
and is capable of raising a temperature rapidly, while
preventing the breakage of the element.
KYOCERA CORP
HETEROGENEOUS CATALYSIS
Three-Way Catalyst with NOx Storage Component
JOHNSON MATTHEY PLC
World Appl. 03/100,228
A spark engine comprises an exhaust system with a
three-way catalyst (TWC) containing Pt, Pd, Rh, Ru,
Os and/or Ir; a NOx storage component of an alkali metal (K or Cs), an alkaline-earth metal (Mg) or a
rare-earth metal (La, etc.); and an engine control unit
to control the air:fuel ratio (1) of the engine. The
amount of NOx contacting the TWC during lean
running operation is determined by response to data
input from a sensor to indicate the remaining NOx
storage capacity (2) of the TWC. (1) is returned to
stoichiometry when (2) is below a predetermined
value, the arrangement being such as to prevent more
NOx entering the atmosphere.
Platinum-Rhenium-Tin Catalyst
U.S. Patent 6,670,490
An improved hydrogenation catalyst (1) comprises
0.5–3% Pt, 1–10% Re and 0.1–5% Sn supported on
C, based on total weight of (1). (1) is used for hydrogenation of an hydrogenatable precursor in an aqueous
solution, especially to produce tetrahydrofuran and
1,4-butanediol at 150–260ºC.
E. I. DU PONT DE NEMOURS CO
84
Platinum Metal Catalysts by Immersion Coating
BASF AG
U.S. Patent 6,676,919
Pt metal catalysts (1) are prepared by immersion
coating a metallic support with at least one Pt metal
complex. An aqueous medium which comprises Pt
metal complex(es), reduction agent(s) and complexer(s) with pH > 4 is brought into contact with the
metallic support to deposit the Pt metal as discreet,
immobilised particles. The platinum metal comprises
80–100% wt.% Pd and 0–20% wt.% Pt or Ir. (1)
are used for producing H2O2 or for hydrogenating
organic compounds.
Three-Way Catalyst
U.S. Patent 6,680,036
A three-way catalyst for vehicles contains an oxygen storage component comprising a mixed oxide (1)
of Mn : Zr with molar ratio of oxides of 50:50–70:30
and surface area < 10 m2 g–1. (1) is obtained by coprecipitation, sol-gel or gel precipitation. The
catalytically active metal is Pt, Pd and/or Rh. (1) can
also contains a dopant selected from ceria and the
oxides of Nd, Pr, La, etc. (1) gives improved capacity
even after exposure to high temperatures.
JOHNSON MATTHEY PLC
Fischer-Tropsch Catalyst Enhancement
U.S. Patent 6,706,661
Both the activity and the CH4 selectivity of a dispersed active metal (DAM) hydrogenation catalyst
are enhanced by low temperature oxidation in a slurry phase forming a stable, unique oxidised catalyst
precursor (1). This is subsequently reduced by treatment with H2 at elevated temperature. Reducible
promoters of Ru, Pd, Re, Fe and/or Co are mixed
with (1) as a solution of their reducible salts. (1)
are recovered from the mixture and treated with Hcontaining gas to simultaneously form the metals and
reactivate the DAM hydrogenation catalyst.
EXXONMOBIL RES. ENG. CO
HOMOGENEOUS CATALYSIS
Rhodium-Catalysed Hydroformylation of Olefins
OXENO OLEFINCHEMIE GmbH World Appl. 03/095,406
Aldehydes and alcohols are produced by the Rhcatalysed hydroformylation of olefins having 6–20C
atoms. The discharge of the hydroformylation reaction is subsequently separated by distillation into the
hydroformylation products and a solution containing
Rh. The latter is redirected into the hydroformylation
reaction. The Rh concentration of the redirected
solution is 20–150 mass ppm.
Cross-Coupling of Alkyl(dialkylphenyl)indenes
BOULDER SCIENTIFIC CO
World Appl. 03/101,601
A cross-coupling synthesis of 2-alkyl-4-(2,6-dialkylphenyl)indenes comprises treating a 2-alkyl haloindene with a 2,6-dialkylboronic acid in non-interfering hydrocarbon solvent. A cross-coupling catalyst
(1) containing PdCl2 and 1,5-cyclooctadiene is present. (1) improves an aryl chloride transformation.
Process for Conjugating C=C Double Bonds in Oils
ARCHER-DANIELS-MIDLAND CO World Appl. 04/016,350
A process for conjugating organic compounds (1)
containing methylene interrupted C=C, such as triglyceride oils (linseed, soybean, sunflower, fish oils,
etc.) comprises: solubilising Ru trichloride hydrate
(~ 5–100 ppm based on the weight of (1)) with an
organic solvent (monoalcohols or carboxylic acid) to
form a first mixture. Then, further contacting this
first mixture with (1) at a sufficient temperature and
time to conjugate (1). This process can conjugate
methylene interrupted C=C found in drying and
semi-drying oils.
Combustion Improvement Device for Petroleum Fuel
Japanese Appl. 2003-227,422
A combustion device noticeably decreases a toxic
substance contained in an exhaust gas by improving
the combustion of petroleum fuel by reforming physical properties of the petroleum fuel. A magnetism
generating device is disposed on a sheet (1) carrying
Au micropowder and a Pt catalyst (2) micropowder
in a semiconductor material. Magnetic flux is released
through (1). (2) contains Pt, Cu, Co, Mo and/or Yb.
Preparing Oxirane Organosilicon Compositions
GENERAL ELECTRIC CO
U.S. Patent 6,706,840
An organosilicon composition is prepared from an
olefin and a SiH with a hydrosilation catalyst PtL2X2.
X is chloride, bromide and iodide, in an amount of <
1 ppm based on the weight of the product. L is triphenylphosphine, etc. The method is useful in lowering
the cost, coloration, and stability of the product, particularly when an oxirane-containing olefin is used in
the hydrosilation. No inhibitor is needed to prevent
undesired polymerisation of oxiranes in the reaction,
and no product purification is required after removal
of volatile components. The cured oxirane-containing organosilicon composition functions as an LED.
Dehydrogenation Catalyst for Alicyclic Compounds
OSAKA GAS CO LTD
Japanese Appl. 2003-320,251
A dehydrogenation catalyst (1) for an alicyclic compound contains a fibrous activated C (2) and at least
one metal selected from Pt, Pd, Rh, Ir, Ru, Ni, Co,
Fe, Cu, Ag, and Au. (2) has a specific surface area of
at least 600 m2 g–1, an entire fine pore volume of at
least 0.2 cm3 g–1, and an average fine pore diameter of
10–70 Å. (1) has a high activity and is capable of promoting the dehydrogenation reaction of an alicyclic
compound at low temperatures.
Japanese Appl. 2003-226,674
A tert-triarylamine (1) is produced by subjecting a
diarylamine bearing 1–4 secondary diarylamino
groups in one molecule and an aryl iodide to a condensation reaction in the presence of Pd acetate, tricyclohexylphosphine and Na or K tert-butoxide as
the catalyst system, at 0–150ºC for 1–24 h. (1) are
selectively produced without forming byproducts.
There is no restriction in manufacturing and handleability. (1) is a raw material for electronic products.
KANTAMU KK
Platinum Metals Rev., 2004, 48, (2)
Triarylamine Production
HODOGAYA CHEM. CO LTD
85
Optically Active 3-Quinuclidinol
KAWAKEN FINE CHEM. CO LTD
Japanese Appl. 2003-277,380
An optically active 3-quinuclidinol (1) is produced
by the hydrogenation of 3-quinuclidinone in the presence of an optically active bidentate phosphine ligand
and an optically active Ru(II) complex (2). (2) contains an optically active 1,2-ethylenediamine type
ligand (with H or an alkyl group; and alkyl, aryl or
aralkyl group which may have a substituent group,
and two of which may form an alkylene) and a base.
A highly optical isomer of (1) is obtained using an
enantioselectively reducible (2).
Polymerisation Initiator System
KURARAY CO LTD
Japanese Appl. 2003-321,509
A polymer of narrow molecular weight distribution
is obtained by subjecting a radically polymerisable
monomer (1) to living polymerisation. A polymerisation initiator of a transition metal complex with an
electron donative group on the indenyl ring of a
chloroindenylbis(triarylphosphine)Ru, and an organic
halogen compound, are present. (1) is a methacrylic
acid ester, etc. A side reaction is suppressed and the
molecular weight is controlled.
FUEL CELLS
Hydrocarbon Reforming in Protonic Ceramic Fuel Cell
PROTONETICS INT. INC
World Appl. 03/099,710
A process to convert hydrocarbons and H2O
vapour into H2, CO and CO2, and a fuel cell to produce electricity are claimed. The fuel cell comprises: a
metallic and/or mixed conducting anode of metallic
Pt, Ni alloy or a mixture of Ni oxide and oxide ceramic, capable of operating at < 850ºC; a cathode; and a
proton-conducting ceramic electrolyte. Gaseous
hydrocarbon fuels contact the anode; O2 and H2O
vapour contact the cathode.
Gas Diffusion Layer for Fuel Cells
al.
World Appl. 04/004,054
A gas diffusion layer for a fuel cell is formed from a
porous material comprising a solid matrix and interconnected pores, where part of at least one external
surface is coated with an electrically conductive material (1) of resistivity < 20 W cm. (1) are metals, such as
Pt, Au, Ni, Co, etc., or their alloys, etc. They may be
applied to the foam strands by electroplating, electroless plating, sputtering, plasma vapour deposition, etc.
A. THOMPSON et
ELECTRICAL AND ELECTRONIC
ENGINEERING
Semiconductor Electronic Device
European Appl. 1,367,644
A semiconductor electronic device (1) comprises a
die of a semiconductor material formed with a plurality of contact pads (2), electrically connected to a
holder by wire leads. (1) comprises a welding stud
bump containing Pd, Au, or their alloys, formed on
each (2). (1) is highly reliable and can be fabricated
simply at low cost.
STMICROELECTRONICS SRL
Semiconductor Device
European Appl. 1,385,218
A semiconductor device (1) able to increase the
mobility of carriers and reduce the current in the OFF
state is claimed. (1) includes a gate electrode (2), a first
and a second electrode formed from Pd, Pt, Cr, Ta,
etc., and an insulating layer of resin, etc., on (2). The
first and second electrodes are on the insulating layer
with an organic semiconductor layer (3) between. A
first resistance layer comprises conductive polymers
and has lower electrical resistance than (3).
RICOH CO LTD
Platinum-Cobalt Sputtering Targets
European Appl. 1,395,689
A Co-Cr-B-Pt sputtering target alloy having multiple phases can also include Cr, B, Ta, Nb, C, Mo, Ti,
V, W, Zr, Zn, Cu, Hf, O, Si or N. The alloy is prepared by mixing Pt powder with a Co-Cr-B master
alloy, ball milling followed by hot isostatic pressing to
densify the powder into the alloy.
HERAEUS INC
Dielectric Interconnect Frame
World Appl. 04/013,934
A frame structure for a transmit/receive module (1)
configured to transmit and receive electromagnetic
radiation comprises a frame component (2) formed as
a single piece from a synthetic resin dielectric material. (2) has a thin film coating including a Pd layer on
top of a Ti getter layer to provide a ground connection and electromagnetic shielding when the frame
structure is incorporated into (1). The synthetic resin
dielectric material provides (2) with a range of compressibility that gives an effective ground connection.
(1) is used for H2 getters for GaAs hermetically-sealed
packaging.
RAYTHEON CO
Contact Resistance Reduction in Organic FETs
World Appl. 04/017,440
Reducing the contact resistance in organic field
effect transistors made with Pd contacts is achieved
by layer(s) of either Pd(0) or Pt(0) phosphines. A first
contact injects charge carriers into the semiconductor
(1) and a second contact extracts charge carriers from
(1). The phosphine layer(s) lie between the contacts
and (1), and allow charge transfer between the first
contact and the organic semiconductor material. The
phosphine gives significantly reduced contact resistance between the contact and the organic material.
INFINEON TECHNOL. AG
Devices Containing Platinum-Iridium Films
SYMYX TECHNOL. INC
U.S. Patent 6,682,837
The electrochemical conversion of a hydrocarbonbased fuel (1) (such as MeOH) and O2 to H2O, CO2
and electricity in a fuel cell (1) is claimed. (1) comprises: an anode, a cathode, a proton exchange
membrane electrolyte, and an external circuit. (1) is
contacted with a ternary metal alloy catalyst (in at. %):
25–50 Pt, 25–55 Ru, and 5–45 Pd, to oxidise the fuel.
The difference between Ru and Pt is £ ~ 20 at. %.
Platinum Metals Rev., 2004, 48, (2)
86
Devices Containing Platinum-Iridium Films
MICRON TECHNOL. INC
U.S. Patent 6,660,631
Pt-Ir films (1), formed on semiconductor devices,
such as capacitors, integrated circuit devices, memory cells, etc., are deposited by vaporising the precursor compositions (1) and directing them toward the
semiconductor substrate by CVD. (1) comprises a Pt
complex selected from CpPt(Me)3 (Cp is substituted
or unsubstituted cyclopentadienyl), Pt(CO)2Cl2, cisPt(CH3)2[(CH3)NC]2, (COD)Pt(CH3)2, etc.
Magnetic Recording Media with Ruthenium
U.S. Patent 6,680,106
The corrosion protection of magnetic recording
media (1) is achieved by using: a thin protective barrier layer of Ru < 10 Å formed of elemental Ru, a Ru
oxide and/or a Ru alloy containing 1–50 at.% of Ti,
Mo, W, Nb, Ta, etc., on the magnetic layer. A C protective layer (10–50 Å in thickness) is then formed on
the corrosion protective layer. (1) are used for drive
programs with reduced flying height, or pseudocontact/proximity recording.
Low Resistance Conductor Leads for GMR Heads
HEADWAY TECHNOL. INC
U.S. Patent 6,706,421
A lead structure for use with a magnetoresistive
sensing element in a magnetic disk system comprises
a layer of Ru or Rh sandwiched between layers of a
Ni-Cr alloy (1). The lower (1) layer acts as a seed layer
to ensure that the Ru and Rh layers have crystal structures corresponding to low resistivity phases. The
interfaces between these three layers introduce a minimum of interfacial scattering of the conduction
electrons thus keeping dimensional increases in resistivity to a minimum.
SEAGATE TECHNOLOGY LLC
Selective Formation of Top Memory Electrode
ADV. MICRO DEVICES INC
U.S. Patent 6,686,263
Electroless plating for the formation of the top
electrode of an organic memory device operates at
relatively low temperatures (35–85ºC). The electroless process is utilised to form conductive layers, such
as electrodes and the like, from Pd, Pt, Ag, Ni, Co, Ti,
Zn, etc., and includes depositing an activation compound, such as SnPd, on selected areas of conductive
organic media. A chemical solution containing metal
ions is then applied. The ions are reduced and are
thus plated onto the conductive layer.
Plated Metal Transistor Gates
MOTOROLA INC
Dye-Sensitised Metal Oxide Semiconductor
NATL. INST. ADV. IND. TECHNOL.
Japanese Appl. 2003-272,721
A dye-sensitised metal oxide semiconductor electrode (1) uses a Ru(II) complex having: a bonding
group selected from a carboxyl group, a sulfonic acid
group, etc.; a diketonate; and a halide, a cyano group
or the like. (1) in a solar battery is thermally and optically stable, and efficiently uses the energy in sunlight
by absorbing light over a wide wavelength range.
Thick Film Circuit Board
Japanese Appl. 2003-332,711
A Ru resistor (1) is formed on an insulating board
in an atmospheric environment; a thick film Cu conductor is then baked onto it at low temperatures of
500–700ºC so as to be electrically connected to (1).
The thick film circuit board (2) so formed has
improved conductor characteristics without (1) losing
its resistance reliability. (2) can cope with increased
wiring density, high frequencies and large currents.
DENSO CORP
MEDICAL USES
U.S. Patent 6,686,282
Metal gates for N-channel and P-channel transistors are formed from a first and second metal layer,
by plating with Ru, Ru oxide, Ir, Pd, Pt, Os, Ni, and
Co, to achieve their appropriate work functions. The
plating is achieved with a seed layer consistent with
the growth of the desired layer. The metal layers are
formed either by electroless or electrolytic plating
with a Pt metal, W, Ru oxide, etc., and at least one
refractory metal or Zr, Hf, La, Lu, Eu, etc.
Sacrificial Anode Stent System
World Appl. 04/002,328
A sacrificial anode stent system comprises a stent
with sacrificial anode portion(s) of Mg, Zn, Al, mild
steel, low alloy steel, etc., at which corrosion can
occur, and a vaso-occlusive device which includes a
coil of Pt. The non-sacrificial portion of the stent
includes stainless steel. The stent comprises
radiopaque portions. The vaso-occlusive device has
at least one portion with a potential different from
that of the sacrificial anode portion.
SCIMED LIFE SYSTEMS INC
Devices with Platinum-Rhodium Layers
U.S. Patent 6,690,055
A capacitor for integrated circuits (ICs) comprises a
first electrode, a dielectric layer of Ti2O5 and a second
electrode, at least one of which consists of a single
layer of a CVD Pt-Rh alloy. Pt-Rh barriers and electrodes for cell dielectrics for ICs, particularly for
DRAM cell capacitors are also claimed. The Pt-Rh
barriers protect surrounding materials from oxidation
during oxidative recrystallisation steps and protect
cell dielectrics from loss of O during high temperature processing steps. Plating a Rh-containing layer
on a semiconductor wafer is also claimed.
MICRON TECHNOL. INC
Platinum Metals Rev., 2004, 48, (2)
High Specific Activity Platinum-195m
World Appl. 04/015,718
High-specific-activity 195mPt is produced by exposing 193Ir to a flux of neutrons sufficient to convert a
portion of the 193Ir to 195mPt to form an irradiated
material. The irradiated material is dissolved in aqua
regia at ³ 217ºC to form an intermediate solution of Ir
and Pt. The Pt is then separated from the Ir by cation
exchange chromatography using HCl, thiourea, followed again by HCl. This method can prepare
medically useful high-specific-activity radioisotopes,
particularly 195mPt with activity ³ 90 mCi mg–1.
UT-BATTELLE LLC
87
FINAL ANALYSIS
Safeguarding Thermocouple Performance
Thermocouples are simple devices that on the
face of it are easy to use and repair. Platinum metals alloy thermocouples are considered to have the
additional benefit of being resistant to all forms of
chemical attack. There are basically three types of
thermocouple: R, S and B. Types R and S are suitable up to 1500°C and Type B up to 1600°C for
continuous use in favourable conditions. In the
metal-clad or mineral-insulated (MI) form they are
often regarded as “fit and forget”. However, sometimes users may experience problems that can be
avoided. Three catagories of problems will be considered:
• drift and thermocouple wire output errors;
• mechanical failure of the wires; and
• errors produced by compensation circuits connecting the thermocouple and the temperature
indicator.
Understanding drift or output errors requires
an understanding of the way the signal is generated. A thermocouple comprises two dissimilar wire
limbs joined at one end to form the hot junction.
When the junction is heated a voltage is produced
across the free ends or cold junction. For characterised wire combinations (thermocouple “types”),
measuring the voltage and the temperature of the
cold junction gives the hot junction temperature
either from look-up tables or, more commonly,
from a digital indicator that combines all three
functions.
It must be appreciated that the voltages produced are very small, and the changes with
temperature are even smaller. For example, a Type
R (Pt versus 13RhPt) thermocouple changes output from 0.013228 volts at 1200ºC to 0.013242
volts at 1201ºC, a fraction over 0.1%, so it is
important that every part of the measuring circuit
is operating correctly.
In fact, the voltage is only generated in the
lengths of wire that are in a temperature gradient;
the remainder provide an electrical connection. A
Pt wire produces a larger charge separation than a
RhPt alloy wire (and the higher the Rh content, the
Platinum Metals Rev., 2003, 48, (2), 88
smaller the charge). As the charge is negative, the
Pt limb in a thermcouple is negative with respect to
the alloy limb.
The size of the voltage generated by a thermocouple depends not only on the temperature
difference and wire combination but also on its
condition. It is useful to consider that any factor
which increases the mechanical hardness or strain
in the limb will also reduce the voltage. These
common factors are:
• residual work hardening from wire manufacture
• deformation during thermocouple assembly;
and
• contamination by alloying elements in service.
Even the act of quenching-in too many vacancies
by cooling too quickly after annealing the Pt limb
is said to produce a very small but detectable
reduction (but much less than not annealing).
The wire manufacturer is responsible for ensuring that the initial composition of the two limbs is
correct and homogeneous: a difference of 100
ppm or 0.01 wt.% Rh affects the output of a Type
S (Pt versus 10RhPt) thermocouple by approximately 7 µV or 0.5ºC.
The amount of work hardening in the limbs is a
joint responsibility as the customer will require a
certain minimum tensile strength, especially in fine
Pt wires, to ease assembly of the thermocouple,
but must then anneal the couple before use to
achieve the specified output. It is always preferable
to anneal an assembled couple as assembly strains
can produce a detectable error of up to 0.5ºC. It is
not sufficient to suggest in-service temperatures
will anneal the couple, as one end remains cold to
produce the voltage.
The issues of contamination in service, Rh drift
and advice on using and looking after thermocouples will be published in the next issue of this
R. WILKINSON
Journal.
Roger Wilkinson is a Senior Materials Scientist at Johnson
Matthey Noble Metals in Royston, U.K. He has worked with
platinum thermocouples since 1987 in manufacturing, calibration
and customer technical support.
88