Allg~ 9, 1950
G. SCHNEIDER Erm.
TuNGsTEN/RHENIUM THERMocouPLEs
2,948,766
Filed April '30, 1956
J
/l
y
v
WE@ @OWL-"A9,
l
ATTORNEY5
2,948,766
.PatenterìmAug. 9,1196()
i2
Y
.
îrhenium `and l0 to 25%, lpreferably Yabout 20%, of
`
rhenium `and the 'remainder iridium, >as >within these com
52,948,766
;positionfranges the change in'rthermoelectric E.M.~F., with
I TUNGS'I‘EN/RI-IENIUM’THERMOCOUPLÉS
»smallvchanges »in composition ‘ofthe-alloys as might oc
cur 'by evaporation of one-of the components lthereof
Aas by oxidation,’is-at »a-,minimum sothatchanges in
»Günther Schneider, Frankfurt » (Main), Eschersheim, and
Alfred .Boettchen'Hanau (Main), ÍI-Iohe Tanne, Ger
Vlnz'iny,."as‘sigiiors'toDeutsclle ÍGold- und Silber-Schei
'ldeans‘talt .vormals iR’oessler, Frankfurt_am Main, Ger
eleetromotive E.M‘.F. produced inuse vare maintained
so low as to be acceptable.
Y'manly
Preferably, the thermocouples-according tothe inven
10 tion are sealed in suitable gastight armatures’or casings
Filed Aprfâil, 4956, Ser. No.r 581,478
YCiniinspriority,‘applicauiouïGermany Apr. 30, 1955
-10 Claims. ‘(Cl. 13d-_5)
The vinvention relates -to ‘apparatus for measurement of 15
l'high rtemperatures and especially'those between 1500 and
in ‘a Iknown’m’anner'to protect-them fully >from the in
fluence of the atmosphere. Preferably, sucharmatur'es
’are tubes'o? metal oxides, such'as aluminum oxide, beryl
lium-‘oxide thorium oxide or zirconium oxide, Vpreferably
filled with hydrogen to provide ~`a non-oxidizingatmos
'phere around the thermocouple.
Y
'2000" C. with the `aid of thermocouples'comprising a
in TheV
m. Yvolts
following
Aof aTable
’thermocouple
-I'gives theproduced
thermoelectric
by joining a
substantially pure tungsten elementîjoined to a’rhenium
substantially'pure tungsten wire‘with a vsubstantially `pure
element.
f
It is known to employ thermoelements in the form of 20 rhenium wire at Ytemperatures from 500° C. to 2100° C.,
as well as the change in'thermoelectric'EMP. for 1° C.
.'the so‘-calle`d thermocouples for »the measurement of tern
change' inj temperature in uvolts:
`>peratures. The best known thermocouple elements “are
v.those of nickel/chromium~nickel andplatinum/platinum
Table I
rhodium.
The 'simplicity o'f'the use of thermocouples, las well as 25
their accuracy, renders it desirable 'to `provide thermo
Vvcouples for use at -temperatures above 1500° C. How
Temperature, ° C.
E m.v.
pv./° C
ever, up until now, the previous attempts employing
combinations of the known high melting metals'have led
‘only to limited solutions. The'thermocouples produced
6.04
either did .not Vmeet -the rtechnological Yrequirements or
were only of limitedfapp'lication. The reason-forlthis` was
especially against thermal iníluences, which can easily
35
18.3
16.34
25.> 58
19.6
13.6
29.30
........ _,
30. 34
that the wire employedforvthe thermocouplesfeither‘still
yhad -too low a melting vpoint or the sensitivitythereof,y
DE/dt
~
........ __
31.30
7. 5
32.05
________ ._
The following Table’II, on the ‘other hand, gives the
lead to undesirable embrittlement and therefore early
thermoelectric E.’M.F. `in m. volts of thermocouples pro
destruction of the elements or at least to a diminished ac
duced by joining pure tungsten wires with rhenium-iridi
um alloy wires yof Various compositions at temperatures
between 500° C. and 2000° C.:
curacy. In a similarmanner, a change'in alloy k'composi
>tion through‘evaporation 'of 'one of the- alloy components
»Table II
Composition of rhenium-iridum alloy Wire in percent
Tempera
ture, ° C.
Ir90
Re 10
3. 83V
Y _
,
2,000. ._
__
during use of thermocouples »at high temperatures -can
lead to difficulties. Also, in platinum metals, the sen
IrSO
R620V
4. 13
i170
Re`30
'4.'19
lr60
'Re`40
Ir50
R'e'50
1r40
AReV 60
lf3()
Re 70
'4. 27
Ir20
YRe'SO
4:33
IrlO
Re 90
"3. 86'
`3. 70
`3. 88
13.10
13. 33
12.75
11.94
11.15
11.47
12.09
12. 38
18. 22
24. 25
24.18
22.82
T21.' 21V
19. 55
19.26
'19. 80
20. 27
21.09
"4; 49
34. 86
33. 66
32. 45
'30522'
27.17
26:47'
25; 93
' 26. 71
27.71
The- thermocouples according to the'invention in using
rhenium as one of the elements `are of >lower cost than
sitivity -to the so-called platinum poisons 'is 'disadvan 55 thermocouples employing a'platinum metal, Ysuch Yas iridi
tageous. Furthermore,-it is, of course, also necessary tot
select such combinations for -thermocouples that a suf
um, and also avoid the diñiculties engendered bythe
alteration of the‘structure of pure iridium elements when
iiciently :high thermoelectric E.M.F. is provided. For
used at high temperatures.
m
example, thermocouples of Ta/W, Mo/Ta and Mo/W
As indicated above, it is preferable to protect vthe
only provide a relatively low thermoelectric’EMF. and 60 thermocouples according to the invention against in
also `the change in thermoelectric
with change in
fluence of the atmosphere by providing a non-metallic
temperature is ytoo low for practical‘purposes.
gas tight casing for-the thermooouples themselves. It is
According to the invention, rit was found that excellent
known that high melting oxides, such as `aluminum oxide,
thermocouples for the measurement ofhigh'temperatures
«zirconium oxide, thorium oxide and others, when suitably
»could'be produced by> joining a substantially pure tungsten 65 pure, can be sintered .to produce practically gas tight
orfniolybdenum element with »a rhenium element, pref
shaped bodies. Such shaped bodies have already been
employed as protective tubes for thermoelements. How
erably-of lpure vrhenium, vvvto'form the hot junction. It
was also found that'certain iridium-rhenium Valloys could
ever, for the purposes of the invention, it is important
that `every influence of the atmosphere, especially of
Talso :be employedin combination with the substantially
:pure-tungsten or molybdenum elements, namely, Yiridium 70 >oxygen containing gases, be excluded with certainty.
.rhenium .',alloys `of Vthe lfollowing composition: ~10--30%,
This, for example, 'can »be accomplished by filling the
casings containing the thermocouples according to the
preferably about 20%, of iridium and the remainder
2,948,766
4
invention with inert gases or `to continuously ñush the
casings with gases which have no deleterious effect upon
sarne material as tube 11. Sealing mass 15 seals the
joint between tube 11 and support 12 and sealing mass
the materials of the thermocouples at the temperatures
to be measured. In accordance with an advantageous
wires of the thermocouple 12 leave such support. The
16 provides a seal at the end of support 12 where the
remove any last traces of air or oxygen. ,The getters can
sealing mass is a mixture of oxides such as given in
Table III. An outer glaze coating 17 of the same ma
terial is provided on tube 11.
be introduced into the casing either in powder form or as
In the modiñcation shown in Fig. 2, the thermocouple
modification according to the invention, it `has been Afound
desirable to introduce a getter metal into the casing to
24 comprises a pure tungsten wire joined with a pure
thorium or zirconium,V are capable of binding gases such 10 rhenium wire at terminal or point 25 to `form the hot
junction of the thermocouple. One of the wires of such
as oxygen, nitrogen or vapors of metalloids with the
thermocouple is provided with a sintered aluminum ox
formation of solid compounds at elevated temperatures,
ide insulating tube 22 and the other with a plurality of
such as when the thermocouple is heated up to measur
short insulating tubes 23 of the same material. A pro
ing temperature for the ñrst time.
l
According to another modification of the invention, 15 tective tube 21 of aluminumr sintered oxide surrounds
shaped bodies. Getter metals, such as titanium, tantalum,
the hot junction of the thermocouple and the open end
thereof is sealed olf with the aid of stopper 26 of sintered
the non-metallic protective casings for the therm‘ocouples
can be provided with a glaze-like coating of mixtures of
aluminum oxide and sealing masses 27 and 28 of an
oxide mixture such as given in Table III. A tube 29
of a getter metal, such as titanium, is provided within
higher melting oxides and appropriate quantities of flux
ing oxides in order to ensure a gas tight seal.
Such
oxide mixtures are especially desirable for bonding and
sealing the joints in the casing when it is not made of
one piece. Preferably, the composition of the glazes is
protective tube 21. An outer glaze coating 30 is also
provided on the tube 11.
We claim:
selected so that its melting or softening point can be se
lected with regard to the temperatures to be measured
between 1000° C. and 1700° C. These glazes wet the
non-metallic material of the casings upon fusion and
form a uniform firmly adhering coating. The bond of
l. A thermocouple comprising a substantially pure
25Y tungsten
element joined with la rhenium element selected
from the group consisting of a substantially pure rhenium
element, rhenium-iridium alloy elements containing 10
such coatings is improved by the fact that they generally
to 30% of iridium and iridium-rhenium alloy elements
'containing 10 to 25% of rhenium.
V2. A thermocouple comprising a substantially pure
position of the oxide kmixtures employed for the glaze
tungsten element joined with a substantially pure rhenium
is easily adjusted so that the coeflicient of heat expansion
element.
of the glaze does not diiîer substantially from that of
r3. A thermocouple comprising a substantially pure
the ceramic casing. The solvent capacity of the oxide
Amixtures employed for the glazes for the material, for 35 >tungsten element joined with a rhenium-iridium allo
-element containing l0 to 30% of iridium.
v
example, aluminum oxide or zirconium oxide, of the
4. A thermocouple comprising ya substantially pure
casing also renders it possible to use such oxide mixtures
to seal the casing and especially the joints thereof for
tungsten element joined with an iridium-rhenium alloy
thermocouples to be used in measuring temperatures of
containing 10` to 25% of rhenium.
up to 2100“ C., even though such temperatures sub»
5. A thermoelectric element comprising a thermocouple
stantially exceed the actual melting point of such oxide
comprising a substantially pure tungsten element joined
mixtures, without danger of failure of the seal. Oxide
with a substantially pure rhenium element sealed in a gas
dissolve minor -amounts of the ceramic casing material
upon which they are applied. Furthermore, the com
mixtures which can be used either to form `a glazed
coating on the casing or to bond the joints between
separate parts of the casings Aare‘given by way of ex
ample in the following table:
tight casing of non~metallic thermostable material.
45
‘
6. A thermoelectric element comprising a thermocouple
comprising a substantially pure tungsten element joined
Table llI
Melting Point
FerOa
MgO
ZrO:
The accompanying drawings illustrate several modiiica 60 with a substantially pure rhenium element sealed under
a non oxidizing gas in a gas tight casing of non-metallic
tions of thermocouple elements according to the inven
tion.
In such drawings:A
Y
.
j
Fig. 1 shows a longitudinal section of `one form of
such an element;l and
.
Fig. 2 shows a longitudinal section of another form`
of such an element.
6 Ul
thermostable material.
7. A thermoelectric element comprising a thermocouple
comprising a substantially pure tungsten element joined
with a substantially pure rhenium element sealed to
gether with a getter in a gas tight casing of non-metallic
thermostable material.
_
In the modification shown in Fig. l, the thermocouple
8. A thermoelectric element comprising a thermocouple
13 comprises a pure tungsten wire joined with a pure
comprising a substantially pure tungsten element joined
rhenium wire at terminalV or point 14 toV form the hot 70 with a substantially pure rhenium element sealed- in a
junction of the thermocouple.> A protective tube 11 of
gas tight casing of a sintered oxide.
a high melting oxide, for example, sintered Yaluminum
9. A thermoelectric element comprising a thermocouple
oxide, surrounds the hot junction and the wires of the
comprising a substantially pure tungsten element joined
thermocouple >are supported in'the two capillaries pro
p'ded in _support 12 which preferably is _formed of the 75 witha substantially pure rhenium element sealed in. a
5
2,948,766
gas tight casing of a sintered oxide' provided with a glaze
having a softening point between 1000° C. and 1700’
C. composed of a mixture of oxides yand a ñux.
10. A thermocouple which comprises one element com
6
References Cited in the tile of this patent
UNITED STATES PATENTS
2,012,465
Godecke ____________ __ Aug. 17, 1935
190,657
Great Britain ________ _.. Dec. 28, 1922
posed of rhenium and another element composed of a
refractory metal from the group consisting of tungsten
and molybdenum, said elements being joined at one end.
‘m1
FOREIGN PATENTS