Copyright ©JCPDS-International Centre for Diffraction Data 2007 ISSN 1097-0002
THE CLAISSE-CALCULATOR
OF SAMPLES ACIDITY
APPLICATIONS
Fernand Claisse
Fernand CLAISSE inc
2270, Léon Harmel, Suite 165
Québec, QC, G1N 4L2
ABSTRACT
The CLAISSE-CALCULATOR is a new tool for XRF analysts who make fusion beads. It
calculates the acidity of a sample and suggests the better Lithium borate flux composition for
it. Its operation is briefly described. In addition, the Calculator has been used by the author to
explain a) what causes the sample to have a preference for a given flux composition, and b)
what causes molten glass sticking to crucibles and moulds.
HISTORICAL
In lithium borate fusion, acidity is the main factor that determines whether or not a fusion
bead will be successfully done. In the old days of fire analysis of ores and rocks for the
extraction of precious metals, the rule was:
“Basic samples need acidic flux, acidic samples need basic flux”.
No rule was used in the early days of fusion for
XRF analysis [1] because only one flux composition
was used, Sodium Tetraborate. On account of the
very high dilution then used, one part sample in 100
parts flux, acidity was ignored. Later, when sodium
became detectable by X-rays, Sodium Tetraborate
was replaced by Lithium Tetraborate, and trouble
began to appear. Various mixtures of chemicals
started being tried. Only ten years ago, selection
rules were proposed [2] for the determination of
optimal flux composition, based on measured
solubility of a number of oxides as a function of
flux composition (Fig. 1).
Fig. 1. Solubility of soe oxides as a
function of flux composition [4]
The rules were simple: “Use Lithium Tetraborate
for clearly basic samples such as Calcium oxide;
Lithium Metaborate for clearly acidic samples such
as Silicon dioxide; and a 50/50 mix of Lithium
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This document was presented at the Denver X-ray
Conference (DXC) on Applications of X-ray Analysis.
Sponsored by the International Centre for Diffraction Data (ICDD).
This document is provided by ICDD in cooperation with
the authors and presenters of the DXC for the express
purpose of educating the scientific community.
All copyrights for the document are retained by ICDD.
Usage is restricted for the purposes of education and
scientific research.
DXC Website
– www.dxcicdd.com
ICDD Website
- www.icdd.com
Copyright ©JCPDS-International Centre for Diffraction Data 2007 ISSN 1097-0002
Tetraborate and Lithium Metaborate for oxides. Then, the problem that arose was: what to
do with complex sample?
Measured values of oxides acidity existed [3] but they were obtained from aqueous solutions,
and some oxides dissolved in lithium borates did not seem to fit well with those of Smith.
Oxides dissolved in a borate glass, in a certain way, should behave similarly to salts that are
dissolved in water, but the values should be different. The solvents are different, and in the
Smith case, one solvent (H2O) is considered as the origin of the acidity scale.
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C h em ica l a cidit y
10
Basic
oxides
5
0
-5
-10
0
0,5
1
1,5
LiM
LiT
2
2,5
Acidic
oxides
-15
-20
Acidity Index (O/Me)
3
It was found necessary to find another way to define
the acidity of oxides in fusion beads. Since the
alkalinity of oxides seems to vary with the
concentration of oxygen in their chemical formula,
then the ratio “number of oxygen atoms per number
of metal atoms” in the chemical formula of oxides,
was used as the “Acidity” of the oxide [2,4].
That looked different from the Smith scale of
acidity, but it was found later that both scales are
related as shown when the values of one are plotted
against those of the other as in Figure 2.
Fig. 2. Comparison of the Smith (aqueous)
and Claisse (fusion) acidity of oxides
COMPLEX OXIDES
Let us start with a given example of complex oxide, Ilmenite. The chemical formula is
FeTiO3, so that the A.I. is 3/2 or 1.5.
That can also be written FeO + TiO2, in which case the A.I. of the two oxides are l and 2, and
the average is (1+2)/2 = 1.5; we may conclude that a homogeneous compound and its
components yield the same results, provided that they are expressed as molecules. Thus, the
acidity of a complex sample may be calculated by expressing its composition in molecules,
and taking the average of the acidity values of all its components. That is something analysts
would normally not like to do frequently.
The CLAISSE CALCULATOR
To help analysts not do these long annoying calculations, a small software was developed [5],
applicable to nearly all oxides of the periodic table in their maximum oxidation state,
assuming that the oxides in fusion beads are in that state. For convenience, some oxides in
other oxidation states were included.
A single table only is needed to use the software (Fig. 3), and the procedure is simple :
1. Since acidity is independent of the size of the sample, its composition can be defined
on any scale: percentage of each oxide, relative weights of oxides in grams, ounces,
etc.
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Copyright ©JCPDS-International Centre for Diffraction Data 2007 ISSN 1097-0002
2. When each of these numbers is entered in the space next to the oxide, the description
of the sample is done.
3. Pressing CALCULATE, the program makes all the calculations and yields the Acidity
of the sample under ACIDITY NUMBER.
4. The objective of knowing the acidity is to chose the optional flux composition for a
given sample. Based on the behaviour of pure oxides, five ranges of acidity were
defined, and five flux compositions that should be the optimal flux for them were also
defined. After the acidity value of the sample appears, the optimal flux composition
also appears under OPTIMAL FLUX, expressed as percents of Li Tetraborate and
Lithium Metaborate.
5. Since pure Lithium Metaborate always crystallizes except with SiO2, Al2O3, most
sulfates and phosphates, when their concentrations are above about 25% in the fusion
bead, the software recommends to switch to a flux composition of 35 Li Tetraborate /
65 Li Metaborate.
Fig. 3. The Claisse-Calculator with data for a cement sample (from the Internet).
RESEARCH APPLICATIONS
1. ACIDITY OF FUSION BEADS
The Calculator can also be used to determine the acidity of fusion beads. It is only necessary
to add the flux composition to that of the sample using the same units. The more units are
the weights of Li2O and B2O3 in the flux, and those of oxides in the bead. This was applied
to a number of oxides, at the composition at which the solubility is maximal. That is the best
flux-sample combination that represents the more stable condition for each particular bead.
Some cases were estimated when the maximum solubility is outside the range of flux.
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Copyright ©JCPDS-International Centre for Diffraction Data 2007 ISSN 1097-0002
Oxide
Li Flux
% Meta
ZnO
BaO
PbO
CaO
Sb2O3
Fe2O3
FeO.TiO2
ZnSO4
CaSO4
TiO2
V2O5
Average
0
0
0
0
50
50
65
50
100
50
70
Solubility.
g oxide/
6g flux
1,5
1,0
0,5
2,0
1,5
1,5
1,3
2,0
2,0
0,7
1,3
A.I.
Oxide
A.I.
Bead
1
1
1
1
1,5
1,5
1,5
1,8
1,8
2
2,2
1,15
1,16
1,14
1,14
1,13
1,15
1,12
1,20
1,16
1,15
1,17
1,15
Table 1. Acidity Index of fusion beads of
some pure oxides at their maximal solubility
(A.I. means Acidity Index)
composition. The results are shown in Table 1.
An interesting observation is that all fusion beads
have essentially the same value of acidity at their
solubility peak. At flux compositions on each side
of the maximal solubility, the solubility is lower
because the flux composition is less optimal. Fusion
beads apparently reach a neutral, more stable
condition when the acidity index reaches 1.15. That
value is not far from that of 1.17 for pure Lithium
Tetraborate. Indeed, that flux is barely acidic; the
term acidic is used for practical reasons to mean
“the lesser basic”.
2. GLASS STICKING TO PLATINUM
Sticking occurs with transition metals oxides only [4], and seems to be due to the
simultaneous existence of all possible oxides of the dissolved metal element in the fusion
bead. These oxides are the result of a chemical
Weight
Acidity Index
equilibrium that depends on the surrounding
Oxide*
g
LiT
50/50
conditions. That is a well known concept in aqueous
Fe2O3
1,0
1,19
1,18
solutions. In borate fusion, it is estimated that the
FeO
0,9
1,11
1,16
responsible oxide for sticking is the metal itself, the
Fe
0,7
1,10
0,81
one with the lowest oxidation state, because free
Weight of oxide for constant amount of metal
in 6g of flux
metal atoms can plate the crucible and induce
sticking. The Calculator helps understand this
Table 2. Acidity index of two Fe oxides
phenomenon for the case of Fe oxides (Table 2).
and Fe, dissolved in two different fluxes
In the 50/50 flux, for the same number of Fe atoms in the fusion beads, and different
oxidation states, the acidity index of Fe2O3 is the closest to the ideal value of 1.15 (Table 1),
so that this oxide is the more stable of the three (Table 2) and the one with a higher solubility
in the bead. FeO should be present also but in a smaller proportion. The probability to have
free Fe atoms is very low compared to Fe2O3, so that sticking is not likely to occur.
In Lithium Tetraborate flux, the situation is different. FeO is the more probable oxide present
in the bead, Fe2O3 should be in lower proportion, and Fe atoms have a greater probability to
exist. The life time of the latter is certainly short, but the atoms that are next to the platinum
surface may continuously alloy with platinum and cause sticking. That is what is observed in
the crucible and in the mould.
Weight
Acidity Index
Oxide*
g
LiT
50/50
CuO
1,0
1,16
1,06
0,9
0,93
Cu2O
1,13
Cu
0,8
1,10
0,81
Weight of oxide for constant amount of metal
in 6g of flux
Table 3. Acidity index of two Cu oxides
and Cu, dissolved in two different fluxes
Copper oxides are in a similar situation except that
the Calculator predicts that the difference of
probability of dissolution is closer between CuO and
Cu in the 50/50 M/T flux (Table 3), so that sticking
is probable in both fluxes. That is what is observed,
and larger concentration of Lithium Metaborate in.
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Copyright ©JCPDS-International Centre for Diffraction Data 2007 ISSN 1097-0002
the flux should improve the situation, although the solubility decreases with the Metaborate
content.
CONCLUSION
The CLAISSE CALCULATOR is a simple but efficient tool for the analyst and for research.
In most analytical work, it might be needed only occasionally, for example when samples are
rather similar. It is actually accessible on the FCinc. website [5]
REFERENCES
[1] Claisse F. (1957) Accurate XRF Analysis Without Internal Standard. Norelco Reporter
III , 3, 3-7, 17-19
[2] Smith D.W. (1947) An Acidity Scale for Binary Oxides. J. Chem. Educ. 64 , 480 481.
[3] Claisse F. (1997) Selection of Fluxes for Fusion of X-Ray Samples : Optimum Lithium
Tetraborate–Metaborate Ratio for Specific Sample Types. Pittsburg Conference
[4] Claisse F., Blanchette J. (2004) “Physics and Chemistry of Borate Fusion” 135 pp,
ed. Fernand Claisse inc.
[5] Claisse F. (2006) www.fernandclaisse.com
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