Katanax K1 PRIME, Manual

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19
Sample preparation
Besides the traditional specifications of a sample to be representative,
uncontaminated and dry, Katanax recommends that the sample be ground to
<100µm. This is to ensure that the fusion be completed within a reasonable time.
Additionally, the sample must be fully oxidized before heating the crucible
containing the sample.
IMPORTANT : Heating a sample containing metallic species at high
temperatures will cause an alloying reaction, damaging the crucible, and
possibly damaging the instrument.
Flux blend
Typical fusions use a mix of lithium metaborate (LiM) and lithium tetraborate
(LiT). Lithium metaborate alone typically offers a better sample solubility, but
generally leads to crystallization of the bead. Tetraborate stabilizes the melt, but
limits solubility. Thus, to optimize solubility and obtain perfect glass disks, one
must use the correct LiT/LiM flux ratio.
The mixing ratio is determined by the acidity of the sample. Acidic samples
require a basic flux (more LiM), while alkaline samples need an acidic flux (more
LiT) and neutral samples call for neutral flux (50% LiT + 50% LiM).
Here is a list of common oxides, along with the recommended flux.
Simple oxide Recommended flux
K
2
O, Na
2
O, BaO, SrO, Li
2
O, CaO,
Ag
2
O, MnO, MgO, PbO, CoO
Lithium tetraborate
Bi
2
O
3
, FeO, ZnO, CuO, NiO, BeO 67% Lithium tetraborate –
33% lithium metaborate
Al
2
O
3
, Fe
2
O
3
, Cu
2
O, Sb
2
O
3
, ZrO
2
,
TiO
2
, SiO
2
, B
2
O
3
, SnO
2
, V
2
O
5
50% Lithium tetraborate –
50% lithium metaborate
CrO
3
, Mn
2
O
7
, SeO
3
Lithium metaborate
Naturally, actual samples are generally composed of more than one oxide type, so
a rough proportion must be calculated to determine the optimal flux type.
The only exception is when one makes solution. Since making a solution involves
the complete dissolution of the melt into an acid, one does not care that the melt
crystallizes when it cools; it is not only unavoidable, it is desirable. Therefore,
when making a solution, one can pretty much always use lithium metaborate
only, to increase sample solubility.
The choice of flux is also governed by the various chemicals that must be added.
For example, many samples are initially un-oxidized, and thus need to be
oxidized; since borate fluxes only dissolve oxides (metallic material ruins crucibles
at high temperatures). Addition of strong acids or bases is often the easiest
solution, but flux type must be adjusted accordingly.