Katanax X-FLUXER, Manual

Page: 27 / 86

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KI, LiI, LiBr and NaI. Only a few milligrams are required. If in doubt, use about
30 mg of Libr and observe the results. Ammonium iodide (NH
4
I) is not
recommended, as its decomposition temperature is too low.
We strongly recommend using such a non-wetting agent, to lengthen the mold’s
life expectancy, and to ensure all the melt is transferred into the mold upon
pouring. The NWA may be added in solid (powder) form, or as an aqueous
solution.
Katanax also sells flux blends that contain predetermined amounts of non-wetting
agent. Please contact Katanax to obtain this time-saving product.
Oxidizing agents
As previously mentioned, it is of key importance that the sample be oxidized.
While it is often safer and easier to oxidize the sample using a liquid acid or base
before fusing, it is also possible to use powder reagents to oxidize the sample in a
one-step operation.
Typical oxidizers are lithium carbonate (Li
2
CO
3
, which reacts at around 700-
800°C), lithium or strontium nitrate (LiNO
3
or Sr
(
NO
3
)
2
which react at around 500-
700°C) and lithium peroxide (Li
2
O
2
, which reacts at around 300-500°C). Several
minutes at the reaction temperature must be allowed before heating up further,
and temperature ramping can be useful to avoid spills due to too fast a reaction
(see page 32, Programming the X-300 (advanced) for details on ramping). The
amount of selected reagent will depend on the sample contents and can be
estimated stoichiometrically. An excess of oxidizer is recommended, but that may
require adjusting the flux mixture.
Manual mixing
Once all the components are selected and weighed into the crucible, some manual
mixing is recommended, to improve contact between the various reagents.
In particular, very fine sample particles have been observed to agglomerate, and
a manual mixing will help breaking the lumps that might have formed during and
after weighing.
Two notable exceptions to this general rule are high-carbonate samples and when
using powder oxidizers. In those special cases, one want to first lay some flux on
the bottom of the crucible, then add the sample (and oxidizer) on top. Manual
mixing would ideally just be done with the sample and oxidizer, because one
wants to have the most intimate contact between the sample and the oxidizer.
Flux will merely act as a shield at first, protecting the crucible from alloying with
the sample. In the case of high carbonate samples, it is best to lay the sample on
top of the flux and not mix; the expelled gases will escape more freely.
Care of the
platinumware
Crucibles and molds should be considered an integral part of your fusion machine.
As such, care must be taken to ensure that they are free from leftover flux,
molten or in powder. If need be, you can use citric acid or hot 20% HCl (and
proper precautions) to clean them. Depending on the amount of deposit, cleaning
time can range from several minutes to a full night.