| HANDLING PLATINUM EQUIPMENT |
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Platinum and the metals of the platinum group are among the most robust metals. Their high degree of
resistance to chemical corrosion and their high melting temperatures make them excellent materials for
equipment in a chemical laboratory. The catalytic effectiveness accelerates the ashing of organic materials,
for example of filter residues. |
| Since pure platinum is very soft and already loses its hardness and deformation resistance at temperatures
of 700 to 1,000 °C (1292 to 1832°F), it is hardened with iridium, gold or rhodium to increase its deformation
resistance and extend its useful life. |
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| HOW TO PROLONG SERVICE LIFE |
The alloys formed by platinum with most metals have substantially lower eutectic points in comparison to
pure platinum. Even at mid-range temperatures, along the grain boundaries of the crucible material metals
or other elements can accumulate and form local low-melting phases which lead to the destruction of the
crucible. |
| In air-tight conditions chemical reduction reactions can cause the release of the platinum poisons. For this
reason checks of mass loss and ashing should always be performed under oxidizing conditions. |
When applying heat with a Bunsen burner you should always ensure that the flame is rich in oxygen. The
presence of carbon and/or organic substances in the sample can lead to the reduction of chemical compounds
and, hence, to the release of elements harmful to platinum.
With other elements such as silicon, phosphorous, boron and sulphur, you must exercise enormous care. In
the process phase shifts occur more frequently along the grain boundary and lead to an embrittlement of the
appliance. You should pay particular attention to this danger when ashing flour and other organic compounds
which contain phosphorous.
Destruction or damage can also occur from an external source, such as when the platinum appliance is in
contact with silicon-carbide heating rods in a muffel furnace or with metallic debris on the oven floor which
are diffused into the appliance during a longer period of contact.
We recommend you keep laboratory surfaces clean at all times where appliances may be placed in order
to avoid soiling the appliance with substances which at higher temperatures can react with platinum. This
includes handling hot platinum appliances with tongs and tweezers whose tips are protected with platinum
shoes. To prevent any corrosion from inside, you must not allow any corrosive media to penetrate between
the tongs and the platinum shoes.
If you heat platinum appliances with a Bunsen burner, they must only come into contact with triangles which
are either ceramic-coated or fitted with platinum knobs. You must prevent any contact between the platinum
appliances and ferrous materials. |
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| IMPACT OF ACIDS AND SALT MELTS |
When conducting wet chemical analyses remember that halogen compounds, aqua regia and other intensely
oxidizing acidic mixtures can chemically corrode platinum even at room temperature (see table on page 26).
More serious are the corrosive effects at higher temperatures of melts of diverse alkali metal hydroxides and
cyanides. In this context potassium compounds generally react more intensively than the corresponding sodium
salts with platinum appliances.
With soda and soda-potash fusions, the crucible is covered to create a CO2 atmosphere over the fusion which
protects the crucible from oxidation. |
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| HEATING |
You must avoid heating platinum appliances for unnecessarily long periods of time since this will lead to a
coarsening of the crystal structure, embrittlement and cracking. Incinerating platinum appliances must not
come into contact with other metals (crucible tongs, tweezers, iron triangles, wire meshes, etc.). The ceramic
surface on which the appliance rests in the oven floor and while cooling must be clean and completely free of
contaminants. When several new platinum appliances are simultaneously incinerating in the muffel oven,
you must ensure that they are not in contact with each other (this applies especially to crucibles with new
lids). As a result of self-diffusion the appliances could weld together.
FKS platinum inhibits crystal growth and extends the useful life of the appliances (by as much as a factor of 3)
owing to the fine-grain stabilizing effects, especially at high temperatures. |
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| TIPS ON OPTIMUM USAGE TIME |
Simple precautionary steps to prolong the service life of your equipment are:
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Use heavily used crucibles when sample constituents are unknown |
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Never place a crucible directly on a silicon-carbide heating rod |
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Oven linings must not contain any platinum-damaging elements |
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In the presence of organic materials assure good oxidizing conditions
(possibly by adding small amounts of ammonium nitrate before heating) |
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Only touch hot appliances with Pt coated tongs |
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Always operate Bunsen burners with a strongly oxidizing flame
(avoid yellow = reducing flame) |
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Use FKS alloys |
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| CLEANING |
Basically, decocting the crucibles and dishes in a suitable solvent is sufficient.
If this does not result in adequate cleaning we recommend melting out with potassium hydrogen
sulphate or potassium diphosphate.
Materials superficially alloyed can be scrubbed out with a corrundum-based polish. Never use a
polish which contains metal carbide.
Any residue of polish containing corrundum can be removed by hydrofluoric acid.
Platinum appliances must not be cleaned by annealing them because this promotes the unwanted
process of diffusion. |
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| HANDLING ELECTRODES |
Electrolytically precipitated metals are dissolved with pure acids and then the electrodes are cleaned
with deionized water and dried in a drying cabinet.
Annealing leads to unwanted softening which in turn makes the net electrodes easier to deform.
Besides, incompletely dissolved metals could be permanently diffused in. |
