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Low Temp Furnace Model ITL-M-17701 13-07/20
PRECAUTIONS TO PREVENT DEVITRIFICATION OF QUARTZ
ENVELOPES
The crucibles (containing the metal) of Isotech sealed fixed point cells are encased in an envelope of pure
fused quartz, whose purpose is to avoid contamination of the enclosed metal, by foreign metal ions or
oxygen. To this end, it contains an inert gas whose pressure is 1 standard atmosphere at the metal freezing
temperature.
Fused quartz is vitreous in nature but, like other glasses, can be stimulated to crystallise (devitrify) by
external influences at high temperatures. The crystalline form is recognisable as a localised cloudy or milky
appearance. Devitrification is progressive and irreversible.
A devitrified cell can no longer be assumed to be gas-tight. It may leak its enclosed gas and atmospheric
air may leak into it. The pressure at the freeze point may, as a consequence, be incorrect and, more
seriously, contamination may occur.
Sealed quartz cells can be used for thousands of hours without devitrification if precautions are taken to
ensure that the outside surface is scrupulously clean before raising them to temperature. Any surface dirt,
a water spot or a single fingerprint is a potential seed for devitrification. Before exposing to high
temperature, the exterior of the cell should be cleaned with a suitable alcohol such as Ethanol and then
thoroughly wiped dry with clean tissue. (Similarly,
SPRT’s to be inserted into the cell’s re-entrant tube
should be previously cleaned in this way).
It is advisable to handle cells with clean cloth gloves.
The precaution applies particularly to cells for use at temperatures in excess of 500°C, although Isotech
advises that all cells be carefully cleaned before use.
METAL CLAD CELLS
Devitrification does not apply to these cells, but in any case, it is good practice to clean these in the manner
described above prior to use.
