Precious metals Refining & harsh chemical processing

Processing materials at elevated temperature is often a challenge as it implies using the suitable container for a dedicated application. A large range of container types is available on the market nowadays. Those containers range from the pre-industrial era clay to alumina or silicon carbide. Each of these product exhibits specific properties that are intrinsic to the raw material it has been manufactured from. Among mineral based containers, fused quartz containers offer unique features.
Whenever processing liquids is required, the container walls must be free from any porosity which is a feature exhibited by Saint-Gobain Quartz crucibles as made through arc-fusion and as opposed to basic porous slipcast containers.
One of the key parameter that leads to the selection of a particular crucible is the processing/firing temperature. The number of candidates starts shrinking rapidly when it comes to temperature as high as 1050°C or above. Quartz is among the few materials that can withstand such level.
crucible oven


When it comes to process parameters, it is common in some industries to have the need for a quick thermal ramp-up.
In such a case fused quartz container is a material of choice as unlike alumina or silicon carbide it survives thermal shock remarkably even if the quartz containers were stored at negative temperatures beforehand.
These benefits directly derive from the intrinsic properties of fused silica having one of the lowest Coefficient of Thermal Expansion (CTE) among all mineral materials. 
As most of the processing using quartz crucibles are operated at elevated temperature, it is critical that the crucible chosen for this operation has an excellent dimensional stability which is the case of quartz material.



Some industries require to combine the parameters described above, thermal survival and dimensional stability, at a processing temperature above 1050°C. In this case, alumina or silicon carbine can still be used but quartz is sometimes the unique solution due to its particular property. The challenge is the weakening of the mechanical properties of fused quartz above 1050°C. This issue can be vercome by using holding elements such as suceptors which is the case in the processing of silicon semiconductor performed at 1425°C.
Today even though the use is obviously not as extensive as before the invention of competing material such as polymers, some industries treating aggressive components combined with temperature tend to still privilege fused quartz against other options. Indeed the lifetime offered by quartz in such harsh environment is much higher than the alternative materials. It is the case for instance in the manufacturing of phosphorous or fluorescent powders.
Preserving the chemical purity of what is melted in a crucible can be key for some industries such as the melting of special glasses or alloys, for precious metal refining but also for silicon melting. Unlike graphite containers, quartz containers do not pollute the melt with carbon and transfer a limited amount of oxygen to it.  

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