Oxide Crucibles for Precious Metals--cs ceramic co.,ltd

Many of the precious metal group of non-ferrous metals can be melted adequately in clay-graphite or silicon carbide crucibles, but for melting temperatures above 1400^oC..and for higher quality casts...then oxide crucibles should be used.

Oxide crucibles for precious metals are normally made by isostatic pressing, but for special shapes and non-standard sizes the equivalent material can be formed by vibro-casting.

Zirconia (zirconium oxide) is the material of choice, and several grades are available.  A cheaper alternative is zircon (zirconium silicate) which is often used for refining platinum-group alloys from glassy material.

The usual arrangement is to prepare an assembly with the crucible packed into a refractory sleeve with a granular backing mix.   The sleeve can be of a lower quality refractory compared to the crucible as it only reaches a fraction of the temperature seen by the crucible; its main qualities should be high strength and good thermal flexibility to accommodate thermal expansion of its¡¯ contents during multiple thermal cycles.

A slow pre-heat schedule should be followed, and if the crucible is allowed to cool towards room temperature between casts the pre-heat schedule should be followed again.

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