Refractory Technology
Beryllia (which is used in making crucibles for melting uranium & thorium) is superior to alumina in all respects for high temperature (> 1900°C ) use, except

Electrical conductivity
Cost
Fusion point
Thermal conductivity

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Refractory Technology
Fireclay refractories

Combine with salts (e.g. chlorides sulphates etc.) & bases (e.g. lime, magnesia etc.) forming fusible aluminates silicates etc
All of these
Are not resistant to the action of basic slags
Shrink during firing

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