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

Thermal conductivity
Electrical conductivity
Fusion point
Cost

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Refractory Technology
What is Thoria?

Thoria Has high fusion temperature (> 3000°C) but poor resistance to thermal shock
Thoria Has high resistance to basic slags
Which is expensive & radioactive, is used in crucibles for melting high purity metals
All of these

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Refractory Technology
Carbon refractories

Have extremely low thermal & electrical conductivities
Are not attacked by slags, as they are not wetted by melts
Do not burn/oxidise, when exposed to air on heating
Do not resist temperature fluctuations

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