Refractory Technology
Quartz is

Stable form of silica upto 870°C
Converted to tridymite on firing between 870 to 1470°C
All of these
Transformed to crystoballite on heating above 1470°C

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Refractory Technology
What is Thoria?

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

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