Refractory Technology
Natural silica

All of these
Is not stable at high temperature
Mainly contains quartz
Transforms to other allotropic forms i.e tridymite and cristoballite involving very high volume changes

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Refractory Technology
What is Thoria?

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

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Refractory Technology
Thermal conductivity of refractory bricks

Is independent of its porosity and is maximum for insulating bricks
Increases with decrease in porosity
Decreases with decreases in porosity
Increases with the amount of air entrapped in pores

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