Refractory Technology
Silica bricks have low spalling resistance below 600°C, due to its

Low refractoriness
High co-efficient of expansion upto this temperature
Very high thermal conductivity
High thermal diffusivity

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Refractory Technology
What is Thoria?

Thoria Has high resistance to basic slags
All of these
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

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Refractory Technology
Quartz is

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

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Refractory Technology
Magnesite chrome refractories

Are not at all resistant to the corrosive action of iron oxide
Have very low (50 kg/cm² ) cold crushing strength (C.C.S.), and can not be used in metalcase form
Have very low thermal co-efficient of expansion
Have better spalling resistance than chrome magnesite refractories

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