Refractory Technology
Refractory bricks with lower permeability is produced by using

Higher moulding pressure
Higher firing temperature
Finer grog size
All of these

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Refractory Technology
Silica refractories

Have lower thermal conductivity than fireclay bricks
All of these
Crack when subjected to sudden change of temperature
Can not be used in the dome of hot blast stoves

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Refractory Technology
What is Thoria?

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

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