Refractory Technology
Grog addition in fireclay during brick manufacture is done to

Impart greater spalling resistance
Reduce its shrinkage on heating
All of these
Enhance the strength of fired refractories

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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
Increases with the amount of air entrapped in pores
Decreases with decreases in porosity

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Refractory Technology
Magnesite chrome refractories

Have better spalling resistance than chrome magnesite 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

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