Refractory Technology
Spalling resistance of a refractory can not be increased by

Decreasing its thermal co-efficient of expansion
Using a coarser grog during its manufacture
Making it denser
Increasing its porosity

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Refractory Technology
Addition of grog in fireclay brick during its manufacture is advantageous, because it results in

High strength & thermal spalling resistance
All of these
Less addition of water to get a workable plasticity & lesser time required for drying the raw refractories and hence increased rate of production
Less shrinkage in heating, decreased apparent porosity & increased specific gravity

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Refractory Technology
Thermal conductivity of refractory bricks

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

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