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

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

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Refractory Technology
Natural silica

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

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