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
Quartz is

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

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