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

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

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Refractory Technology
Natural silica

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

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