Refractory Technology
Thoria is an expensive refractory material and is radioactive in nature. Thorium oxide is used in the manufacture of

Muffles for muffle furnaces
Segar cones
Crucibles used for melting of high purity metals
Insulating bricks

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Refractory Technology
Fireclay refractories

All of these
Shrink during firing
Combine with salts (e.g. chlorides sulphates etc.) & bases (e.g. lime, magnesia etc.) forming fusible aluminates silicates etc
Are not resistant to the action of basic slags

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Refractory Technology
Quartz is

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

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