Sillimanite is most widely used as a refractory raw material owing to its perfectly suited thermal properties.
- Thermal stability: It is stable in all temperatures up to 1550ºC after which it gets converted to mullite.
- It has high melting point.
- It has low coefficient of thermal expansion.
- It has low expansion in conversion to mullite: Between 1545º to 1550ºC, as it changes over to mullite there is a fairly rapid permanent expansion of 2-3%. The maximum expansion by volume noted in sillimanite is 4%, which too has been rarely observed. The linear expansion is less than 1%. The mineral thus shows negligible expansion while changing over to mullite and can hence be used without pre-calcination.
- Minimum increase in porosity upon heating: One outstanding feature of sillimanite is that the volume porosity of grains hardly exceeds 6% after heating. Moreover, if heating is prolonged, it tends to decrease as a consequence of vitrification. Such compactness offers great advantage in all applications in which problems of corrosion and abrasion arise.
- Favorable mechanical properties: strength and toughness, resistance to mechanical shock
- It has low electrical conductivity
- Neutral reaction and resistivity to corrosive slags and to oxidizing and reducing conditions. It is very resistant to glass slag and hence widely used as lining material in glass melting furnace. Iron corrodes it rapidly hence it is not suitable in iron smelting. It is also not highly resistant to molten metallic oxides and, therefore, rather unsuitable for metallurgical operations.
Anand talc is an established supplier of raw, refractory grade sillimanite. Our sillimanite gives successful results whether used raw or post calcination.