A Fire brick or refractory brick is a block of ceramic material used in lining furnaces and kilns. A refractory brick is built primarily to withstand temperature. This does not usually accompany resistance to heat flow; in fact, most refractory bricks usually have the highest thermal conductivities. This is logical, as thermally-related fractures are caused by tensions within the mass of the material. In turn, these fractures are caused by different degrees of dilation within the mass; these varying degrees are caused by different degrees of heat being absorbed by thermally non-conductive materials. Using a thermally conductive material negates the whole causality chain presented here by allowing the material to absorb heat uniformly, thus dilating uniformly and avoiding the internal tensions which lead to fracture. It is important for refractory brick to have a high resistance to erosion by ash-laden gases and to the fluxing action of molten slag; it should not spall badly under rapid temperature change, and its structural strength should hold up well under rapid temperature changes. Fire-brick is baked in the kiln until it is partly vitrified, and for special purposes may also be glazed. Fire-bricks usually contain 30-40% aluminium oxide and 50% silicon dioxide. For bricks of extreme refractory character, the aluminium oxide content can be as high as 50-80% (with correspondingly less silica), and silicon carbide may also be present. The standard size of fire-brick is 9 x 4.5 x 2.5 in. (228mm x 115mm x 64mm)

See also

Ceramics