Fire clay & fire clay bricks

*Fire clay is a specific kind of clay used in the manufacture of ceramics, especially fire brick.

*A clay which is highly resistant to heat without deforming and used for making brick.

*A coarse, refractory (heat resistant), secondary clay. Fireclays vary in plasticity; some are plastic enough to throw on the wheel, while others are grog-like. These are known as ‘flint clays,’ and are used for refractory shapes, grog, and oil-dry.

**Fire clays are hydrated aluminum  silicates which Al2O3.2SiO2.2H2O

In this composition 39.5% aluminium

46.5% Silica

14% Water

At high temperature the water is driven off from these hydrated silicates leading a waternal consisiting of alumina and silica.

WIKI:

The fire attribution is given for its refractory characteristics. There are two types of fire clay: flint clay and plastic fire clay. The raw materials normally used for making fireclay refractories consist of natural argillaceous materials whose mineral composition is represented by the general formula Al₂O₃ (aluminium oxide). The impurities in these raw materials are mainly present in the form of evenly distributed quartz, oxides and hydroxides of iron, hydrated haemetite and magnetite. Organic matter and sulphur compounds also may be present as impurities.

E.g: Fire clay bricks (A fire brick, firebrick, or refractory brick is a block of refractory ceramic material used in lining furnaces, kilns, fireboxes, and fireplaces)

Composition :Fire bricks usually contain 30-40% aluminium oxide or alumina and 50% silicon dioxide or silica. They can also be made of chamotte and other materials. For bricks of extreme refractory character, the aluminium oxide content can be as high as 50-80% (with correspondingly less silica),^[1] and silicon carbide may also be present.

High temp. Application :

The silica firebricks that line steel-making furnaces are used at temperatures up to 1650°C (3000°F), which would melt many other types of ceramic, and in fact part of the silica firebrick liquefies. HRSI, a material with the same composition, is used to make the insulating tiles of the space shuttle.