WHAT ARE THE INGREDIENTS OF GOOD BRICK EARTH ?

For the preparation of bricks, clay or other suitable earth is moulded to the desired shape after subjecting it to several processes. After drying, it should not shrink and no crack should develop.The clay used for brick making consists mainly of silica and alumina mixed in such a proportion that the clay becomes plastic when water is added to it. It also consists of small proportions of lime, iron, manganese, sulphur, etc.

INGREDIENTS OF GOOD BRICK EARTH

Silica, alumina, lime, magnesia, ferric oxide, alkalis, carbon dioxide, sulpur trioxide and small percentage of water are the ingredient of good brick. the percentage of ingredient used for making brick are give below

PROPORTIONS

Silica                      50–60%

Alumina                  20–30%

Lime                       10%

Magnesia             < 1%

Ferric oxide          < 7% } Less than 20%

Alkalis                 < 10%

Carbon dioxide           } Very small percentage Water

Sulphur trioxide          } Very small percentage Water

FUNCTION OF BRICK INGREDIENTS

Silica

Silica enables the brick to retain its shape and imparts durability, prevents shrinkage and warping. Excess of silica makes the brick brittle and weak on burning. A large percentage of sand or uncombined silica in clay is undesirable. However, it is added to decrease shrinkage in burning and to increase the refractoriness of low alumina clays.

Alumina 

Lime normally constitutes less than 10 per cent of clay. Lime in brick clay has the following effects:

1) Reduces the shrinkage on drying.

2) Causes silica in clay to melt on burning and thus helps to bind it.

3) In carbonated form, lime lowers the fusion point.

4) Excess of lime causes the brick to melt and the brick looses its shape.

5) Red bricks are obtained on burning at considerably high temperature (more than 800°C) and buff-burning bricks are made by increasing the lime content.

Alumina absorbs water and renders the clay plastic. If alumina is present in excess of the specified quantity, it produces cracks in brick on drying. Clays having exceedingly high alumina content are likely to be very refractory.

Magnesia 

Rarely exceeding 1 per cent, affects the colour and makes the brick yellow, in burning; it causes the clay to soften at slower rate than in most case is lime and reduces warping.

Iron

Iron oxide constituting less than 7 per cent of clay, imparts the following properties:

1) Gives red colour on burning when excess of oxygen is available and dark brown or even black colour when oxygen available is insufficient, however, excess of ferric oxide makes the brick dark blue.

2) Improves impermeability and durability.

3) Tends to lower the fusion point of the clay, especially if present as ferrous oxide.

4) Gives strength and hardness.