Chemical Composition and It's Function of Brick Clay

The chemical composition of brick clay is as follows-

                                              Silica - 55%

                                              Alumina - 30%

                                              Iron oxide - 8%

                                              Magnesia - 5%

                                               Lime - 1%

                                              Alkali and organic matter-1%
Silica:
Silica is present in brick clay as the chemical composition of alumina and forming silicate of alumina.Sometimes silica is present in pure form termed as flint.
Silica prevents shrinking,cracking and warping of brick clay.High amount cause uniform texture.Too much presence of silica cause brick to be brittle and weak.

Alumina:
Alumina imparts plasticity to brick clay which is very important in molding.It also imparts density.Excess alumina cause brick to crack and warp during drying and very hard when heated.

Iron oxide:
The presence of iron oxide increases impermeability and durability of brick.The color of brick depend upon iron oxide and color changes from light yellow to orange and red as iron oxide goes up to 8%.

Magnesia:
Presence of small quantity of magnesia decreases shrinkage and gives yellowish tint.

Lime:
Lime melts silica in burning and binds the particles of brick together.It also reduces the shrinkage of brick during drying.
Excess of lime cause the brick to fuse and shape will be lost.

Alkali and Organic Matter:
Small quantity assist burning of brick clay.It also reduces the fusion point.If excess amount is present and not burned properly the brick would be porous.