Chemical composition of fire clay bricks

Fire clay brick is the refractory brick containing 30-46% SiO2. It is made of clinkers calcined from refractory clays as the oxidant and bond clay as a binder agent.
The main raw material is refractory clay. Clay is an earthy mineral. It can form plastic mud pie when mixed with water and maintain the shape after drying. It has rock-like hardness after fired at high temperature.
Additionally, the clay contains a certain amount of impurities such as quartz, mica, pyrite, feldspar and organic substances. The impurities, especially iron, can reduce the quality of clay and are harmful to the fire clay bricks.
Alkalis such as Na2O and K2O exist as mica. It can improve the sintering properties of clay and form dense products after sintered. It should be fewer than 2%.
The content of CaO is generally under 11.5% and distributed evenly. So, it will not affect the refractory properties of raw materials.
There is a certain amount of TiO2 in the bond clay. It exists as diamond. When it is less than 1%, it has no big effect on the quality of bond clay. In the chemical analysis, its content is not tested alone but counted in the content of A1203 + TiO2.
When the impurities in the clay exceed 6%, the refractoriness of clay will decease and cannot be used as the raw materials. The content of organic substances in the clay is fluctuated greatly, up to 5%.