Flint Clay

Flint clay or Kaolin clay is a high-quality hard refractory clay produced in Zibo area, Shandong Province, China. The Al2O3 content of the standard raw ore is 38%, the Al2O3 content after calcination is about 44%, and the Fe2O3<2%. Color of flint clay is white. With stable composition, uniform texture, dense structure,and shell-shaped section, it is used to produce high-quality clay refractory materials. It is first-grade hard clay clinker, the main chemical components are AL2O3 and SiO2, accompanied by a small amount of Fe2O3 and traces of Na2O and K2O, and the main mineral is kaolin. Generally, it could also be used as a raw material for ordinary ceramic fibers after calcination.

The mineral composition and chemical composition of flint clay are complex, with no fixed structure and composition. Flint clay is not easy to disperse in water and have low plasticity. From the perspective of chemical composition, it is close to the theoretical composition of kaolinite (Al2O3/3SiO2=0.85), and contains impurities such as free quartz and a small amount of iron-containing minerals and alkali metal oxides. The common colors of flint claytones after high-temperature calcination are: pure white, light gray, light yellow brown, and a small amount is covered by brown spots.

Flint clay is a mixture of several aluminosilicates. The main chemical components are two oxides of Al2O3 and SiO2, and the impurities are mainly oxides of alkali, alkaline earth, iron, titanium, etc., and some organic substances. All kinds of oxides play a fluxing role, which will reduce the refractoriness of raw materials. Therefore, the lower the content of impurities in flint clay, especially the content of Na2O+K2O, the higher its refractoriness. The closer the ratio of Al2O3/3SiO2 to the theoretical value (A/S=0.85), the higher the purity of the flint clay. The larger the A/S, the higher the refractoriness of it, and the wider the range of sintering and melting. The refractoriness of high-quality flint clay could reach above 1750°C

Flint clay has the characteristics of stable volume, high strength and low water absorption after high-temperature calcination. The indicators to measure the degree of sintering of this item generally include true specific gravity, bulk density, porosity, water absorption, and shrinkage rate. The water absorption rate of the flint clay with good sintering degree is less than 5%, and the bulk density is greater than 2.55g/cm3.