From view point of industries, a type of clay that contains large amount of kaolinite is called kaolin. From view of physical properties kaolin is a semi-crystalline material and somewhat amorphous. Special properties of kaolin include adhesion (which increases with increasing purity), colloidal and water absorption ability. Kaolin ore based on type of bond is divided to two group soft bond and hard bond. Kaolin with soft bond and hard bond can be used mainly in tile, ceramic industries and rubber, paper industries, respectively. Kaolin is also widely used in the refractory industry. This material contains 20 to 45 percent of alumina. In chemical and industrial conditions, kaolin in the pH range 3 to 9 may be stable, thus so easily can be used as pigments, coatings and fillers with other compounds. Among the important economic characteristics of kaolin is its particle size.
Characteristics of consumable kaolin in ceramic industry are related to impurities that may cause discoloration of the product after firing. The most important impurity is iron oxide. Other impurities can be copper, chromium and manganese. Allowable amount of Fe2O3 in ceramic is 0.6 to 0.7 percent. Iron oxide in consumable kaolin in porcelain should be less than 0.5% because iron and titanium in ceramic body will react and will reduce transparency. Potash in consumable kaolin in porcelain should be less than 1.5 percent and amounts of titanium and silica should be minimal.
Fine-grained kaolin is preferred in ceramic industry, because fine-grained kaolin increases plasticity and raw body resistance. Selection the type of grading is also very important, although small and soft kaolin reduces the degree of casting but causes contraction during firing.
To summarize the major characteristic of kaolin, which has led to its frequent consumptions can be named as followed:
From chemical view kaolin remains unchanged in a wide range of pH
Having white color
Having a good coating properties
kaolin is soft and non-abrasive
Limited ability to conduct electrical current and heat
Due to the fact that ceramic industries need to Kaolin with constant physical and chemical characteristics, and major consumptions of kaolin are in tile, sanitary ware, and refractory, glaze and color industries. APA Group attempts to be active in importing and supplying of grading kaolin with high purity and constant or uniform quality.