Character: It is mostly lusterless, white and delicate when it is pure, and can be gray, yellow and brown when it contains impurities; The appearance can be in loose soil block shape and dense rock block shape depending on the cause of formation, with plasticity. Wet soil can be molded into various shapes without breaking, and can remain unchanged for a long time.
Density: 2.54-2.60 g/cm3.
Melting point: about 1785 ℃.
Brightness is a process property similar to whiteness, equivalent to 4570 ∨; Whiteness under (angstrom) wavelength light.
The color of kaolin is mainly related to its metal oxides or organic matter. Generally, Fe2O3 is rose red and brown yellow; Fe2+is light blue and light green; It is light brown with MnO2; Organic matter is light yellow, gray, green, black, etc. The existence of these impurities reduces the natural whiteness of kaolin, in which iron and titanium minerals also affect the calcination whiteness, resulting in color spots or molten scars on porcelain.
The clay formed by the combination of kaolin and water can deform under the action of external force. After the external force is removed, it can still maintain this deformation property, which is called plasticity. Plasticity is the basis of forming process of kaolin in ceramic body, and it is also the main technological index. Plasticity index and plasticity index are usually used to express the plasticity. Plasticity index refers to the liquid limit water content of kaolin clay minus plastic limit water content, expressed as a percentage, that is, W plasticity index=100 (W liquid limit - W plastic limit). The plasticity index represents the molding performance of kaolin clay. It can be obtained by directly measuring the load and deformation of clay balls when crushed under pressure with a plastometer. It is expressed in kg · cm. The higher the plasticity index, the better the molding performance. The plasticity of kaolin can be divided into four levels.
Ceramics not only have strict requirements on the plasticity, bonding, drying shrinkage, drying strength, sintering shrinkage, sintering properties, refractoriness and whiteness of kaolin, but also involve chemical properties, especially the presence of iron, titanium, copper, chromium, manganese and other chromogenic elements, which reduce the whiteness after burning and produce spots.
The grain size of kaolin is generally the finer the better, so that the porcelain clay has good plasticity and drying strength. However, for the casting process that requires rapid casting, faster grouting speed and dehydration speed, the grain size of ingredients needs to be increased. In addition, the difference in the crystallinity of kaolinite in kaolin will also significantly affect the technological performance of porcelain body. With a good crystallinity, the plasticity and bonding ability will be low, the drying shrinkage will be small, the sintering temperature will be high, and the impurity content will also be reduced; On the contrary, it has high plasticity, large drying shrinkage, low sintering temperature and high impurity content.
Kaolin has become a mineral raw material for papermaking, ceramics, rubber, chemical industry, coating, and other industries. Kaolin has certain plasticity, cohesiveness, suspension and cohesiveness, which endows ceramic clay and glaze with good formability, and makes ceramic clay body conducive to vehicle body and grouting, and easy to form.
In the old society and the three-year difficult period, the poor often lived on Guanyin soil during the lean years or famine years; This kind of soil can satisfy hunger, but it cannot be digested and absorbed by the human body. After eating it, the abdomen will be distended, and it is difficult to defecate. A small amount of it is not fatal; Although not hungry, people will die because of lack of nutrition. In the famine years, because of eating Guanyin soil, the stomach was distended and unable to defecate, countless people suffocated to death alive.
