ISO9001 Approved White Calcined Kaolin Powder for Ceramic Manufacturing Process

 Application of kaolin in refractory industry
Kaolin has a high degree of refractoriness and is commonly used to produce refractory materials. Its products have the ability to withstand high temperatures and withstand loads at high temperatures without deformation. Kaolin, which is mainly composed of kaolinite, and bentonite and bauxite, are collectively referred to as refractory clay according to their high temperature resistance. China's clay with a refractoriness of more than 1580 ° C, bauxite with a refractoriness of more than 1770 ° C, is commonly known as refractory clay. The former is divided into hard clay, soft clay, semi-soft clay, and the latter is called high alumina clay. Some colored kaolins cannot be used in ceramics and papermaking, but are good raw materials for refractory materials. Therefore, refractory materials are an important market for the comprehensive application of kaolin.

There are two main types of kaolin used as refractory products: refractory bricks, silicon aluminum wool. The former has a refractoriness of not less than 1730 ° C, a softening start temperature of 2 × 105 Pa load is not lower than 1350 ° C, and the refrigerating line shrinkage is less than 0.5% (1400 ° C, 2 h), and can be made into various sizes and shapes as needed. brick. The latter is a lightweight refractory insulation material, which is manufactured by kaolin, calcined at 1000 to 1100 ° C, and then melted with an electric arc furnace at 2000 ° C to be blown into cotton under high-speed air flow.
The quality requirements of refractory materials for kaolin are not very strict, but the ratio of the ratio of Al2O3 and SiO2 in kaolin directly affects the change of refractoriness. The value of Al2O3/SiO2 in high quality kaolin is generally between 0.7 and 0.8 or slightly higher. The ratio of Al2O3/SiO2 in pure kaolin is 0.85. When the ratio is greater than 0.85, there is an aluminum-rich mineral, which will improve the refractoriness. When it is less than 0.7, the kaolin content is low, and there is quartz, which will reduce the refractoriness. In addition, the high content of Fe2O3, TiO2 and K2O in kaolin will reduce the refractoriness and have certain harmfulness.

process characteristics of refractory raw material kaolin
1, whiteness and brightness
Whiteness is one of the main parameters of kaolin's process performance, and the high purity kaolin is white. Kaolin whiteness is divided into natural whiteness and whiteness after calcination. For ceramic raw materials, the whiteness after calcination is more important, and the higher the whiteness of calcination, the better the quality. The ceramic process stipulates that the drying temperature of 105 ° C is the classification standard of natural whiteness, and the calcination of 1300 ° C is the classification standard of the whiteness of calcination. The whiteness can be measured by a whiteness meter. A whiteness meter is a device that measures the reflectivity of light at 3800-7000 wavelengths. In the whiteness meter, the reflectance of the sample to be tested is compared with the reflectance of the standard sample (such as BaSO4, MgO, etc.), that is, the whiteness value (for example, the whiteness of 90 means 90% of the reflectance of the standard sample).
Brightness is a process property similar to whiteness, which is equivalent to the whiteness of 4570 wavelength light.
The color of kaolin is mainly related to the metal oxide or organic matter contained in it. Generally, Fe2O3 is reddish brown and brownish yellow; Fe2+ is light blue and light green; MnO2 is light brown; and organic matter is yellowish, gray, green and black. The presence of these impurities reduces the natural whiteness of the kaolin. The iron and titanium minerals also affect the whiteness of the calcination, causing stains or melting of the porcelain.
2, particle size distribution
Particle size distribution refers to the proportion (in percent) of particles in natural kaolin that are within a given range of different particle sizes (represented by the mesh of millimeter or micrometer mesh). The particle size distribution characteristics of kaolin are of great significance to the ore selectivity and process application. The particle size has a great influence on its plasticity, mud viscosity, ion exchange capacity, forming property, drying performance and firing performance. Kaolin mines require technical processing and are easy to process to the required fineness of the process. It has become one of the criteria for evaluating ore quality. Each industrial sector has specific particle size and fineness requirements for kaolin for different uses. For example, in the United States, the content of kaolin used as a coating is less than 2 μm, and the content of papermaking filler is less than 2 μm, which is 78-80%.