Abstract：Kaolin is clay or clay rock mainly composed of kaolinite clay minerals. The main components are alumina and silica, and contain a small amount of impurities such as iron oxide and titanium oxide.
Kaolin is clay or clay rock mainly composed of kaolinite clay minerals. The main components are alumina and silica, and contain a small amount of impurities such as iron oxide and titanium oxide. At present, it is mainly used in ceramics, papermaking, rubber and plastics, enamel, coatings and other fields, among which ceramics is the largest application market of kaolin.
The three basic raw materials of ceramic products are plastic raw materials, barren raw materials and flux raw materials, among which the plastic raw materials are mainly clay mineral raw materials, mainly kaolin.
The role of kaolin in ceramics is to introduce Al2O3, which can improve its chemical stability and sintering strength. The mullite formed by the decomposition of kaolin during firing is the main framework for forming the strength of the green body, which can prevent the deformation of the product and make the firing temperature Widening can also make the green body have a certain degree of whiteness. At the same time, kaolin has a certain degree of plasticity, cohesiveness, suspension and binding ability, which can improve the formability of porcelain clay and enamel, and is more conducive to the processing of car blanks, grouting, and ceramic forming.
The application in the field of ceramics generally requires the particle size of kaolin to be as fine as possible, so that the porcelain clay has good plasticity and drying strength. In addition, the difference in the degree of crystallization of kaolinite in kaolin will also affect the process performance of the porcelain blank. If the degree of crystallization is good, 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 be low. On the contrary, its plasticity will be high. , the drying shrinkage is large, the sintering temperature is low, and the corresponding impurity content is also high.
In recent years, the total output of the global ceramic market has increased steadily, and the ceramic market demand has shown the characteristics of art, diversification, individualization and matching. In response to changes in domestic and foreign market demand, the industrial structure of my country's ceramic industry is being adjusted, which will not only expand the demand for kaolin, but also promote the development of my country's kaolin products to medium and high grades.
Honeycomb ceramics is a kind of porous industrial ceramics. Its internal structure is many through parallel channels. These honeycomb units are divided by lattice-like thin partition walls of different shapes. Compared with general solid block ceramics, honeycomb ceramics have excellent characteristics such as large specific surface area, light weight, low thermal expansion coefficient, large specific heat capacity, good thermal conductivity, and good thermal shock resistance.
Since the advent of honeycomb ceramics, the development tends to be diversified. The main materials are cordierite, aluminum titanate, silicon carbide, zirconia, silicon nitride, corundum, mullite, quartz, etc., and can also be two or more of them. made. At present, honeycomb ceramics can be divided into heat storage body, catalyst carrier, filter material and so on according to the application field.
In order to meet the high emission standards, the honeycomb ceramic carrier needs to improve the treatment efficiency of exhaust gas. Its main development trend is: high pore density, thin wall, low thermal expansion coefficient. In addition, DPF and GPF also need to meet high porosity and narrow pore size. distribution and low thermal expansion coefficient requirements. This requires cordierite honeycomb ceramics as the mainstream catalyst carrier to have better thermal shock resistance, and its thermal expansion coefficient must reach a sufficiently low level.
The upstream raw materials of honeycomb ceramics mainly include kaolin, zeolite, talc, bauxite, additives, etc., which together account for about 48% of the production cost of honeycomb ceramics, and the cost accounts for a large proportion. The quality and performance parameters of kaolin have a great influence on the final performance of honeycomb ceramics when preparing China VI standard honeycomb ceramics.
As we all know, kaolin is flaky crystal, so regardless of its chemical composition or crystal structure, kaolin should be used as the main raw material for synthesizing cordierite. High-purity flaky raw materials help to reduce the thermal expansion coefficient of honeycomb ceramics; the thermal expansion coefficient of cordierite single crystal is anisotropic, the a and b axes are positive expansion, and the c axis is negative expansion. The cordierite honeycomb ceramic carrier is usually formed by extrusion. When the sheet-shaped raw material is extruded and passed through the mold, the mud particles are subjected to mutual shearing action, so that the sheet-shaped raw material is oriented along the wall of the honeycomb grid, and the crystallization of cordierite When firing, it is generated based on the raw materials aligned in order to reduce its coefficient of thermal expansion.
In addition, moderate SiO2 content makes honeycomb ceramics have higher thermal stability, and higher Al2O3 content helps to improve the compressive strength and wear resistance of ceramics. CaO content should be low to reduce expansion and shrinkage problems during sintering. The ultra-low content of K2O and Na2O solves the problem of expansion and melting during the sintering process of honeycomb ceramics.
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