Kaolin, named after Gaoling Village in Jingdezhen, Jiangxi, China, is the “soul raw material” of ceramics. Its main component is kaolinite (chemical formula Al₂[(OH)₄/Si₂O₅]), which is formed by the weathering of silicate minerals such as feldspar. It has a fine and white texture and is both plastic and refractory. From the “binary formula” in the Song Dynasty that innovated ceramic technology to its application in modern papermaking, the chemical industry, and aerospace materials, the kaolin has always been the “hidden champion” of the industry. The uses of Kaolin has a crucial impact for many industries.
Six Core Process Characteristics of Kaolin
Whiteness and Brightness: Determining the “Purity” of Quality
Natural whiteness: Whiteness at 105°C after drying. Impurities (such as Fe₂O₃, MnO₂) can cause it to appear yellow, brown, or other colors.
Calcination whiteness: The whiteness after calcination at 1300°C directly affects the glossiness of ceramics and coatings. The whiteness of high-quality kaolin after calcination can reach more than 90%.
Calcination whiteness: The whiteness after calcination at 1300°C directly affects the glossiness of ceramics and coatings. The whiteness of high-quality kaolin after calcination can reach more than 90%.
Brightness: The reflectivity under 4570Å wavelength light. The papermaking industry pays particular attention to this indicator.
Particle Size Distribution: The “Golden Indicator” of Industrial Applications
The finer the particles (such as those less than 2μm), the stronger the plasticity and suspension. For example, in the United States, more than 90% of the kaolin particles used in coatings must be less than 2μm.
Particle size control technology (such as water-pestle crushing and magnetic separation for iron removal) is key to increasing added value.
The plasticity index (the difference between liquid limit and plastic limit moisture content) and the plasticity coefficient (resistance to deformation) are core parameters. Kaolin with strong plasticity (index > 15) can be easily shaped and is less likely to crack.
Jingdezhen’s “binary formula” (kaolin + porcelain stone) utilizes its high plasticity to solve the problem of single porcelain stone being prone to deformation.
Bonding and Viscosity: The “Adhesive” of Industrial Formulas
Bonding refers to the strength after mixing with non-plastic materials (such as quartz sand). The higher the amount of sand, the stronger the bonding.
Viscosity affects the fluidity of the slurry. Papermaking coatings require a viscosity as low as 0.5 Pa·s (low-speed coating).
Drying and Sintering Performance: The Transformation from Mud to Porcelain
Drying shrinkage: The linear shrinkage rate is 3%-10%. Excessive shrinkage can easily cause cracking of the ceramic body.
Refractoriness: The refractoriness of pure kaolin reaches 1700°C, but impurities significantly reduce its high-temperature resistance.
Adsorption and Insulation: Potential for Cross-Border Applications
Kaolin has weak ion adsorption capacity but can be used in environmental protection fields (such as wastewater treatment) after modification.
It has excellent electrical insulation properties and is an important material for manufacturing high-voltage electric porcelain and radio components.
Main Uses of Kaolin
Ceramic Industry (Accounting for About 40%)
Daily-use porcelain, architectural ceramics, and electrical porcelain all rely on the molding and high-temperature resistance of kaolin.
Papermaking and Coatings (Accounting for About 30%)
As fillers and coatings, kaolin improves the gloss and smoothness of paper.
Refractory Materials
Refractory bricks, crucibles, and other materials need to withstand high temperatures above 1600°C, and kaolin is the core raw material.
New Materials Field
Modified kaolin is used for rubber reinforcement and plastic filling; nano kaolin is used in biomedicine.
Environmental Protection and Energy
Tailing comprehensive utilization technology (such as porcelain stone processing developed by Longgao Co., Ltd.) reduces resource waste.
In recent years, companies such as Longgao Co., Ltd. have promoted efficient resource development through “tailings utilization” and “old mine new mining” technologies, achieving an annual production capacity of 800,000 tons.
From the “binary formula” of Jingdezhen’s ancient kilns to modern nanotechnology, the uses of kaolin has been constantly redefined. With the tightening of environmental protection policies and the growing demand for new materials, the deep processing and recycling of kaolin will become a new direction for the industry. This piece of “white gold” is writing a legend for the next millennium.
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