Overview
Kaolin, commonly referred to as china clay in the ceramics industry, is a naturally occurring hydrated aluminum silicate mineral. Its name derives from the Chinese 'Gaoling' (高岭), meaning 'high ridge', where it was originally mined. In pottery, high-quality kaolin is prized for its plasticity, whiteness, and thermal stability. Unlike other clays, kaolin has a low impurity content, making it ideal for producing delicate porcelain and fine ceramics. Its refractory properties allow it to withstand high kiln temperatures without deforming. The global ceramics industry consumes approximately 40% of all mined kaolin.
Physical and Chemical Properties
Pottery-grade kaolin typically contains 90-95% kaolinite (Al₂Si₂O₅(OH)₄), with quartz and mica as common impurities. Its plate-like particle structure contributes to exceptional workability when mixed with water. The material exhibits low shrinkage (3-10%) during firing compared to ball clays. Chemically inert, kaolin maintains stability across a wide pH range (4-9). Its brightness (85-90% ISO) and low iron content (<0.8%) prevent discoloration in finished ceramics. The material becomes chemically active only when calcined above 550°C, undergoing dehydroxylation to form metakaolin.
Main Applications
In ceramic production, kaolin serves as the primary component in porcelain bodies (typically 25-50% of the recipe) and glaze formulations. Its high alumina content (39.5% by weight) ensures structural integrity during firing. Potters value specific kaolin varieties like English China Clay for throwing quality and New Zealand kaolin for its translucent properties. Beyond traditional pottery, kaolin finds use in technical ceramics including kiln furniture, dental porcelains, and electrical insulators. The paper industry consumes about 35% of global production as a coating pigment, while smaller quantities are used in cosmetics, pharmaceuticals, and as a food additive (E559).
Safety and Storage
While kaolin is generally non-toxic, prolonged inhalation of dust particles may cause respiratory irritation or silicosis. OSHA recommends a permissible exposure limit (PEL) of 15 mg/m³ for total dust and 5 mg/m³ for respirable fraction. Proper PPE including N95 masks should be used when handling dry powder. Bulk kaolin should be stored in moisture-proof containers or silos to prevent lump formation. The material remains stable indefinitely when kept dry but may develop microbial growth if contaminated with water. Fire hazards are minimal as kaolin is non-combustible and chemically unreactive under normal conditions.
B2B Procurement Guide
Industrial buyers should specify ceramic-grade kaolin with particle size distribution of 70-90% <2μm for optimal plasticity. Key quality parameters include brightness (>85%), iron oxide content (<0.5%), and loss on ignition (LOI) of 12-14%. Samples should be tested for workability and fired color before large-scale purchase. Major global suppliers include Imerys (France), KaMin (USA), and BASF (Germany), with Chinese producers like Longyan Kaolin offering competitive pricing. Containerized shipments (25kg bags or bulk) are common, with sea freight being cost-effective for international orders. Minimum order quantities typically range from 10-20 metric tons for bulk purchases.
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