Calcined Kaolin (Anhydrous, d50 2µm)

Calcined kaolin is produced by calcining water-washed kaolin clay at temperatures above 900°C, driving off all chemically combined water and converting the layered aluminosilicate structure into a mixed anhydrous alumina-silica phase (primarily metakaolin and mullite). This calcination process dramatically improves several key properties compared to hydrated kaolin, making calcined grades significantly more valuable as composite fillers.

The anhydrous nature of calcined kaolin (LOI typically <0.5%) makes it ideal for moisture-sensitive formulations including 1K polyurethanes, epoxy-anhydride systems, and formulations where residual moisture causes processing problems. The calcination also creates a harder, more angular particle shape compared to soft hydrated kaolin, which improves the abrasion resistance of filled composites and provides mild scratch-resistance in surface coatings.

Calcined kaolin is a premium extender in gelcoats, primers, and filled polyester systems where good electrical insulation properties, chemical resistance, and low gloss are required. Its white color (reflectance ~90%), plate-like morphology, and relatively low surface area make it an excellent extender for TiO2 pigments. The material also contributes improved fire resistance compared to organic fillers, as it is non-combustible and produces minimal smoke on exposure to flame.