Effects of kaolinite and halloysite as raw material on solid-state reaction to form kalsilite

This study investigated the effects of the stacking order, morphology, and calcination of kaolinite and halloysite specimens, 1:1 type layered aluminosilicates (Al₂Si₂O₅(OH)₄), as raw materials for the solid-state reaction to form kalsilite (KAlSiO₄). Thus, this study mainly investigated the solid-state reaction of potassium carbonate (K₂CO₃) with kaolinite or halloysite specimens at 1000 °C after wet grinding of the reactants. Compared with pristine kaolinite, amorphous KAlSiO₄ was generated using disorderly stacked kaolinite by the expansion of its layers as the raw material. Such an amorphous KAlSiO₄ was also obtained when halloysite having a tubular morphology with a disputed stacking order was used as the raw material. In addition, the resultant amorphous KAlSiO₄ was composed of smaller particles than the KAlSiO₄ prepared using kaolinite. When metakaolinite and metahalloysite (i.e., amorphous and dehydroxylated layered aluminosilicates (Al₂O₃・2SiO₂)) were used as raw materials, crystalline kalsilite specimens were obtained. Therefore, the results demonstrated that the crystallinity and particle shape of KAlSiO₄ were controlled by the specific types of kaolinite and halloysite as raw materials. Importantly, the stacking order, particle size, morphology, and impurities of kaolinite or halloysite typically vary depending on their geographical origin. Consequently, this study lays the groundwork for the development of cost-effective and environmentally friendly methods for preparing ceramic materials.