Facilitated phase transformation of CaAl₂Si₂O₈ by kaolinite-derived aluminosilicate nanoscrolls

Aluminosilicate nanoscrolls, derived from two-dimensional layered materials, were studied for their role in facilitating phase transformations in solid-state materials. This study focused on kaolinite (Al₂Si₂O₅(OH)₄), a layered clay mineral with platy morphology, as a nanoscroll precursor. Rolling-up of kaolinite layers occurs via an inherently incomplete intercalation, producing incompletely rolled-up kaolinite containing nanoscrolls. This morphology serves as an ideal model to investigate the effect of halloysite-a naturally occurring nanoscroll mineral with the same layer structure and composition as kaolinite-on kaolinite solid-state reactions. Notably, kaolin clay, widely used as a raw material in industrial inorganic materials, primarily consists of kaolinite but often contains by-products, including halloysite. In this study, purified Kanpaku kaolinite (Si/Al = 1.01) was mixed in a 1 : 1 molar with calcium carbonate (CaCO₃) and calcined to evaluate phase transformation into metastable and stable CaAl₂Si₂O₈. At 900 °C, where the metastable phase predominates, X-ray diffraction pattern revealed a weak reflection corresponding to anorthite-the stable phase of CaAl₂Si₂O₈-in products containing nanoscrolls. Although this reflection is still weak, it is noticeably stronger than that observed in the specimen prepared using only kaolinite with platy morphology. This result indicates nanoscrolls in platy particles accelerate the transformation from metastable to the stable phases. The results in this study highlight the role of kaolinite-derived nanoscroll morphology in influencing solid-state reactions of kaolinite.