Preparation and Properties of Aluminum Phosphates and Phosphate-Bonded Bodies in the CaO⋅n Al₂O₃-H₃PO₄(H₂O) System

Abstract

Aluminum phosphates were synthesized by hydrothermal treatment of the CaO⋅n Al₂O₃ in H₃PO₄ solutions at 100°Cor 200°C under a pressure of 10 MPa. Their thermal change w as examined, together with the strength of hardened bodies. Three types of AlPO₄⋅2H₂O (i. e. Lucin-type variscite, Messbach-type variscite and Metavariscite) are produced as aluminum phosphate at 100°C and 3 types of AlPO4 (Berlinite, Tridymite form and Cristobalite form) at 200°C.
Decomposition and transformation of variscites during heating were also studied in air by TG-DTA and X-ray diffractometry. The strength of hardened bodies increased with the decrease of their CaO/Al₂O₃ ratio and was enhanced up to 150 to 290 MPa for the products in the system of CA₆.