Synthesis of Calcium Aluminate Hydrates, their characterization and dehydration

This study is focused on the description of the dehydration of calcium aluminate hydrates (CAHs) and their identification. Four calcium aluminates (CA, C12A7, C3A, CA2) prepared by high temperature solid-state synthesis or modified Pechini synthesis served as precursors for CAHs. Hydration was carried out at the various temperatures in a range of 5 – 60 °C for 48 hours. CAHs were identified by X-ray diffraction analysis (XRD) and their dehydration was characterized by Thermogravimetry and effluent gas analysis (TG/EGA) and high temperature XRD. Pure C3AH6 and CAH10 were successfully prepared, other CAHs (C2AH8, C4AH19, AH3, C4A H11) were present in the mixtures. The results indicate that dehydration of C3AH6 takes place at a temperature of about 300 °C, followed by the formation of a new product with a structure similar to C12A7. C2AH8 dehydration can be described in three steps. The dehydration is accompanied by the formation of crystalline intermediate products. CAH10 dehydration can be assigned to a broad peak on the DTG curve with a maximum at approximately 100 °C. The decomposition of C4A H11 takes place in two steps, with CO2 evolving in the temperature range 500 – 700 °C.