Hydration of Ca7ZrAl6O18 phase

The hydraulic properties of the Ca7ZrAl6O18 (C7A3Z) phase as well as the hydration products and thermal decomposition mechanism of this hydrated phase were studied. Microcalorimetric analysis has shown that the C7A3Z phase reacts with water very quickly, especially in the first 2 h after the start of the experiment. Hydration of calcium zirconium aluminate proceeds with the formation of high refractory calcium zirconate (with melting point 2345 °C), apart from the hydrated, nearly amorphous material. According to the DTA–TG–EGA, FT-IR and SEM/EDS examinations it has been found that not only the hydrates CAH10, C2AH8 and C4AH19 are present, but also C3AH6 (C = CaO, A = Al2O3, H = H2O), the only hydrated calcium aluminate which is a thermodynamically stable phase above 40 °C. Unhydrated Ca7ZrAl6O18 and CaZrO3 phases have been found by XRD, but crystalline hydrates have not been detected.