Hydrothermal transformation of the calcium aluminum oxide hydrates CaAl2O4·10H2O and Ca2Al2O5·8H2O to Ca3Al2(OH)12 investigated by in situ synchrotron X-ray powder diffraction

The hydrothermal transformation of calcium aluminate hydrates were investigated by in situ synchrotron X-ray powder diffraction in the temperature range 25 to 170 °C. This technique allowed the study of the detailed reaction mechanism and identification of intermediate phases. The material CaAl2O4·10H2O converted to Ca3Al2(OH)12 and amorphous aluminum hydroxide. Ca2Al2O5·8H2O transformed via the intermediate phase Ca4Al2O7·13H2O to Ca3Al2(OH)12 and gibbsite, Al(OH)3. The phase Ca4Al2O7·19H2O reacted via the same intermediate phase to Ca3Al2(OH)12 and mainly amorphous aluminum hydroxide. The powder pattern of the intermediate phase is reported.