High temperature X-ray studies of mayenite synthesized using the citrate sol–gel method

Room temperature and high temperature x-ray powder diffraction and differential thermal analysis/thermo-gravimetric analysis (DTA/TGA) have been used to characterize the phase evolution of bulk mayenite (Ca12Al14O33) prepared using the citrate sol–gel method. These studies have shown that single phase mayenite forms at 900 °C in air after approximately three hours. High temperature x-ray powder diffraction data show that when firing in air at temperatures 600 °C and below only amorphous content is observed; above 600 °C CaCO3 is the first phase to crystallize. For samples quenched at 800 °C and evaluated using room temperature x-ray powder diffraction mayenite, CaAl2O4, and CaCO3 were present. High temperature x-ray diffraction data collected while firing in 4% H2/96% N2 reveals that CaCO3 does not form and Ca12Al14O33 starts to form around 850 °C. DTA/TGA data collected either in a nitrogen environment or air on samples synthesized using the citrate gel method support the complete decomposition of metastable phases and the formation of mayenite at 900 °C, although the phase evolution is different depending on the environment.