Synthesis of SrAl2O4 and Sr3Al2O6 at high temperature, starting from mechanically activated SrCO3 and Al2O3 in blends of 3:1 molar ratio

The synthesis of strontium aluminates of the SrAl2O4 and Sr3Al2O6 type using SrCO3–Al2O3 blends was investigated. Blends 3:1 molar ratio of Al2O3 and mechanically activated SrCO3 were prepared and conformed into pellets by uniaxial compression at 100 MPa. In an experimental stage, thermogravimetric analysis was used to investigate the isothermal decomposition of mechanically activated SrCO3 powders in the blend, in the range of temperatures from 900 to 1100 °C. Then, samples were sintered at 1450 °C for several periods of time (4–36 h), and the products obtained were analyzed by X-ray diffraction and scanning electron microscopy. The results obtained showed that the formation of Sr3Al2O6 starts after 4 h of heat treatment, and it is completed at 36 h. Moreover, other phase such as SrAl2O4 formed in small amounts in the samples sintered for 12 h. Kinetic measurements showed that the conversion of SrCO3 into Sr3Al2O6 follow two different reaction mechanisms, with different controlling steps. The first mechanism relates to the order of reaction model for the Sr3Al2O6 phase formation, whereas the second mechanism relates to the nucleation and growth of these phase particles. The activation energy measured for both processes was 88.59 kJ and 54.06 kJ, respectively.