Synthesis and densification of single-phase mayenite (C12A7)

Mayenite (C12A7) powders have been synthesized by self-combustion method (glycine/nitrate procedure - GNP and a newly suggested modified glycine/nitrate procedure - MGNP). The MGNP is derived from the GNP by substituting a portion of Al-nitrate with the less expensive Al-acetate. The effect of synthesis conditions of both procedures on the phase evolution was studied. Mayenite samples, obtained by using GNP and MGNP, followed by thermal treatment in air, were analyzed by using XRD method. The obtained results showed that crystallization started at 900 °C for the GNP and at 750 °C for the MGNP while below these temperatures samples are amorphous. Also, only observed phase was mayenite for MGNP, while a secondary phase is present in samples synthesized by using GNP. Scanning electron microscopy (SEM), electron paramagnetic resonance (EPR) and nuclear magnetic resonance spectroscopy (NMR) were used to characterize the pure mayenite phase at room temperature. Sintering behavior was studied by dilatometry. A relative density of 94% is obtained at 1300 °C.