Microstructures and sintering kinetics of pressureless sintered alumina doped with diopside and AlTiB

► Sintering densification process of the composites was studied. ► The apparent activation energies were calculated. ► The sintering kinetic equations were deduced. ► The sintering mechanism of monolithic Al2O3 was volume diffusion. ► The sintering mechanism of composites was volume diffusion and grain boundary diffusion. In the present work, diopside and AlTiB were simultaneously introduced in alumina using pressureless sintering. Microstructures of the composites were observed at a given temperature of 1520°C and different holding time. Sintering densification process of the composites was studied. Experiments were performed in the temperature at equal increments: 1420, 1520, 1620 and 1720°C, and with four holding times, i.e. 100, 140, 180 and 220min. The apparent activation energies of 17.7–28.8kJ/mol for alumina matrix ceramic materials were calculated by least squares. The sintering kinetic equations were deduced. Results showed that the sintering of monolithic alumina was controlled by volume diffusion, and that of alumina matrix ceramic materials doped with diopside and AlTiB was controlled by grain boundary diffusion and volume diffusion.