Effect of process factors of microwave hydrothermal method on the preparation of micron-sized spherical α-Al2O3 particles

Abstract Spherical α-Al2O3 particles with the size of 1–2 μm were obtained by microwave hydrothermal(M-H) method and subsequent microwave calcination. In the synthesis, Al2(SO4)3·18H2O was used as the aluminum sources, and CH4N2O was used as the precipitant. The effects of M-H temperature, heating preservation time and pressure in the reactor on the morphology, phase composition, particle size and surface area of the particles were studied. The results show that amorphous precursors with high sphericity and good dispersion can be rapidly (30 min) produced by M-H method at low temperature (100 °C). Increasing the temperature or extending the holding time will destroy the spherical morphology of the precursor, while transforming its phase from amorphous to γ-AlOOH. Pressure in the reactor does not change the phase composition of the precursor, but affects its dispersion and homogeneity. The precursor retains its spherical morphology after microwave calcination at 1100 °C for 90 min. The resulting powders were hot pressed and sintered at 1650 °C for 30 min to obtain a high-performance ceramic plate with a thermal conductivity of 27.1 W/(m·K) and a Vickers hardness of 21.4 GPa.