Comparative study on coprecipitation and microwave hydrothermal synthesis of magnesium aluminum spinel

MgAl₂O₄ was synthesized by microwave hydrothermal method and coprecipitation method, respectively. X-ray diffractometer (XRD), scanning electron microscope (SEM), BET, Archimedes method and an automatic micro-Vickers hardness tester were used to characterize the phase composition, microstructure, powder activity, relative density, and hardness of MgAl₂O₄. The results showed that, compared with the microwave hydrothermal synthesis method, the powder synthesized by the coprecipitation method was purer, the particle size was smaller and the distribution was more uniform, and the particles had no agglomeration phenomenon. The specific surface area of the powder synthesized by the coprecipitation method was 79.011 m²/g, three times larger than the powder synthesized by microwave hydrothermal synthesis. The optimum sintering temperature of MgAl₂O₄ synthesized by coprecipitation method or microwave hydrothermal method is 1700 °C. At this temperature, the sintered sample synthesized by coprecipitation method has the densest microstructure, the relative density is 98.83% and the hardness is 1411 kgf/mm²; while the relative density of the sintered sample synthesized by the microwave hydrothermal synthesis method is 92.77% and the hardness is 1407 kgf/mm².