关键词: 微晶菱镁矿, 轻烧MgO, 高致密度镁砂, 显微结构, 烧结动力学

Abstract: Microcrystalline magnesite (60-90 mm) was used as the raw material,primarily calcined at 600-1 200 ℃ for 3 h,and then held at the temperature of complete decomposition of magnesite for 1-3 h.Then,the prepared high-activity light burned MgO was broken and ground to ≤0.045 mm,pressed and formed,then baked at 110 ℃ for 12 h,and secondarily calcined at 1 700-1 900 ℃ for 1-3 h to obtain sintered magnesia.The results show that the decomposition rate of microcrystalline magnesite increases significantly with the calcination temperature rising.The activity of the prepared light burned MgO increases first and then decreases slightly with the primary calcination temperature rising,but that decreases with the prolongation of the holding time.The appropriate primary calcination schedule is 900 ℃ for 1 h.In order to prepare high density sintered magnesia,the secondary calcination temperature is ≥1 850 ℃ with holding time ≥2 h.With the sintering temperature rising (1 700-1 900 ℃),sintering mechanism gradually changes from volume diffusion control to grain boundary diffusion control.The activation energy is lower when grain boundary diffusion is dominant,the pores are easier to migrate along grain boundaries and gradually expel,achieving better densification.

Key words: microcrystalline magnesite, light burned magnesia, high density magnesia, microstructure, sintering kinetics