Sintering Characteristics in the System MgO-Cr2O3 and Formation of (Mg8-xCrx)Cr16O32 (0≤x≤2.88)

MgO and Cr2O3 powders were mixed in various ratios and pressed to form compacts. They were heated in the carbon powder bed. Starting compacts containing 53 to 63mol% Cr2O3 were densely sintered, particularly the sintered compact with 55mol% Cr2O3 was about 93% in relative density, and composed of (Mg8-xCrx)Cr16O32 (0≤x≤2.88). Pores with globular shape in the compacts suggested the sintering in the presence of a liquid. Under reductive atmosphere coexisting with carbon, a liquid of the Cr-Cr2O3-MgO system is considered to form due to reduction of the Cr2O3 in the compact. During cooling, the (Mg8-xCrx)Cr16O32 may precipitate from the liquid. When the compound was exposed to air during heating, this phase was unstable and changed to MgCr2O4 and Cr2O3 at about 300°C.