Physical and mechanical properties of hot-press sintering ternary CM₂A₈ (CaMg₂Al₁₆O₂₇) and C₂M₂A₁₄ (Ca₂Mg₂Al₂₈O₄₆) ceramics

The new ternary CM₂A₈ (CaMg₂Al₁₆O₂₇) and C₂M₂A₁₄ (Ca₂Mg₂Al₂₈O₄₆) pure and dense ceramics were first prepared by a hot-press sintering technique, and their physical and mechanical properties were investigated. The purity of obtained CM₂A₈ and C₂M₂A₁₄ ceramics reaches 98.1 wt% and 97.5 wt%, respectively. Their microstructure is dense with few observable pores, and their grain size is about a few dozen microns. For their physical properties, the average apparent porosity of CM₂A₈ and C₂M₂A₁₄ ceramics is 0.18% and 0.13%, and their average bulk density is 3.66 g/cm³ and 3.71 g/cm³, respectively. The relative density of CM₂A₈ ceramic is 98.12% and that of C₂M₂A₁₄ ceramic is 98.67%. The thermal expansivity (50–1400 ℃) of CM₂A₈ and C₂M₂A₁₄ ceramics is 9.24×10^–6 K^–1 and 8.92×10^–6 K^–1, respectively. The thermal conductivity of CM₂A₈ and C₂M₂A₁₄ ceramic is 21.32 W/(m·K) and 23.25 W/(m·K) at 25 ℃ and 18.76 W/(m·K) and 19.42 W/(m·K) as temperature rises to 350 ℃, respectively. In addition, the mechanical properties are also achieved. For CM₂A₈ ceramic, the flexural strength is 248 MPa, the fracture toughness is 2.17 MPa·m^1/2, and the Vickers hardness is 12.26 GPa. For C₂M₂A₁₄ ceramic, the flexural strength is 262 MPa, the fracture toughness is 2.23 MPa·m^1/2, and the Vickers hardness is 12.95 GPa.