Microstructure, thermal/mechanical properties and corrosion behaviors of ternary and quaternary equimolar rare-earth monosilicates

The properties of rare-earth (RE) monosilicates can be regulated by solid solution engineering based on the mixture rule. The combination and number of RE principals are critical factors for better performances. In the present study, four single-phase equimolar multicomponent RE-monosilicate solid solutions including (Dy1/3Er1/3Yb1/3)2SiO5, (Ho1/3Er1/3Yb1/3)2SiO5, (Y1/4Er1/4Tm1/4Lu1/4)2SiO5 and (Dy1/4Er1/4Tm1/4Yb1/4)2SiO5 were synthesized by solid-state reaction and hot-pressing method. The microstructures, thermal and mechanical properties, and corrosion resistance to high-temperature water vapor were systematically investigated. Compared to the single-principal and ternary RE-monosilicates, the quaternary RE-monosilicates exhibited lower thermal conductivity of 1.32 Wm-1K-1 at 400 oC, matched thermal expansion coefficients (3.3 × 10−6/oC ∼ 5.8 × 10−6/oC from 200 oC to 1000 oC) with SiC, and much lower weight loss during water vapor corrosion. The results indicate that the increase of the RE element number can promote the grain growth, lower the thermal conductivity and thermal expansion coefficient, and enhance corrosion resistance.