Microstructure and Thermal Property of Atmospheric Plasma Sprayed Yb₂Si₂O₇ Coating

In this work, Yb₂Si₂O₇ powder was synthesized from Yb₂O₃ and SiO₂ powders and applied to aluminum substrates by atmospheric plasma spraying. Phase composition and microstructure were examined and density, porosity, and hardness were assessed. Thermal stability was evaluated by thermogravimetry and differential thermal analysis and thermal conductivity was measured. The as-sprayed coating was mainly composed of crystalline Yb₂Si₂O₇ with a small amount of Yb₂SiO₅ and amorphous Yb₂Si₂O₇. It had a dense structure containing pores, microcracks, and other types of defects. TG-DTA tests showed that there was almost no mass change from room temperature to 1200 °C, although a sharp exothermic peak appeared at 1038 °C, indicating that the amorphous phase had crystallized. The thermal conductivity of the coating decreased with increasing temperature, reaching a minimum of 0.68 W/(m·K) at 600 °C, followed by an increase at higher temperatures.