Influences of SiO2 Additions on the Structures and Thermal Properties of AlTaO4 Ceramics as EBC Materials

Ceramic matrix composites (CMCs) are extensively utilized in aero engines due to their high-temperature stability; however, they are prone to environmental corrosion at high temperatures, and environmental barrier coatings (EBCs) are necessary to resist oxidation and corrosion. Among various EBC materials, AlTaO4 offers high cost-effectiveness and low thermal expansion coefficients (TECs), but its resistance to SiO2 erosion and high-temperature stability remain unclear. We investigated the influences of SiO2 additions on the structures and thermal properties of AlTaO4; and AlTaO4 mixtures containing 10 wt.% SiO2 were kept at 1400 °C for 30–120 h. AlTaO4 exhibited excellent high-temperature phase stability, and SiO2 dissolved into AlTaO4 to generate a solid solution. XRD Rietveld refinement was employed to confirm the position of Si in the lattices, while SEM and EDS characterizations demonstrated the homogeneous distribution of Si, Al, and Ta elements. At 1200 °C, the TECs of SiO2-AlTaO4 (4.65 × 10−6 K−1) were close to those of SiC (4.5–5.5 × 10−6 K−1). Additionally, the addition of SiO2 could reduce TECs of AlTaO4, a feature that helped alleviate the interface thermal stress between AlTaO4 and the Si bond coat in the EBC systems. At 900 °C, the thermal conductivity was reduced by 26.9% compared to that of AlTaO4, and the lowest value was 1.65 W·m−1·K−1. Accordingly, SiO2 will enter the lattices of AlTaO4 after heat treatments at 1400 °C, and SiO2 additions will reduce the thermal conductivity and TECs of AlTaO4, which is beneficial for its EBC applications.