Synthesis and characterization of yttrium and ytterbium silicates from their oxides and an oligosilazane by the PDC route for coating applications to protect Si3N4 in hot gas environments

Environmental barrier coatings are required to protect Si₃N₄ against hot gas corrosion and enable its application in gas turbines, among which yttrium and ytterbium silicate-coatings stand out. Thus, the polymer-derived ceramic route was used to synthesize these silicates for basic investigations regarding their intrinsic properties from a mixture of Y₂O₃ or Yb₂O₃ powders and the oligosilazane Durazane 1800. After pyrolysis above 1200 °C in air, the silicates are predominant phases. The corrosion behaviour of the resulting composites was tested at 1400 °C for 80 h in moist environments. The material containing x₂-Yb₂SiO₅ and Yb₂Si₂O₇ undergoes the lowest corrosion rate (?1.8 μg cm^?2 h^?1). Finally, the processing of Y₂O₃/Durazane 1800 as well-adherent, crack-free and thick (40 μm) coatings for Si₃N₄ was achieved after pyrolysis at 1400 °C in air. The coating consisted of an Y₂O₃/Y₂SiO₅ top-layer and an Y₂O₃/Y₂Si₂O₇ interlayer due to the interaction of the coating system with the substrate.