LAUSR

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.