Preparation and characterization of 50SiO2–50Y2O3 sol–gel coatings on glass and SiC(C/SiC) composites

Yttrium silicate (Y2SiO5) coatings can complement internal SiC coatings for protecting carbon-fiber-reinforced SiC composites (C/SiC). 50SiO2–50Y2O3 coatings were prepared by dipping samples into sol–gel solutions. The coatings were deposited on soda-lime glass substrates to evaluate their homogeneity and critical thickness. Crack-free coatings were obtained at withdrawal rates below 16 cm/min with a critical thickness of 80 nm. Thicker coatings (2 μm) were prepared on SiC-coated C/SiC composites using a multilayer deposition process. The gelled sol was also studied by transmission electron microscopy (TEM), thermal analysis (TGA–DTA) and X-ray diffraction (XRD).