Yttrium silicate coating system for oxidation protection of C/C–Si–SiC composites: Electrophoretic deposition and oxygen self-diffusion measurements

Abstract

Yttrium silicate (YSI) coatings are promising complements to SiC coatings for protecting C/C–Si–SiC composites against oxidation owing to the pronounced chemical and mechanical properties of this material (low Young's modulus, low thermal expansion coefficient, low evaporation rate and oxygen permeability, good erosion resistance). Under control of deposition voltage and duration, yttrium silicate coatings of various thicknesses were electrophoretically deposited from powder suspensions. The protectiveness of these coatings was tested by means of thermogravimetric analysis in air. Diffusion data for oxygen in yttrium silicate needed to correlate the experimentally obtained oxidation rates in a phenomenological model were obtained by the IEDP (isotope exchange depth profiling) method from tracer diffusion measurements in single crystalline yttrium silicate and compared to diffusion data in mullite.