Investigations on B-doped SiO2 thermal protective coatings by hybrid sol–gel method

This study first prepared B-doped SiO2 coating by hybrid sol–gel method. SiO2 coatings had been successfully used for thermal protection, but its toughness, oxidation resistance and cost are weak points. Hybrid sol–gel method could prepare ultra thin and low cost SiO2 coatings on nickel alloys. And doping B could improve the coatings’ toughness and oxidation resistance. Thermogravimetry, differential thermal analysis and Fourier transform infrared spectroscopy were used to investigate the additives’ effect on coatings’ formations at different temperatures. X-ray photoelectron spectroscopy and X-ray diffraction were used to investigate the coatings’ element distribution and phase. The results showed that B-doped SiO2 thermal protective coatings could withstand 1050 °C, and Si–O–B bond was generated to improve the coatings’ toughness. A crystal mullite phase formed on the coatings’ surface at high temperature by thermal diffusion of Al, which significantly improved B-doped SiO2 thermal protective coatings’ oxidation resistance.