Sol-gel preparation and thermo-mechanical properties of porous xAl2O3–ySiO2 coatings on SiC Hi-Nicalon fibres

Porous thin films of mixed aluminium silica oxides were elaborated by the sol-gel process from aluminium tri-sec-butoxide and tetraethylorthosilicate on Hi-Nicalon fibres. The porosity was generated by addition of a surfactant, namely cetyltrimethylammonium bromide (CTAB). SiC Hi-Nicalon fibres were coated by the dip-coating technique. After annealing in air (500–1200 °C) crack-free coatings were observed, with a thickness in the range 100–1000 nm. The fibres were tensile tested and results were analysed by the Weibull statistic. They showed good mechanical properties compared to the commercial fibres. The systems were characterized by thermal gravimetry, differential scanning calorimetry, X-ray diffraction, BET and scanning electron microscopy. The powders obtained in the same conditions as the coatings were highly porous with surface areas in the range 540–150 m2/g depending on the annealing temperature (400–1000 °C).