Preparation and microstructure of Al2O₃–SiO₂–TiO₂ coating on three-dimensional braided carbon fiber by sol–gel technology

Highlights: • The preparation of the Al₂O₃–SiO₂–TiO₂ sol was formed at room temperature. • The Al₂O₃–SiO₂–TiO₂ coating sintered at low temperatures. • The preparation process of the sol is a new simple sol–gel process. • The coatings formed on the surface of 3-D braided carbon fiber. • Stirring time and aging time of the sol preparation is short. Al₂O₃–SiO₂–TiO₂ coatings were synthesized on the surface of three-dimensional (3-D) braided carbon fiber by the sol–gel method. The Al₂O₃–SiO₂–TiO₂ coating was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The effect of immension–pyrolysis cycle, immension time and heat treatment temperature on the microstructures and phase composition of the coating was investigated. The mechanical properties of the carbon fiber coated with various coating thickness were also measured. The results showed that the good morphology of the coating obtained was use of heat treatment at 750 °C for 2 immension–pyrolysis cycles by the immersion time of 40 min per cycle. The thickness was about 150–1200 nm along with the increase of immersion time from 40 to 120 min. Tensile strength measurement revealed that the Al₂O₃–SiO₂–TiO₂ coated carbon fiber maintained 96.8% of its original strength when the thickness of the coating was 470 nm.