Humidity-induced curing and anti-corrosion properties of GPTMS-modified polyorganosilazane functionalized silica coating on AA2024-T3 aluminum alloy

Relative humidity (RH) is one of the key parameters that significantly affect the curing kinetics and final properties of polysilazane-based coatings. Thus, the paper discusses the effect of relative humidity during the curing process and the anti-corrosion properties of (3-glycidyloxypropyl) trimethoxysilane (GPTMS)-modified polyorganosilazane (OPSZ) functionalized silica coatings on AA2024-T3. Modified polyorganosilazane sol was prepared and then deposited on AA2024-T3 substrates varying the curing conditions. After the deposition, the coated aluminum substrates were exposed to different RH levels; 15%, 40% and 80%, and then cured at 120 degrees C for 2 h. Transparent and crack-free GPTMS-modified polyorganosilazane coatings with a thickness of around 15-17 mu m were obtained. The exposure to the relative humidity increased the crosslinking and hydrolysis-condensation reactions of the OPSZ and GPTMS molecules, showing more Si-O-Si bonds. The incorporation of GPTMS affected the crosslinking structure, enhancing the corrosion protection properties of the coating. GPTMS-modified polyorganosilazane coatings cured at 40%RH had the best anti-corrosive properties after immersion in 3.5 wt% NaCl solution. The impedance modulus of similar to 109 Omega.cm2 at a low frequency was obtained, which was five orders of magnitude higher than that for the AA2024-T3 alloy. GPTMS-modified polyorganosilazane solution was successfully synthesized by sol-gel method.RH affects the crosslinking and hydrolysis-condensation reactions of the OPSZ and GPTMS molecules.Crack-free GPTMS-modified polyorganosilazane coatings with thickness of 17 mu m were obtained on AA2024.EIS results confirmed as the humidity-induced curing affects the anti-corrosion ability of coating.