Preparation and protective effects of carbon nanotube-containing organicinorganic composite coatings on aluminum alloys

To improve the corrosion resistance, (MWCNTs-OH)-containing organic-inorganic coatings were prepared on the aeronautic aluminum alloy substrates via the sol-gel process in which tetraethoxysilane (TEOS), KH-550 and some hydroxylated multi-walled carbon nanotubes (MWCNTs-OH)  were used as precursors. HAc was added as catalyst in the sol-gel process to control the limited hydrolysis. Sols were coated on the surface of aluminum alloy substrates by dip-coating technique and the composite coatings were obtained through necessary heat treatment afterwards. The results of electrochemical analysis show that the composite coatings with nanotubes can effectively improve the corrosion resistance of aluminium alloy substrates in 3.5wt% NaCl solution. When the content of MWCNTs-OH is 0.04wt% and the heat treatment temperature is 130℃, the corrosion current density for coated sample is about 3.056×10-8A/cm2, which is 3 order lower than that for bared sample (7.216×10^-5A/cm²). The SEM morphology of the coatings also reveals that the introduction of MWCNTs-OH to coatings is beneficial to prevent from the coating cracking.