PTMS/OH-MWCNT sol-gel nanocomposite for corrosion protection of magnesium alloy

In this work, hydroxylated Multi-Walled Carbon Nanotubes (OH-MWCNTs) were embedded in phenyl-trimethoxysilane (PTMS) sol-gel coating at different concentrations to improve the corrosion protection capacity. The obtained nanocomposites (PTMS/OH-MWCNT) were applied on AM6OB magnesium alloy for effective corrosion protection. Chemical interaction between OH-MWCNTs and PTMS silane matrix was confirmed by STIR. The SEM images were revealed that a uniform but cracked sol-gel coating was obtained without incorporation of OH-MWCNTs. Also, uniform sol-gel nanocomposites without any micro-cracks were achieved when various concentrations of OH-MWCNT (200, 500, and 1000 ppm) were embedded in the silica film. Both the pure and nanocomposite coatings showed suitable adhesion to the substrate and thickness of the pure coating (1.4-1.5 mu m) was not changed significantly by incorporation of OH-MWCNTs. The average roughness of the pure PTMS film was about 0.2 nm and was increased to 0.5 nm by incorporation of OH-MWCNTs at 200 ppm concentration. However, the surface roughness was decreased by further increasing the carbon nanotube content in the sol-gel coating probably due to formation of more compact silica film. Corrosion resistance of the magnesium alloy in Harrison's corrosive electrolyte was significantly increased after application of PTMS coating which was ascribed to barrier properties of the film along with hydrophobic nature of the phenyl group. Also, the corrosion resistance of PTMS sol-gel film was considerably promoted after incorporation of OH-MWCNTs at 500 ppm concentration which was attributed to the chemical interaction between incorporated OH-MWCNTs and silane matrix, filling of the defects of coating by the carbon nanotubes, and also formation of longer tortuous pathways for the corrosive species. The water contact angle on the pure sol-gel coating was increased from about 86.95 to 94.65 degrees by incorporating 500 ppm of OH-MWCNTs indicating considerable improvement in the hydrophobic property.