Studying the effect of sol-gel coatings on aluminum corrosion protection

For their investigations they studied the effect of addition of amino silane and sulfur silane by 2 wt% into a reference coating solution by using two basic silane coupling agents methyl-tri-ethoxy silane (MTEO) and glycidoxy-propyl-tri-ethoxy silane (GPTS) in 1:1 molar ratio by sol-gel technique.

Evaluation methods

The change in hydrophobicity due to the addition of amino group and thiol group was investigated by contact angle study and sol-gel kinetics was studied by Fourier transform infrared spectroscopy. The thermal resistance and surface morphology was analysed by thermo gravimetric method and scanning electron microscope. The anti-corrosion property of all three coatings were evaluated by potentiodynamic polarization study, AC impedance and salt spray method. X-ray photoelectron spectroscopic method was used to monitor the bonding mechanism of coating matrix with the metal surface.

Amine containing silane provided poorest performance

All type of investigations revealed that, addition of thiol group containing silane coating to the reference coating solution has caused remarkable improvement in hydrophobicity and corrosion resistance properties where as amine group rendred the surface less hydrophobic and showed no sign of improvement in corrosion protection. The most probable reason behind this improved performance is due to the additional hydrophobicity imparted by much less polar thiol group. But amino silane provided comparatively poor performance due to the presence of polar amine group.

The study is published in: Progress in Organic Coatings, Volume 88, November 2015, Pages 293–303