Comparative Study of Corrosion Protection of Sol–Gel Coatings with Different Organic Functionality on Al-2024 substrate

• We have studied the effect of different sol–gel coatings on aluminum corrosion protection.
• The thiol containing silane imparted hydrophobicity to the coated surface.
• Amine silane rendered the coated surface more hydrophilic.
• The thiol containing silane was found to give the best anti corrosion protection.
• Amine containing silane provided the poorest performance.

In this paper we have 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. 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 analyzed 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. 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.