Nano-structured sol-gel coatings as protective films against zinc corrosion in 0.5 M HCl solution

The protection abilities of unmodified and modified GPTMS-VTMS sol-gel films with different Ti- and Al-alkoxides concentrations against zinc corrosion in 0.5 M HCl solution are examined. Prepared samples are characterized by FTIR and TGA. It was shown that the presence of the modifiers, either Ti or Al, facilitates the formation of the network structure and increases slightly the thermal stability of sol-gel materials. SEM and TEM show that morphology is smooth and uniform by using low modifiers concentrations, while surface deterioration appears at higher concentrations. Gravimetric measurement, polarization and EIS show that the protection ability of GPTMS-VTMS sol-gel is increased by being modified with low concentrations of Ti and Al moities. Protection efficiency value is 69.2% for unmodified film and increased to 96.2 and 95.8% by using 0.005 M of Ti and Al modifiers, respectively. This improvement is caused by both the non-permeable nature of the sol-gel coating and the enhanced structure of the sol-gel by the presence of Ti and Al modifiers. On the other hand, it is found that further increase of the modifier content allows high chance for galvanic corrosion that resulted in a decrease in protection efficiency values.