Electrochemical Studies on Corrosion Resistance of Coatings Based on Polyaniline and Silica Gel

Abstract

Organic acid doped polyaniline (PANI), hybrid with silica gel (SiG) and composites with metal primer have been prepared by chemical oxidative polymerization of double-distilled aniline in an acidic medium at 0-5 °C in an ice bath using ammonium persulphate as oxidant and p-toluene sulphonic acid (p-TSA) as the dopant. The anticorrosive property of PANI coatings containing alkyd primer, zinc chromate and silica gel was investigated. The coatings were characterized by FTIR spectroscopy, scanning electron microscopy and electrochemical impedance spectroscopy. The corrosion studies were carried out in a 3.5 wt% NaCl solution. On introduction of SiG, PANI, and PANI-SiG hybrid, the corrosion current decreased from 0.03626 μA to 0.007856 μA, 0.02042 μA, and 0.011 μA, respectively. The penetration rates calculated in mm/yr. for the composites: SiG/Primer, PANI/Primer and PANI-SiG/Primer were 0.430× 10-4, 1.110× 10-4, and 0.599 × 10-4, respectively and that of neat primer was 1.977 × 10-4. The corrosion protection efficiency of the primer was improved up to 7% on introduction of the PANI-based fillers. The 5 wt% of 1:1 PANI-SiG/primer composite, which contains 2.5wt% of PANI, showed better results than that of 5wt% PANI in Primer and these results are very close to that of 5wt% SiG/Primer composites.