The Influence of pH on the corrosion protection performance of a hybrid sol-gel derived coatings on carbon steel in aqueous medium

摘要

Materials such as carbon steel has since cemented its place in various industries such as oil and gas industry for the transportation of petroleum products, due to their high strength, good hardness, toughness and low cost. The problem of low corrosion resistance that is associated with carbon steel can be curtailed by a combination of active and passive corrosion protection. Sol-gel derived hybrid thin films coating present one of the most viable pre-treatments alternative to the toxic chromate. In this study, the influence of pH on the passive protection of carbon steel was investigated. Sol-gel hybrid derived coating was formed using (3-mercaptopropyl)trimethoxysilane (MPTMS) and Tetraethoxysilane (TEOS) as precursors materials. Isopropanol was added as a solvent, while the desired pH of 2, 3 and 4 were achieved using nitric acid. Spray coating technique was used to deposit the coating on the substrate. The influence of pH on the corrosion protection performance of the hybrid coatings were examined using potentiodynamic polarisation scan (PDS) and electrochemical impedance spectroscopy (EIS) in aerated 3.5 wt.% NaCl solution at room temperature. The morphology and elemental composition was investigated using optical microscopy, scanning electron microscopy (SEM) and Energy-dispersive X-ray (EDX). The results show that after 1hr of immersion, the substrate with pH of 2 has better performance. However, after 216 hrs of immersion pH of 4 has better protection properties.