Study Of Corrosion Inhibitive Functional Self-assembled Monolayers On The Surface Of Stainless Steel

Stainless steel is widely used for the processing performance, but as a result of low anti-corrosion inhibitive in the condition of halogen anion environment and the heavily environmental pollution of traditional anticorrosion technology, as one of the environmentally friendly techniques, self-assembled monolayers (SAMs) technique has attracted tremendous attention due to its easy-processing, mild assembling condition and friendly to environment advantages compared with the tranditional inhibition corrosion techniques. Meanwhile, it is so convenient to study the mechanism of inhibition corrosion of SAMs with excellent stability and high packing order that the molecular structure could be designed ideally.In our work, SAMs of both1-tetradecylphosphonic acid (TDPA) and lauric acid were prepared on430SS surface respectively. Research into the various factors (assembly time, pre-treatment, the concentration of assembly solution and the water content in the solvent) that affect the inhibitive efficiency of the SAMs were studied by electrochemical tests (potential dynamic scanning and electrochemical impedance spectrum), the spectroscopy technologies (X-ray photoelectron spectroscopy and fourier infaredspectrum), and the surface analysis techchniques (Scanning electron microscope and water contact angle). The results are shown as following:1. It was found that SAMs have been successfully prepared on both the unoxidized and oxidized430SS surfaces and the corrosion resistance of the substrates was improved prominently. The results of electrochemical measurement showed that the time period for SAMs on430SS to reach the maximal corrosion inhibition efficiency is6hrs, oxidized pre-treatment was benefit to improve the inhibition efficiency from87.43%to97.3%. The water contact angel shows the TDPA SAMs on 430SS is a hydrophobic film. FT-IR and electrochemical test showed that the water in solvent is bad for the formation of TDPA on unoxidized430SS, but it is adversely for the oxidized ones. The water in solvent promotes the adsorption of TDPA molecule on oxidized430SS, the more water, the higher inhibitive efficiency. XPS showed inhibitive films was constructed by TDPA molecule trough monolayer, there is no polymerization or chain-breaking reaction during the adsorption processing.2. SAMs assembled by lauric acid have good corrosion inhibition performance to metal surface. FT-IR results have proved the successful adsorption of lauric acid on430SS. Electrochemical testing demonstrates that SAMs treated in the lauric acid with concentration of5×10-3mol/L exhibit the best corrosion inhibition performance. Inhibition efficiency increased with the assembly period prolonged. SEM morphologies showed that the water in solvent promote the adsorption of TDPA molecule on oxidized430SS, the more water, the higher inhibitive efficency.Much higher contact angle on SAMs compared with the substrate was obtained, which indicate the SAMs was obtained on430SS substrate and the hydrophobic group in lauric acid has decreased the surface wettability.As a result, both TDPA and lauric acid have been assembled on430SS and their SAMs are dense enough to inhibit the corrosion on430SS. As a new corrosion inhibition technique, the SAMs are expected to replace the traditional chromate coating technique which is causing a serious environmental problem because of its toxicity.