Study Of Corrosion Inhibitive Self-assembled Monolayers On The Surface Of430Stainless Steel

The traditional corrosion inhibition techniques of the430stainless steel (SS430) such as electrodeposited coating and chromate coating are inevitably causing very serious air and water pollution problems. Furthermore inhaled hexavalent chromium is recognized as a human carcinogen. 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 phytic acid were prepared on SS430surface respectively. The performance of corrosion inhibition of SAMs has been studied by potentiodynamic scanning, Electrochemical Impedance Spectrum (EIS)), Fourier Transform Infrared Spectroscopy (FT-IR), X-ray Photoelectron Spectroscopy (XPS). Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM) and contact angle measurement. The results are shown as following:1. It was found that SAMs have been successfully prepared on both the unoxidized and oxidized SS430surfaces and the corrosion resistance of the substrates was improved prominently. The results of electrochemical measurement show that the time period for SAMs on unoxidized SS430to reach the maximal corrosion inhibition efficiency (87.13%) is1hr, however for SAMs on oxidized SS430this time period reduces to half an hour and these two SAMs samples have no difference in the corrosion inhibition efficiency. It has been shown in morphologies by AFM that SAMs treated in6%FeCl3aqueous solution have more significant corrosion inhibition function compared with the bare substrate.2. SAMs assembled by phytic acid, a new multi-complexing agent for metal ions, have good corrosion inhibition performance to metal surface. XPS results have proved the successful adsorption of phytic acid on SS430. Electrochemical testing demonstrates that SAMs treated in the phytic acid with concentration of5×10-3mol/L for1hr exhibit the best corrosion inhibition performance. Much lower contact angle on SAMs compared with the substrate was obtained, which indicate the SAMs was obtained on SS430substrate and the hydrophilic group in phytic acid has increased the surface wettability.As a result, both TDPA and phytic acid have been assembled on SS430and their SAMs are dense enough to inhibit the corrosion on SS430. 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.