Study Of Corrosion Inhibitive Self-assembled Monolayers On The Surface Of316L Stainless Steel

As medical implant and tool material, AISI316L stainless steel (316L SS) is widely used in clinical practice owing to its good mechanical properties, excellent processing performance, great biocompatibility and low price. However, few studies have reported the pitting corrosion characteristics and related corrosion inhibition technology of316L SS in close contact with physiological fluids. The self-assembled monolayers (SAMs) are highly oriented and closely packed monolayer ordered films that active molecules absorb on the solid/liquid or solid/gas interface spontaneously by chemical bonding. It is widely used in some areas, such as surface modification, metal protection and biomedical engineering. The obvious advantages of the self-assembly technology include their ease of manufacture in various shapes without external aid and strong chemical bonding to the substrate.In our work, SAMs of two natural and non-toxic molecules, namely phytic acid and dopamine were prepared on316L SS surface respectively by immersion method. Potential dynamic scanning, electrochemical impedance spectroscopy (EIS), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDX), Fourier Transform Infrared Spectroscopy (FT-IR), and X-ray Photoelectron Spectroscopy (XPS) were introduced to research the corrosion inhibition performance, adsorption behavior, composition and structure of the self-assembled films. The results were shown as following:1. The results of SEM, EDX and XPS showed that whether with oxidation treatment for sample surface or not, phytic acid SAMs could be successfully prepared on the316L SS surface and the corrosion resistance of the substrates was improved prominently. The electrochemical tests revealed that, for the samples without chemical oxidation treatment, the optimum PH for the assembly of phytic acid was6.90, and the best assembly time was12h corresponding to the maximal corrosion inhibition efficiency of76.75%. And for those with chemical oxidation, the optimum PH was still6.90while the best assembly time reduced to4h, and the maximal corrosion inhibition efficiency reached to82%. The SEM corrosion morphologies revealed that the SAMs on the sample surface with chemical oxidation had more significant corrosion inhibition function compared with those without chemical oxidation. The FTIR and XPS results demonstrated that phytic acid was chemically absorbed on316L SS by forming P-O-M bonds.2. The results of EDX and XPS showed that whether with oxidation treatment for sample surface or not, dopamine SAMs could be successfully prepared on the316L SS surface and the corrosion resistance of the substrates was improved prominently. The potential dynamic scanning tests revealed that, for the samples without chemical oxidation treatment, the optimum concentration for the assembly of dopamine was20g·L-1, and the best assembly time was12h corresponding to the maximal corrosion inhibition efficiency of77.13%. And for those with chemical oxidation, the optimum concentration was still20g·L-1, while the best assembly time reduced to2h, but the maximal corrosion inhibition efficiency decreased to58.83%. The SEM corrosion morphologies revealed that the samples without chemical oxidation had more significant corrosion inhibition function compared with those with chemical oxidation. The SEM topographies also showed that dopamine could self-polymerize and formed polydopamine coatings. However, the EIS results revealed that the polydopmine coatings are not dense. The FTIR and XPS results demonstrated that dopamine was chemically absorbed on316L SS by coordination reaction between catechol groups and metal ions.In conclusion, phytic acid and dopamine could be assembled on316L SS and their SAMs were dense enough to inhibit the corrosion on316L SS. And this study proved that it was fully feasible to improve the corrosion resistance of316L SS by self-assembly modification.