Corrosion resistance of plasma treated carbon steel

Abstract

Although carbon steel is a widely used material in sculptures, house ware, transportation facilities, construction materials, and tools, it is easily oxidized in atmosphere. To avoid this problem, some works suggest the development of protective coatings, using the plasma deposition technique based on hexamethyldisiloxane, HMDSO compound. Altering the plasma parameters, enables to deposit organic to oxide films. Silicon oxide films are more resistant to corrosion than organosilicone ones, however they present low adherence aside to structural defects. Considering that, the present work aims to combine the good corrosion resistance of silicon oxide films with the good adherence of the organosilicon coatings to improve the carbon steel performance in corrosive environments. For that, it is proposed the deposition of organosilicon-silica gradual layers by plasma deposition technique with additional ion bombardment. Firstly, the condition that provides good adhesion of organosilicon films to the carbon steel will be determined. During the deposition process, the plasma and the ion bombardment conditions will be varied to reduce the content of organic of the film gradually to obtain a completely oxide layer. A single layer without interfaces and with gradually modified physical and chemical properties will be created, thus avoiding adherence problems and internal stress. This will enable the deposition of thicker films, which are more attractive as barriers against permeation of oxidative species. It will be investigated the effect of plasma excitation parameters, as total pressure, gas proportion and RF power signal, as well as of the polarization pulses on the properties of the layers. Scanning Electron Microscopy, SEM and Atomic Force Microscopy, AFM, will be used to evaluate the surface microstructure of the layers. X-ray photoelectrons spectroscopy, XPS, and Infrared spectroscopy, FTIR, will be applied to analyze the chemical composition and molecular structure of the layers. Electrochemical Impedance Spectroscopy, EIS, will be employed to evaluate the corrosion resistance the steel/film system while the deposition rate will be calculated from the film thickness, determined by profilometry. The density will be evaluated by gravimetry and the wettability by the sessile drop method. To determine the physical stability of the layers, the tape tests will be used. (AU)