Characterization of steel corrosion in an aggressive environment

As part of the Sustainable Green Manufacturing Program, the corrosion resistance of sputtered tantalum is being studied in order to evaluate it as a replacement coating for electroplated chrome. To accomplish this, studies were conducted to evaluate corrosion properties of the gun barrel steel by employing corrosion rate and bulk measurements including x-ray diffraction (XRD), scanning electron microscopy (SEM)/energy dispersive x-ray spectroscopy (EDX), and x-ray fluorescence (XRF), as well as synchrotron-based x-ray absorption spectroscopy (XAS). Corrosion behavior of steel immersed in an aggressive environment of 37.8 % hydrochloric acid at room temperature was investigated as a function of time from 10 minutes to 41 hours. The corrosion rate peaked between I and 8 hours of exposure, and revealed a gradual decrease as exposure time increased. SEM/EDX analysis showed that the surface of corroded steel was attacked differently as a function of time, but time had no significant effect on the composition of corrosion product. During the tests, defects on the surface of the polished steel resulted in pitting corrosion. With XRF the bulk composition of the corroded products was found to be consistent with the surface analysis using EDX. XRD analyses of this corrosion product on the surfaces indicated the formation of ßFeOOH (akaganeite) and possibly minor amounts of other oxides. In XAS analysis, the spectra revealed that iron has different coordination environments in steel and the oxide. However, iron in all the corroded specimens appears to have oxygen as the first neighbor. This study provides a baseline for future corrosion research and an exploration of characterization methods for the corroded surface