The Effects of Hydrogen on Corrosion Products Formed on Iron in Chloride Solutions

Abstract

The effects of charged hydrogen on the properties of the surface films formed on iron in pure water and 10-4 to 0.5 mol/L NaCl solutions at 25°Cwere investigated by open circuit potential (OCP) measurements, optical microscope, scanning electron microscope and X-ray diffraction (XRD). After 21h immersion in pure water, the surface of non-charged iron did not significantly and showed only local corrosion sites, while the surface of hydrogen-charged iron was covered with dark film with many yellow corrosion sites on it. After 21h immersion in 10-4 mol/L NaCl solution, the non-charged iron was partly covered by surface film, while the hydrogen-charged iron was fully covered by surface film, as shown in Fig. 1. After 21h immersion in 0.5 mol/L NaCl solution, the surface of the non-charged iron was partly dark and partly covered with yellow rusts, and the surface of the hydrogen-charged iron had a larger area covered with more yellow rusts than that on the non-charged iron, as shown in Fig. 2. Results of OCP monitoring showed that OCP values for hydrogen-charged iron in pure water, 10-3 and 10-4 mol/L NaCl solutions were lower than those for non-charged iron, as partly shown in Fig. 3a. In 0.5 mol/L NaCl solution, the OCP differences between non-charged iron and hydrogen-charged iron was at first big but gradually became smaller with increasing immersion time, as shown in Fig. 3b. Raman spectra showed the presence of magnetite in the film on hydrogen-charged iron after immersion in 10-4 mol/L NaCl solution, as shown in Fig. 4a, which was supported by XRD results. Yellow rust and the XRD peak for hematite in the films on non-charged and hydrogen iron specimens (Fig. 4) indicated that the mechanism for the effect of hydrogen on the corrosion products of iron in dilute NaCl solutions could be different from that in concentrated NaCl solutions. In solutions with a high chloride concentration, hydrogen in iron might be able to promote the formation of high valence iron oxide, while in many other cases it was found that the formation of magnetite was promoted by hydrogen in iron. Figure 1