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 after 21 h immersion in pure water and 10-4 to 0.5 mol/L NaCl solutions at 25 °C are investigated by open circuit potential (OCP) measurements, optical microscope, Raman spectroscopy and X-ray diffraction (XRD). Hydrogen-charging favors the formation of with dark film with yellow corrosion sites on iron. After immersion in 10-4 mol/L NaCl solution, the non-charged iron is partly covered by surface film, while the hydrogen-charged iron is fully covered by surface film. After immersion in 0.5 mol/L NaCl solution, the surface of the non-charged iron is partly dark and partly covered with yellow rusts, and the surface of the hydrogen-charged iron has a larger area covered with yellow rusts than that on the non-charged iron. OCP values for hydrogen-charged iron in pure water, 10-3 and 10-4 mol/L NaCl solutions are lower than those for non-charged iron. In 0.5 mol/L NaCl solution, the OCP difference between non-charged iron and hydrogen-charged iron is at first large and gradually becomes smaller with increasing immersion time. Raman spectra and XRD patterns show the presence of magnetite in the film on hydrogen-charged iron after immersion in 10-4 mol/L NaCl solution. In solutions with a high chloride concentration, hydrogen in iron can promote the formation of high valence iron oxide layer by precipitation.