Effects of Hydrogen on the Surface Films Formed on Iron in Pure Water at Various Temperatures

Abstract

Effects of hydrogen on the types, morphologies and electrochemical properties of the surface films formed on iron in aerated pure water at 25, 40, 50 and 70 oC were investigated by using optical microscopy, X-ray diffraction measurements, Raman spectroscopy, electrochemical impedance spectroscopy (EIS) and Mott-Schottky (M-S) plots. Increasing temperature from 25 oC to 70 oC significantly accelerated the corrosion of non-charged iron. Yellow rusts formed on the non-charged iron after immersion 21 h at 40 oC, while the surface of hydrogen-charged iron after immersion in the same condition was gray. The film formed on the non-charged iron after immersion 21 h at 70 oC was dark, while the surface of hydrogen-charged iron was covered with loosely distributed yellow rust particles. Raman spectra showed the different compositions of formed films on non-charged and hydrogen-charged iron specimens. Normally the high valence iron oxides were formed on non-charged iron while relative low valence iron oxides were formed on the hydrogen-charged iron, with exceptions. The stability and semiconductor properties of the surface films formed on non-charged and hydrogen-charged specimens were characterized by EIS and M-S plot measurements in boric acid-borate buffer solutions, showing significant effect of hydrogen.