Alpha localized radiolysis and corrosion mechanisms at the iron/water interface: Role of molecular species

This paper is devoted to the iron corrosion phenomena induced by the α (⁴He²⁺) water radiolysis species studied in conjunction with the production/consumption of H₂ at the solid/solution interface. On one hand, the solid surface is characterized during the ⁴He²⁺ ions irradiation by in situ Raman spectroscopy; on another hand, the H₂ gas produced by the water radiolysis is monitored by ex situ gas measurements. The ⁴He²⁺ ions irradiation experiments are provided either by the CEMHTI (E = 5.0 MeV) either by the ARRONAX (E = 64.7 MeV) cyclotron facilities. The iron corrosion occurs only under irradiation and can be slowed down by H₂ reductive atmosphere. Pure iron and carbon steel solids are studied in order to show two distinct behaviors of these surfaces vs. the ⁴He²⁺ ions water irradiation: the corrosion products identified are the magnetite phase (Fe(II)Fe(III)₂O₄) correlated to an H₂ consumption for pure iron and the lepidocrocite phase (γ-Fe(III)OOH) correlated to an H₂ production for carbon steel sample. This paper underlined the correlation between the iron corrosion products formation onto the solid surface and the H₂ production/consumption mechanisms. H₂O₂ species is considered as the single water radiolytic species involved into the corrosion reaction at the solid surface with an essential role in the oxidation reaction of the iron surface. We propose to bring some light to these mechanisms, in particular the H₂ and H ₂O₂ roles, by the in situ Raman spectroscopy during and after the ⁴He²⁺ ions beam irradiation. This in situ experiment avoids the evolution of the solid surface, in particular phases which are reactive to the oxidation processing.