XAS and XRD in situ characterisation of reduction and reoxidation processes of iron corrosion products involved in atmospheric corrosion

•In situ structural characterisation with XAS and XRD during electrochemical reduction.•Structural identification of phases formed during the wetting stage of iron AC.•Understanding the reduction and reoxidation processes during the wet–dry cycle of iron AC. An electrochemical cell has been used for performing in situ X-ray diffraction and absorption spectroscopy structural characterisation by transmission during electrochemical measurements. This cell has been used to reduce lepidocrocite and ferrihydrite, two iron oxides involved in low-carbon steel atmospheric corrosion mechanisms. The reduced phases have been identified in situ as magnetite and iron II hydroxide, two phases that can play a key role in corrosion mechanisms. The reoxidation of the reduced phases was also studied, and lead to the formation of magnetite/maghemite and to the formation of the initial reducible phases lepidocrocite and ferrihydrite.