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.