In-situ characterisation of the corrosion products formed on C-steel immersed in a soil-simulating solution

In this research C-steel corrosion products are allowed to form in a water-based solution containing 1000 ppm of SO42-, which simulates a highly corrosive soil. The electrode Fermi level was controlled with a three electrodes electrochemical set-up, scanning a potential window between the corrosion and the passivation regions. This, combined with in-situ Raman spectroscopy, allows to characterise the surface chemistry of the products formed according to the ongoing electrochemical reactions. When the potential is held in the stability region of the ionic species the surface state of the metal is characterised principally by the presence of lepidocrocite (gamma-FeOOH) and green rust (GR-SO42- ). The application of an anodic potential, simulating the effect of a DC anodic interference, combined with factors like moisture, presence of oxygen and sulphate ions contribute to develop a multicoloured (mix orange-like, yellow and green) mainly amorphous reaction product composed by a mix of iron oxide and oxi-hydroxide phases.