The corrosion of Fe12Cr iron-chromium alloys in o-Phosphoric acid


Corrosion rates of Fe12Cr in o-phosphoric acid have been studied as a function of temperature and acid concentration. The chemical composition and thickness of corrosion product layers on the surface of the metal have also been investigated by the technique of X-ray photoelectron spectroscopy. It is found that, within the limits of accuracy, the amount of corrosion is linearly dependent on time and independent of the thickness of the corrosion layer despite the observation that the thickness is significantly affected by temperature and acid concentration. Under all conditions studied the corrosion layer consists of a mixture of CrPO4 and Fe2O3 and, deduced from empirical formulae for the mixture of corrosion products, that FePO4 is most likely present as well. It is suggested that the variation of corrosion rate with acid concentration is associated with the amount of FePO4 in the corrosion products. No strong correlation is found between the thermodynamic stabilities and solubilities of the constituents of the corrosion products and it is suggested that the structure of the corrosion layer which is determined by its composition is important in determining the corrosion resistance of the alloy. © 1980.

Publication Title

Corrosion Science