Use of (Nd, pr) sulphates obtained from electronic scrap as corrosion inhibitors for a c-mn steel in 3.5 nacl

A rare earth-containing sulfate obtained from permanent magnets has been evaluated as a corrosion inhibitor for a C-Mn steel in 3.5% NaCl solution. The electrochemical techniques used include potentiodynamic polarization, linear polarization resistance and electrochemical impedance spectroscopy measurements. The inhibitor obtained is not a pure compound but a mixture of neodymium and praseodymium sulphates, in a proportion of ca. 65:35. The open circuit potential value shifts towards more cathodic values during the first 2 hours, but it moves towards more anodic values after this time until it reaches a relatively constant value, indicating the formation of a protective layer. The results show that this compound is a good corrosion inhibitor, with an efficiency that increases with time and its concentration up to 500 ppm, but decreases with a further increase in its concentration. The inhibitor does not induce the formation of a passive layer but the polarization resistance values increase almost 10-fold upon addition of the inhibitor. Although the compound affects both the anodic and cathodic electrochemical reactions, it has a stronger effect on the cathodic reaction. It forms a film of protective corrosion products by chemical adsorption on the steel surface following the Langmuir adsorption isotherm. The corrosion mechanism is controlled by charge transfer and remains unaltered with addition of the inhibitor.