Sodium tripolyphosphate (STPP) as a novel corrosion inhibitor for mild steel in 1 M HCl

摘要

The corrosion inhibition of mild steel in 1 M HCl solution by sodium triphosphate (STPP), Na_5P_3O_(10), has been studied using potentiodynamic polarisation as an electrochemical technique, weight loss and UV-vis spectrophotometric measurement. The results of weight loss and Tafel polarization measurements showed that this compound has fairly good inhibiting properties for steel corrosion in acidic bath, with 87% inhibition efficiency at optimum concentration 10~(-3) M. The inhibition is of a mixed anodic-cathodic nature. The adsorption behaviour of the investigated compound is found to obey Langmuir adsorption isotherm. Negative value was calculated for the energy of adsorption indicating the spontaneity of the adsorption process. The formation of complex between metal cations and sodium triphosphate is also proposed as additional inhibition mechanism of mild steel corrosion.