Green inhibitor formulations containing ascorbic acid for corrosion control of carbon steel

摘要

Synergistic effect of ascorbic acid in the presence of three different phosphonic acids and Zn~(2+) for corrosion inhibition of carbon steel in low chloride and aqueous environment has been investigated. Ascorbic acid, an environmentally friendly organic compound is proved to be an excellent synergist in combination with Zn~(2+) and phosphonic acids namely 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC), 1-hydroxyethane-1,1-diphosphonic acid (HEDP) and nitrilotris (methylenephosphonic acid) (NTMP) in the corrosion control of carbon steel. In the case of the binary formulations of phosphonic acid and Zn~(2+), higher concentrations of both the components are required for effective inhibition. However, the same inhibition efficiency could be achieved by the addition of just 25 ppm of ascorbic acid to relatively low levels of both phosphonic acid and Zn~(2+). Further, the concentrations of these components required for maintenance of the protective film on the surface are still lower. As the concentrations of Zn~(2+) and phosphonic acid are reduced to a significant extent, these new inhibitor formulations are more environmentally friendly. The inhibition efficiencies of the formulations have been evaluated by gravimetric studies, electrochemical impedance and potentiodynamic polarisation studies. All the three ternary inhibitor formulations are found to be effective in a wide pH range and up to a temperature of 60°C. The surface films have been characterised by X-ray photoelectron spectroscopy and reflection absorption FTIR spectroscopy. Based on the results of all these studies, a plausible mechanism of corrosion inhibition is proposed.