Environmentally friendly ternary inhibitor formulation based on N,N-bis(phosphonomethyl) glycine

Abstract

Studies on an environmentally friendly ternary inhibitor formulation consisting of N,N-bis(phosphonomethyl) glycine (BPMG), with Zn²⁺ ions as primary synergist and ascorbate ions as secondary synergist to protect carbon steel from corrosion in low chloride environment are presented in this paper. Although the binary system, BPMG–Zn²⁺, is an effective inhibitor, it demands relatively higher concentrations of both BPMG and Zn²⁺. In the present study, ascorbate was added to lower the effective concentrations of BPMG and Zn²⁺. The effect of addition of ascorbate is quite significant. While the binary system consisting of 20 ppm of BPMG and 30 ppm of Zn²⁺ accelerated corrosion of carbon steel, addition of just 25 ppm of ascorbate to the above system afforded an inhibition efficiency of 94%. The ternary inhibitor formulation is found to be effective in the pH range 5-11. The uniqueness of this system is that it has shown excellent inhibition efficiency even at pH 11, at which all the other phosphonate based formulations fail. This inhibitor system functions as a mixed inhibitor. The nature and composition of the protective film have been investigated by X-ray photoelectron spectra and Fourier transform infrared (FTIR) spectra. The mechanistic aspects of corrosion inhibition are discussed.