An investigation on the inhibition effects of some new dithiophosphonic acid monoesthers on the corrosion of the steel in 1 M HCl medium

Abstract

o-Methyl-p-methoxyphenyldithiophosphonic acid (MTPA), o-ethyl-p- methoxyphenyl-dithiophosphonic acid (ETPA) and o-isopropyl-p-methoxy phenyl dithiophosphonic acid (IPTPA) ammonium salts were used as inhibitors on steel corrosion in 1 M HCl medium. Concentration of the inhibitors were in the used-as inhibitors on steel corrosion in 1 M HCl medium. Concentrations of the inhibitors were in the range 10 -3 to 2 × 10 -2 M, five different temperatures between 298 and 338 K were tried; Tafel extrapolation and linear polarisation techniques were employed. Corrosion parameters and adsorption isotherms were determined from current-potential curves. At room temperature, the three compounds were found to decrease the corrosion rate by around 80% at 1 × 10 -3 M, and 95% at 2 × 10 -2 M concentration. The inhibition efficiencies weaken slightly at higher concentrations but in any case, more than 75% inhibition is observed at a temperature of 338 K with an inhibitor concentration of 2 × 10 -2 M. Surface coverage degrees indicate that the adsorption pattern is consistent with the Temkin isotherm. © 2005 Elsevier B.V. All rights reserved.