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

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.