The inhibition action of ammonium salts of O,O′-dialkyldithiophosphoric acid on carbon dioxide corrosion of mild steel

Ammonium salts of O,O′-dialkyldithiophosphoric acids (RО)2 Р(S) S− HN+R′R2″, were synthesized and tested as inhibitors for carbon dioxide corrosion of mild steel using weight loss, polarization curves, electrochemical impedance spectroscopy and scanning electron microscopy methods. High inhibition efficiency has been found for all compounds (η = 70–99%) at very low concentrations (0.25–5) mg l−1. Polarization curves show that the title compounds can be considered as inhibitors of the mixed type. The absorption of inhibitor molecules on the mild steel surface obeys the Langmuir isotherm. Inhibition efficiency for some ammonium salts increases with temperature. The activation energy and some thermodynamic parameters were computed.

Research highlights
► 5 ammonium salts of dialkyldithiophosphoric acid were synthesized on basis of white P.
► Salts have high efficiency at low concentrations as inhibitors CO2 corrosion of Fe.
► Inhibition efficiency for some ammonium salts increases with temperature.
► The absorption of inhibitor molecules on the steel surface obeys Langmuir isotherm.