Inhibition of steel corrosion in HCl media by phosphite compound

The purpose of this paper is to investigate the inhibitive effect of the phosphite NaCo(H₂PO₃)₃•H₂O (PhCo) for the corrosion of mild steel in HCl solutions. The study is another trial to find a mineral inhibitor for mild steel corrosion.

The inhibitory effect has been evaluated by gravimetric and polarisation techniques at various temperatures. The type of adsorption inhibition and adsorption and kinetic data are determined.

Results show that PhCo inhibits the corrosion of steel in acidic solution. The inhibition efficiency at 308 K increases with the inhibitor concentration to reach 96 per cent for 10⁻⁴ M, and then decreases at higher temperatures. Kinetic parameters such as E_a, ΔH_a^∘ and ΔS_a^∘ were calculated. The adsorption of inhibitor obeys the Langmuir isotherm model. Thermodynamic parameters of adsorption including ΔG_ad, ΔH_ad, ΔS_ad, and K_eq(ad) were calculated in the presence of inhibitor.

Electrochemical studies (polarization method) show the partial action of inhibitor on anodic and cathodic reactions of the corrosion inhibition.

The efficiency of the tested phosphite increases with its concentration to reach 96 per cent. It can be used in chemical cleaning and pickling processes at moderate temperature.

This paper reveals the possible application of phosphites as environmentally valid inhibitors for corrosion under the specified conditions.