Corrosion Inhibition Study of Mild Steel in the Acidic Mediums Containing a Mineral Compound-Based Phosphate

1. Introduction

The use of acids is widely applied in the industrial field. However, acidic aqueous solutions generally constitute aggressive media for metals and alloys. To overcome this undesirable phenomenon, the organic inhibitors whose mode of action generally results from their adsorption on the surface of the metal are the most frequently used. Their choice depends on the type of acid, its concentration, the temperature and the metallic material exposed to the action of the acid solution. Thus, sulfur-containing inhibitors are effective in sulfuric acid (Agrawal, 1990; El Azhar, 2001; Quraishi, 1997), while those containing nitrogen, such as nitrogen-containing heterocycles (Galai, 2017; Serrar, 2018; Kadiri, 2018) and amino acids (Kertit, 1997) are effective in hydrochloric acid. The use of a corrosion inhibitor based on dicalcium phosphate-dihydrate (DCPD), can form a protective surface which inhibits or slows the rate of corrosion film; the effectiveness of this medium apatite was observed in the distribution of drinking water, but little study to understand how it works and why is effective (Holm,1991; Schock,1985), the presence of calcium in solution (Larsen, 1986) claims that a minimum concentration of calcium ions is required to form a protective film and limit the dissolution of iron, and he also claims that the Ca/P ratio should be at least 1/5 of the work (Boffardi, 1993), showed that the precipitation of calcium and phosphate ions depends on the concentrations of the two species and the pH of the solution. However, according to (Atkinson, 1971; He, 1996) calcium ions are not actively involved in the protection of corroded surfaces. G. Saha et al (Saha, 1986) have studied the adsorption of the complex iron phosphates that only the surface of the iron hydroxides is combined with phosphate ions; no trace of calcium was detected in the complex iron phosphates.

The aim of the present work is to study the inhibition efficiencies of ((Ca)₉(PO₄)₅(OH)(Ca-HP)), on mild steel corrosion in 1 M HCl, H₂SO₄ 0.5 M and 2.0 M H₃PO₄ using electrochemical measurements such as polarization curves and electrochemical impedance spectroscopy.