Preparation and properties of modified montmorillonite by zinc-phosphate for anticorrosion applications in protective coatings

Abstract

Anticorrosion pigments based on natural montmorillonite modified with zinc cations and phosphate anions were obtained by liquid-phase two-stage ion exchange. They are the promising of being used as part of protective coatings on steel. The primary exchangeable calcium and sodium cations of montmorillonite were replaced by Zn²⁺ in its interlayer space, and bonds of PO₄⁻³ anions were formed on the edge surfaces of aluminium hydroxyl octahedra and silica tetrahedra of the montmorillonite structure by modification in the Na₃PO₄ solution with the addition of Zn(NO₃)₂ solution. The corrosion resistance of low-carbon steel increases in an acid rain environment with the addition of 2 g/l of modified Zn/P montmorillonites using potentiodynamic polarization, electrochemical impedance spectroscopy and weight loss test. The inhibitory efficiency of the montmorillonites depends on the concentration of the Na₃PO₄ solution. The Zn/P montmorillonite obtained from 0.05 M Na₃PO₄ solution had the highest inhibitory efficiency, which remained above 90 %. The protective effect of modified montmorillonites in an acid rain environment is based on the release of zinc cations from the interlayer space of the montmorillonite, which interact with OH⁻ anions to form metal hydroxides and the formation of iron phosphates with the stabilization of a protective film.