Thin-film Al2O3 coating on low carbon steel obtained by the sol–gel method with different peptizing acids: Corrosion investigation

Abstract

Thin alumina films were obtained on low carbon steel using boehmite gel prepared by the sol–gel method with aluminium isopropoxide and peptizers – nitric, acetic and maleic acids. The paper considers the acid nature effect on steel corrosion in the studied colloidal systems for obtaining film coatings. It shows that the substrate corrosion behaviour in these systems depends on two factors: medium acidity and complex formation from Fe(III) ions and anions of acid peptizers. Barrier type alumina films can be prepared in the presence of nitric acid as the latter increase boehmite peptization effectiveness. The thin-layer aluminium oxide coatings (prepared from alumina gel using HNO3 as a peptizing agent), can shift the electrode steady-state potential in a 3.5% NaCl by over 0.6 V and effectively slow down steel corrosion in this solution. The electrochemical impedance spectroscopy method was applied to study the kinetics of changes in the electrical parameters of the metal | alumina films | sodium chloride solution phase boundary.