Novel preparation system of an organic–inorganic hybrid chemical conversion layer with high chlorine tolerance: A characterization and mechanism study

Abstract The quality of the pretreatment layer on steel was obviously affected by the chloridion concentration in the layer bath. In this study, the effects of chloridion on the micro- anti-corrosion performance, structure and chemical composition of polyacrylic acid (PAA) based layer were investigated. PAA-Zn layer and PAA-Zn-NaCl layers were fabricated on steel surface through immersion the steel in the layer bath without and with different concentrations of chloridion for 20 min. The electrochemical impedance spectroscopy and polarization curve results indicated that the anti-corrosion performance of the PAA–Zn layer could be improved due to the existence of chloridion in the layer bath and reached the best anti-corrosion performance when the concentration of chloridion was 2 wt%. Scanning electron microscopy results reflected that the thickness of the PAA-Zn-2%NaCl layer was higher than that of PAA-Zn layer. X-ray photoelectron spectroscopy results demonstrated that the concentrations of iron and zinc for the PAA-Zn-2%NaCl layer were higher than that of the PAA-Zn layer. The all experimental results indicated that chloridion could accelerate the steel corrosion during the initial immersion and thus promote PAA ionization and produce numerous iron ions. The formed PAA anions could chelate iron and zinc ions to form layers on steel, leading to the high chlorine tolerance characteristic of the PAA layer bath.