Mobility and Mode of Inhibition of Chromate at Defected Areas of Organic Coatings Under Atmospheric Conditions Available to Purchase

The ability of chromate as an anticorrosive pigment incorporated into primer coatings to inhibit the corrosion of galvanized steel has been studied using cell modeling conditions at defects of painted sheets. The experiments were performed at different temperatures (4, 22, and 40°C) and chloride concentrations (1 mmol/L and 10 mmol/L) with coatings releasing from 20 mg/m² to 100 mg/m² chromate per 48 h. After 1 h to 48 h of exposure, the solutions were analyzed by ion chromatography (IC) and the metal samples were studied using Fourier transformed infrared (FTIR), energy-dispersive x-ray (EDX), and x-ray absorption near-edge structure (XANES) spectroscopy. The XANES measurements detected the presence of a Cr(III)/Cr(VI) layer containing approximately 15% of Cr(VI) on the initially bare zinc surface. Corrosion of the samples exposed with the chromated primers was clearly inhibited in comparison with blank samples, with an inhibition efficiency ranging from 50% to 95% according to the exposure conditions. Thus, the results showed that chromate was transported from the pigmented primer to the bare metal surface and formed a protective layer on it. Moreover, an enrichment of the pit centers with chromium was found with EDX, suggesting the ability of chromate to seek the active, or formerly active, corrosion sites and preferentially adsorb at these locations. The extent of corrosion deterioration of the samples and chromate consumption was regarded with respect to temperature, chloride concentration, total amount of released chromate, and the kinetics of the release. The developed experimental technique was tested on a vanadate system as well. The experimental setup proved to be a simple and efficient tool for future testing of paints, inhibitors, materials, or aggressiveness of environment, as well as for fundamental studies.