The electrochemical determination of the proportions of metal and oxide in zinc‐base coatings obtained by hot spraying Available to Purchase

Summary This paper describes an electrochemical procedure useful to the determination of metallic and oxidised parts in zinc‐base coatings obtained by thermal spraying. The procedure has been successfully applied to the examination of coatings made of pure zinc or of a zinc alloy containing 15% in weight of aluminium, as well as on corroded as on uncorroded samples. The method allows the degree of advancement of oxidation in the coating to be determined as a function of the exposure time; this permits an evaluation of the corrosion resistance to be made without having to wait for the appearance of rust on the protected steel plate. By this manner, the better resistance of the studied alloy compared to the pure zinc has been evidenced under severe conditions of attack by an aerated 5% NaCl solution. This could be attributed to a decrease in the oxidation rate of the metallic zinc in the alloy, owing to its higher aptitude to self‐sealing. The improved behaviour of the alloy has been attributed to the existence through the whole thickness of the coating of a coherent network made of an α‐aluminium‐rich phase, this explanation being in good agreement with the results of other investigations carried out by SEM + EDAX or by X‐Rays diffraction techniques, which have been reported elsewhere. Each studied coating was obtained from wires produced by Vieille‐Montagne under the trade‐names Zinacor 100 (pure electrolytic zinc) and Zinacor 850 (zinc‐base alloy containing 15% aluminium).