Abstract: It was found that H₃PMo₁₂O₄₀ was an excellent passivator in comparison with H₄SiMo₁₂O₄₀, H₃PW₁₂O₄₀, H₄SiW₁₂O₄₀ and chromates. The optimium conditions of passivation with H₃PMo₁₂O₄₀ on the zinc-plating coating as follows:H₃PMo₁₂O₄₀ 5g/L, pH 1.1, passivation time 35s, passivation temperature 15℃, retention time in air 10s, confinement temperature 100℃(water). The surface appearence, composition and possible structure of the passivated film were determined by scanning electron microscopy, X-ray photoelectron spectroscopy, Auger electron spectroscopy, IR and Raman spectrometry. The results showed that a dense corrosion-resistant film was formed on the zinc surface consisting of P, Mo, O and Zn. Molybdenum existed in Mo (Ⅵ), Mo (Ⅴ) and Mo(Ⅵ) in the film with a P/Mo ratio 1:3.0. A certain complex passivated film, Zn_x(PMo₃)_yO_x/ZnO/Zn is assumed to be formed.

Key words: zinc-plating coating, passivation, heteropoly acid