Cr(Ⅲ)Colorful Passivation Technolon For Zinc Coating

The traditional Cr(Ⅵ) passivation solution is applying very widely in galvanization layer, zinc alloy coatings and metal surface etc. The passivation technology is more mature and stable as the development in the technology. And the passivation film gains highly ability of corrosion resistance. But the Cr(Ⅵ) with high toxicity triggers serious environmental pollution, brings damage to workers’ health through its carcinogenicity. The European Union already formulated extremely strict control measures to limit its use. Moreover, WEEE and ELV guidance has already clearly clarified Cr(Ⅵ) were banned in use in electric fields from July 1,2006 and in automotive fields from July1,2007 separately. Therefore, it is imperative to develop alternative technology in substitute of Cr(Ⅵ). Cr(Ⅲ) with good performance as Cr(Ⅵ) in passivation processes shares many similarities but the toxicity related to Cr(Ⅲ) passivation is just only one percent of the latter one. Thus, it attracts more and more attentions from scientists. Cr(Ⅲ) passivation film with high corrosion resistance can be white, blue white, multicolour, black, golden, etc., which are suitable for the coating to pure zinc, zinc iron, zinc nickel and zinc alloy, also include directly passivation to zinc alloy and aluminum alloy. Therefore Cr(Ⅷ) passivation will become most likely alternative and acceptable technology to substitute Cr(Ⅵ) passivation.A lot of experiments has been conducted and explored Cr(Ⅲ) passivation formula and its corresponding technology under room temperature successfully. In this passivation solution, Cr2(SO4)3 is the main element of the conversion layer; nitrate ion is the oxidant, lactic acid form as coordination agent, cobalt ions and nickel ions present as metal ions, acetate is used for buffer agent. The time of passivation is adjusted through controlling the pH of the passivation solution, and organic silicon A is used for seal treatment to close the gap between films after passivation process. During the tons of experiments, the passivation time, temperature, pH and times of workpiece swing which impact the performance of corrosion resistance of passivation film are analyzed, and the initial exploration to the forming process of passivation film is delivered.Moreover,3 main aspects which affect physical and chemical properties of Cr(Ⅲ) are tested:1) Monitor micro properties of Cr(Ⅲ) passivation coating through using the electron microscope; 2) Detected corrosion potentials of Cr(Ⅲ) by applying electricity chemistry workstation detection; 3) Detected properties of corrosion resistance of Cr(Ⅲ) passivation coating by conducting salt fog experiments.