电镀锌钢板的黑变机理

Mechanism of black patina on electrogalvanized steel sheets

在发现铅是导致电镀锌钢板黑变发生的关键因素的基础上 ,对电镀锌钢板的黑变机理提出了锌铅共沉积假说和硫酸铅胶体膜假说 ;并对不同工艺中获得的电镀锌钢板进行了黑变培养 ,通过丁达尔和界面电泳实验研究了铅在硫酸锌溶液中的存在形式 ,通过钝化及破胶实验研究了钝化工艺和镀后清洗对黑变的影响 ,验证了黑变是由于硫酸铅胶体膜在镀锌层外表面被吸附而造成的。

On the basis of finding that lead is the vital factor to bring patina on galvanized steel sheets, two hypothesizes, colloid film of lead sulfate and the codeposition of zinc and lead, were employed. The experiments were carried out on the Tyndall phenomenon in zinc sulfate solution, the electrophoresis on interface, chromate treatment parameters, the cleaning after electroplating and the formation of black patina in high humidity to clarify the form of lead existing in bath, plating and chromate film. It is found that the colloidal PbSO 4 in bath is adsorbed on the surface plating during electrolysis and gathered in the outer film of passivated zinc plate. It is proved that the adsorption of lead sulfate colloid on plate accelerates the generation of black patina, and the elimination of colloidal lead sulphate before or after passivation will prevent from black patina.