柠檬酸铵对5,5-二甲基乙内酰脲配位体系碱性无氰镀镉的影响

Effect of ammonium citrate on the non-cyanide cadmium electroplating from alkaline 5,5-dimethylhydantoin coordination system

选用5,5-二甲基乙内酰脲(DMH)为主配位剂开发碱性无氰镀镉体系,通过赫尔槽试验、电化学测试、扫描电镜等分析研究了柠檬酸铵作为辅助配位剂对碱性DMH镀镉体系中镉电沉积行为及镀层性能的影响。结果表明:柠檬酸铵可以拓宽碱性DMH镀镉体系的光亮电流密度窗口,阻碍镉配离子的放电还原,增大阴极极化,提高电流效率,细化镀层晶粒,改善镀层耐蚀性。少量柠檬酸铵的阴极极化作用较弱,镀层结晶不够细致;过量的柠檬酸铵会增大析氢反应,降低镀液稳定性;30 g/L的柠檬酸铵辅助配位效果较佳,所得镀层结晶细致、耐蚀性良好。

The alkaline cyanide-free cadmium plating process with 5,5-dimethylhydantoin(DMH)as the main complexing agent was developed.The effects of ammonium citrate as the auxiliary complexing agent on the electrodeposition behavior of cadmium in alkaline DMH plating bath and the coating properties were studied by Hull cell test,electrochemical test and scanning electron microscope.The results show that the ammonium citrate can broaden the bright current density window of alkaline DMH cadmium plating system,hinder the discharge reduction of cadmium complex ions,increase the cathodic polarization,improve current efficiency,refine the coating grain and improve the corrosion resistance of the coatings.The cathodic polarization effect in the bath with a small amount of ammonium citrate is weak, and the crystallization of the coating is not detailed enough. Excessive ammonium citrate will increase the hydrogen evolution reaction and reduce the stability of the plating bath. The auxiliary coordination effect of 30 g/L ammonium citrate on the cadmium plating in alkaline DMH system is better, meanwhile, the obtained coating has fine grains and good corrosion resistance.