乙内酰脲体系无氰电镀镉工艺

Cyanide Free Cadmium Plating Process for Hydantoin System

目的开发一种新型的无氰镀镉工艺,替代传统的氰化镀镉。方法以海因和柠檬酸为主、辅络合剂,通过选用光亮剂和表面活性剂获得无氰镀镉工艺配方,优化pH值、电流密度和温度等工艺参数。按规定的方法测试镀液的分散能力、深镀能力。利用SEM、三维显微镜观察镀层的微观形貌,通过极化曲线和循环伏安曲线讨论镀液的极化度和成膜机理,利用塔尔菲尔曲线和点滴实验测试其耐蚀性。结果镉电沉积是通过"成核/生长"机理进行的,乙内酰脲体系无氰镀镉双络合剂协同作用明显,镀液极化能力强。与氰化镀镉相比,该工艺电流效率提高20%,沉积速率提高30%,分散能力可达89%以上,镀液深镀能力和镀层结合力检验合格,镀层表面光亮细致,钝化膜彩虹色明显。无氰镀镉层耐蚀性优于氰化镀镉层,与氰化镀镉钝化层相比,钝化封闭后,自腐蚀电流密度降低至之前的1/15,耐蚀性显著提高。结论该配方及工艺条件为:硫酸镉30～50 g/L,硫酸钠60～100 g/L,乙内酰脲60～70 g/L,柠檬酸20～40 g/L,光亮剂1～3 g/L,表面活性剂1～3g/L,pH=5～6,温度15～35℃。镀液镀层各项性能优越,完全可以替代氰化镀镉工艺用于我国飞机和航空发动机钢结构的防护。

The work aims to develop a new cyanide free cadmium plating process to replace the traditional cyanide cadmium plating.The formulation of cyanide-free cadmium plating process was obtained with hydantoin and citric acid as the main material and complexing agents as auxiliary materials by selecting brightener and surface active agent.The processing parameters like pH value,current density and temperature were optimized.The dispersing ability and deep plating ability of the bath were tested according to the prescribed method.The micro-morphology of the coating was observed by SEM and 3D microscope.The polarization and film-forming mechanism were discussed by polarization curve and cyclic voltammetry.The corrosion resistance of the coating was tested by Tarfield curve and drop test.Cadmium electrodeposition was carried out through the mechanism of nucleation/growth.The synergistic effect of double complexing agents on cyanide-free cadmium plating in hydantoin system was obvious and the polarization ability of the plating solution was strong.Compared with cyanide cadmium plating,the current efficiency of the process was increased by 20%,the deposition rate was increased by 30%,and the dispersing ability was over 89%.The deep plating ability of the bath and the adhesion of the coating were qualified.The surface of the coating was bright and meticulous,and the iridescent color of the passive film was obvious.The corrosion resistance of cyanide-free cadmium plating layer was better than that of cyanide cadmium plating layer.Compared with cyanide cadmium plating passivation layer,after passivation and closure,the corrosion current density decreased to 1/15 before,and the corrosion resistance was significantly improved.The formulation and technological conditions are:cadmium sulfate of 30~50 g/L,sodium sulfate of 60~100 g/L,hydantoin of 60~70 g/L,citric acid of 20~40 g/L,brightener of 1~3 g/L,surfactant of 1~3 g/L,pH=5~6 and temperature of 15~35℃.The plating bath has superior properties and can completely replace the cyanide cadmium plating process to protect aircraft and aeroengine steel structures in China.