铬电沉积过程及H2SO4的作用

在铬镀液(CrO_3/H_2SO_4=250/2.5Wt.)中,电流扫描实验结果表明,铬在玻璃碳电极上沉积需要成核过电位;而在铜电极上不需要成核过电位,其晶核由电极表面氧化膜(CuO CrOH)还原生成的金属Cr提供。铬电沉积前后,CrO_3还原机理不同,H_2SO_4 的作用也不同,沉积前,H_2SO_4的作用主要是活化电极表面,促使CrO_3还原,同时还使表面氧化膜溶解。沉积后,H_2SO_4 则起着保持电极表面附近阴极膜相对稳定的作用,还可能与 Cr(Ⅳ)形成易还原的配合物。

The Processes of Chromium Electrodeposition and the Roles of H2SO4

The chromium electroplating solution (CrO3 250 g/dm3 and HZSO4 2. 5 g/dm3) has been studied by chronopotentiometry with linear current scanning. The results indicated that nucleation overpotential was observed on vitreous carbon cathode,although it was not observed on Cu electrode, but the nuclei were produced by the reduction of oxide film (CuOCrOH.) on Cu electrode. The mechanism of CrOs reduction before chromium electrodeposition was different from that after. Before Cr deposition, H2SO4 was acted to activate the electrode surface and to catalyze CrO3 reduction, and to dissolve the oxide film on the cathode. After Cr deposition, H2SO4 was acted to keep the cathod ic film more steady and to form the complex compound with Cr( IV ) or its reduction intermediates.