氯化物三价铬电镀的电化学形核机理

为研究Cr³⁺在金属电极表面的电结晶行为,在氯化物三价铬电镀溶液中,采用电化学工作站测试了Cr³⁺沉积的时间电流曲线,并利用扫描电镜(SEM)分析镀层形貌。结果表明:在镍电极、铜电极和铬电极表面,Cr³⁺的电沉积均经历了成核过程;铜电极和镍电极表面表现为连续成核转为瞬时成核的机理,铬电极的(I/Im)2-t/tm曲线偏离理论曲线较大,但其表现出较正的形核阶跃电位(-1.1 V);随着阶跃电位的负移,3种电极电沉积的电流极大值逐渐增加,电结晶的扩散速率增加,成核数密度减少,镀层由平整光滑逐渐转变为球状晶胞紧密堆砌,晶胞尺寸逐渐增大;在相同的阶跃电位下,铬电极的沉积电流值更小,成核数密度更大,晶胞尺寸更小。

Electrochemical Nucleation Mechanism of Trivalent Chromium in Chloride System

In order to study the electrocrystallization behavior of Cr3+on the surface of metal electrode,the chronoamperometry curves of Cr3+deposition in chloride trivalent chromium plating solution were analyzed by electrochemical workstation,and the morphology of as-prepared coating was observed by scanning electron microscope( SEM). Results showed that the electrodeposition of Cr3+on nickel electrode,copper electrode and chromium electrode underwent the nucleation process. The nucleation mechanism of Cr3+on copper electrode and nickel electrode changed from instantaneous to progressive mechanism. The( I/Im)^2-t/tmcurves of the chromium electrode deviated from the theoretical curves obviously,and the nucleation potential of the chromium electrode was more positive(-1. 1 V) than the other two electrodes. With the step potential turned to negative direction,the maximum current value increased gradually,and the diffusion rate of electrocrystallization increased as well as the nucleation density decreased. Moreover,the coating morphology changed from smooth to globular cell,and the cell size increased gradually. Besides,at the same step potential,the deposition current of chromium electrode was smaller,and the nucleation density was higher,as well as the cell size was smaller than the other two electrodes.