Transactions of Nonferrous Metals Society of China
JOURNAL OF RAILWAY SCIENCE AND ENGINEERING
|Vol. 16 No. 1 February 2006|
（1. Department of Chemistry, Zhejiang University, Hangzhou 310027, China;
2. State Key Laboratory for Corrosion and Protection, Shenyang 110015, China ）
Abstract:The nickel electroplating process was investigated by means of electrochemical noise(EN), cyclic voltammetry in conjunction with the scanning electron microscopy(SEM) technique. The results show that, in the experimental conditions and with the increase of current density, the growth mechanism of nickel crystallites changes from 2-D to 3-D with the potential turning point of about －1.15 V, and the potential for the onset of diffusion control of the ensemble nickel electroplating process was about －1.4 V. In the case of activation-control, the two-dimensional (2-D) nucleation / growth process of nickel often results in the electrocrystallization EN features of only slowly small positive potential drift and the corresponding compact layer-by-layer deposit structure, and the maximum relative energy of the RP-EDP (re-plotted relative energy distribution plot), which is obtained from wavelet analysis, defined in the region with smaller scales. While under the diffusion-control, the three-dimensional (3-D) nucleation / growth process of nickel, often results in the electrocrystallization EN features of both the fast positive potential drift and subsequent remarkable negative potential drift and the corresponding dentritic/large conglomerate structure of nickel deposit, and the maximum relative energy of the RP-EDP defined in the region with larger scales. The electroplating time affects the nickel deposit structure mainly through its influence on the growth rate of crystallites and the Ni2+ ions diffusion process around each crystallite.
Key words: nickel electroplating; electrochemical noise; electrodeposit structure