Deposition Mechanism and Coating Characterization for the Trivalent Chromium Electrodeposition in Sulphate Electrolyte

doi:10.13208/j.electrochem.170441

Abstract

Abstract:

Linear sweep voltammetry (LSV) and cyclic voltammetry (CV) were used to study the electrodeposition mechanism of trivalent chromium on a copper electrode in the novel sulphate electrolyte for thick trivalent chromium plating. The thickness, morphology, composition, microhardness, and structure, as well as the corrosion resistance in 3.5wt% NaCl solution of the trivalent chromium coatings were investigated by X-ray fluorescence gage, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), microhardness tester, X-ray diffraction (XRD) and Tafel curve measurements. The results showed that the electrodeposition of trivalent chromium involved two consecutive one electron reduction steps. The first step, Cr³⁺ + e → Cr²⁺,is controlled by the electrochemical reduction and diffusion processes, and the second step, Cr²⁺ + 2e → Cr, is an irreversible process under the diffusion control. The trivalent chromium coating exhibited nodular nanocrystalline structure and contained a small amount of iron (1.10wt%). The microhardness of the coating reached to 789.2 Hv. The corrosion potential (E_corr) and corrosion current density (j_corr) of the coating in 3.5wt% NaCl solution were determined to be -0.29 V and 9.26×10^-5 A·dm^-2, respectively.

Key words: Trivalent chromium, Sulphate, Hard chromium, Electrodeposition, Mechanism, Coating Characterization.

CLC Number:

O646

YAN Hui，HUANG Shuai-shuai，YANG Fang-zu，TIAN Zhong-qun， ZHOU Shao-min. Deposition Mechanism and Coating Characterization for the Trivalent Chromium Electrodeposition in Sulphate Electrolyte[J]. Journal of Electrochemistry, 2018, 24(1): 20-27.

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