标题: Electroplating of Thick Hard Chromium Coating from a Trivalent Chromium Bath Containing a Ternary Complexing Agent: A Methodological and Mechanistic Study
作者: Xu, LY (Xu, Lingyun); Pi, L (Pi, Liu); Dou, YH (Dou, Yiheng); Cui, Y (Cui, Yin); Mao, XH (Mao, Xuhui); Lin, A (Lin, An); Fernandez, C (Fernandez, Carlos); Peng, C (Peng, Chuang)
来源出版物: ACS SUSTAINABLE CHEMISTRY & ENGINEERING 卷: 8 期: 41 页: 15540-15549 DOI: 10.1021/acssuschemeng.0c04529 出版年: OCT 19 2020
摘要: Trivalent chromium electroplating is considered a greener alternative to hexavalent chromium electroplating. However, the electrochemical reduction of Cr(III) in aqueous solution is extremely unstable and the thickness of the coating can hardly grow beyond 10 mu m, which limits its industrial applications. We herein report a trivalent chromium bath containing a ternary complexing agent, which yields bright and uniform chromium coatings with thickness exceeding 30 mu m, as well as high hardness and corrosion resistance. The electroplating behaviors and first principal calculations reveal that the Cr(II) intermediate plays a vital role in sustained electroplating in Cr(III) baths. The composition of complexing agents has a profound effect on the geometry and electron accepting ability of the Cr(II) complex ions. The failure to grow thick Cr coating is attributed to the accumulation of inactive hydroxo-bridged complexes. In the bath with ternary complexing agent, the Cr(II) complex ions are dsp(3) or dsp(2) hybridized with high electron affinity, which can be readily reduced to metallic Cr. The bath also shows a strong competitive ligand-binding effect that renders Cr(II) to preferentially bind with an organic ligand rather than a hydroxy ligand. Furthermore, the planar geometry of dsp(2) hybridization does not favor the formation of hydroxo-bridged complexes because of the steric hindrance effect. The above merits of the ternary complexing agent lead to sustained electroplating, and thick Cr coatings are obtained.
作者关键词: trivalent chromium electroplating; complexing agent; steric hindrance; electron affinity; divalent intermediates
地址: [Xu, Lingyun; Pi, Liu; Dou, Yiheng; Cui, Yin; Mao, Xuhui; Lin, An; Peng, Chuang] Wuhan Univ, Sch Resource & Environm Sci, Wuhan 430072, Peoples R China.
[Xu, Lingyun; Pi, Liu; Mao, Xuhui; Lin, An; Peng, Chuang] Wuhan Univ, Hubei Int Sci & Technol Cooperat Base Sustainable, Wuhan 430072, Peoples R China.
[Fernandez, Carlos] Robert Gordon Univ, Sch Pharm & Life Sci, Aberdeen AB10 7GJ, Scotland.
通讯作者地址: Peng, C (通讯作者)，Wuhan Univ, Sch Resource & Environm Sci, Wuhan 430072, Peoples R China.
Peng, C (通讯作者)，Wuhan Univ, Hubei Int Sci & Technol Cooperat Base Sustainable, Wuhan 430072, Peoples R China.
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