硫酸盐体系三价铬沉积机理及镀层表征

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

在新研发的硫酸盐三价铬镀厚铬的镀液体系中,运用线性扫描伏安法(LSV)和循环伏安法(CV)对三价铬在铜电极表面的电沉积过程进行研究,并运用X射线荧光测厚仪、扫描电子显微镜(SEM)、X射线能量色散谱(EDS)、X射线衍射仪(XRD)、显微硬度计和Tafel曲线表征铬镀层厚度、形貌、组成、结构、显微硬度及在3.5wt%NaCl溶液中的耐蚀性.结果表明,在该体系中三价铬的沉积过程分两步进行(Cr^(3+)+e→Cr^(2+),Cr^(2+)+2e→Cr),第一步得到1个电子,受电化学过程和扩散过程共同控制;第二步得到2个电子,为扩散控制下的不可逆过程.该镀层为瘤状纳米晶结构,镀层中含有少量的铁元素(1.10wt%),显微硬度达到789.2 Hv,镀层在3.5wt%NaCl溶液中的腐蚀电位E_(corr)为-0.29 V,腐蚀电流密度j_(corr)为9.26×10^(-5)A·dm^(-2).

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 3.5 wt% 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, Cr^3＋＋ e → Cr^2＋, is controlled by the electrochemical reduction and diffusion processes, and the second step, Cr^2＋＋ 2 e → Cr, is an irreversible process under the diffusion control. The trivalent chromium coating exhibited nodular nanocrystalline structure and contained a small amount of iron（1.10 wt%）. The microhardness of the coating reached to 789.2 Hv. The corrosion potential（Ecorr） and corrosion current density（jcorr） of the coating in 3.5 wt% NaCl solution were determined to be-0.29 V and 9.26 × 10-5 A·dm^-2, respectively.