卤素提高镀铬阴极效率的机理

Mechanism of Increasing Cathode Efficiency by Halide on Chromium Plating

研究了铬酸—硫酸体系中卤素对铬电沉积的效率和阴极极化曲线的影响.用电子能谱(XPS和AES)测定了该体系中形成的阴极膜的组成.结果表明,硫酸能有效地催化光亮铬的形成,F^-、Cl^-能显著地提高铬电沉积的电流效率.除Br^-外,F^-、Cl^-均参加成膜.由膜的深度剖析曲线表明,卤素分布在膜的深层,SO_4^(2-)集中在膜的表面.由此可推测,F^-、Cl^-在金属表面和铬酸的还原产物重铬酸铬形成了易发生电子转移反应的表面过渡态配合物〔Cr~Ⅰ-X-Cr~Ⅱ〕~≠.

Current efficiency of chromium electrodeposition and cathodic polarization curves were determined in halidechromie acid-sulphurie acid systems. Composition of the cathodic films formed was determined by XPS and AES. The results show that sulphate is an effective catalyst for the deposition of bright chromium aod that the current efficiency of chromium deposition increases remarkably when F^- and Cl^- are added to the bath, and also that F^- and Cl^- participate in the formation of the films. The depth profile curves of the film show that halide is distributed in the inner layer of the film and SO_4~2- in the surface layer. It is deduced that F^- and Cl^- form a bridged complex, [Cr~Ⅱ -X^- -Cr~Ⅱ ],~≠ in which electron transition is easily carried out.