苄胺对硫酸盐体系镀黑铑的影响

Effect of benzylamine on black rhodium electroplating in sulfate system

向由2g/L自制Rh_2(SO_4)_3、20mL/L浓硫酸和4mL/L CH_3OH组成的酸性镀液中加入0~80mL/L苄胺,在电流密度2A/dm^2;温度40℃和时间120s的条件下对铜基体电镀,得到铑镀层。采用分光测色仪、扫描电镜、X射线光电子能谱仪、拉曼光谱仪、纳米压痕仪等表征了铑镀层的颜色、微观形貌、组织结构和耐磨性。结果表明,镀液中加入苄胺后,镀层由白色变为黑色,较优的苄胺添加量为20 mL/L。采用含20 mL/L苄胺的镀液电镀所得黑铑层厚度约为2.34μm,表面连续均匀,结合力良好。在人工汗液中浸泡10d后的颜色变化不大,耐蚀性和抗变色能力良好。铑层为黑色的可能原因是:在电镀过程中苄胺还原生成有机物并沉积在镀层表面。

0-80 mL/L benzylamine was added to an acid bath consisting of 2 g/L home-made R.h2（SO4）3, 20 mL/L concentrated sulfuric acid and 4 mL/L CHaOH for preparing a black rhodium coating on copper substrate by electroplating under the conditions of current density 2 A/dm2, temperature 40℃ and time 120 s. The color, microscopic morphology, structure and wear resistance of the rhodium coating were characterized by spectrophotometer, scanning electron microscope, X-ray photoelectron spectroscope, Raman spectroscope and nanoindentor. The results showed that the rhodium coating changes from white to black with the addition of benzylamine to the bath with an optimal dosage being 20 mL/L. The black rhodium coating obtained with 20 mL/L benzylamine features a thickness of ca.2.34 um, continuous and uniform surface and strong adhesion. The color of black rhodium coating is not much changed after immersing in artificial sweat for 10 days, exhibiting good corrosion resistance and anti-tarnishing performance. The probable cause for rhodium coating to be black is that benzylamine is reduced to certain organic compound which is deposited on the surface of coating during electroplating process.