锡杂质引起的氯化钾无氰镀镉故障及其排除方法

A problem caused by tin impurities for cyanide-free cadmium electroplating in potassium chloride-based bath and countermeasures

某氯化钾无氰镀镉生产线出现了镀层粗糙,高温除氢后六价铬钝化所得钝化膜无光泽的故障。调查后确认是镉阳极板中含有的锡杂质溶入镀液后与镉共沉积所致。向镀液中加入氟化钠和双氧水,将二价锡氧化成四价锡,并与氟离子生成稳定的[SnF6]^2-配离子,可保证镀液中锡杂质的质量浓度小于10 mg/L 时对镀镉层的质量无影响。

The formation of rough surfaces of cadmium coatings as plated and matt surfaces after dehydrogenation followed by hexavalent chromium passivation occurred in a production line of cyanide-free cadmium plating using potassium chloride-based bath. The investigation result confirmed that the reason for such problem was the codeposition of cadmium and tin which was derived from the tin impurities in the cadmium anode through dissolution. It was solved by adding hydrogen peroxide and sodium fluoride to the bath due to the oxidation of Sn(Ⅱ) into Sn(IV) and the formation of stable [SnF6]^2- complex ions. The cadmium coatings obtained from the bath containing less than 10 mg/L of tin were qualified after being treated by the method.