仿金镀液中氯化铵的作用机理探讨

Discussions on the Effect Mechanism of Ammonium Chloride in a Brass Plating Bath

研究了氰化物仿金镀液中氯化铵的作用机理和监控方法。实验表明,当氯化铵的质量浓度≤1g/L时,镀层的颜色不够均匀,高电流密度区呈暗红色,氯化铵≥4g/L时,镀层发红。仿金镀液中不加氯化铵时,锌络离子的组成为[Zn(CN)_4]^(2-),锌的沉积速度较慢,镀层发红。向镀液中加2g/L-3g/L氯化铵,锌络离子转化为[Zn(CN)_3NH_3]^-,锌的沉积速度相对变快,镀层为仿金色。向镀液中过量加入氯化铵时,锌络离子转化为[Zn(CN)_2(NH_3)_2],锌的沉积速度重新变慢,镀层发红。用霍尔槽实验能够定性测定仿金镀液中氯化铵的浓度。

The effect mechanism and control methods of NH4C1 in a brass plating bath was studied. Experiments show that, eolour of the coating is not symmetrical and the coating is dull -red in the low current density area when concentration of NH4CI≤1 g/L, and the coating tend to red when NH4C1≥4 g/L. When there is no NH4C1 in the brass solution, 2-3 g/L NH4 comes quick re the zinc complex forms [ Zn（CN） 2 （NH3）2 ], the depositing rate of zinc become slow over again, which causes the coating to tend to red. Qualitative analysis of NH4C1 in the brass solution can be carried out by Hull cell test.