氨络合物体系中杂质Zn~(2+)对电沉积镍的影响

通过霍尔槽试验研究氨络合物体系中杂质Zn~(2+)对镍电沉积的影响,采用电化学工作站测试不同Zn~(2+)浓度时的循环伏安曲线、稳态极化曲线及电流时间暂态曲线.结果表明:杂质Zn~(2+)的含量为0.1 g/L时,在小于2.78 A/dm的电流密度范围内可正常沉积出金属镍;杂质Zn~(2+)含量大于0.5 g/L时,在较大的电流密度范围内均无法正常沉积出金属镍;过电位小于640 mV时,Zn~(2+)的存在不影响阴极反应的传递系数,且不改变阴极反应机理;当过电位大于640 mV,且杂质Zn~(2+)的浓度大于0.5 g/L时,阴极反应的传递系数减小,阴极反应机理发生改变;杂质Zn~(2+)浓度大于0.5 g/L时,严重影响镍电结晶过程的成核速率,这是其抑制金属镍电沉积的主要原因.因此,采用镍氨络合物体系电积金属镍,应控制杂质Zn~(2+)的含量小于0.1 g/L.

Effect of impurity Zn~(2+) on nickel electrodeposition in solution containing ammonia complex

In nickel ammonia system, the influence of impurity Zn~(2+) on the nickel electrodeposition was studied intensively by Hull Cell experiments, and the cyclic voltammetry, cathodic polarization and chronoamperometric curves were tested at different Zn~(2+) concentration by electrochemistry working station. The results show that nickel can be deposited normally when the concentration of impurity Zn~(2+) is 0.1 g/L and the cathodic current density is less than 2.78 A/dm. When the concentration of impurity Zn~(2+) is greater than 0.5 g/L, nickel can't be deposited normally in a wide range of current density. The cathodic transfer coefficient α and reaction mechanism will not change with the addition of impurity Zn~(2+) when the overpotential is less than 640 mV. The cathodic transfer coefficient α decreases and the reaction mechanism changes when the overpotential is greater than 640 mV and the concentration of impurity Zn~(2+) is greater than 0.5 g/L. The nucleation rate during nickel electrocrystallization is restrained greatly when the impurity Zn~(2+) concentration is greater than 0.5 g/L, which is the main reason that inhibits the nickel electrodeposition. So, during electrowinning nickel from ammonia system, the content of purity Zn~(2+) should be controlled less than 0.1 g/L.