硫脲对Ni-P镀层腐蚀行为的影响

Effect of Thiourea on Corrosion Resistance of Ni-P Coating

在镀液中添加硫脲,分析了硫脲对Ni-P镀层沉积速度、表面形貌、孔隙率等的影响,并通过极化曲线和交流阻抗测试了硫脲对Ni-P镀层腐蚀性的影响。结果表明,当镀液中添加1mg/L硫脲时,镀层的沉积速率加快,腐蚀速率增大。这主要是因为镀液添加硫脲后,镀层的孔隙率加大,促进了腐蚀介质渗入到基体表面,增加了腐蚀微电池的数量,形成了大阴极(镀层)-小阳极(基体)腐蚀微电池,使自腐蚀电流密度增大,电荷转移电阻减小。当镀液中添加硫脲质量浓度大于3mg/L时,镀液被毒化,无法施镀。

The thiourea was added in the electroless plating solution to analyze the influence of thiourea on the Ni--P coating deposition rate, surface morphology and porosity, etc.. The corrosion resistance was evaluated through polarization curves and electrochemical impedance spectroscopy. The results show that when 1 mg/L thiourea in the electroless plating solution was added, the deposition rate of coating accelerates and the corrosion rate increases. This is mainly reason after thiourea was added in the electroless plating solution, the porosity of coating increases, which promote the corrosive medium to seep deeply into the surface of the substrate resulting in increasing the number of corrosion micro cells and forming a corrosion cell of the large cathode（coating）- the small anode （substrate）. The corrosion current density increases and the charge transfer resistance reduces. While thiourea was added more than 3 mg/L, the electroless plating solution is poisoned and unable to plating.