杂质铜离子对电镀镍层组织形貌及耐蚀性的影响

Effects of Impurity Copper Ions on the Morphology and Corrosion Resistance of Electroplated Nickel Layer

目的研究电镀镍液中存在的铜离子杂质对电镀镍层微观组织和耐蚀性能的影响。方法以五水合硫酸铜的形式向电镀镍液中加入不同质量浓度(5、10、30 mg/L)的铜离子杂质,并以初始配制的电镀镍液(0 mg/L Cu^(2+))为空白组对照。选用低电流密度(0.5 A/dm^(2))在Q235钢上电镀镍层,并通过扫描电子显微镜(SEM)、X射线衍射仪(XRD)、X射线光电子能谱(XPS)和电化学分析技术对电镀镍层的表面微观形貌、晶体织构、表面各元素化学态信息及耐蚀性能进行表征和分析。结果随着电镀镍液中铜离子浓度的增加,镍层的颜色逐渐变灰,外观质量降低。当电镀镍液中铜离子的含量在工业容忍度范围内时(≤10 mg/L),镍层的颜色较为光亮,晶粒尺寸较小且均匀。当铜离子的浓度大于工业容忍度时(>10 mg/L),晶粒开始变得粗大,且尺寸不均匀。镍晶的生长方式并未改变,仍以螺旋位错的方式进行生长。镀液中存在的铜离子改变了镍晶体的结构,主峰的衍射角度向大角度发生偏移,半峰宽逐渐变大,晶面间距减小,同时影响了镍晶体的择优生长取向,晶粒逐渐由(111)和(200)面转为(111)和(220)面生长。XPS测试结果显示,铜离子浓度的增加导致镍的析出效率降低,铜离子在镍层中析出,并以单质铜和氧化铜的形式存在于镍层中。电化学测试结果表明,电镀镍液中存在的铜离子降低了镍层的耐蚀性能。当铜离子的质量浓度从0 mg/L增加至30 mg/L时,镍层在质量分数为3.5%的NaC1溶液中的开路电位(OCP)逐渐降低,自腐蚀电位由−0.487 mV降至−0.547 mV,自腐蚀电流密度由7.8989μA/cm^(2)增加至17.316μA/cm^(2)。电化学阻抗模值和相位角变小,电荷转移电阻(Rct)由1798Ω·cm^(2)减小至851Ω·cm^(2)。结论在瓦特液中,微量铜离子杂质会导致镍结晶粗大,镀层外观灰暗。镍层中的杂质铜原子会引起一定程度的晶格畸变,使晶格常数变小,晶粒生长择优取向发生改变。随着铜离子杂质浓度的增加,电镀镍层在质量分数3.5%的NaCl溶液中的自腐蚀电流密度增大,阻抗值相应地降低,抗腐蚀性能下降。

The work aims to study the effects of copper ion impurities in nickel plating solution on the microstructure and corrosion resistance of electroplated nickel layer.In the form of copper sulfate pentahydrate,different mass concentration(5,10,30 mg/L)of copper ions were introduced into the nickel plating solution as copper ion impurity,and compared with the initially prepared nickel plating solution(0 mg/L Cu^(2+))as a blank group.Low current density(0.5 A/dm^(2))was used to electroplate nickel layer on Q235 steel,then scanning electron microscope(SEM),X-ray diffractometer(XRD),X-ray photoelectron spectroscopy(XPS)and electrochemical analysis techniques were used to characterize and analyze the surface micromorphology,crystal texture,chemical state information of various elements on the surface and corrosion resistance of different electroplated nickel layers.The results showed that the electroplated nickels layer gradually became gray,and the appearance quality decreased when the concentration of copper ions in the nickel plating solution increased;when the content of copper ions in the nickel plating solution was within the industrial tolerance range(≤10 mg/L),the nickel layer was bright in color,while the crystal grain size was small and uniform.When the concentration of copper ions was greater than the industrial tolerance,the crystal grains began to become coarser,and the size was not uniform.The growth mode of nickel crystal remained unchanged,which grew in the form of spiral dislocation.The copper ion in the plating solution changed the nickel crystal structure,the diffraction angle for the main peak shifted to a large angle,the half peak width increased gradually,and the crystal plane spacing decreased.At the same time,it affected the preferred growth orientation of nickel crystal,the grain growth gradually changed from(111)and(200)planes to(111)and(220)planes.XPS test results showed that the increase of copper ion concentration led to the decrease of nickel precipitation efficiency.Copper ions precipitated in the nickel layer and existed in the nickel layer in the form of elemental copper and copper oxide.The electrochemical test results showed that the copper ion in the nickel plating solution reduced the corrosion resistance of the nickel layer.With the increase of copper ion concentration from 0 mg/L to 30 mg/L,the open circuit potential(OCP)of nickel layer in 3.5wt.%NaC1 solution gradually decreased,the self-corrosion potential decreased from−0.487 mV to−0.547 mV,the self-corrosion current density increased from 7.8989μA/cm^(2)to 17.316μA/cm^(2),the electrochemical impedance modulus and phase angle became smaller,and the charge transfer resistance(Rct)decreased from 1798Ω·cm^(2)to 851Ω·cm^(2).In summary,trace copper ion impurities in watt solution will lead to coarse nickel crystal and gray appearance of the coating.The impurity copper atoms in the nickel layer will cause a certain degree of lattice distortion,reduce the lattice constant and change the preferred orientation of grain growth.With the increase of copper ions impurity concentration,the self-corrosion current density increases,the impedance value decreases accordingly,and the corrosion resistance decreases in 3.5wt.%NaCl solution.