Abstract: A large part of the failure of nickel plating process is caused by the excessive content of impurities in the nickel plating solution. This article summarizes the sources and effects of common impurities in nickel plating solutions, and details the treatment methods of related impurity pollution.
， 镍镀层 在装饰， 防腐 以及电子 等领域得到 广泛 的 应用， 其 生产方式上已经从以前的 小批次 大批量 逐渐过渡到 多品种小批量的生产方式，而且对产品质量要求更高 。 In recent years , nickel plating has been widely used in the fields of decoration, anti-corrosion, and electronics . Its production method has gradually transitioned from the previous small batch and large batch to the multi-variety small batch production method, and it has higher requirements for product quality . 。 With the change of production methods, plating managers must use the same plating solution to electroplat various workpieces . 电镀管理人员 对防止 电镀不良 的发生，必须有充分的知识和管理技术，并且在 电镀不良 发生时，必须立即采取合适的处理方法，使镀液恢复正常。 Therefore, plating managers must have sufficient knowledge and management skills to prevent the occurrence of plating defects , and when plating defects occur, they must immediately take appropriate treatment methods to restore the plating solution to normal.
主要 介绍瓦特型光亮镀镍液中杂质的 产生原因，对镀液的影响及除杂方法 。 This article mainly introduces the causes of impurities in Watt-type bright nickel plating solution, the effect on the plating solution and the method of removing impurities .
杂质的种类和混入途径 1 ) Types of impurities and mixing routes
硝酸根，磷酸根等阴离子杂质； 油脂类，光亮剂分解产物等有机杂质；以及活性炭粒等固体型杂质。 The impurities that pollute the nickel plating solution can be roughly divided into metal impurities such as copper, zinc, and iron; anionic impurities such as nitrate and phosphate; organic impurities such as greases and brightener decomposition products; and solid impurities such as activated carbon particles. The main ways of mixing impurities are the introduction of electroplating raw materials, the dissolution of workpieces in the plating bath, and other process solutions.  。 Residual carry-in, new equipment comes with impurity carry-in, etc.  . In addition, although the closed-loop circulation system is beneficial to the recovery of electroplated chemicals and reduces the cost of drainage treatment, it causes problems of concentration and accumulation of impurities. 电镀用水 也以使用杂质少的去离子水为宜。 Therefore, it is preferable to use deionized water with less impurities for the electroplating water . One type of impurity is mixed in as follows
Inclusion of metal impurities
掉入镀槽的零件的基体或镀铜层等异金属的溶解 1. Dissolution of dissimilar metals such as the substrate or copper plating of parts falling into the plating tank
前工序镀液的带入 2 , the introduction of the plating solution in the previous process
从挂具，导电杆上混入的异种金属 3 , dissimilar metals mixed from hangers, conductive rods
电镀原物料中异种金属的带入。 4 , the introduction of dissimilar metals in the electroplating raw materials.
Incorporation of organic impurities
基体除油不干净带入的油脂类 1. Greases brought in by degreasing of substrate
从滤布，滤袋，镀槽处理材料中溶解的杂质 2. Dissolved impurities from filter cloth, filter bag, plating tank treatment material
大气污染物质从压缩空气喷嘴中混入 3 , air pollutants are mixed in from the compressed air nozzle
有机光泽剂分解生成物 4 , organic gloss agent decomposition products
过量的有机添加剂 5 , excess organic additives
的混入途径 Incorporation of solid impurities
在基体表面附着的抛光粉 1 , polishing powder adhered to the surface of the substrate
大气中的尘埃，电镀设备上的粉尘，涂料等落入镀液 2. Dust in the atmosphere, dust on plating equipment, paint, etc. fall into the plating solution
阳极袋中阳极泥漏入镀液 3 , the anode mud in the anode bag leaks into the plating solution
处理槽液时未处理干净的活性炭粉等。 4. The clean activated carbon powder and so on are not processed when processing the bath solution.
杂质的影响 2 ) Influence of impurities
， The effects of impurities on nickel plating can be divided into the following types ,
目视能够判断的针孔，麻点，镀层发雾，色泽不均，无镀层等的外观不良故障 。 1. Pinholes, pits, fogging, uneven color, and no appearance defects such as plating can be judged visually .
镀层应力大，硬度大，延展性差等的物理性能降低 。 2. Physical properties such as high plating stress, high hardness, and poor ductility are reduced .
镀层结合力差，耐蚀性降低 。 3. Poor adhesion of the coating and reduced corrosion resistance .
对策 3 ) countermeasures
往往 难以弄清楚原因的。 If the mixed impurities are predictable substances in advance, regular countermeasures can be taken. However, if the mixed impurities other than impurities are slowly accumulated to exceed the allowable limit, it is often difficult to find out the cause of sudden bad failures. . At this time, it is necessary to carry out simulation experiments in the laboratory to make bad faults reappear, so that corresponding countermeasures can be taken. 哈氏 槽实验。 This simulation experiment method can use the Hastelloy test.
-- 哈氏 槽实验 Method for confirming impurities - Hastelloy test
槽实验，在镀液管理上比较容易掌握镀液的状态，判断杂质，因此被广泛应用。 The Hastelloy experiment is widely used in the management of the plating solution, because it is relatively easy to grasp the state of the plating solution and determine impurities. 再现 杂质的影响的最合适的方法。 Since the current density is not fixed and can be freely controlled, it can be said that it is the most suitable method to reproduce the influence of impurities. For example, if it is a metal that is easily precipitated in a low-current region, the current is reduced and the air is stirred. 就 在无搅拌的静置状态 下进行试验  。 To determine the organic impurities, the test is carried out in a static state without agitation  . As mentioned above, relying on the Hastelloy test, the influence of impurities is reproduced on the test strip, which will become an important basis for removing impurities. If the bad failure can be reproduced on the test piece, according to the method of judging the removal of such impurities, a preliminary experiment is performed in a beaker, and then an impurity removal process is performed on site.
净化方法 ： Plating solution purification method :
电解法 1 , electrolytic method
( 又称假阴极 ) 。 Electrolytic treatment is also an electroplating process. The only difference is that instead of hanging parts on the cathode, it is an electrolytic plate ( also called a false cathode ) made by hanging instead to remove impurities . 或 还原成相对无害的物质。 In the case of energization, the impurities are deposited, trapped, or reduced on the cathode electrolytic plate to a relatively harmless substance.  。 In a few cases, the removal of impurities by electrolysis is also performed on the anode, so that certain impurities that can be oxidized, when energized, reach the anode and oxidize to gas to escape or become relatively harmless substances  .
The electrolytic method is suitable for removing impurities that are easily removed or reduced in the electrode.
(1) Selection of electrolytic conditions. The purpose of electrolysis mentioned here is to remove impurities in the plating solution, but when the impurities are removed electrolytically, it is often accompanied by the discharge deposition of the main metal ions in the solution. In order to increase the rate of removing impurities and slow down the deposition rate of the main metal ions in the solution, it is necessary to pay attention to the operating conditions of the electrolytic treatment.
① Current density: It is better to control the current density during electrolytic treatment. In principle, the current density range in which the impurities are adversely affected during electroplating should be used. That is, during the electroplating process, if the influence of impurities is reflected in the low current density region, the electrolytic treatment should be controlled at a low current density. If the influence of impurities is reflected in the high current density region, a high current density should be selected. Carry out electrolysis; if the impurities are affected in both the high current density area and the low current density area, the high current density electrolytic treatment can be used for a period of time, and then the low current density electrolytic treatment can be used until the plating solution returns to normal. In general, in order to reduce the deposition of the main discharge metal ions in the plating solution, impurities that can be removed by low current density electrolysis are generally used. 0.1 A ／ dm 2 -0.5 A ／ dm 2 之间 . In fact, the effects of most impurities in electroplating production are reflected in the low current density region, so the current density of the electrolytic treatment is usually controlled between 0.1 A / dm 2 -0.5 A / dm 2. 
pH 值：电解处理时温度和 pH 的选择，原则上也是要根据电镀时杂质起不良影响较大的温度和 pH 范围。 ②Temperature and pH : The choice of temperature and pH during electrolytic treatment should , in principle, also be based on the temperature and pH range where impurities have a greater adverse effect during electroplating . NO 3- 杂质，在 pH 较低时的影响较大，所以电解去除镀镍溶液中的铜杂质和 NO 3- 杂质时，应选用低 pH 进行电解，在这样的条件下，去除杂质的速率较快。 For example, copper impurities and NO 3- impurities in nickel plating solutions have a greater impact at lower pH , so when electrolytic removal of copper impurities and NO 3- impurities in nickel plating solutions, low pH should be used for electrolysis. Under the conditions, the rate of removing impurities is faster. ( 如 NO 3- 在阴极上还原为氮氧化物或氨 ） 等，这时就应选用高温电解，使电解过程中形成的气体挥发逸出 ( 气体在溶液中的溶解度，一般随温度升高而降低 ) ，从而防止它溶解于水而重新沾污镀液。 Some impurities will be decomposed into gases during the electrolysis process ( such as NO 3- reduced to nitrogen oxides or ammonia on the cathode ) . At this time, high temperature electrolysis should be used to evaporate the gas formed during the electrolysis process ( gas in solution The solubility in water generally decreases with increasing temperature ) , so as to prevent it from dissolving in water and re-staining the plating solution.
According to the general rule, as the temperature of the plating solution increases, the rate of electrolytic removal of impurities also increases. Therefore, when the heating has no effect on the main components of the plating solution, the electrolytic treatment should be performed under heating. But it is better to control at what temperature, it is best to determine through small experiments.
( 或阳极 ) 的表面上反应而被除去，那么就应创造条件，使杂质与电极表面有充分的接触机会。 ③ Stirring: Since the electrolytic treatment is removed by the reaction of impurities on the surface of the cathode ( or anode ) , conditions should be created to allow the impurities to have sufficient contact with the electrode surface. Stirring can accelerate the movement of impurities and increase the chance of contact with the electrode, so in order to improve the processing effect, the plating solution should be stirred during electrolysis. According to foreign data, the use of ultrasonic agitation in the electrolytic treatment can improve the treatment effect. Therefore, the conditional unit should accelerate the stirring of the plating solution as much as possible during the electrolytic treatment.
(2) Requirements for electrolytic treatment
First of all, it is necessary to find out whether the harmful impurities originate from the electrolytic process: electrolytic treatment can remove some impurities, but sometimes it also produces impurities. For example, harmful impurities originate from impure anodes, and such anodes are still used in electrolytic treatment. As the electrolytic process proceeds, impurities will accumulate more and more; if impurities originate from the decomposition of certain compounds on the electrode, then the Such decomposition products will gradually increase. Such electrolytic treatment not only fails to purify the plating solution, but also continuously increases the pollution of the plating solution. Therefore, before the electrolytic treatment, necessary inspections should be carried out to prevent the generation of harmful impurities during the treatment.
( 假阴极 ) 面积要尽可能大：用电解法去除杂质，大多是在阴极表面上进行的，所以增大阴极面积，可以提高去除杂质的效率 ， 同时为了在不同的电流密度部位电解去除镀液中不同杂质或同一种杂质，要求电解用的阴极做成凹凸的表面 ( 如瓦楞形 ) ，这样可以提高电解处理的效果。 The area of the cathode ( false cathode ) used for electrolysis should be as large as possible: most of the removal of impurities by electrolytic method is performed on the surface of the cathode. Electrolytic removal of different impurities or the same impurities in the plating solution requires that the cathode used for electrolysis be made into a concave and convex surface ( such as a corrugated shape ) , which can improve the effect of electrolytic treatment. However, the recesses on the cathode should not be too deep, in order to prevent the current density from being too small so that impurities cannot be deposited or reduced in these parts. 
During the electrolysis process, the cathode should be brushed regularly. As the electrolytic treatment time is generally longer, during the long-term electrolysis process, loose deposits may be generated on the cathode, and its fall-off will re-contaminate the plating solution. After a period of time, the cathode should be taken out and washed, and the loose or bad deposits on the cathode should be brushed off before continuing the electrolysis.
Before the electrolytic treatment, it is best to conduct a small test to estimate the effect and time of the electrolytic treatment: some impurities are difficult to remove with the electrolytic treatment. If the electrolytic treatment is used blindly, it may take a long time to restore the plating solution to normal.
Because the plating solution taken in the small test is small and the total amount of impurities is also small, a sufficient amount of electricity is often passed in, and it can be seen in a short time whether the electrolytic treatment is fruitful. 2L 有故障的镀液，挂人 2dm 2 左右的阴极 ( 瓦楞形 ) ，电流 2A ，电解 4h 镀液基本好转， 5h 镀液恢复正常，则小试验表明：每升有故障的镀液，通入 5A·h 电量就能使镀液恢复正常。 For example, take 2L of defective plating solution, hang the cathode ( corrugated ) of about 2dm 2 , the current is 2A , the electrolytic solution for 4h basically improves, and the plating solution returns to normal for 5h . The small test shows that: 5A · h electricity can bring the bath back to normal.
1000L ，则需通人 5000 A·h 左右的电量。 From this, it can be estimated that if the faulty plating solution to be processed is 1000L , it needs to pass about 5000 A · h of electricity. 100 A ，那么约需电解 50 h 。 If the control current is 100 A during electrolytic treatment , it will take about 50 hours for electrolysis . Since the small test is not the same as the operation conditions of the large tank electrolysis, the small test cannot be used as the basis for the large tank electrolysis treatment. It can only be used as a pre-estimation to make sure.
(3) Operation method of electrolytic treatment. The electrolytic treatment can be performed by either a batch method or a continuous method. The intermittent method is to stop the production when the plating solution is contaminated by impurities to affect the quality of the coating. The cathode is suspended from the electrolytic plate and electrolytic treatment is performed until the plating solution returns to normal before it is converted to formal plating production.
The continuous method is to place a small auxiliary tank beside the electroplating tank. This auxiliary tank is dedicated to electrolytic removal of impurities. A pump is used to draw the plating solution that needs electrolytic treatment from the electroplating tank to the auxiliary tank. An overflow port allows the electroplated bath to return to the plating bath to keep the bath in the bath constantly circulating back and forth. The continuous method allows the plating and electrolytic processes to be performed in parallel without stopping production. This method is suitable for operations where the impurity content will gradually increase during the electroplating process. For example, nickel plating of zinc products, zinc impurities in the nickel plating solution are likely to increase; bright sulfate copper plating after nickel plating, copper impurities in the nickel plating solution are likely to increase. An auxiliary electrolytic cell is placed next to this type of nickel plating tank for continuous electrolysis, which can suppress the growth of zinc or copper impurities and prevent failure. 
The continuous method can only be performed when the impurity content has not risen to affect the quality of the product. Otherwise, if the impurity content has reached to affect the quality of the coating, the batch method must first be used to reduce the impurity content to a permissible range, and then converted to a continuous method. Perform electrolysis.
PH 值沉淀法 2 , high pH precipitation method
pH 沉淀法又称碱化沉淀法。 The high pH precipitation method is also known as the alkaline precipitation method. pH ，使镀液中的金属杂质生成难溶于水的氢 氧化 物沉淀。 It is to increase the pH of the plating solution with an alkali , so that the metal impurities in the plating solution form a hydroxide precipitate that is difficult to dissolve in water . Such as:
2+ +2 OH - =Fe(OH) 2 ↓ Fe 2+ +2 OH- = Fe (OH) 2 ↓
2+ +3 OH - =Fe(OH) 3 ↓ Fe 2+ +3 OH- = Fe (OH) 3 ↓
2+ +2 0H - =Cu(OH) 2 ↓ Cu 2+ +2 0H- = Cu (OH) 2 ↓
2+ +2 OH - =Zn(OH) 2 ↓ zn 2+ +2 OH- = Zn (OH) 2 ↓
3+ +3 OH - =Cr(OH) 3 ↓ Cr 3+ +3 OH- = Cr (OH) 3 ↓
2+ +2 0H - =Pb(OH) 2 ↓ Pb 2+ +2 0H- = Pb (OH) 2 ↓
pH 沉淀法适用于弱酸性的镀液，如 镀镍 、铵盐 镀锌 和无铵氯化物镀锌液等。 The high pH precipitation method is suitable for weakly acidic plating solutions, such as nickel plating , ammonium salt zinc plating and ammonium chloride-free zinc plating solutions. pH 值，应根据镀液的具体情况。 When processing, what alkali is used to increase the pH of the plating solution should be based on the specific conditions of the plating solution. 镀镍液用 NiC O 3 提高 PH 值 ， 在特殊情况下也可使用 NaOH 。 Generally, NiC O 3 is used to increase the pH value of nickel plating solution , and NaOH can also be used in special cases .
pH 前，应将镀液加热至 65ºC ～ 70ºC ，以防止在提高 pH 时生成的氢氧化物形成胶体，使之容易 过滤 而除去沉淀。 Before adding alkali to the plating solution to increase the pH , the plating solution should be heated to 65ºC to 70ºC to prevent the hydroxide formed when the pH is raised from forming a colloid, making it easy to filter and remove the precipitate.
The above is a general method for removing impurities. In addition, we can choose a corresponding treatment method for a specific impurity. Common impurities in nickel plating solutions are copper, zinc, lead, iron, and chromium. , Nitrate and so on. The corresponding processing methods for various impurities are as follows
: 1.copper impurities :
Incorporation method: The copper parts (or copper-plated parts) that have fallen into the plating tank are dissolved, the copper plating solution is brought in from the previous process, and the copper scraps of the anode conductive rod or the residual oxides of copper fall off.
: 当镀镍液中铜离子含量达 5mg/L 以上，钢铁及锌压铸件电镀时就会产生置换铜，造成结合力不良，特别在电流中断及低电流密度区最易发生。 Impact : When the content of copper ions in the nickel plating solution is above 5mg / L , the replacement of copper will occur during the plating of steel and zinc die castings, resulting in poor bonding, especially in the current interruption and low current density areas. , 疏松 , 呈海绵状等不良镀层。 Copper impurities often make the appearance of the coating in the low current density area appear gray or even black, and often appear rough , loose , sponge-like and other poor coatings. Using Hastelloy grooves, the plating in the low current area will appear gray or even black. When the copper impurities are low, the coating in the low current region is found to be matte.
2ml ，加 2mol/LH 2 SO 4 ， 使溶液呈酸性，再加 1mol/LK 4 [Fe(CN) 6 ] 2ml ；如产生沉淀 [Cu 2 [Fe(CN) 6 ] ，此沉淀溶于氨水呈现兰色，示有 Cu 2+ 存在。 Identification method: Take 2ml of plating solution , add 2mol / LH 2 SO 4 to make the solution acidic, and then add 1mol / LK 4 [Fe (CN) 6 ] 2ml ; if precipitation [Cu 2 [Fe (CN) 6 ] occurs , This precipitate was dissolved in ammonia water and appeared blue, showing the presence of Cu 2+ . PH=2-3 ，浸入用 HCl The simple method in production is to adjust PH = 2-3 with dilute sulfuric acid and HCl for immersion. 3-5 分钟取出，观察有否红色置换铜。 Activate the treated steel wire and take it out for about 3-5 minutes, and observe whether there is red replacement for copper.
0.2-0.4A/dm 2 如激烈搅拌可用稍大电流密度。 1) Electrolytic method: 0.2-0.4A / dm 2 If it is vigorously stirred, a slightly larger current density can be used. 3-5 小时即可。 The corrugated iron plate for cathode is generally 3-5 hours for electrolysis .
, 如加入铜含量 ( 摩尔 )2 倍左右喹啉酸，可使铜含量下降到 2) Chemical agent method: It is removed by agents that selectively precipitate only copper ions . For example, adding quinolinic acid with a copper content ( molar ) of about 2 times can reduce the copper content to 以下。 1mg / L or less. 2- 巯基苯并噻唑生成沉淀后过滤。 Potassium ferrocyanide can also be added, and 2- mercaptobenzothiazole is precipitated and filtered. PH=6.3 ，会有相当多的氢氧镍沉淀生成。 If copper hydroxide precipitates are to be formed , a considerable amount of nickel hydroxide precipitates will be generated due to the need to adjust pH = 6.3 . PH=6.3 生成氢氧化铜沉淀的方法，镀槽镍损失达 30% 。 According to test results, if the method of adjusting the pH = 6.3 to generate copper hydroxide precipitation is used, the nickel loss in the plating bath reaches 30% . PH 值沉淀法。 Unless extremely special circumstances, try not to adjust the pH precipitation method.
锌杂质 : 2 , zinc impurities :
入途径：锌基合金工件，黄铜件在镀槽中的溶解。 Incorporation method: dissolution of zinc-based alloy workpieces and brass parts in the plating bath.
： 光亮镀镍溶液中如如含微量锌所得镀层呈白色 ， 如含量再提高 ， 低电流密度处呈灰黑色 ， 镀层呈现条纹状 。 Impact : In the bright nickel plating solution, if the plating layer obtained by containing a trace amount of zinc is white , if the content is further increased , it is gray-black at low current density , and the plating layer is striped . PH 较高镀液中 ， 由于锌的存在还会使镀层出现针孔 ， 锌允许极限因光亮剂不同而异 ， 一般在 20-100mg/L 范围内 . In higher pH baths , pinholes will appear in the coating due to the presence of zinc. The allowable limit of zinc varies with different brighteners , and is generally in the range of 20-100mg / L.
方法： 取 2ml 镀液加于试管中 ， 加蒸馏水 30ml ， 1% 甲基紫 1 滴 ， 1:1 HCl 2 滴 ， 15%KCNS 1 滴 ， 若镀液变紫 ， 示有锌 。 Identification method: Add 2ml of plating solution to the test tube , add 30ml of distilled water , 1 drop of 1% methyl violet, 2 drops of 1: 1 HCl , 1 drop of 15% KCNS . If the plating solution turns purple , it shows zinc . 2ml 镀液加于试管中 ， 调 PH 至石蕊试纸呈中性 ， 再加 CH 3 COOH 1-2 滴及 0.5mol/LK 3 [Fe(CN) 6 ] 1ml 。 Or take 2ml of plating solution and add it to the test tube , adjust the pH to litmus paper to be neutral , and add 1-2 drops of CH 3 COOH and 0.5 mol / LK 3 [Fe (CN) 6 ] 1ml . ， 且该沉淀溶于 HCl 及氨水中 ， 示有 Zn 2+ 存在 。 At this time, if there is a yellow-brown precipitate , and the precipitate is dissolved in HCl and ammonia water , the presence of Zn 2+ is shown . 
方法： Removal method:
电解法 ： 当 Zn 2+ 较低时 ， 用瓦楞形铁板作阴极 ， 搅拌 条件 下 ， 0.2--0.4A/dm 2 1) Electrolytic method : When Zn 2+ is low , use corrugated iron plate as cathode , under stirring condition , 0.2--0.4A / dm 2
化学沉淀法 ：当锌离子浓度较高时， 用稀 NaOH 或 CaCO 3 ( 优于 NaOH ) 将电镀液调 PH = 6.2 ; 加热至 5 0 -70℃ , 搅拌 1-2h , 再调 PH 稳定在 6.2 , 静置 4h 以上 , 过滤 , 除 Zn(OH) 2 及 CaCO 3 沉淀 ( 本法镍盐损失较大 ，非特殊情况不建议采用 ) 。 2) Chemical precipitation method : When the zinc ion concentration is high, adjust the plating solution pH to 6.2 with dilute NaOH or CaCO 3 ( better than NaOH ) ; heat to 50-70 ℃ , stir for 1-2h , and then adjust the pH to stabilize At 6.2 , let stand for more than 4h , filter , and remove Zn (OH) 2 and CaCO 3 precipitation (the nickel salt loss in this method is large , and it is not recommended in special cases ) .
铅杂质： 3 , lead impurities:
Incorporation: Dissolution of brazed parts in the plating bath.
： 类似于铬杂质对镀层质量影响 。 Impact : Similar to the effect of chromium impurities on the quality of the coating . 5mg/L 以上时 ， 得到灰色甚至黑色镀层 ， 镀层粗糙 ， 甚至无镀层 。 When the plating solution reaches 5 mg / L or more , a gray or even black plating layer is obtained , and the plating layer is rough or even has no plating layer .
方法 ：取 2ml 镀液加于试管中 ， 调 PH 至石蕊试纸呈中性 ， 加 1mol/LK 2 CrO 4 1-2 滴 。 Identification method : Take 2ml of plating solution and add it to a test tube , adjust the pH to litmus paper to be neutral , and add 1mol / LK 2 CrO 4 1-2 drops . ， 将此沉淀溶于 NaOH 中 ， 通入 H 2 S 或加入 (NH 4 ) 2 S 。 If there is a yellow precipitate , dissolve the precipitate in NaOH , pass in H 2 S or add (NH 4 ) 2 S. Pb 2+ , 可出现黑色 PbS 沉淀 。 If Pb 2+ is present in the test solution, a black PbS precipitate may appear .
方法： 低电流密度电解除去 。 Removal method: Low current density electrolytic removal .
铁杂质： 4 , iron impurities:
Incorporation method: dissolution of iron base parts in the plating solution (especially parts with complex shapes of tubular parts boxes), and iron impurities in the water.
： 铁是镀镍液中最主要的杂质 ， 主要是 钢铁 零件未及时捞出或未镀上锌的部位溶解而成 。 Impact : Iron is the main impurity in the nickel plating solution , which is mainly caused by the parts that are not removed in time or that are not plated with zinc . 。 Divalent iron can be co-deposited with nickel . PH 在 3.5 以上时 ， 此时阴极区 PH 更高 ， 三价铁可形成 Fe(OH) 3 ， 并夹杂于镀层中 ， 使镀层发脆 ， 粗糙 ， 是形成斑点及针孔主要原因 。 When the pH of the plating solution is above 3.5 , the pH of the cathode region is higher at this time , and the trivalent iron can form Fe (OH) 3 , which is mixed in the plating layer , making the plating layer brittle and rough . . 一般铁杂质在较高 PH 溶液中 ， 应在 0.03g/L 以下 ， PH 较低时不超过 0.05g/L 放不会对镀液造成影响。  Generally, iron impurities in higher pH solutions should be below 0.03g / L. When the pH is lower, it will not exceed 0.05g / L. It will not affect the plating solution.
方法： 取 2ml 镀液加于试管中 ， 加 2mol/L 硫酸使之呈明显酸性 ， 然后再多加 2-3 滴 ， 加入亚铁氰化钾 K 4 [Fe(CN) 6 ] 。 Identification method: Take 2ml of plating solution and add it to the test tube , add 2mol / L sulfuric acid to make it obviously acidic , then add 2-3 drops , and add potassium ferrocyanide K 4 [Fe (CN) 6 ] . 2 O 2 3 滴 ， 如有 Fe 2+ 则生成亚铁氰化钾兰色沉淀 。 3 drops of H 2 O 2. If Fe 2+ is formed, a blue precipitate of potassium ferrocyanide is formed . 2ml 镀液加于 250ml 烧杯中 ， 加蒸馏水 20ml ， 加 1:1 HNO 3 ， 煮沸 ， 冷却后加 KCNS 或 NH 4 CNS( 约 15%) 数滴 ， 摇匀静置 ， 此时出现红色溶液 ， 示有 Fe 3+ Or add 2ml of plating solution to a 250ml beaker , add 20ml of distilled water , add 1: 1 HNO 3 , boil , add a few drops of KCNS or NH 4 CNS ( about 15%) after cooling , shake and let stand , at this time a red solution appears , Shown with Fe 3+ . NH4F 或 KF 后 ， 颜色消失 。 For example, after adding NH4F or KF in this solution , the color disappears .
3+ +3CNS - =Fe(CNS) 3 Fe 3+ + 3CNS- = Fe (CNS) 3 Fe(CNS) 3 ; Fe (CNS) 3 - =[FeF 6 ] 3- + 3CNS - + F- = [FeF 6 ] 3- + 3CNS-
方法： Removal method:
电解 ： :0.4A/dm 2 1) Electrolysis : 0.4A / dm 2
化学法 ： 稀硫酸调 PH 2) Chemical method : pH adjustment with dilute sulfuric acid 3 左右 ， 加 30% H 2 O 2 = 3 or so , add 30% H 2 O 2 65-70℃, 使 Fe 2+ 转化为 Fe 3+ 0.5-1mol / L, heating at 65-70 ℃ to convert Fe 2+ to Fe 3+ 加热搅拌 除去多余的 H 2 O 2 ， 用 BaCO 3 或 NiCO 3 ,Ba(OH) 2 调 PH 至 6 ， 搅拌 2h ， 重复调 PH, 使之稳定在 6 ， 静置过滤 。 And heat and stir to remove excess H 2 O 2 , adjust the pH to 6 with BaCO 3 or NiCO 3 , Ba (OH) 2 , stir for 2 h , repeatedly adjust the pH to stabilize it at 6 and let it stand for filtration .
铬杂质 ： 5 , chromium impurities :
Mixed in: hexavalent chromium tank chromium mist, hexavalent chromium entrapped by the hanger.
： 铬是镀镍液中最敏感的金属元素之一 ， 微量铬的存在 ， 使镀液分散能力 ， 电流效率降低 ， 镀层发灰 ， 结合力下降 。 Impact : Chromium is one of the most sensitive metal elements in the nickel plating solution. The presence of trace chromium will reduce the dispersion ability of the plating solution , reduce the current efficiency, reduce the grayness of the coating, and reduce the binding force . 3-5ml/L 时 ， 在低电流密度区镍层难以沉积 ， 如含量达到 5ml/L 以上时 ， 就会使镀层产生条纹 ， 引起镀层剥落 。 When the content of hexavalent chromium reaches 3-5ml / L , it is difficult to deposit the nickel layer in the low current density region . If the content exceeds 5ml / L , it will cause streaks in the plating layer and cause the plating layer to peel . 。 No plating at low current density . PH = 3.5 以上就会产生沉淀 ， 使镀镍层粗糙 。 Precipitation of trivalent chromium above PH = 3.5 will make the nickel coating rough .
： 取 2ml 镀液加于试管中 ， 加 3mol/L NaOH 至偏碱性 ， 加 H 2 O 2 (30%) 2-3 滴 ， 加热至沸 ， 有铬存在则变成黄色溶液 ， 冷至室温 ， 用 1mol/L Identification : Add 2ml of plating solution to the test tube , add 3mol / L NaOH to the alkaline , add 2-3 drops of H 2 O 2 (30%) , heat to boiling , turn yellow solution in the presence of chromium , and cool to At room temperature , use 1mol / L ， 加乙醚 3-5 滴 ， 再慢慢滴加 H 2 O 2 ， 同时摇动试管 ， 乙醚层有兰色出现 ， 则有 Cr 6+ 存在 。 Sulfuric acid was acidified to acidity , 3-5 drops of ether were added , and then H 2 O 2 was slowly added dropwise . While shaking the test tube , a blue color appeared in the ether layer , and Cr 6+ was present .
Cr 2 O 7 2- 占优势 ， 在碱性溶液中 CrO 4 2- 占优势 ， 通过调 PH 使之相互转化 ， 在酸性溶液中 Cr 2 O 7 2- 是强氧化剂 ， 此时加 H 2 O 2 则 Cr 6+ Cr 2 O 7 2- dominates in acid solutions, CrO 4 2- dominates in alkaline solutions, and they are converted into each other by adjusting the pH . Cr 2 O 7 2- is a strong oxidant in acid solutions . At this time, add H 2 O 2 then Cr 6+ Cr 3+ 而出现兰色 。 It is reduced to Cr 3+ and appears blue .
方法： 将六价铬还原成三价铬 ， 然后用化学沉淀法去除 。 Removal method: Hexavalent chromium is reduced to trivalent chromium , and then removed by chemical precipitation .
连二亚硫酸钠 ( 保险粉 ) 法 ： 2H 2 CrO 4 +Na 2 S 2 O 4 +H 2 SO 4 =Na 2 SO 4 +Cr 2 (SO 4)3 +4H 2 O A , sodium dithionite ( safety powder ) method : 2H 2 CrO 4 + Na 2 S 2 O 4 + H 2 SO 4 = Na 2 SO 4 + Cr 2 (SO 4) 3 + 4H 2 O
2 (SO 4 ) 3 +6NaOH=Cr(OH) 3 ↓+3Na 2 SO 4 Cr 2 (SO 4 ) 3 + 6NaOH = Cr (OH) 3 ↓ + 3Na 2 SO 4
PH 至 3 ， 再按 0.2-0.4g/L 量加入保险粉 ， 加热 60-70℃ ， 搅拌 1h ， 用稀 NaOH 或 Ba(OH) 2 ， 也可用 NiCO 3 或 BaCO 3 调 PH ， 使其稳定在 6.2 ， 静置 2-3h ， 过滤 。 Adjust the pH to 3 with dilute sulfuric acid , add insurance powder at 0.2-0.4g / L , heat at 60-70 ° C , stir for 1h , use dilute NaOH or Ba (OH) 2 , or adjust the pH with NiCO 3 or BaCO 3 It is stable at 6.2 , left to stand for 2-3h , and filtered . 0.2-0.4mol/L 量加入 H 2 O 2 (30%) 以除去过量保险粉 ， 调 PH 至工艺规范 ， 试镀 。 Finally, add H 2 O 2 (30%) in an amount of 0.2-0.4 mol / L to remove excess insurance powder , adjust the pH to the process specification , and try plating .
， 硫酸亚铁法 ： 六价铬被还原成三价铬 ， 二价铬被氧化成三价铬 ， 提高 PH B , ferrous sulfate method : hexavalent chromium is reduced to trivalent chromium , and divalent chromium is oxidized to trivalent chromium to increase pH ， 分别生成 Fe(OH) 3 或 Cr(OH) 3 沉淀 ， 加入 H 2 O 2 , 使多余二价铁氧化成三价铁 。 Value , respectively, Fe (OH) 3 or Cr (OH) 3 precipitates , and H 2 O 2 is added to oxidize the excess ferric iron to ferric iron .
2 Cr 2 O 7 +6FeSO 4 +6H 2 SO 4 =Cr(SO 4 ) 3 +3Fe(SO 4 ) 3 +7H 2 O H 2 Cr 2 O 7 + 6FeSO 4 + 6H 2 SO 4 = Cr (SO 4 ) 3 + 3Fe (SO 4 ) 3 + 7H 2 O
PH = 3 ， 按 1g/L 加入 FeSO 4 ， 搅拌 1h ， 加入 H 2 O 2 (30%) 1mol/L ， 调 PH 值至 6.2 ， 加热 60-70℃ ， 并保温 4h( 目的是便于沉淀 ， 凝聚 ) 。 Dilute sulfuric acid to adjust pH = 3 , add FeSO 4 at 1g / L , stir for 1h , add H2O2 (30%) 1mol / L , adjust pH to 6.2 , heat 60-70 ° C , and keep it for 4h (the purpose is to facilitate Precipitation , condensation ) . ， 重复调 PH 使之稳定在 6.2 ， 静置 2-3h ， 过滤 ， 最后用硫酸调 PH 至正常 。 Stir , repeatedly adjust the pH to stabilize it at 6.2 , let it stand for 2-3h , filter , and finally adjust the pH to normal with sulfuric acid .
， 高锰酸钾法 ： 调 PH=3 ， 加热至 60℃ ， 加高锰酸钾 (10%) 至呈紫色 ， 加 2-6g/L 碳酸铅 ( 醋酸铅 ) ， 搅拌 ， 用 NaOH 调 PH=5-5.5 ， 静置 2h ， 过滤 。 C , Potassium permanganate method : adjust PH = 3 , heat to 60 ° C , add potassium permanganate (10%) to purple , add 2-6g / L lead carbonate ( lead acetate ) , stir , adjust pH = with NaOH 5-5.5 , let stand for 2h , filter .
6 , aluminum impurities:
Mixing in: Dissolution of zinc-aluminum alloy die-castings of aluminum substrate parts boxes that fall into the plating tank.
10ppm ，开始影响镀层质量，光泽不良，高电流密度部分易烧焦 Impact: The content of aluminum in the plating solution reaches 10ppm , which begins to affect the quality of the coating, poor gloss, and the high current density part is easy to burn
PH 值调高到 5.0 ，生成氢氧化铝沉淀过滤除去。 Removal: The pH value of the plating solution is increased to 5.0 , and the aluminum hydroxide precipitate is formed and removed by filtration.
7 , calcium impurities:
Mixing way: water is brought in, oil removal process is brought in.
Effect: Calcium sulfate particles are generated in the plating solution, and are mixed into the coating to make the coating rough.
PH 值调高至 5 ，并保证镀液温度在 60 ℃ 以上（此时若镀液 PH 值偏低，会产生反效果），加入 2 倍钙含量的氟氢酸钠（氟氢酸钠要提前溶解），充分搅拌后，静置，用活性炭过滤。 Removal method: increase the pH value of the plating solution to 5 and ensure that the temperature of the plating solution is above 60 ℃ (at this time, if the pH value of the plating solution is low, it will have an adverse effect). Sodium fluorohydrogen should be dissolved in advance), after stirring well, let it stand and filter with activated carbon.
8 , sodium and potassium impurities:
Mixing way: bring in the pre-plating process and bring in water.
Impact: The high sodium and potassium content in the plating solution will make the coating brittle.
Removal method: None. Therefore, special attention should be paid to washing thoroughly after pre-treatment to avoid bringing sodium and potassium into the nickel plating bath.
硝酸根 杂质： 9 , nitrate impurities:
因硫酸镍不纯而带入 ，电镀挂具退除镀层后水洗不良带入，化学抛光液酸雾飞溅落入镀液。 Mixing in: brought in due to impure nickel sulfate . After the plating rack removes the coating, it is brought in badly, and the acid mist of the chemical polishing solution splashes into the plating solution.
对镀镍极有害 ， 微量的硝酸根可使镀层 呈 灰色 ， 脆性增大 。 Impact: It is extremely harmful to nickel plating . A trace amount of nitrate can make the coating appear gray and increase brittleness . 0.2g/L 以上 ， 镀层呈黑色 ， 阴极电流效率显著下降 。 When the content is more than 0.2g / L , the coating is black , and the cathode current efficiency is significantly reduced .
Identification: Judging by Hastelloy.
高电流密度时 ， 硝酸根在阴极还原为铵 ( 为避免镍的沉积可调 PH=3) 。 Removal method: strong current electrolysis, because at high current density , nitrate is reduced to ammonium at the cathode ( adjustable PH = 3 to avoid nickel deposition ) .
10 , cyanide impurities:
Incorporation method: The workpiece is not washed well after cyanide copper plating
Impact: Decrease the leveling of the coating, at the same time reduce the tolerance of the coating to metal impurities, and cause the coating to change color and reduce adhesion.
PH 值调值 5 以上，加入双氧水使氰化物分解，升温 60 ℃ 以上，打气搅拌后，活性炭过滤。 Exclusion method: adjust the pH value of the plating solution to 5 or more, add hydrogen peroxide to decompose the cyanide, raise the temperature to 60 ℃ or higher, and stir the air, then filter the activated carbon.
11 , phosphate impurities:
Mixing way: bring in chemical polishing liquid, bring in pre-treatment solution
Impact: Reduce the limiting current density of the plating solution, which is easy to burn in the high current area. At the same time, nickel phosphate particles inclusions such as plating are generated, making the plating rough and increasing stress
PH 调高至 5.5 ，生成磷酸镍除去。 Exclusion method: Adjust the pH of the plating solution to 5.5 to remove nickel phosphate.
12 , Ammonium salt impurities:
Mixing way: Pretreatment solution is brought into the nickel plating tank, and deplating solution is brought into the nickel plating tank
Influence, the content of the ammonium salt impurities is too high will reduce the brightness and levelness of the coating, and at the same time increase the coating stress.
Exclusion method: add new solution to reduce the unit content of ammonium salt impurities in the plating solution.
13 , peroxide impurities:
Incorporation method: Residual oxidant used in the treatment of plating bath impurities
Impact: Residual peroxides in the plating solution easily lead to non-plating in the lower region of the coating, the coating becomes brittle, it is easy to burn, and it is easy to form pinholes.
60 ℃ ，强烈搅拌后，小电流电解。 Exclusion method: Raise the temperature to 60 ℃ , and stir it at a low current.
14 , common organic impurities:
Mixing way: the grease brought in by the workpiece, the air is not filtered and the organic matter in the pump is brought in when the air is stirred, excessive additives, additive decomposition products. The plating tank lining material and filter material are dissolved in the plating solution.
Impact: Reduce the brightness of the plating layer, form pinholes, and make the high current area easy to burn.
Identification: When the plating solution is left to stand, the Hastelloy film is played. Black stripes appear on the boundary line of the Hastelloy film, indicating that there is organic pollution in the plating solution.
Exclusion method: activated carbon filtration. To enhance the effect, it is often treated with strong oxidants such as hydrogen peroxide before filtering.
15 , amine organic impurities:
Mixing way: Add it by mistake. For electroless nickel plating products, the cleaning after chemical nickel is not complete. The lining material and filter material of the plating bath are dissolved in the plating solution.
Impact: Reduce the brightness of the plating layer, form pinholes, and make the high current area easy to burn.
PH 值调至 1 以下，搅拌，加亚硝酸盐 7g/l ， 1.5-2A/dm 2 电解，达 15Adm 2 /L 后，将镀液恢复正常即可。 Exclusion method: Adjust the pH value to below 1 with sulfuric acid , stir, add 7g / l of nitrite , electrolyze at 1.5-2A / dm 2 to 15Adm 2 / L , then restore the plating solution to normal.
固体颗粒杂质： 16 , solid particle impurities:
Mixing way: peeling of the inner lining of the plating tank, entrainment of filter materials, and introduction of gas agitation
Impact: Inclusions, such as pits, form pits and reduce plating stress.
Exclusion method: activated carbon filtration.
The main impurities mixed in the nickel plating solution and the countermeasures are as described above. To effectively prevent the pollution of impurities, the entire process of manufacturing and plating processes of nickel-plated workpieces must be controlled. Pay attention to each production link and strictly control each operation step. Try to keep impurities to a minimum.