A method of depositing a layer of nickel on a metal or some non-metal by electrolysis or chemical method is called nickel plating. Nickel plating is electroplated with nickel and electroless nickel plating. Nickel plating is nickel plating in an electrolyte composed of a nickel salt (called a main salt), a conductive salt, a pH buffer, and a wetting agent.
A method of depositing a layer of nickel on a metal or some non-metal by electrolysis or chemical method is called nickel plating. Nickel plating is electroplated with nickel and electroless nickel plating. Nickel plating is in an electrolyte consisting of a nickel salt (called a main salt), a conductive salt, a pH buffering agent, a wetting agent, a metal nickel for the anode, a cathode for the plating, and a direct current, on the cathode (plated). A uniform, dense nickel coating is deposited on top of it. Obtained from the plating solution to which the brightener is added is bright nickel, and in the electrolyte without the brightener added, dark nickel is obtained. Electroless nickel plating is a method of obtaining a nickel plating layer on a surface of a material by an autocatalytic reaction in a solution to which a metal salt, a reducing agent, or the like is added.
Nickel plating characteristics, properties, uses
(1) Characteristics, properties and uses of electroplated nickel: 1 The stability of electroplated nickel layer in air is very high. Because metal nickel has strong passivation ability, a very thin passivation film can be quickly formed on the surface. Resistant to atmospheric, alkali and certain acid corrosion. 2 Electroplated nickel crystals are extremely fine and have excellent polishing properties. The polished nickel coating gives a mirror-like finish and maintains its luster for a long time in the atmosphere. Therefore, the plating layer is often used for decoration. 3 The hardness of nickel plating is relatively high, which can improve the wear resistance of the surface of the product. In the printing industry, the plating layer is often used to improve the hardness of the lead surface. Due to the high chemical stability of metallic nickel, some chemical equipment also uses thicker town coatings to prevent corrosion by the medium. Nickel plating is also widely used in functional aspects, such as repairing worn, corroded parts and partial plating using brush plating. The electroforming process is used to make electroformed plates, record molds and other molds for the printing industry. The thick nickel plating layer has good wear resistance and can be used as a wear resistant coating. In particular, in recent years, composite plating has been developed to deposit a composite nickel coating with wear-resistant particles, which has higher hardness and wear resistance than a nickel-plated layer. If graphite or fluorinated graphite is used as the dispersed fine particles, the obtained nickel-graphite or nickel-fluorinated graphite composite plating layer has good self-lubricity and can be used as a lubricating coating. Black nickel plating is also widely used as a plating or decorative plating for optical instruments. 4 Nickel plating has a wide application surface and can be used as protective decorative coating. It protects the base material from corrosion or bright decoration on the surface of steel, zinc die casting, aluminum alloy and copper alloy. It is also often used as the middle of other coatings. The coating is further coated with a thin layer of chrome or a layer of imitation gold, which has better corrosion resistance and a more beautiful appearance. In terms of functional applications, nickel plating on parts of special industries is about 1~3mm thick, which can be used for repair purposes. In particular, in recent years, applications such as continuous casting of molds, molds for electronic component surfaces, die-casting molds for alloys, manufacture of complex aerospace engine parts, and manufacture of microelectronic components have become more widespread. 5 In electroplating, because electroplated nickel has many excellent properties, its processing volume ranks second only to electro-galvanizing, and its consumption accounts for about 10% of total nickel production.
(II) Characteristics, properties and uses of electroless nickel plating: 1 Uniform thickness uniformity and uniform plating capacity are a major feature of electroless nickel plating and one of the reasons for wide application. Electroless nickel plating avoids electroplating due to current The thickness is uneven due to uneven distribution. During electroless plating, as long as the surface of the part is in contact with the plating solution, the components consumed in the plating solution can be replenished in time, and the plating thickness of the plated part is basically the same, even for grooves, slits, and blind holes. 2. The plated parts do not seep hydrogen, no hydrogen embrittlement, and do not need to remove hydrogen after electroless nickel plating. 3. Many materials and components have better functions such as corrosion resistance and high temperature oxidation resistance than nickel plating. 4. It can be deposited on the surface of various materials, such as steel nickel-based alloys, zinc-based alloys, aluminum alloys, glass, ceramics, plastics, semiconductors, etc., thus creating conditions for improving the performance of these materials. 5. No DC motor or control equipment required for general plating is required. 6 The heat treatment temperature is low, as long as it has different corrosion resistance and wear resistance after 400 ° C or less, it is especially suitable for functional coatings of parts with complex shapes and wear and corrosion resistance. Wait
Types of nickel plating solution The types of nickel plating liquid are mainly sulfate type, chloride type, sulfamate type, citrate type, fluoroborate type and the like. Among them, the sulphate type (low chloride), which is called Watts nickel plating liquid, is most commonly used in industry. The physical properties of the nickel-plated layer obtained in several different nickel plating solutions are listed in Tables 2-3-45. The sulfamate type and fluoroborate type are suitable for thick nickel plating or electroforming. The citrate type is suitable for direct nickel plating on zinc die castings. The cost of these plating solutions is relatively high.
â—† Ordinary nickel plating (dark plating) 1. Ordinary plating is also called dark nickel process. According to the performance and use of the plating solution, ordinary nickel plating can be divided into low concentration pre-liquid, ordinary plating liquid, watt liquid and barrel plating liquid. Pre-plating solution: Pre-plating ensures that the bonding force of the layer with the copper-iron substrate and the subsequent copper-plated layer is good. Ordinary liquid: The plating solution has good conductivity and can be electroplated at a lower temperature, which saves energy and is convenient to use. Watt liquid: to meet the plating of small parts, but the plating solution must have good conductivity and coverage. 2. Preparation method of plating solution According to the volume calculation, the required chemicals are dissolved in hot water, mixed in a container, diluted with distilled water to the required volume, left to the required volume, and allowed to stand for clarification. Or the filtration method introduces the plating solution into the plating tank, and then adds the already dissolved sodium dodecyl sulfate solution, stirs evenly, samples and analyzes, and after adjusting the test plating, it can be produced. 3. The purity of the anode nickel anode material for nickel plating is the most important condition in electroplating. The content of nickel is >99%. The impure anode causes contamination of the plating solution, which deteriorates the physical properties of the coating. The preferred nickel anodes for nickel plating are as follows: 1. carbon-containing nickel anode, 2. oxygen-containing nickel anode, 3. sulfur-containing nickel anode.
â—† Bright nickel plating bright nickel has many advantages, not only can save heavy polishing process, improve operating conditions, save plating and polishing materials, but also improve the hardness of the coating, and facilitate automatic production, but the bright nickel plating layer contains sulfur. Internal stress and brittleness are large, and corrosion resistance is not as good as that of dark nickel plating. To overcome these shortcomings, a multi-layer nickel plating process can be used to significantly improve the mechanical properties and corrosion resistance of the coating.
â—† High sulfur nickel The high content of high sulfur nickel is 0.12~~0.25%. This nickel has higher electrochemical activity than copper, copper tin, dark nickel, bright nickel, semi-bright nickel, and chromium. The high-sulfur nickel coating is mainly used for the intermediate layer of the anti-protective-decorative composite coating of steel and zinc alloy substrates. The principle is that the upper layer of nickel has higher sulfur content than the lower layer of semi-bright nickel, thus making the potential difference between the two layers to 100. ~~140mV, so that the double-layer nickel is transformed from the longitudinal corrosion of a single layer of nickel to the lateral corrosion, which constitutes an electrochemical protection effect on the steel substrate.
â—† Nickel seal nickel seal is to add insoluble solid particles (Sio2, etc.) with a diameter of 0.01~~1um in the general bright nickel liquid. With the help of appropriate co-deposition promoter, these particles and nickel are co-deposited to form a composite. Nickel plated. When a chromium layer is deposited on the composite nickel-plated layer surface, since the solid particles on the surface of the composite nickel plating layer are not electrically conductive, chromium cannot be deposited on the surface of the fine particles, and thus a large number of micropores are formed on the entire chromium plating layer, that is, formation Microporous chrome layer. The large amount of micropores on the surface can largely eliminate the huge internal stress in the ordinary chrome layer, thus reducing the stress corrosion of the coating. It is especially important that a large number of micropores on the chrome layer will be under the chrome layer. The nickel layer is exposed to a large area. Under the action of corrosive medium, chromium and nickel constitute an etching cell, the chromium layer is a cathode, and the exposed nickel layer at the micropores is anodized and corroded, thereby changing the corrosion mode of the large cathode and small anode. So that the corrosion current is almost dispersed on the entire nickel plating layer, thereby preventing a large amount of corrosion of grooves and pits of the large and deep through-base metal, and reducing the corrosion rate of the plating layer and developing laterally. The base metal is protected, which significantly improves the corrosion resistance of the coating.
â—† Satin nickel Satin nickel is also called satin nickel. There is no essential difference between satin nickel and nickel sealing processes. It has a satin-like appearance, and it does not shine like a bright nickel plating chrome after plating. Therefore, the human eye does not feel tired after gazing, and can be used as an anti-glare coating to avoid light reflection. Such coatings have been widely used in automotive mirrors, vehicle interior sighting parts, medical surgical instruments, machine tool parts, eyeglass frames and the like.
â—† High-stress nickel Adding an appropriate amount of additives to a specific nickel plating solution can obtain a nickel layer which is easily stressed and cracked into micro-cracks. This nickel layer is called high-stress nickel. The high-stress nickel is further coated with a layer of nickel of about 1 um on the surface of bright nickel. Due to the high internal stress of high-stress nickel, after the ordinary chromium layer of 0.2~~0.3um is regularly plated on its surface, the high-stress nickel layer generates a large amount of micro-interval at the interaction between the chromium layer and the high-stress nickel stress. Cracks and the formation of uniform microcracks on the surface of the chrome layer. Like the nickel seal, the chromium layer becomes micro-intermittent chromium, but the high-stress is obtained by micro-intermittent chromium. Under the action of the corrosive medium, these cracks are turned into numerous micro-cells, so that the corrosion current is dispersed in the micro-cracks. The corrosion performance of the entire coating is significantly improved
â—† Multi-layer nickel-plated multi-layer nickel is on the same substrate, using different plating composition and process conditions to obtain two or three layers of nickel plating, in order to not increase the thickness of the nickel layer or reduce the nickel layer. On, increase the corrosion resistance of the nickel layer. Multi-layer nickel/chromium composite layer currently used in production has double-layer nickel semi-bright nickel/bright nickel/chromium three-layer nickel semi-light nickel/high-sulfur nickel/bright nickel/chrome semi-light nickel/ Bright nickel/nickel seal/chromium (microporous chrome) semi-light nickel/bright nickel/high stress nickel/chromium (microcracked chrome)
â—† Nickel sulfamate nickel plating The main advantage of nickel sulfamate nickel plating is that the obtained plating layer has low stress and fast deposition rate, but it is expensive and used for electroless plating and nickel plating before gold plating on printed circuit boards.
â—† Citrate nickel plating The citrate nickel plating process is mainly used for electroplating of zinc die castings. The main maintenance measures are: control the ratio of nickel sulfate to citrate at 1:1.1~~1.2, the temperature should not be too high, to prevent the decomposition of citrate, strict control, pH value, the inrush current of the parts into the trough (2 ~3A/dm2) to ensure good bonding. The application of citrate nickel plating is still not widespread, and there are not many manufacturers that have successfully produced.
Causes and countermeasures of white spots appearing in electroplated nickel
1, the reason for the emergence
The white spots appearing in electroplated nickel are caused by a high-carbon substance which is produced by the heat treatment carburizing process and the pickling process during the pre-plating treatment. (1) After the normal carburization of 1018, the surface carbon (mainly Fe and C) can reach 0.8-1.2. The particles protruding in the coating are due to the incomplete cleaning of the pre-treatment, so that the particles on the surface of the workpiece fall into the plating solution. These particles which are free in the plating solution are co-deposited with nickel ions due to agitation during the electroplating process.
(2) The holes not covered in the plating layer are mainly caused by excessive corrosion (surface decarburization) in the pretreatment pickling process. The main component of the electroplating plant pickling solution is HCl 1:1; H2SO4 (98%) 50 mL / L; the formula can be used for ordinary carbon steel, and the concentration of high carbon steel is too high. The higher the carbon content, the more severe the pickling reaction. After the surface is decarburized, it has a great influence on the electrical conductivity of the workpiece and the adhesion of the coating. The holes in the coating are actually caused by poor conductivity (or poor adhesion) of the high carbon portion, which is difficult to cover.
2, the solution
(1) The pre-treatment cleaning process is improved, and the ultrasonic cleaning method is adopted to make the particles having poor adhesion after carburization fall off during washing.
(2) Filter the plating solution in time.
(3) Improve the pickling process: mainly to reduce the concentration of the pickling solution, add a suitable corrosion inhibitor and properly control the pickling time to avoid over-corrosion. By adopting the above measures, the problem of electroplating white spots on the product has been fundamentally solved.
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