Nickel electroplating is a technique of electroplating a thin layer of nickel onto a metal object. The nickel layer can be decorative, provide corrosion resistance, wear resistance, or used to build up worn or undersized parts for salvage purposes. [1] [2]
Nickel electroplating is a process of depositing nickel onto a metal part. Parts to be plated must be clean and free of dirt, corrosion, and defects before plating can begin. [3] To clean and protect the part during the plating process, a combination of heat treating, cleaning, masking, pickling, and etching may be used. [1] Once the piece has been prepared it is immersed into an electrolyte solution and is used as the cathode. The nickel anode is dissolved into the electrolyte to form nickel ions (Ni2+). Just like in other electrodeposition processes, the ions travel through the solution and deposit on the cathode. [4] [5]
The anode efficiency for nickel dissolution is close to 100%, unless the anode becomes passive due to problems with the process, in which case the efficiency drops to 0. The cathode efficiency depends on the process and varies between 90 and 97%. Due to this mismatch, during the plating the nickel concentration in the solution and the pH will slowly rise. [6] The process takes minutes to hours depending on the current density and the intended thickness of the plating. [7]
Nickel electroplating was developed in the first half of the 19th century, with notable experiments made by Golding Bird (1837) and nickel nitrate patent by Joseph Shore (1840). The first practical recipe, an aqueous solution of nickel and ammonium sulfates, was invented by Böttger in 1843 and was in use for 70 years. [8] The commercial success was achieved by Isaac Adams Jr., whose patent for a solution of nickel ammonium sulfate, while similar to Böttger's, had neutral pH that made the process easier to control. Adams enjoyed a near-monopoly in nickel plating from 1869 to 1886, when the consumption of nickel for plating reached 135 tons. [4] In the US, Remington tried to use the nickel ammonium chloride solution (1868), in the process establishing the anode construction in the form of a platinum basket filled with nickel pieces, [4] Edward Weston initiated the use of boric acid (patent issued in 1878), [9] Bancroft figured out the role of chlorides in dissolving the anode (1906). [4] [10] Finally, Oliver P. Watts in 1916 established the Watts bath, variations of which are still widely used for decorative plating, with sulfamate solutions challenging it in the engineering applications. [4]
A Watts bath, named for its inventor Oliver Patterson Watts, is an aqueous electrolyte solution for plating nickel from a nickel anode. It can deposit both bright and semi-bright nickel. Bright nickel is typically used for decorative purposes and corrosion protection. Semi-bright deposits are used for engineering applications where high corrosion resistance, ductility or electrical conductivity is important, and a high luster is not required. [2] [11] [12]
Chemical Name | Formula | Bright [11] | Semi-bright [11] | ||
---|---|---|---|---|---|
Metric | US | Metric | US | ||
Nickel sulfate | NiSO4·6H2O | 150–300 g/L | 20–40 oz/gal | 225–300 g/L | 30–40 oz/gal |
Nickel chloride | NiCl2·6H2O | 60–150 g/L | 8–20 oz/gal | 30–45 g/L | 4–6 oz/gal |
Boric acid | H3BO3 | 37–52 g/L | 5–7 oz/gal | 37–52 g/L | 5–7 oz/gal |
Type of the added brighteners and their concentrations determine the deposit appearance: brilliant, bright, semi-bright, satin.
Sulfamate nickel plating is used for many engineering applications. It is deposited for dimensional corrections, abrasion and wear resistance, high efficiency coating and corrosion protection. It is also used as an undercoat for chromium. [2] [13]
Chemical name | Formula | Bath concentration [5] | |
---|---|---|---|
Metric | US | ||
Nickel sulfamate | Ni(SO3NH2)2 | 300-450 g/L | 40–60 oz/gal |
Nickel chloride | NiCl2·6H2O | 0-30 g/L | 0–4 oz/gal |
Boric acid | H3BO3 | 30-45 g/L | 4–6 oz/gal |
All-chloride solutions allow for the deposition of thick nickel coatings. They do this because they run at low voltages. However, the deposition has high internal stresses. [2] [5]
Chemical name | Formula | Bath concentration [5] |
---|---|---|
Nickel chloride | NiCl2·6H2O | 30–40 oz/gal |
Boric acid | H3BO3 | 4–4.7 oz/gal |
A sulfate-chloride bath operates at lower voltages than a Watts bath and provide a higher rate of deposition. Although internal stresses are higher than the Watts bath, they are lower than that of an all-chloride bath. [2] [5]
Chemical name | Formula | Bath concentration [5] |
---|---|---|
Nickel sulfate | NiSO4·6H2O | 20–30 oz/gal |
Nickel chloride | NiCl2·6H2O | 20–30 oz/gal |
Boric acid | H3BO3 | 4–6 oz/gal |
An all-sulfate solution is used for electro-depositing nickel where the anodes are insoluble. For example, plating the insides of steel pipes and fittings may require an insoluble anode. [2] [12]
Chemical name | Formula | Bath concentration [5] |
---|---|---|
Nickel sulfate | NiSO4·6H2O | 30–53 oz/gal |
Boric acid | H3BO3 | 4–6 oz/gal |
A hard nickel solution is used when a high tensile strength and hardness deposit is required. [2] [5]
Chemical name | Formula | Bath concentration [5] | Metric |
---|---|---|---|
Nickel sulfate | NiSO4·6H2O | 24 oz/gal | 179.7g/L |
Ammonium chloride | NH4Cl | 3.3 oz/gal | 24.7 g/L |
Boric acid | H3BO3 | 4 oz/gal | 29.96 g/L |
"Black nickel" is a dark coating that consists primarily of nickel sulfide and metallic zinc and nickel. [14] It is typically plated on brass, bronze, or steel in order to produce a non-reflective surface. [15] This type of plating is used for decorative and military purposes and does not offer much protection. [1] [2] [15]
Chemical name | Formula | Bath concentration [15] |
---|---|---|
Nickel ammonium sulfate | NiSO4·(NH4)2SO4·6H2O | 8 oz/gal |
Zinc sulfate | ZnSO4 | 1.0 oz/gal |
Sodium thiocyanate | NaCNS | 2 oz/gal |
Decorative bright nickel is used in a wide range of applications. It offers a high luster finish, corrosion protection, and wear resistance. In the automotive industry bright nickel can be found on bumpers, rims, exhaust pipes and trim. It is also used for bright work on bicycles and motorcycles. Other applications include hand tools and household items such as lighting and plumbing fixtures, wire racks, firearms, and appliances. [11]
Modern coating technology makes deposited nickel to appear mirror-bright with no need of polishing, multi-layer applications are frequently used to improve the corrosion resistance of coated steel, zinc, copper, aluminum, and other metals. In order to prevent tarnishing, decorative electroplated nickel is typically coated with a thin layer of chromium. [8]
Engineering nickel is used where brightness is not desired. Non decorative applications provide wear and corrosion protection as well as low-stress buildups for dimensional recovery, [11] [16] nickel or its nickel alloys usually having matte or dull finish. [8] The method can be used for making nanocomposite wear resistance coatings. [17] [18]
Nickel electroforming has nickel plating applied for fabrication of nickel products. For example, nickel can be deposited onto a mandrel and then lifted off the latter, creating a nickel-only part. [8]
Nickel is also used as an undercoat for chrome or gold plating, as it improves adhesion and the longevity of the final layer. [19] [20] In manufacturing and repair, nickel electroplating can also restore worn parts to their original dimensions, allowing them to function effectively without replacement. [21]
Electroplating, also known as electrochemical deposition or electrodeposition, is a process for producing a metal coating on a solid substrate through the reduction of cations of that metal by means of a direct electric current. The part to be coated acts as the cathode of an electrolytic cell; the electrolyte is a solution of a salt whose cation is the metal to be coated, and the anode is usually either a block of that metal, or of some inert conductive material. The current is provided by an external power supply.
Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials by chemical or electrochemical reaction with their environment. Corrosion engineering is the field dedicated to controlling and preventing corrosion.
Chrome plating is a technique of electroplating a thin layer of chromium onto a metal object. A chrome plated part is called chrome, or is said to have been chromed. The chromium layer can be decorative, provide corrosion resistance, facilitate cleaning, and increase surface hardness. Sometimes a less expensive substitute for chrome, such as nickel, may be used for aesthetic purposes.
Anodizing is an electrolytic passivation process used to increase the thickness of the natural oxide layer on the surface of metal parts.
Plating is a finishing process in which a metal is deposited on a surface. Plating has been done for hundreds of years; it is also critical for modern technology. Plating is used to decorate objects, for corrosion inhibition, to improve solderability, to harden, to improve wearability, to reduce friction, to improve paint adhesion, to alter conductivity, to improve IR reflectivity, for radiation shielding, and for other purposes. Jewelry typically uses plating to give a silver or gold finish.
Copper electroplating is the process of electroplating a layer of copper onto the surface of a metal object. Copper is used both as a standalone coating and as an undercoat onto which other metals are subsequently plated. The copper layer can be decorative, provide corrosion resistance, increase electrical and thermal conductivity, or improve the adhesion of additional deposits to the substrate.
Gold plating is a method of depositing a thin layer of gold onto the surface of another metal, most often copper or silver, by a chemical or electrochemical (electroplating) process. Plating refers to modern coating methods, such as the ones used in the electronics industry, whereas gilding is the decorative covering of an object with gold, which typically involve more traditional methods and much larger objects.
Metallizing is the general name for the technique of coating metal on the surface of objects. Metallic coatings may be decorative, protective or functional.
Electrophoretic deposition (EPD), is a term for a broad range of industrial processes which includes electrocoating, cathodic electrodeposition, anodic electrodeposition, and electrophoretic coating, or electrophoretic painting. A characteristic feature of this process is that colloidal particles suspended in a liquid medium migrate under the influence of an electric field (electrophoresis) and are deposited onto an electrode. All colloidal particles that can be used to form stable suspensions and that can carry a charge can be used in electrophoretic deposition. This includes materials such as polymers, pigments, dyes, ceramics and metals.
Electrowinning, also called electroextraction, is the electrodeposition of metals from their ores that have been put in solution via a process commonly referred to as leaching. Electrorefining uses a similar process to remove impurities from a metal. Both processes use electroplating on a large scale and are important techniques for the economical and straightforward purification of non-ferrous metals. The resulting metals are said to be electrowon.
Compact disc manufacturing is the process by which commercial compact discs (CDs) are replicated in mass quantities using a master version created from a source recording. This may be either in audio form (CD-DA) or data form (CD-ROM). This process is used in the mastering of read-only compact discs. DVDs and Blu-rays use similar methods.
Electroless deposition (ED) or electroless plating is defined as the autocatalytic process through which metals and metal alloys are deposited onto conductive and nonconductive surfaces. These nonconductive surfaces include plastics, ceramics, and glass etc., which can then become decorative, anti-corrosive, and conductive depending on their final functions. Electroplating, unlike electroless deposition, only deposits on other conductive or semi-conductive materials when an external current is applied. Electroless deposition deposits metals onto 2D and 3D structures such as screws, nanofibers, and carbon nanotubes, unlike other plating methods such as Physical Vapor Deposition ( PVD), Chemical Vapor Deposition (CVD), and electroplating, which are limited to 2D surfaces. Commonly the surface of the substrate is characterized via pXRD, SEM-EDS, and XPS which relay set parameters based their final funtionality. These parameters are referred to a Key Performance Indicators crucial for a researcher’ or company's purpose. Electroless deposition continues to rise in importance within the microelectronic industry, oil and gas, and aerospace industry.
Electroless nickel-phosphorus plating, also referred to as E-nickel, is a chemical process that deposits an even layer of nickel-phosphorus alloy on the surface of a solid substrate, like metal or plastic. The process involves dipping the substrate in a water solution containing nickel salt and a phosphorus-containing reducing agent, usually a hypophosphite salt. It is the most common version of electroless nickel plating and is often referred by that name. A similar process uses a borohydride reducing agent, yielding a nickel-boron coating instead.
Electrogalvanizing is a process in which a layer of zinc is bonded to steel in order to protect against corrosion. The process involves electroplating, running a current of electricity through a saline/zinc solution with a zinc anode and steel conductor. Such Zinc electroplating or Zinc alloy electroplating maintains a dominant position among other electroplating process options, based upon electroplated tonnage per annum. According to the International Zinc Association, more than 5 million tons are used yearly for both hot dip galvanizing and electroplating. The plating of zinc was developed at the beginning of the 20th century. At that time, the electrolyte was cyanide based. A significant innovation occurred in the 1960s, with the introduction of the first acid chloride based electrolyte. The 1980s saw a return to alkaline electrolytes, only this time, without the use of cyanide. The most commonly used electrogalvanized cold rolled steel is SECC, acronym of "Steel, Electrogalvanized, Cold-rolled, Commercial quality". Compared to hot dip galvanizing, electroplated zinc offers these significant advantages:
The IsaKidd Technology is a copper electrorefining and electrowinning technology that was developed independently by Copper Refineries Proprietary Limited (“CRL”), a Townsville, Queensland, subsidiary of MIM Holdings Limited, and at the Falconbridge Limited (“Falconbridge”) now-dismantled Kidd Creek refinery that was at Timmins, Ontario. It is based around the use of reusable cathode starter sheets for copper electrorefining and the automated stripping of the deposited “cathode copper” from them.
Electroless nickel-boron coating is a metal plating process that can create a layer of a nickel-boron alloy on the surface of a solid substrate, like metal or plastic. The process involves dipping the substrate in a water solution containing nickel salt and a boron-containing reducing agent, such as an alkylamineborane or sodium borohydride. It is a type of electroless nickel plating. A similar process, that uses a hypophosphite as a reducing agent, yields a nickel-phosphorus coating instead.
Galvanic corrosion is an electrochemical process in which one metal corrodes preferentially when it is in electrical contact with another, in the presence of an electrolyte. A similar galvanic reaction is exploited in primary cells to generate a useful electrical voltage to power portable devices. This phenomenon is named after Italian physician Luigi Galvani (1737–1798).
Chemical coloring of metals is the process of changing the color of metal surfaces with different chemical solutions.
Electrochemical coloring of metals is a process in which the surface color of metal is changed by electrochemical techniques, i.e. cathodic or anodic polarization. The first method of electrochemical coloring of metals are certainly Nobili's colored rings, discovered by Leopoldo Nobili, an Italian physicist in 1826. In addition to the multicolored coatings mentioned, he has also been able to obtain monochrome coatings, and he called that technique metallocromia. Electrochemical coloring of metals based processes are black, green and blue nickel plating, black chromium plating, black rhodium plating and black ruthenium plating. Anodic oxidation of aluminum, titanium, niobium, tantalum and stainless steel are also electrochemical colouring processes. Multi-colored and green electrolytic patinas for copper and its alloys are also significant.
Isaac Adams Jr. was an American inventor and businessman, primarily notable for the invention of the first commercially viable nickel plating process.