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Electroplating, also known as electrochemical deposition or electrodeposition, is a process for producing a
metal A metal (from ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electrical resistivity and conductivity, e ...
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 A cathode is the electrode from which a conventional current leaves a polarized electrical device. This definition can be recalled by using the mnemonic ''CCD'' for ''Cathode Current Departs''. A conventional current describes the direction in whi ...
(negative
electrode An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or air). Electrodes are essential parts of batteries that can consist of a variety of materials ...
) of an electrolytic cell; the
electrolyte An electrolyte is a medium containing ions that is electrically conducting through the movement of those ions, but not conducting electrons. This includes most soluble salts, acids, and bases dissolved in a polar solvent, such as water. Upon ...
is a
solution Solution may refer to: * Solution (chemistry), a mixture where one substance is dissolved in another * Solution (equation), in mathematics ** Numerical solution, in numerical analysis, approximate solutions within specified error bounds * Solutio ...
of a
salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quant ...
of the metal to be coated; and the
anode An anode is an electrode of a polarized electrical device through which conventional current enters the device. This contrasts with a cathode, an electrode of the device through which conventional current leaves the device. A common mnemonic is ...
(positive electrode) is usually either a block of that metal, or of some inert conductive material. The current is provided by an external
power supply A power supply is an electrical device that supplies electric power to an electrical load. The main purpose of a power supply is to convert electric current from a source to the correct voltage, current, and frequency to power the load. As ...
. Electroplating is widely used in industry and decorative arts to improve the surface qualities of objects—such as resistance to abrasion and
corrosion Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engi ...
, lubricity,
reflectivity The reflectance of the surface of a material is its effectiveness in reflecting radiant energy. It is the fraction of incident electromagnetic power that is reflected at the boundary. Reflectance is a component of the response of the electronic ...
,
electrical conductivity Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that measures how strongly it resists electric current. A low resistivity indicates a material that readily allows ...
, or appearance. It is used to build up thickness on undersized or worn-out parts, or to manufacture metal plates with complex shape, a process called electroforming. It is used to deposit copper and other conductors in forming printed circuit boards, and
copper interconnects In semiconductor technology, copper interconnects are interconnects made of copper. They are used in silicon integrated circuits (ICs) to reduce propagation delays and power consumption. Since copper is a better conductor than aluminium, ICs usin ...
in integrated circuits. It is also used to purify metals such as
copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pink ...
. The term "electroplating" may also be used occasionally for processes that use an electric current to achieve
oxidation Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or ...
of
anion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...
s on to a solid substrate, as in the formation of
silver chloride Silver chloride is a chemical compound with the chemical formula Ag Cl. This white crystalline solid is well known for its low solubility in water (this behavior being reminiscent of the chlorides of Tl+ and Pb2+). Upon illumination or heat ...
on silver wire to make silver/silver-chloride (AgCl) electrodes. Electropolishing, a process that uses an electric current to remove metal cations from the surface of a metal object, may be thought of as the opposite of electroplating.


Process

The electrolyte should contain positive ions (cations) of the metal to be deposited. These cations are reduced at the cathode to the metal in the zero valence state. For example, the electrolyte for copper plating can be a solution of copper(II) sulphate, which dissociates into Cu2+ cations and anions. At the cathode, the Cu2+ is reduced to metallic copper by gaining two electrons. When the anode is made of the coating metal, the opposite reaction may occur there, turning it into dissolved cations. For example,
copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pink ...
would be oxidized at the anode to Cu2+ by losing two electrons. In this case, the rate at which the anode is dissolved will be equal to the rate at which the cathode is plated and thus the ions in the electrolyte bath are continuously replenished by the anode. The net result is the effective transfer of metal from the anode to the cathode. The anode may instead be made of a material that resists electrochemical oxidation, such as
lead Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cut, ...
or
carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon ma ...
.
Oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...
,
hydrogen peroxide Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscous than water. It is used as an oxidizer, bleaching agent, and antiseptic, usually as a dilute solution (3 ...
, or some other byproducts are then produced at the anode instead. In this case, ions of the metal to be plated must be periodically replenished in the bath as they are drawn out of the solution. The plating is most commonly a single metallic element, not an
alloy An alloy is a mixture of chemical elements of which at least one is a metal. Unlike chemical compounds with metallic bases, an alloy will retain all the properties of a metal in the resulting material, such as electrical conductivity, ductili ...
. However, some alloys can be electrodeposited, notably
brass Brass is an alloy of copper (Cu) and zinc (Zn), in proportions which can be varied to achieve different mechanical, electrical, and chemical properties. It is a substitutional alloy: atoms of the two constituents may replace each other wi ...
and solder. Plated "alloys" are not "true alloys" (solid solutions), but rather they are tiny crystals of the elemental metals being plated. In the case of plated solder, it is sometimes deemed necessary to have a true alloy, and the plated solder is melted to allow the tin and lead to combine into a true alloy. The true alloy is more corrosion resistant than the as-plated mixture. Many plating baths include
cyanide Cyanide is a naturally occurring, rapidly acting, toxic chemical that can exist in many different forms. In chemistry, a cyanide () is a chemical compound that contains a functional group. This group, known as the cyano group, consists of ...
s of other metals (such as potassium cyanide) in addition to cyanides of the metal to be deposited. These free cyanides facilitate anode corrosion, help to maintain a constant metal ion level and contribute to conductivity. Additionally, non-metal chemicals such as
carbonate A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate ...
s and
phosphate In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid . The phosphate or orthophosphate ion is derived from phosph ...
s may be added to increase conductivity. When plating is not desired on certain areas of the substrate, ''stop-offs'' are applied to prevent the bath from coming in contact with the substrate. Typical stop-offs include tape, foil,
lacquer Lacquer is a type of hard and usually shiny coating or finish applied to materials such as wood or metal. It is most often made from resin extracted from trees and waxes and has been in use since antiquity. Asian lacquerware, which may be c ...
s, and waxes. The ability of a plating to cover uniformly is called '; the better the throwing power the more uniform the coating.


Strike

Initially, a special plating deposit called a ''strike'' or ''flash'' may be used to form a very thin (typically less than 0.1 μm thick) plating with high quality and good adherence to the substrate. This serves as a foundation for subsequent plating processes. A strike uses a high current density and a bath with a low ion concentration. The process is slow, so more efficient plating processes are used once the desired strike thickness is obtained. The striking method is also used in combination with the plating of different metals. If it is desirable to plate one type of deposit onto a metal to improve corrosion resistance but this metal has inherently poor adhesion to the substrate, a strike can be first deposited that is compatible with both. One example of this situation is the poor adhesion of electrolytic
nickel Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow t ...
on
zinc Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...
alloys, in which case a copper strike is used, which has good adherence to both.


Pulse electroplating

The pulse electroplating or pulse electrodeposition (PED) process involves the swift alternating of the electrical potential or current between two different values resulting in a series of pulses of equal amplitude, duration and polarity, separated by zero current. By changing the pulse amplitude and width, it is possible to change the deposited film's composition and thickness. The experimental parameters of pulse electroplating usually consist of peak current/potential, duty cycle, frequency and effective current/potential. Peak current/potential is the maximum setting of electroplating current or potential. Duty cycle is the effective portion of time in a certain electroplating period with the current or potential applied. The effective current/potential is calculated by multiplying the duty cycle and peak value of the current or potential. Pulse electroplating could help to improve the quality of electroplated film and release the internal stress built up during fast deposition. A combination of the short-duty cycle and high frequency could decrease surface cracks. However, in order to maintain the constant effective current or potential, a high-performance power supply may be required to provide high current/potential and a fast switch. Another common problem of pulse electroplating is that the anode material could get plated and contaminated during the reverse electroplating, especially for the high-cost, inert electrode such as
platinum Platinum is a chemical element with the symbol Pt and atomic number 78. It is a dense, malleable, ductile, highly unreactive, precious, silverish-white transition metal. Its name originates from Spanish , a diminutive of "silver". Pla ...
. Other factors that could affect the pulse electroplating include temperature, anode-to-cathode gap and stirring. Sometimes pulse electroplating can be performed in heated electroplating bath to increase the depositing rate since the rate of almost all the chemical reaction increases exponentially with temperature per Arrhenius law. The anode-to-cathode gap is related to the current distribution between anode and cathode. Small gap to sample area ratio may cause uneven distribution of current and affect the surface topology of plated sample. Stirring may increase the transfer/diffusion rate of metal ions from bulk solution to the electrode surface. Stirring setting varies for different metal electroplating processes.


Brush electroplating

A closely related process is brush electroplating, in which localized areas or entire items are plated using a brush saturated with plating solution. The brush, typically a
stainless steel Stainless steel is an alloy of iron that is resistant to rusting and corrosion. It contains at least 11% chromium and may contain elements such as carbon, other nonmetals and metals to obtain other desired properties. Stainless steel's r ...
body wrapped with an absorbent cloth material that both holds the plating solution and prevents direct contact with the item being plated, is connected to the
anode An anode is an electrode of a polarized electrical device through which conventional current enters the device. This contrasts with a cathode, an electrode of the device through which conventional current leaves the device. A common mnemonic is ...
of a low voltage
direct current Direct current (DC) is one-directional flow of electric charge. An electrochemical cell is a prime example of DC power. Direct current may flow through a conductor such as a wire, but can also flow through semiconductors, insulators, or ev ...
power source, and the item to be plated connected to the
cathode A cathode is the electrode from which a conventional current leaves a polarized electrical device. This definition can be recalled by using the mnemonic ''CCD'' for ''Cathode Current Departs''. A conventional current describes the direction in whi ...
. The operator dips the brush in plating solution then applies it to the item, moving the brush continually to get an even distribution of the plating material. Brush electroplating has several advantages over tank plating, including portability, ability to plate items that for some reason cannot be tank plated (one application was the plating of portions of very large decorative support columns in a building restoration), low or no masking requirements, and comparatively low plating solution volume requirements. Disadvantages compared to tank plating can include greater operator involvement (tank plating can frequently be done with minimal attention), and inability to achieve as great a plate thickness.


Barrel plating

This technique of electroplating is one of the most common used in the industry for large numbers of small objects. The objects are placed in a barrel-shaped non-conductive cage, and then immersed in the chemical bath containing suspended atoms of the metal that is to be plated onto them. The barrel is then rotated, and electrical currents are run through the various pieces in the barrel which complete circuits as they touch one another. The result is a very uniform and efficient plating process, though the finish on the end products will likely suffer from abrasion during the plating process. It is unsuitable for highly ornamental or precisely engineered items.


Cleanliness

Cleanliness is essential to successful electroplating, since molecular layers of oil can prevent adhesion of the coating.
ASTM ASTM International, formerly known as American Society for Testing and Materials, is an international standards organization that develops and publishes voluntary consensus technical standards for a wide range of materials, products, systems, an ...
B322 is a standard guide for cleaning metals prior to electroplating. Cleaning includes solvent cleaning, hot alkaline detergent cleaning, electrocleaning, and acid treatment etc. The most common industrial test for cleanliness is the waterbreak test, in which the surface is thoroughly rinsed and held vertical.
Hydrophobic In chemistry, hydrophobicity is the physical property of a molecule that is seemingly repelled from a mass of water (known as a hydrophobe). In contrast, hydrophiles are attracted to water. Hydrophobic molecules tend to be nonpolar and, ...
contaminants such as oils cause the water to bead and break up, allowing the water to drain rapidly. Perfectly clean metal surfaces are
hydrophilic A hydrophile is a molecule or other molecular entity that is attracted to water molecules and tends to be dissolved by water.Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon'' Oxford: Clarendon Press. In contrast, hydrophobes are n ...
and will retain an unbroken sheet of water that does not bead up or drain off. ASTM F22 describes a version of this test. This test does not detect hydrophilic contaminants, but electroplating can displace these easily since the solutions are water-based.
Surfactant Surfactants are chemical compounds that decrease the surface tension between two liquids, between a gas and a liquid, or interfacial tension between a liquid and a solid. Surfactants may act as detergents, wetting agents, emulsion#Emulsifiers , ...
s such as
soap Soap is a salt of a fatty acid used in a variety of cleansing and lubricating products. In a domestic setting, soaps are surfactants usually used for washing, bathing, and other types of housekeeping. In industrial settings, soaps are us ...
reduce the sensitivity of the test and must be thoroughly rinsed off.


Effects

Electroplating changes the chemical, physical, and mechanical properties of the workpiece. An example of a chemical change is when
nickel Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow t ...
plating improves corrosion resistance. An example of a physical change is a change in the outward appearance. An example of a mechanical change is a change in
tensile strength Ultimate tensile strength (UTS), often shortened to tensile strength (TS), ultimate strength, or F_\text within equations, is the maximum stress that a material can withstand while being stretched or pulled before breaking. In brittle materials ...
or surface
hardness In materials science, hardness (antonym: softness) is a measure of the resistance to localized plastic deformation induced by either mechanical indentation or abrasion. In general, different materials differ in their hardness; for example hard ...
which is a required attribute in tooling industry. Electroplating of acid gold on underlying copper- or nickel-plated circuits reduces contact resistance as well as surface hardness. Copper-plated areas of mild steel act as a mask if case hardening of such areas are not desired. Tin-plated steel is chromium-plated to prevent dulling of the surface due to oxidation of tin. Electroplating, or electroless plating may be used as a way to render a metal part
radioactive Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is consi ...
, by using an aqueous solution prepared from nickel–
phosphorus Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ea ...
concentrates which contain radioactive hypophosphite 32P ions.


Specific metals


Alternatives to electroplating

There are a number of alternative processes to produce metallic coatings on solid substrates that do not involve electrolytic reduction: * Electroless plating uses a bath containing metal ions and chemicals that will reduce them to the metal by redox reactions. The reaction should be autocatalytic, so that new metal will be deposited over the growing coating, rather than precipitated as a powder through the whole bath at once. Electroless processes are widely used to deposit nickel-phosphorus or nickel-boron alloys for wear and corrosion resistance,
silver Silver is a chemical element with the symbol Ag (from the Latin ', derived from the Proto-Indo-European ''h₂erǵ'': "shiny" or "white") and atomic number 47. A soft, white, lustrous transition metal, it exhibits the highest electrical ...
for
mirror A mirror or looking glass is an object that reflects an image. Light that bounces off a mirror will show an image of whatever is in front of it, when focused through the lens of the eye or a camera. Mirrors reverse the direction of the im ...
-making,
copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pink ...
for
printed circuit board A printed circuit board (PCB; also printed wiring board or PWB) is a medium used in electrical and electronic engineering to connect electronic components to one another in a controlled manner. It takes the form of a laminated sandwich str ...
s, and many more. A major advantage of these processes over electroplating is that they can produce coatings of uniform thickness over surfaces of arbitrary shape, even inside holes, and the substrate need not be electrically conducting. Another major benefit is that they don't need power sources or especially shaped anodes. Disadvantages include lower deposition speed, consumption of relatively expensive chemicals, and limited choice of coating metals. *
Immersion coating Immersion may refer to: The arts * "Immersion", a 2012 story by Aliette de Bodard * ''Immersion'', a French comic book series by Léo Quievreux * ''Immersion'' (album), the third album by Australian group Pendulum * ''Immersion'' (film), a 2021 ...
processes exploit displacement reactions in which the subtrate metal is oxidized to soluble ions while ions of the coating metal get reduced and deposited in its place. This process is limited to very thin coatings, since the reaction stops after the subtrate has been completely covered. Nevertheless, it has some important applications, such as the electroless nickel immersion gold (ENIG) process used to obtain gold-plated electrical contacts on printed circuit boards. * Sputtering uses an electron beam or a plasma to eject microscopic particles of the metal onto the substrate in a vacuum. * Physical vapor deposition transfer the metal onto the substrate by evaporating it. *
Chemical vapor deposition Chemical vapor deposition (CVD) is a vacuum deposition method used to produce high quality, and high-performance, solid materials. The process is often used in the semiconductor industry to produce thin films. In typical CVD, the wafer (subst ...
uses a gas containing a volatile compound of the metal, which gets deposited onto the substrate as a result of a chemical reaction. * Gilding is a traditional way to attach a gold layer onto metals by applying a very thin sheet of gold held in place by an
adhesive Adhesive, also known as glue, cement, mucilage, or paste, is any non-metallic substance applied to one or both surfaces of two separate items that binds them together and resists their separation. The use of adhesives offers certain advant ...


History

It has been theorized that the first electroplating was done in
Parthian Empire The Parthian Empire (), also known as the Arsacid Empire (), was a major Iranian political and cultural power in ancient Iran from 247 BC to 224 AD. Its latter name comes from its founder, Arsaces I, who led the Parni tribe in conqu ...
era. Wilhelm König was an assistant at the
National Museum of Iraq The Iraq Museum ( ar, المتحف العراقي) is the national museum of Iraq, located in Baghdad. It is sometimes informally called the National Museum of Iraq, a recent phenomenon influenced by other nations' naming of their national muse ...
in the 1930s had observed a number of very fine silver objects from ancient Iraq, plated with very thin layers of gold, and speculated that they were electroplated. He corroborated his idea by referring to a possible Parthian battery discovered in 1938 near the metropolis of
Ctesiphon Ctesiphon ( ; Middle Persian: 𐭲𐭩𐭮𐭯𐭥𐭭 ''tyspwn'' or ''tysfwn''; fa, تیسفون; grc-gre, Κτησιφῶν, ; syr, ܩܛܝܣܦܘܢThomas A. Carlson et al., “Ctesiphon — ܩܛܝܣܦܘܢ ” in The Syriac Gazetteer last modi ...
, the capital of the Parthian (150 BC – 223 AD) and
Sasanian The Sasanian () or Sassanid Empire, officially known as the Empire of Iranians (, ) and also referred to by historians as the Neo-Persian Empire, was the last Iranian empire before the early Muslim conquests of the 7th-8th centuries AD. Named ...
(224–650 AD) empires of
Persia Iran, officially the Islamic Republic of Iran, and also called Persia, is a country located in Western Asia. It is bordered by Iraq and Turkey to the west, by Azerbaijan and Armenia to the northwest, by the Caspian Sea and Turkmeni ...
. However this has been widely debunked by researchers. Modern archaeologists, however, now generally agree that the objects seen by König were not, in fact, electroplated at all, but rather fire-gilded using mercury. There are therefore no known examples of objects from ancient Mesopotamia that can be reliably described as showing signs of electroplating. Electroplating was invented by Italian chemist Luigi Valentino Brugnatelli in 1805. Brugnatelli used his colleague
Alessandro Volta Alessandro Giuseppe Antonio Anastasio Volta (, ; 18 February 1745 – 5 March 1827) was an Italian physicist, chemist and lay Catholic who was a pioneer of electricity and power who is credited as the inventor of the electric battery and th ...
's invention of five years earlier, the voltaic pile, to facilitate the first electrodeposition. Brugnatelli's inventions were suppressed by the
French Academy of Sciences The French Academy of Sciences (French: ''Académie des sciences'') is a learned society, founded in 1666 by Louis XIV at the suggestion of Jean-Baptiste Colbert, to encourage and protect the spirit of French scientific research. It was at ...
and did not become used in general industry for the following thirty years. By 1839, scientists in Britain and
Russia Russia (, , ), or the Russian Federation, is a transcontinental country spanning Eastern Europe and Northern Asia. It is the largest country in the world, with its internationally recognised territory covering , and encompassing one-ei ...
had independently devised metal-deposition processes similar to Brugnatelli's for the copper electroplating of
printing press A printing press is a mechanical device for applying pressure to an inked surface resting upon a print medium (such as paper or cloth), thereby transferring the ink. It marked a dramatic improvement on earlier printing methods in which the ...
plates.
Boris Jacobi Moritz Hermann or Boris Semyonovich (von) Jacobi (russian: Борис Семёнович Якоби; 21 September 1801, Potsdam – 10 March 1874, Saint Petersburg) was a Prussian and Russian Imperial engineer and physicist of Jewish descent. Jac ...
in Russia not only rediscovered galvanoplastics, but developed electrotyping and
galvanoplastic sculpture Electrotyping (also galvanoplasty) is a chemical method for forming metal parts that exactly reproduce a model. The method was invented by Moritz von Jacobi in Russia in 1838, and was immediately adopted for applications in printing and several o ...
. Galvanoplastics quickly came into fashion in Russia, with such people as inventor
Peter Bagration Prince Pyotr Ivanovich Bagration (10 July 1765 – 24 September 1812) was a Georgian general and prince serving in the Russian Empire, prominent during the Napoleonic Wars. Bagration, a member of the Bagrationi dynasty, was born in Tbilisi. Hi ...
, scientist Heinrich Lenz and science fiction author Vladimir Odoyevsky all contributing to further development of the technology. Among the most notorious cases of electroplating usage in mid-19th century Russia were gigantic galvanoplastic sculptures of St. Isaac's Cathedral in
Saint Petersburg Saint Petersburg ( rus, links=no, Санкт-Петербург, a=Ru-Sankt Peterburg Leningrad Petrograd Piter.ogg, r=Sankt-Peterburg, p=ˈsankt pʲɪtʲɪrˈburk), formerly known as Petrograd (1914–1924) and later Leningrad (1924–1991), i ...
and gold-electroplated
dome A dome () is an architectural element similar to the hollow upper half of a sphere. There is significant overlap with the term cupola, which may also refer to a dome or a structure on top of a dome. The precise definition of a dome has been a m ...
of the
Cathedral of Christ the Saviour The Cathedral of Christ the Saviour ( rus, Храм Христа́ Спаси́теля, r=Khram Khristá Spasítelya, p=xram xrʲɪˈsta spɐˈsʲitʲɪlʲə) is a Russian Orthodox cathedral in Moscow, Russia, on the northern bank of the Moskv ...
in
Moscow Moscow ( , US chiefly ; rus, links=no, Москва, r=Moskva, p=mɐskˈva, a=Москва.ogg) is the capital and largest city of Russia. The city stands on the Moskva River in Central Russia, with a population estimated at 13.0 million ...
, the tallest Orthodox church in the world. Soon after, John Wright of
Birmingham Birmingham ( ) is a city and metropolitan borough in the metropolitan county of West Midlands in England. It is the second-largest city in the United Kingdom with a population of 1.145 million in the city proper, 2.92 million in the We ...
, England discovered that potassium cyanide was a suitable
electrolyte An electrolyte is a medium containing ions that is electrically conducting through the movement of those ions, but not conducting electrons. This includes most soluble salts, acids, and bases dissolved in a polar solvent, such as water. Upon ...
for gold and silver electroplating. Wright's associates, George Elkington and Henry Elkington were awarded the first patents for electroplating in 1840. These two then founded the electroplating industry in
Birmingham Birmingham ( ) is a city and metropolitan borough in the metropolitan county of West Midlands in England. It is the second-largest city in the United Kingdom with a population of 1.145 million in the city proper, 2.92 million in the We ...
from where it spread around the world. The Woolrich Electrical Generator of 1844, now in
Thinktank, Birmingham Science Museum Thinktank, Birmingham (formerly known as simply Thinktank) is a science museum in Birmingham, England. Opened in 2001, it is part of Birmingham Museums Trust and is located within the Millennium Point complex on Curzon Street, Digbeth. H ...
, is the earliest electrical generator used in industry. It was used by Elkingtons. The
Norddeutsche Affinerie Aurubis AG (formerly Norddeutsche Affinerie AG) is listed on the stock exchange and is the largest copper producer in Europe (the second largest in the world) and the largest copper recycler worldwide. Its headquarters is in Hamburg, German ...
in
Hamburg Hamburg (, ; nds, label=Hamburg German, Low Saxon, Hamborg ), officially the Free and Hanseatic City of Hamburg (german: Freie und Hansestadt Hamburg; nds, label=Low Saxon, Friee un Hansestadt Hamborg),. is the List of cities in Germany by popul ...
was the first modern electroplating plant starting its production in 1876. As the science of
electrochemistry Electrochemistry is the branch of physical chemistry concerned with the relationship between electrical potential difference, as a measurable and quantitative phenomenon, and identifiable chemical change, with the potential difference as an out ...
grew, its relationship to electroplating became understood and other types of non-decorative metal electroplating were developed. Commercial electroplating of
nickel Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow t ...
,
brass Brass is an alloy of copper (Cu) and zinc (Zn), in proportions which can be varied to achieve different mechanical, electrical, and chemical properties. It is a substitutional alloy: atoms of the two constituents may replace each other wi ...
, tin, and
zinc Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...
were developed by the 1850s. Electroplating baths and equipment based on the patents of the Elkingtons were scaled up to accommodate the plating of numerous large scale objects and for specific manufacturing and engineering applications. The plating industry received a big boost with the advent of the development of
electric generator In electricity generation, a generator is a device that converts motive power ( mechanical energy) or fuel-based power (chemical energy) into electric power for use in an external circuit. Sources of mechanical energy include steam turbines, g ...
s in the late 19th century. With the higher currents available, metal machine components, hardware, and automotive parts requiring corrosion protection and enhanced wear properties, along with better appearance, could be processed in bulk. The two World Wars and the growing
aviation Aviation includes the activities surrounding mechanical flight and the aircraft industry. ''Aircraft'' includes airplane, fixed-wing and helicopter, rotary-wing types, morphable wings, wing-less lifting bodies, as well as aerostat, lighter- ...
industry gave impetus to further developments and refinements including such processes as hard chromium plating,
bronze Bronze is an alloy consisting primarily of copper, commonly with about 12–12.5% tin and often with the addition of other metals (including aluminium, manganese, nickel, or zinc) and sometimes non-metals, such as phosphorus, or metalloids suc ...
alloy plating, sulfamate nickel plating, along with numerous other plating processes. Plating equipment evolved from manually operated
tar Tar is a dark brown or black viscous liquid of hydrocarbons and free carbon, obtained from a wide variety of organic materials through destructive distillation. Tar can be produced from coal, wood, petroleum, or peat. "a dark brown or black bi ...
-lined wooden tanks to automated equipment, capable of processing thousands of kilograms per hour of parts. One of the American physicist Richard Feynman's first projects was to develop technology for electroplating metal onto
plastic Plastics are a wide range of synthetic or semi-synthetic materials that use polymers as a main ingredient. Their plasticity makes it possible for plastics to be moulded, extruded or pressed into solid objects of various shapes. This adapta ...
. Feynman developed the original idea of his friend into a successful invention, allowing his employer (and friend) to keep commercial promises he had made but could not have fulfilled otherwise.


Hull cell

The ''Hull cell'' is a type of test cell used to semi-quantitatively check the condition of an electroplating bath. It measures useable current density range, optimization of additive concentration, recognition of impurity effects and indication of macro-throwing power capability. The Hull cell replicates the plating bath on a lab scale. It is filled with a sample of the plating solution, an appropriate anode which is connected to a
rectifier A rectifier is an electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC), which flows in only one direction. The reverse operation (converting DC to AC) is performed by an inve ...
. The "work" is replaced with a Hull cell test panel that will be plated to show the "health" of the bath. The Hull cell is a trapezoidal container that holds 267 milliliters of a plating bath solution. This shape allows one to place the test panel on an angle to the anode. As a result, the deposit is plated at a range current densities along its length, which can be measured with a hull cell ruler. The solution volume allows for a semi-quantitative measurement of additive concentration: 1 gram addition to 267 mL is equivalent to 0.5 oz/gal in the plating tank. The equation for calculating quantitative measurement of liquid additives is: *milliliters added to hull cell divided by 267 multiplied by production bath volume (gallons) equals addition of additive needed in gallons to production bath you could break it down further and multiply the gallons needed by 3785 to convert to milliliters *milliliters added to hull cell/267 • (production bath volume gallons) = addition to production bath in gallons *milliliters added to hull cell/267 • (production bath volume gallons) • 3785 = addition to production bath in milliliters


Haring–Blum cell

The Haring–Blum cell is used to determine the macro throwing power of a plating bath. The cell consists of two parallel cathodes with a fixed anode in the middle. The cathodes are at distances from the anode in the ratio of 1:5. The macro throwing power is calculated from the thickness of plating at the two cathodes when a
direct current Direct current (DC) is one-directional flow of electric charge. An electrochemical cell is a prime example of DC power. Direct current may flow through a conductor such as a wire, but can also flow through semiconductors, insulators, or ev ...
is passed for a specific period of time. The cell is fabricated out of perspex or glass.


See also

* Anodizing * Electrochemical engineering * Electrogalvanization * Electropolishing * Nanolamination


References


Bibliography

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External links

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FINISHING SERVICE ELECTROPOLISHING – REVERSE PLATING
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