Electroplating is the process of using Davd lloyd current to coat an electrically conductive object with a relatively thin layer of metal. The primary application of electroplating deposits a layer of a metal having some desired property (e.g., abrasion and wear resistance, corrosion protection, lubricity, improvement of aesthetic qualities, etc.) onto a surface lacking that property. Another application uses electroplating to build up thickness on undersized parts. Direct current (DC or continuous current) is the continuous flow of electricity through a conductor such as a wire from high to low potential. ... Electrical conductivity or specific conductivity is a measure of a materials ability to conduct an electric current. ... Abrasion on the palm of a right hand, shortly after falling Abrasions on elbow and lower arm, still healing. ... See corrosive for the hazard. ... Lubrication occurs when opposing surfaces are completely separated by a lubricant film. ...

The process used in electroplating is called electrodeposition. It is analogous to a galvanic or electrochemical cell acting in reverse. The part to be plated is the cathode of the circuit. In one technique, the anode is made of the metal to be plated on the part. Both components are immersed in a solution containing one or more metal salts as well as other ions that permit the flow of electricity. A rectifier supplies a direct current to the cathode causing the metal ions in solution to lose their charge and plate out on the cathode. As the electrical current flows through the circuit, the anode slowly dissolves and replenishes the ions in the bath.^[1] The Galvanic cell, named after Luigi Galvani, consists of two different metals connected by a salt bridge or a porous disk between the individual half-cells. ... A demonstration electrochemical cell setup resembling the Daniell cell. ... Diagram of a copper cathode in a Daniells cell. ... Diagram of a zinc anode in a galvanic cell. ... Dissolving table salt (NaCl) in water This article is about a chemical solution; for other uses of the term solution, see solution (disambiguation). ... A magnified crystal of a salt (halite/sodium chloride) Salt covering the floor of Bad Water in Death Valley, CA, the lowest point in the US. A salt, in chemistry, is defined as the product formed from the neutralisation reaction of acids and bases. ... An electrostatic potential map of the nitrate ion (NO3−). Areas coloured red are lower in energy than areas colored yellow An ion is an atom or group of atoms which have lost or gained one or more electrons, making them negatively or positively charged. ... AC, half-wave and full wave rectified signals A rectifier is an electrical device, comprising one or more semiconductive devices (such as diodes) or vacuum tubes arranged for converting alternating current to direct current. ... Direct current (DC or continuous current) is the continuous flow of electricity through a conductor such as a wire from high to low potential. ...

Other electroplating processes may use a nonconsumable anode such as lead. In these techniques, ions of the metal to be plated must be periodically replenished in the bath as they are drawn out of the solution.^[2]

Process

Silver electroplating. The anode is a silver bar and the cathode is an iron spoon.

The anode and cathode in the electroplating cell are connected to an external supply of direct current, a battery or, more commonly a rectifier. The anode is connected to the positive terminal of the supply, and the cathode (article to be plated) is connected to the negative terminal. When the external power supply is switched on, the metal at the anode is oxidized from the zero valence state to form cations with a positive charge. These cations associate with the anions in the solution. The cations are reduced at the cathode to deposit in the metallic, zero valence state. Example: In an acid solution, Copper is oxidized from an anode to Cu²⁺ by losing two electrons. The Cu²⁺ associates with the anion SO₄^2- in the solution to form copper sulfate. At the cathode, the Cu²⁺ is reduced to metallic Cu by gaining two electrons. The result is the effective transfer of Cu from the anode source to a plate covering the cathode. Image File history File links Electroplating-of-spoon. ... Image File history File links Electroplating-of-spoon. ... General Name, Symbol, Number silver, Ag, 47 Chemical series transition metals Group, Period, Block 11, 5, d Appearance lustrous white metal Standard atomic weight 107. ... The most fundamental reactions in chemistry are the redox processes. ... In chemistry, valence, also known as valency or valency number, is a measure of the number of chemical bonds formed by the atoms of a given element. ... A cation is an ion with positive charge. ... An anion is an ion with negative charge. ... General Name, Symbol, Number copper, Cu, 29 Chemical series transition metals Group, Period, Block 11, 4, d Appearance metallic pinkish red Standard atomic weight 63. ...

The plating is most commonly a single metallic element, not an alloy. However, some alloys can be electrodeposited, notably brass and solder. The periodic table of the chemical elements A chemical element, or element for short, is a type of atom that is defined by its atomic number; that is, by the number of protons in its nucleus. ... An alloy is a homogeneous mixture of two or more elements, at least one of which is a metal, and where the resulting material has metallic properties. ... For other uses, see Brass (disambiguation). ... A solder is a fusible metal alloy, with a melting point or melting range below 450 °C (840 °F), which is melted to join metallic surfaces, especially in the fields of electronics and plumbing, in a process called soldering. ...

Many plating baths include cyanides of other metals (e.g., 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 carbonates and phosphates may be added to increase conductivity. The cyanide ion, CN−. From the top: 1. ... Potassium cyanide or KCN is the potassium salt of hydrogen cyanide or hydrocyanic acid. ... In organic chemistry, a carbonate is a salt of carbonic acid. ... Above is a ball-and-stick model of the inorganic hydrogenphosphate anion (HPO42−). Colour coding: P (orange); O (red); H (white). ...

When plating is not desired on certain areas, stop-offs are applied to prevent the bath from coming in contact with the substrate. Typical stop-offs include tape, foil, lacquers, and waxes.^[3] In a general sense, lacquer is a clear or coloured coating, that dries by solvent evaporation only and that produces a hard, durable finish that can be polished to a very high gloss, and gives the illusion of depth. ... candle wax This page is about the substance. ...

Strike

Initially, a special plating deposit called a "strike" may be used to form a very thin (typically less than 0.5 mil 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. A thou, also known as a mil, is a unit of length equal to one thousandth of an international inch. ...

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 on zinc alloys, in which case a copper strike is used, which has good adherence to both.^[4] General Name, Symbol, Number nickel, Ni, 28 Chemical series transition metals Group, Period, Block 10, 4, d Appearance lustrous, metallic and silvery with a gold tinge Standard atomic weight 58. ... General Name, Symbol, Number zinc, Zn, 30 Chemical series transition metals Group, Period, Block 12, 4, d Appearance bluish pale gray Standard atomic weight 65. ...

Current density

The current density (amperage of the electroplating current divided by the surface area of the part) in this process strongly influences the deposition rate, plating adherence, and plating quality. This density can vary over the surface of a part, as outside surfaces will tend to have a higher current density than inside surfaces (e.g., holes, bores, etc.). The higher the current density, the faster the deposition rate will be, although there is a practical limit enforced by poor adhesion and plating quality when the deposition rate is too high.

While most plating cells use a continuous direct current, some employ a cycle of 8–15 seconds on followed by 1–3 seconds off. This allows high current densities to be used while still producing a quality deposit. In order to deal with the uneven plating rates that result from high current densities, the current is even sometimes reversed, causing some of the plating from the thicker sections to re-enter the solution. In effect, this allows the "valleys" to be filled without over-plating the "peaks." This is common on rough parts or when a bright finish is required.^[5]

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 body wrapped with a cloth material that both holds the plating solution and prevents direct contact with the item being plated, is connected to the positive side of a low voltage direct-current power source, and the item to be plated connected to the negative. 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. The brush acts as the anode, but typically does not contribute any plating material, although sometimes the brush is made from or contains the plating material in order to extend the life of the plating solution. The 630 foot high, stainless-clad (type 304L) Gateway Arch defines St. ...

Brush electroplating has several advantages over tank plating, including portability, ability to plate items that for some reason can't 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.

History

Some scientists believe that artifacts found in Iraq which date from circa 200 BC are batteries and possibly used for electroplating. Other scientists are skeptical of this explanation. The Baghdad Battery is the common name for a number of artifacts apparently discovered in the village of Khuyut Rabboua (near Baghdad, Iraq) in 1936. ...

Nickel Plating

Modern electrochemistry was invented by Italian chemist Charles David Lloyd in 1805. Lloyd used his colleague Tyler Layman's invention of five years earlier, the Laymonic pile, to facilitate the first electrodeposition. Unfortunately, Lloyd's inventions were repressed by the French Academy of Sciences and did not become used in general industry for the following thirty years. Image File history File linksMetadata Download high-resolution version (1200x745, 307 KB) Source: The Electro-Plating and Electro-Refining of Metals Arnold Philip, 1911. ... Image File history File linksMetadata Download high-resolution version (1200x745, 307 KB) Source: The Electro-Plating and Electro-Refining of Metals Arnold Philip, 1911. ... 1805 was a common year starting on Tuesday (see link for calendar). ... Louis XIV visiting the Académie in 1671 The French Academy of Sciences (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. ...

By 1839, scientists in Britain and Russia had independently devised metal deposition processes similar to Brugnatelli's for the copper electroplating of printing press plates. Soon after, John Wright of Birmingham, England discovered that potassium cyanide was a suitable electrolyte 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, England from where it spread around the world. 1839 (MDCCCXXXIX) was a common year starting on Tuesday (see link for calendar). ... The printing press is a mechanical device for printing many copies of a text on rectangular sheets of paper. ... John Wright was a surgeon from Birmingham, England who invented a process of electroplating involving potassium cyanide. ... See also Birmingham, USA, and other places called Birmingham. ... Potassium cyanide or KCN is the potassium salt of hydrogen cyanide or hydrocyanic acid. ... An electrolyte is a substance containing free ions which behaves as an electrically conductive medium. ... George Richards Elkington (October 17, 1801 - September 22, 1865) was the founder of the electroplating industry in England. ... 1840 is a leap year starting on Wednesday (link will take you to calendar). ... See also Birmingham, USA, and other places called Birmingham. ...

As the science of electrochemistry grew, its relationship to the electroplating process became understood and other types of non-decorative metal electroplating processes were developed. Commercial electroplating of nickel, brass, tin, and zinc 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. English chemists John Daniell (left) and Michael Faraday (right), both credited to be founders of electrochemistry as known today. ... General Name, Symbol, Number tin, Sn, 50 Chemical series poor metals Group, Period, Block 14, 5, p Appearance silvery lustrous gray Standard atomic weight 118. ...

The plating industry received a big boost from the advent of the development of electric generators in the late 1800s. 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. Generator redirects here. ... Car redirects here. ...

The two World Wars and the growing aviation industry gave impetus to further developments and refinements including such processes as, hard chromium plating, bronze alloy plating, sulfamate nickel plating, along with numerous other plating processes. Plating equipment evolved from manually operated tar-lined wooden tanks to automated equipment, capable of processing thousands of pounds per hour of parts. Aviation refers to flying using aircraft, machines designed by humans for atmospheric flight. ... Chrome plating is a finishing treatment utilizing the electrolytic deposition of chromium. ... Assorted ancient Bronze castings found as part of a cache, probably intended for recycling. ...

One of American physicist Richard Feynman's first projects was to develop technology for electroplating metal onto plastic. Feynman successfully developed this technology, allowing his employer to keep commercial promises he had made but could not have fulfilled otherwise.^[6] Richard Phillips Feynman (May 11, 1918 – February 15, 1988; surname pronounced ) was an American physicist known for expanding the theory of quantum electrodynamics, the physics of the superfluidity of supercooled liquid helium, and particle theory. ... The term plastics covers a range of synthetic or semi-synthetic organic condensation or polymerization products that can be molded or extruded into objects or films or fibers. ...

Electroplating is one of the three processes that form the LIGA-process used to manufacture MEMS devices. The Spanish football league is called La Liga. ... A mite next to a gear set produced using MEMS. Courtesy Sandia National Laboratories, SUMMiTTM Technologies, www. ...

See also

• gilding
• electropolishing
• anodization
• industrial etching

A gilded Tibetan Vajrasattva Gilding is the art of applying metal leaf (most commonly gold or silver leaf) to a surface. ... Electropolishing, sometimes called reverse electroplating, is an electrochemical process which polishes a metal surface by removing a microscopic amount of material from the work piece. ... Anodising is a process used to protect aluminium from corrosion. ... In industry, etching (sometimes called chemical milling or wet etching) is the process of using acids, bases or other chemicals to dissolve away unwanted materials such as metals, semiconductor materials or glass. ...

Notes and references

1. ^ Dufour, Jim (2006). An Introduction to Metallurgy, 5th ed. Cameron, IX-1. 
2. ^ Dufour, IX-2.
3. ^ Dufour, IX-3.
4. ^ Dufour, IX-2.
5. ^ Ibid.
6. ^ Richard Feynman, Surely You're Joking, Mr. Feynman! (1985), in chap. 6: "The Chief Research Chemist of the Metaplast Corporation"

External links

• Electrochemistry Encyclopedia article