Electroplating is the process of using electrical current to reduce cations of a desired material from a solution and coat a conductive object with a thin layer of the material such as a metal, for example. Direct current ( DC) is the unidirectional flow of Electric charge. Redox (shorthand for reduction-oxidation reaction describes all Chemical reactions in which atoms have their Oxidation number ( Oxidation state An ion is an Atom or Molecule which has lost or gained one or more Valence electrons giving it a positive or negative electrical charge Electrical conductivity or specific conductivity is a measure of a material's ability to conduct an Electric current. Electroplating is primarily used for depositing a layer of material to bestowe a desired property (e. g. , abrasion and wear resistance, corrosion protection, lubricity, aesthetic qualities, etc. Corrosion means the breaking down of essential properties in a material due to Chemical reactions with its surroundings Lubrication is the process or technique employed to reduce wear of one or both surfaces in close proximity and moving relative to each another by interposing a substance called ) to a surface that otherwise lacks that property. Another application uses electroplating to build up thickness on undersized parts.

The process used in electroplating is called electrodeposition. It is analogous to a galvanic cell acting in reverse. 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 The part to be plated is the cathode of the circuit. A cathode is an Electrode through which (positive Electric current flows out of a polarized electrical device In one technique, the anode is made of the metal to be plated on the part. An anode is an Electrode through which Electric current flows into a polarized electrical device Both components are immersed in a solution called an electrolyte containing one or more dissolved metal salts as well as other ions that permit the flow of electricity. In Chemistry, a solution is a Homogeneous Mixture composed of two or more substances An electrolyte is any substance containing free Ions that behaves as an electrically conductive medium Salt is a Dietary mineral composed primarily of Sodium chloride that is essential for Animal life but toxic to most land plants An ion is an Atom or Molecule which has lost or gained one or more Valence electrons giving it a positive or negative electrical charge A rectifier supplies a direct current to the cathode causing the metal ions in the electrolyte solution to lose their charge and plate out on the cathode. A rectifier is an electrical device that converts Alternating current (AC to Direct current (DC a process known as rectification. Direct current ( DC) is the unidirectional flow of Electric charge. As the electrical current flows through the circuit, the anode slowly dissolves and replenishes the ions in the bath. [1]

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

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. Redox (shorthand for reduction-oxidation reaction describes all Chemical reactions in which atoms have their Oxidation number ( Oxidation state In Chemistry, valence, also known as valency or valency number, is a measure of the number of Chemical bonds formed by the Atoms An ion is an Atom or Molecule which has lost or gained one or more Valence electrons giving it a positive or negative electrical charge These cations associate with the anions in the solution. An ion is an Atom or Molecule which has lost or gained one or more Valence electrons giving it a positive or negative electrical charge The cations are reduced at the cathode to deposit in the metallic, zero valence state. For example, in an acid solution, copper is oxidized from an anode to Cu2+ by losing two electrons. Copper (ˈkɒpɚ is a Chemical element with the symbol Cu (cuprum and Atomic number 29 The Cu2+ associates with the anion SO42- 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.

The plating is most commonly a single metallic element, not an alloy. A chemical element is a type of Atom that is distinguished by its Atomic number; that is by the number of Protons in its nucleus. An alloy is a Solid solution or Homogeneous mixture of two or more elements, at least one of which is a Metal, which itself has However, some alloys can be electrodeposited, notably brass and solder. Brass is any Alloy of Copper and Zinc; the proportions of zinc and copper can be varied to create a range of brasses with varying properties A solder is a fusible metal Alloy with a melting point or melting range of 90 to 450 ° C (200 to 840 ° F) used in a process called

Many plating baths include cyanides of other metals (e. A cyanide is any Chemical compound that contains the cyano group (C≡N which consists of a Carbon Atom triple-bonded to a g. , potassium cyanide) in addition to cyanides of the metal to be deposited. Potassium cyanide is an Inorganic compound with the formula KCN 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. In Chemistry, a carbonate is a salt or Ester of Carbonic acid. A phosphate, an Inorganic chemical, is a salt of Phosphoric acid.

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. In a general sense lacquer is a clear or coloured Varnish, that dries by solvent evaporation and often a curing process as well that produces a hard durable finish in any Wax has traditionally referred to a substance that is secreted by Bees ( Beeswax) and used by them in constructing their [3]

### Strike

Initially, a special plating deposit called a "strike" or "flash" may be used to form a very thin (typically less than 0. 1 micrometer 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 on zinc alloys, in which case a copper strike is used, which has good adherence to both. Nickel (ˈnɪkəl is a metallic Chemical element with the symbol Ni and Atomic number 28 Zinc (ˈzɪŋk from Zink is a Metallic Chemical element with the symbol Zn and Atomic number 30 [4]

### 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. In Metallurgy, stainless steel is defined as a Steel Alloy with a minimum of 11 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.

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.

### Electroless deposition

Usually an electrolytic cell (consisting of two electrodes, electrolyte, and external source of current) is used for electrodeposition. An electrolytic cell decomposes chemical compounds by means of electrical energy in a process called Electrolysis; the Greek word Lysis means to break up In contrast, an electroless deposition process uses only one electrode and no external source of electrical current. However, the solution for the electroless process needs to contain a reducing agent so that the electrode reaction has the form:

$M^{z+} + Red_{solution} \stackrel{\text{catalytic surface}} \Longrightarrow M_{solid} + Oxy_{solution}$

For example, an electroless process is used for electroless nickel plating. Electroless nickel plating, or "EN" is an Electroplating technique used to deposit a layer of Nickel - phosphorous alloy on a solid work piece such as metals

### Cleanliness

Cleanliness is essential to successful electroplating, since molecular layers of oil can prevent adhesion of the coating. Parts cleaning is essential to many industrial processes as a prelude to Surface finishing or to protect sensitive components ASTM B322 is a standard guide for cleaning metals prior to electroplating. ASTM International ( ASTM) originally known as the American Society for Testing and Materials is an international Standards organization that develops and publishes Cleaning processes include solvent cleaning, hot alkaline detergent cleaning, electrocleaning, and acid etch. The most common industrial test for cleanliness is the waterbreak test, in which the surface is thoroughly rinsed and held vertical. Hydrophobic contaminants such as oils cause the water to bead and break up, allowing the water to drain rapidly. Perfectly clean metal surfaces are hydrophilic 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 the electroplating process can displace these easily since the solutions are water-based. Surfactants such as soap reduce the sensitivity of the test and must be thoroughly rinsed off.

## History

Nickel plating

Modern electrochemistry was invented by Italian chemist Luigi V. Brugnatelli in 1805. Brugnatelli used his colleague Alessandro Volta's invention of five years earlier, the voltaic pile, to facilitate the first electrodeposition. Count Alessandro Giuseppe Antonio Anastasio Volta was a Lombard physicist known especially for the development of the first electric cell in A voltaic pile is a set of individual Voltaic cells placed in series Brugnatelli's inventions were repressed by the French Academy of Sciences and did not become used in general industry for the following thirty years. The French Academy of Sciences ( French: Académie des sciences) is a Learned society, founded in 1666 by Louis XIV at the

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. The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom, the UK or Britain,is a Sovereign state located Russia (Россия Rossiya) or the Russian Federation ( Rossiyskaya Federatsiya) is a transcontinental Country extending A printing press is a mechanical device for applying pressure to an inked surface resting upon a medium (such as paper or cloth thereby transferring an image Soon after, John Wright of Birmingham, England discovered that potassium cyanide was a suitable electrolyte for gold and silver electroplating. John Wright was a surgeon from Birmingham, England who invented a process of Electroplating involving Potassium cyanide. Birmingham ( ˈbɜːmɪŋəm Ber -ming-um England is a Country which is part of the United Kingdom. Its inhabitants account for more than 83% of the total UK population whilst its mainland Potassium cyanide is an Inorganic compound with the formula KCN An electrolyte is any substance containing free Ions that behaves as an electrically conductive medium Wright's associates, George Elkington and Henry Elkington were awarded the first patents for electroplating in 1840. George Richards Elkington ( October 17, 1801 &ndash September 22, 1865) was a Manufacturer from Birmingham, England These two then founded the electroplating industry in Birmingham from where it spread around the world. Birmingham ( ˈbɜːmɪŋəm Ber -ming-um

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. Electrochemistry is a branch of Chemistry that studies Chemical reactions which take place in a Solution at the interface of an electron conductor Commercial electroplating of nickel, brass, tin, and zinc were developed by the 1850s. Tin is a Chemical element with the symbol Sn (stannum and Atomic number 50 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 from the advent of the development of electric generators in the late 19th century. In Electricity generation, an electrical generator is a device that converts Mechanical energy to Electrical energy, generally using Electromagnetic 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 automotive industry is the industry involved in the design development manufacture marketing and sale of Motor vehicles In 2007 more than 73 million motor vehicles

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. Aviation refers to activities involving man-made flying devices ( Aircraft) including the people organizations and regulatory bodies involved with them Chrome plating, often referred to simply as chrome, is a technique of Electroplating a thin layer of Chromium onto a Metal object Bronze is any of a broad range of Copper alloys, usually with Tin as the main additive but sometimes with other elements such as Phosphorus Plating equipment evolved from manually operated tar-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. Richard Phillips Feynman (ˈfaɪnmən May 11 1918 – February 15 1988 was an American Physicist known for the Path integral formulation of quantum Plastic is the general common term for a wide range of synthetic or semisynthetic organic solid materials suitable for the manufacture of industrial products 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. [6]

Electroplating is one of the three processes that form the LIGA-process used to manufacture MEMS devices. LIGA, a German acronym for ″ Li thographie G alvanoformung A bformung" in English ( X-ray) Lithography, Electroplating Microelectromechanical systems ( MEMS) is the technology of the very small and merges at the nano-scale into Nanoelectromechanical systems (NEMS and Nanotechnology