Coating is the surface cover where the metal is deposited on a conductive surface. Plating has been done for hundreds of years; it is also important 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 increase IR reflectivity, for radiation shielding, and for other purposes. Jewelery usually uses coating to produce silver or gold. The thin film deposition has coated objects as small as atoms, therefore plating finds usefulness in nanotechnology.
There are several coating methods, and many variations. In one method, the solid surface is covered with a sheet of metal, and then heat and pressure are applied to integrate it (this version is a Sheffield plate). Other coating techniques include electroplating, vapor deposition under vacuum pressure and sputter. Recently, coating often refers to the use of fluids. Metallizing refers to metal coating on nonmetallic objects.
Video Plating
Elektroplating
In electroplating, ionic metals are supplied with electrons to form non-ionic layers on the substrate. The general system involves a chemical solution with an ionic form of metal, an anode (a negative charge) which may comprise a plated metal (dissolved anode) or an insoluble anode (usually carbon, platinum, titanium, lead, or steel), and finally, a cathode (positively charged) in which electrons are supplied to produce non-ionic metal films.
Maps Plating
Electrolysis coating
Electrolytic coating, also known as chemical or automatic-catalytic coating, is a non-galvanic coating method involving multiple simultaneous reactions in an aqueous solution, which occurs without the use of external electrical power. The reaction is achieved when the hydrogen is released by the reducing agent, usually sodium hypophosphite (Note: hydrogen leaves as hydride ion) or thiourea, and oxidized, resulting in a negative charge on the surface of the part. The most common electroless plating method is nickel-free coating, although silver, gold and copper layers can also be applied in this way, as in Angel plating techniques.
Specific case
Gold plating
Gold plating is a method of depositing a thin layer of gold on a glass or metal surface, most commonly copper or silver.
Gold coatings are often used in electronics, to provide a stainless-resistant electrical conductive coating on copper, usually in electrical connectors and printed circuit boards. With direct gold-on-copper coating, copper atoms have a tendency to spread through the gold layer, causing staining of its surface and the formation of oxide/sulphide layers. Therefore, an appropriate barrier metal layer, usually nickel, must be deposited on a copper substrate, forming a copper-nickel-gold sandwich.
Metals and glass can also be coated with gold for decorative purposes, using a number of different processes usually referred to as plating .
Sapphires, plastics, and carbon fibers are some other materials that can be gilded using a coating technique. Usable substrate is almost unlimited.
Silver plating
- This section is about adding a thin layer of silver to an object. For Manhattan Project operations, see Silverplate .
Silver plating has been used since the 18th century to provide a cheaper version of household goods that should be made of solid silver, including cutlery, ships of various kinds, and candlesticks. In the UK, the testing offices, and silver merchants and collectors, use the term "silver plate" for items made of solid silver, which originated long before the plating silver was found from the Spanish word for silver "plata", silver leaks from Spanish vessels carrying silver from America became the source of silver at the time. This can cause confusion when talking about silver items; plates or plated. In the UK it is illegal to describe silver items as "silver". It is not illegal to describe silver-plated items as "silver plates", although these are not grammatically correct, and should also be avoided to prevent confusion.
The earliest form of silver plating is the Sheffield Plate, where thin sheets of silver coalesce with a base metal layer or core, but in the 19th century new production methods (including electroplating) were introduced. The Britannia metal is an alloy of tin, antimony and copper developed as a base metal for plating with silver.
Another method that can be used to apply a thin layer of silver to an object such as glass, is to place the Tollens reagent in a glass, add glucose/dextrose, and shake the bottle to encourage the reaction.
- AgNO 3 KOH -> AgOH KNO 3 soup> [OH] - (Note: see Tollens Reagent)
- [Ag (NH 3 ) 2 [OH] - aldehyde (usually glucose/dextrose) -> Ag 2 NH 3 H 2 O
For applications in electronics, silver is sometimes used for copper plating, due to lower electrical resistance (see resistivity of various materials); more at higher frequencies due to skin effect. Variable capacitors are considered to have the highest quality when they have silver plated plates. Similarly, silver plated, or even solid silver cable, is appreciated in audiophile applications; However some experts consider that in practice coating is often poorly implemented, making the result lower than copper wires at the same price.
Treatment should be used for parts exposed to high humidity environments because in such environments, when the silver layer is porous or containing cracks, the underlying copper undergoes rapid galvanic corrosion, peeling off the coating and exposing the copper itself; a process known as the red plague. Silver-plated copper kept in a steam-free environment will not experience this type of corrosion.
Copper plating
Copper coating is an electrolysis process that forms a copper layer on the surface of an object.
Rhodium Coating
Rhodium plating is sometimes used in white gold, silver or copper and its alloys. The nickel barrier layer is usually deposited on the first silver, although in this case it does not prevent the silver migration through rhodium, but to prevent the contamination of rhodium bath with silver and copper, slightly soluble in sulfuric acid is usually present in the bath composition.
Chrome Coating
Chromating is the final treatment using electrolytic deposition of chromium. The most common form of chrome plating is thin, decorative bright chromium, which is usually a 10-μm layer above the underlying nickel plate. When plating on iron or steel, the underlying copper layer allows the nickel to attach. The pores (small holes) in the nickel and chromium layers work to reduce stress caused by mismatched thermal expansion but also injure the corrosion resistance of the coating. Corrosion resistance depends on what is called the passivation layer, determined by chemical composition and processing, and is damaged by cracks and pores. In special cases, micropores can help distribute electrochemical potential that speeds galvanic corrosion between the nickel and chromium layers. Depending on the application, layers of different thickness will require a balance different from the previously mentioned properties. Sleek and bright chrome gives a mirror-like finish to items such as metal furniture and automotive trim. A thicker deposit, up to 1000 Âμm, is called hard chrome and is used in industrial equipment to reduce friction and wear.
The traditional solution used for the hard chrome plating industry consists of about 250 g/L CrO 3 and about 2.5 g/L SO 4 - . In solution, chromium exists as chromic acid, known as hexavalent chromium. High currents are used, in part to stabilize the thin layer of chrome (2) on the layered work surface. Chromic acid has poor throwing power, fine detail or deeper holes and receives less current that results in poor coating.
Zinc plating
The zinc coating prevents the oxidation of the protected metal by forming a barrier and by acting as the sacrificial anode if the barrier is damaged. Zinc oxide is a fine white dust which (in contrast to iron oxide) does not cause damage to the surface integrity of the substrate as it is formed. Indeed, zinc oxide, if uninterrupted, may act as a barrier for further oxidation, in a manner similar to the protection afforded to aluminum and stainless steels by the oxide layer. Most hardware parts are zinc-coated, and not cadmium-plated.
Zinc-coating
Zinc-nickel coating is one of the best corrosion-resistant layers available, offering more than 5 times the protection of conventional zinc coating and up to 1,500 hours of neutral salt spray test performance. This coating is a combination of a high nickel-nickel-nickel alloy (10-15% nickel) and several chromate variations. The most common chromate blends include colorful hexavalent, trivalent or black trivalent chromate. Used to protect steel, cast iron, brass, copper, and other materials, this acid coating is a safe choice for the environment. Hexavalent chromate has been classified as a human carcinogen by EPA and OSHA.
Tin coating
The tin coating process is widely used to protect the surface of iron and nonferrous. Tin is a useful metal for the food processing industry because it is non-toxic, ductile and corrosion-resistant. The excellent tin ductility allows tin-coated metal sheets to be formed into various shapes without damaging the surface tin layer. It provides sacrificial protection for copper, nickel and other non-ferrous metals, but not for steel.
Tin is also widely used in the electronics industry because of its ability to protect base metals from oxidation so as to maintain its adhesiveness. In electronic applications, a 3% to 7% lead can be added to improve soldering capability and to prevent the growth of metal "mustache" in compression pressure, which otherwise would cause electrical short circuit. However, the RoHS regulations (Restriction of Hazardous Substances) enacted in 2006 require that no lead is added intentionally and that the maximum percentage does not exceed 1%. Several exceptions have been issued for RoHS requirements in important electronic applications because known failures have occurred as a result of the formation of tin whiskers.
Alloy coating
In some cases, it is desirable to store together two or more metals which produce an alloyed deposited deposit. Depending on the alloy system, the coated alloy may be a solid solution reinforced or precipitation hardened by heat treatment to improve the physical and chemical properties of plating. Nickel-Cobalt is a common electroplated alloy.
Composite coating
The metal matrix composite coating can be made when the substrate is coated in a bath containing ceramic particle suspension. Careful selection of particle size and composition can improve deposits for wear resistance, high temperature performance, or mechanical strength. Tungsten carbide, silicon carbide, chromium carbide, and aluminum oxide (alumina) are commonly used in composite electroplating.
Cadmium plating
Cadmium coating is being investigated because of the environmental toxicity of cadmium metal. Cadmium coatings are widely used in several applications in the aerospace, military, and aviation fields. However, it has been removed due to its toxicity.
Cadmium plating (or Plastic ) offers a long list of technical advantages such as excellent corrosion resistance even at relatively low thickness and in salt atmosphere, softness and flexibility, freedom from sticky and/or large corrosion products , galvanized compatibility with aluminum, the freedom from stick-slip thereby enabling reliable torquing of layered threads, can be dyed into many colors and clear, has good lubrication and solderability, and works well either as a final finish or as a base of paint.
If important environmental problems, in many aspects, cadmium coatings can be replaced directly with gold coating because most of the material properties, but gold is more expensive and can not serve as a base paint.
Nickel plating
The chemical reactions for nickel plating are:
At cathode: Ni -> Ni 2 2 e -
Pada anode: H 2 PO 2 H 2 O -> H 2 PO 3 2 H
Compared with cadmium plating, nickel coating offers a brighter and harder finish, but lower corrosion, lubrication, and flexibility, resulting in a tendency to crack or flake if the piece is further processed.
Cordless nickel coating
Electroless nickel plating, also known as enickel and NiP , offers many advantages: uniform layer thickness on the most complex surface, direct coating of ferrous metals, superior wear and corrosion resistance to nickel or chrome coated. Most chrome plating performed in the aerospace industry can be replaced by nickel plating without electricity, again environmental costs, hexavalent chromium waste disposal costs and the well-known trend of uneven distribution of current supporting nickel plating without electricity.
Electroless nickel plating is a self-catalyzing process, the resulting nickel layer is a NiP compound, with a 7-11% phosphorus content. The resulting hardness of the coating and wear resistance is greatly modified by the bath composition and the deposition temperature, which must be adjusted to a precision of 1 Â ° C, usually at 91 Â ° C.
During the water circulation, each particle in it will also be nickel-plated; This effect is used to advantage in processes that store plating with particles such as silicon carbide (SiC) or polytetrafluoroethylene (PTFE). While superior compared to many other coating processes, it is expensive because the process is complex. Moreover, the process is long even for thin layers. When only corrosion resistance or surface treatment is of concern, very tight shower composition and temperature control are not required and this process is used to coat many tons in one bath at a time.
The electroless nickel plating layer is known to provide extreme surface adhesion when coated properly. Electroless nickel plating is non-magnetic and amorphous. The electrolytic nickel coating layer is not easily fitted, nor does it seize with other metals or other nickel-plated objects without electricity under pressure. This effect benefits nickel-plated nickel screws made of soft materials such as titanium. Higher electrical resistance compared to pure metal plating.
See also
- Anodization
- Hull Cell
- Mechanical coating
- Organic Solderability Solders
- Materials Science & amp; Federation of Engineering
References
External links
- Encyclopedia of Electrochemistry
- The new nano-ceramic coating technology presents zinc plating completely free of chromate and heavy metal ions
Source of the article : Wikipedia
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