Plating is a surface covering in which a metal A metal is a chemical element that is a good conductor of both electricity and heat and forms cations and ionic bonds with non-metals. In chemistry, a metal is an element, compound, or alloy characterized by high electrical conductivity. In a metal, atoms readily lose electrons to form positive ions (cations). Those ions are surrounded by is deposited on a conductive In physics and electrical engineering, a conductor is a material which contains movable electric charges. In metallic conductors, such as copper or aluminum, the movable charged particles are electrons . Positive charges may also be mobile in the form of atoms in a lattice that are missing electrons (known as holes), or in the form of ions, such surface. Plating has been done for hundreds of years, but 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, for radiation shielding, and for other purposes. Jewelry Jewellery or jewelry (see American and British English spelling differences) signifies items of personal adornment, such as necklaces, rings, brooches, earrings and bracelets. Jewellery may be made from any material, such as gemstones, precious metals or shells, besides other materials, depending on cultural differences and availability of typically uses plating to give a silver Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal. The metal occurs naturally in its pure, free form (native silver), as an alloy with gold and other metals, and or gold Gold is a chemical element with the symbol Au (from Latin: aurum, "shining dawn", hence adjective, aureate) and an atomic number of 79. It has been a highly sought-after precious metal for coinage, jewelry, and other arts since the beginning of recorded history. The metal occurs as nuggets or grains in rocks, in veins and in alluvial finish. Thin-film deposition Thin films are thin material layers ranging from fractions of a nanometre to several micrometres in thickness. Electronic semiconductor devices and optical coatings are the main applications benefiting from thin film construction has plated objects as small as an atom, therefore plating finds uses in nanotechnology Nanotechnology, shortened to "nanotech", is the study of the controlling of matter on an atomic and molecular scale. Generally nanotechnology deals with structures sized between 1 to 100 nanometer in at least one dimension, and involves developing materials or devices within that size.
There are several plating methods, and many variations. In one method, a solid surface is covered with a metal sheet, and then heat and pressure are applied to fuse them (a version of this is Sheffield plate). Other plating techniques include vapor deposition under vacuum In everyday usage, vacuum is a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than atmospheric pressure. The word comes from the Latin term for "empty". Even putting aside the complexities of the quantum vacuum, the classical notion of a perfect vacuum with gaseous pressure of exactly and sputter deposition Sputter deposition is a physical vapor deposition method of depositing thin films by sputtering, that is ejecting, material from a "target," that is source, which then deposits onto a "substrate," such as a silicon wafer. Resputtering is re-emission of the deposited material during the deposition process by ion or atom. Recently, plating often refers to using liquids. Metallizing Metallizing is the general name for the technique of coating metal on the surface of non-metallic objects. Because a non-metallic object tends to be a poor electrical conductor, the object's surface must be made conductive before plating can be performed refers to coating metal on non-metallic objects.
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Electroplating
Main article: Electroplating Electroplating is a plating process that uses 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. Electroplating is primarily used for depositing a layer of material to bestow a desired property to a surface that otherwise lacks that propertyIn electroplating, an ionic An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. An anion , from the Greek word ἀνω (anο), meaning "up", is an ion with more electrons than protons, giving it a net negative charge (since electrons are negatively metal is supplied with electrons The electron is a subatomic particle carrying a negative electric charge. It has no known components or substructure, and therefore is believed to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton. The intrinsic angular momentum of the electron is a half integer value in units of ħ, which means that to form a non-ionic coating on a substrate. A common system involves a chemical solution with the ionic form of the metal, an anode An anode is an electrode through which electric current flows into a polarized electrical device. Mnemonic: ACID (positively charged) which may consist of the metal being plated (a soluble Solubility is the property of a solid, liquid, or gaseous chemical substance called solute to dissolve in a liquid solvent to form a homogeneous solution of the solute in the solvent. The solubility of a substance fundamentally depends on the used solvent as well as on temperature and pressure. The extent of the solubility of a substance in a anode) or an insoluble Solubility is the property of a solid, liquid, or gaseous chemical substance called solute to dissolve in a liquid solvent to form a homogeneous solution of the solute in the solvent. The solubility of a substance fundamentally depends on the used solvent as well as on temperature and pressure. The extent of the solubility of a substance in a anode (usually carbon, platinum, titanium, lead, or steel), and finally, a cathode A cathode is an electrode through which electric current flows out of a polarized electrical device. Mnemonic: CCD (negatively charged) where electrons are supplied to produce a film of non-ionic metal.
Electroless plating
Electroless plating, also known as chemical or auto-catalytic Catalysis is the change in rate of a chemical reaction due to the participation of a substance called a catalyst. Unlike other reagents that participate in the chemical reaction, a catalyst is not consumed by the reaction itself. A catalyst may participate in multiple chemical transformations. Catalysts that speed the reaction are called positive plating, is a non-galvanic Galvanization classically refers to any of several electrochemical processes named after the Italian scientist Luigi Galvani. Now the term generally refers to an electrodeposition process used to add a thin layer of another metal to an item made of steel, in order to prevent rusting. More recently, though, the term has been broadened in common type of plating method that involves several simultaneous reactions in an aqueous solution An aqueous solution is a solution in which the solvent is water. It is usually shown in chemical equations by appending to the relevant formula. The word aqueous means pertaining to, related to, similar to, or dissolved in water. As water is an excellent solvent as well as naturally abundant, it is a ubiquitous solvent in chemistry, which occur without the use of external electrical power. The reaction is accomplished when hydrogen Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of 1.00794 u (1.007825 u for Hydrogen-1), hydrogen is the lightest and most abundant chemical element, constituting roughly 75 % of the Universe's elemental mass. Stars in the main sequence are mainly composed of hydrogen in its is released by a reducing agent, normally sodium hypophosphite Sodium hypophosphite is the sodium salt of hypophosphorous acid and is often encountered as the monohydrate, NaPO2H2·H2O. It is a solid at room temperature, appearing as odorless white crystals. It is soluble in water, and easily absorbs moisture from the air (Note: the hydrogen leaves as a hydride ion), and oxidized thus producing a negative charge on the surface of the part. The most common electroless plating method is electroless nickel plating.
Specific cases
Gold plating
Main article: Gold plating Gold plating is a method of depositing a thin layer of gold onto the surface of another metal, most often copper or silver , by chemical or electrochemical means. This article covers methods used in the modern electronics industry; more traditional methods, often used for much larger objects, are covered in gildingGold plating Gold plating is a method of depositing a thin layer of gold onto the surface of another metal, most often copper or silver , by chemical or electrochemical means. This article covers methods used in the modern electronics industry; more traditional methods, often used for much larger objects, are covered in gilding is a method of depositing a thin layer of gold Gold is a chemical element with the symbol Au (from Latin: aurum, "shining dawn", hence adjective, aureate) and an atomic number of 79. It has been a highly sought-after precious metal for coinage, jewelry, and other arts since the beginning of recorded history. The metal occurs as nuggets or grains in rocks, in veins and in alluvial on the surface of other metal, most often copper Copper is a chemical element with the symbol Cu (Latin: cuprum) and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is rather soft and malleable, and a freshly exposed surface has a pinkish or peachy color. It is used as a thermal conductor, an electrical conductor, a building material, and a or silver Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal. The metal occurs naturally in its pure, free form (native silver), as an alloy with gold and other metals, and.
Gold plating is often used in electronics, to provide a corrosion Corrosion is the disintegration of an engineered material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means electrochemical oxidation of metals in reaction with an oxidant such as oxygen. Formation of an oxide of iron due to oxidation of the iron atoms in solid solution is a-resistant electrically conductive layer on copper Copper is a chemical element with the symbol Cu (Latin: cuprum) and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is rather soft and malleable, and a freshly exposed surface has a pinkish or peachy color. It is used as a thermal conductor, an electrical conductor, a building material, and a, typically in electrical connectors An electrical connector is a conductive device for joining electrical circuits together. The connection may be temporary, as for portable equipment, or may require a tool for assembly and removal, or may be a permanent electrical joint between two wires or devices. There are hundreds of types of electrical connectors. In computing, an electrical and printed circuit boards A printed circuit board, or PCB, is used to mechanically support and electrically connect electronic components using conductive pathways, tracks or traces etched from copper sheets laminated onto a non-conductive substrate. It is also referred to as printed wiring board or etched wiring board. A PCB populated with electronic components is a. With direct gold-on-copper plating, the copper atoms have the tendency to diffuse through the gold layer, causing tarnishing of its surface and formation of an oxide/sulfide layer. A layer of a suitable barrier metal, usually nickel, has therefore to be deposited on the copper substrate, forming a copper-nickel-gold sandwich.
Metals may also be coated with gold for ornamental purposes, using a number of different processes usually referred to as gilding The term gilding covers a number of decorative techniques for applying fine gold leaf or powder to solid surfaces such as wood, stone, or metal to give a thin coating of gold. A gilded object is described as "gilt". Where metal is gilded it was traditionally usually silver in the West, to make silver-gilt objects, but gilt-bronze is much.
Silver plating
A silver-plated alto saxophone The alto saxophone is a member of the saxophone family of woodwind instruments invented by Belgian instrument designer Adolphe Sax in 1841. It is smaller than the tenor but larger than the soprano, and is the type most used in classical compositions. The alto and tenor are the most common types of saxophoneFor less demanding applications in electronics, silver Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal. The metal occurs naturally in its pure, free form (native silver), as an alloy with gold and other metals, and is often used as a cheaper replacement for gold. (Although silver is a better conductor than gold it does oxidize and so gold is better for contacts. However, variable capacitors are considered of the highest quality when they have silver plated plates. In this application there is no make and break contact so gold would not offer any advantage over silver).
Care should be used for parts exposed to high humidity Humidity is the amount of water vapor in the air. Relative humidity is defined as the ratio of the partial pressure of water vapor in a parcel of air to the saturated vapor pressure of water vapor at a prescribed temperature. Humidity may also be expressed as specific humidity. Relative humidity is an important metric used in forecasting weather environments. When the silver layer is porous or contains cracks, the underlying copper undergoes rapid galvanic corrosion Galvanic corrosion is an electrochemical process in which one metal corrodes preferentially when in electrical contact with a different type of metal and both metals are immersed in an electrolyte. Conversely, a galvanic reaction is exploited in primary batteries to generate a voltage. A common example is the carbon-zinc cell where the zinc, flaking off the plating and exposing the copper itself; a process known as red plague.
Historically, silver plate was used to provide a cheaper version of items that might otherwise be made of silver, including cutlery Cutlery refers to any hand implement used in preparing, serving, and especially eating food in the Western world. It is more usually known as silverware or flatware in the United States, where cutlery can have the more specific meaning of knives and other cutting instruments. This is probably the original meaning of the word. Since silverware and candlesticks. The earliest kind was Old Sheffield Plate, but in the 19th century new methods of production (including electroplating) were introduced: see Sheffield Plate.
Another method that can be used to apply a thin layer of silver to several objects, such as glass, is the Tollen's Test method, which usually is prepared as follows. Using this method the final reaction can occur by placing Tollen's Reagent in a glass and then adding Glucose/Dextrose and shaking the bottle to perform the reaction.
AgNO3 + KOH -> AgOH + KNO3
AgOH + 2NH3 -> [Ag(NH3)2]1+ + [OH]1- (Note: See Tollen's Reagent)
[Ag(NH3)2]1+ + [OH]1- + Aldehyde An aldehyde is an organic compound containing a formyl group. This functional group, with the structure R-CHO, consists of a carbonyl centre bonded to hydrogen and an R group. The group without R is called the aldehyde group or formyl group. Aldehydes differ from ketones in that the carbonyl is placed at the end of a carbon skeleton rather than(Usually Glucose/Dextrose) -> Ag + 2NH3 + H2O
Rhodium plating
Rhodium plating is occasionally used on white gold, silver or copper and its alloys. A barrier layer of nickel is usually deposited on silver first, though in this case it is not to prevent migration of silver through rhodium, but to prevent contamination of the rhodium bath with silver and copper, which slightly dissolve in the sulfuric acid Sulfuric acid is a strong mineral acid with the molecular formula H2SO4(aq). It is soluble in water at all concentrations. Sulfuric acid has many applications, and is one of the top products of the chemical industry. World production in 2001 was 165 million tonnes, with an approximate value of US$8 billion. Principal uses include lead-acid usually present in the bath composition.[1]
Chrome plating
Main article: Chrome plating Chrome plating, often referred to simply as chrome, is a technique of electroplating a thin layer of chromium onto a metal object. The chromed layer can be decorative, provide corrosion resistance, ease cleaning procedures, or increase surface hardnessChrome plating is a finishing treatment utilizing the electrolytic deposition Electroplating is a plating process that uses 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. Electroplating is primarily used for depositing a layer of material to bestow a desired property to a surface that otherwise lacks that property of chromium Chromium is a chemical element which has the symbol Cr and atomic number 24, first element in Group 6. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odorless, tasteless, and malleable. The name of the element is derived from the Greek word "chrōma" (χρώμα), meaning color,. The most common form of chrome plating is the thin, decorative bright chrome, which is typically a 10-µm A micrometre is one millionth of a metre, or equivalently one thousandth of a millimetre or one thousand nanometres. It can also be written in scientific notation as 1×10−6 m, meaning 1⁄1000000 m layer over an underlying nickel Nickel is a chemical element, with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. It is one of the four ferromagnetic elements that exist around room temperature, the other three being iron, cobalt and gadolinium plate. When plating on iron or steel, an underlying plating of copper allows the nickel to adhere. The pores (tiny holes) in the nickel and chromium layers also promote corrosion resistance. Bright chrome imparts a mirror A mirror is a shiny object with at least one reflective surface. The most familiar type of mirror is the plane mirror, which has a flat surface. Curved mirrors are also used, to produce magnified or diminished images or focus light or simply distort the reflected image-like finish to items such as metal furniture frames and automotive trim. Thicker deposits, up to 1000 µm, are called hard chrome and are used in industrial equipment to reduce friction Friction is the force resisting the relative lateral motion of solid surfaces, fluid layers, or material elements in contact. Its colloquial opposite is slipperiness. Friction is usually subdivided into several varieties: and wear.
The traditional solution used for industrial hard chrome plating is made up of about 250 g/l of CrO3 and about 2.5 g/l of SO4-. In solution, the chrome exists as chromic acid, known as hexavalent chromium. A high current is used, in part to stabilize a thin layer of chromium(+2) at the surface of the plated work. Acid chrome has poor throwing power, fine details or holes are further away and receive less current resulting in poor plating.
Zinc plating
Main article: Galvanization Galvanization classically refers to any of several electrochemical processes named after the Italian scientist Luigi Galvani. Now the term generally refers to an electrodeposition process used to add a thin layer of another metal to an item made of steel, in order to prevent rusting. More recently, though, the term has been broadened in commonZinc Zinc , also known as spelter, is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2. Zinc is the 24th most abundant element in the coatings prevent oxidation Redox describes all chemical reactions in which atoms have their oxidation number (oxidation state) changed. This can be either a simple redox process, such as the oxidation of carbon to yield carbon dioxide (CO2) or the reduction of carbon by hydrogen to yield methane (CH4), or a complex process such as the oxidation of sugar(C6H12O6) in the of the protected metal by forming a barrier and by acting as a sacrificial anode An anode is an electrode through which electric current flows into a polarized electrical device. Mnemonic: ACID if this barrier is damaged. Zinc oxide is a fine white dust that (in contrast to iron oxide) does not cause a breakdown of the substrate's surface integrity as it is formed. Indeed the zinc oxide, if undisturbed, can act as a barrier to further oxidation, in a way similar to the protection afforded to aluminum and stainless steels by their oxide layers. The majority of hardware parts are zinc plated, rather than cadmium plated.[2]
Tin plating
See also: TinplateThe tin-plating process is used extensively to protect both ferrous and nonferrous surfaces. Tin is a useful metal for the food processing industry since it is non-toxic, ductile and corrosion resistant. The excellent ductility of tin allows a tin coated base metal sheet to be formed into a variety of shapes without damage to 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 the base metal from oxidation thus preserving its solderability. In electronic applications, lead may be added to prevent the growth of metallic "whiskers" in compression stressed deposits, which would otherwise cause electrical shorting.
Alloy plating
In some cases, it is desirable to co-deposit two or more metals resulting in an electroplated alloy deposit. Depending on the alloy system, an electroplated alloy may be solid solution strengthened or precipitation hardened by heat treatment to improve the plating's physical and chemical properties. Nickel-Cobalt is a common electroplated alloy.
Composite plating
Metal matrix composite plating can be manufactured when a substrate is plated in a bath containing a suspension of ceramic particles. Careful selection of the size and composition of the particles can fine-tune the deposit 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 plating is under scrutiny because of the environmental toxicity of the cadmium metal. However, cadmium plating is still widely used in some applications such as aerospace fasteners and it remains in military and aviation specs.[3] Cadmium plating (or "cad plating") offers a long list of technical advantages such as excellent corrosion resistance even at relatively low thickness and in salt atmospheres, softness and malleability, freedom from sticky and/or bulky corrosion products, galvanic compatibility with aluminum, freedom from stick-slip thus allowing reliable torquing of plated threads, can be dyed to many colors and clear, has good lubricity and solderability, and works well either as a final finish or as a paint base.[2][4] If environmental concerns matter, in most aspects cadmium plating can be directly replaced with gold plating as it shares most of the material properties - gold is more expensive and cannot serve as a paint base.
Nickel plating
The chemical reaction for nickel plating is:[citation needed]
At cathode: Ni -> Ni2+ + 2e-
At anode: H2PO2 + H2O -> H2PO3 + 2H+
Compared to cadmium plating, nickel plating offers a shinier and harder finish, but lower corrosion resistance, lubricity, and malleability, resulting in a tendency to crack or flake if the piece is further processed.[2]
Electroless nickel plating
| The following text needs to be harmonized with text in Electroless nickel plating. |
Electroless nickel plating, also known as enickel and NiP, offers many advantages: uniform layer thickness over most complicated surfaces, direct plating of ferrous metals (steel), superior wear and corrosion resistance to electroplated nickel or chrome. Much of the chrome plating done in aerospace industry can be replaced with electroless nickel plating, again environmental costs, costs of hexavalent chromium waste disposal and notorius tendency of uneven current distribution favor electroless nickel plating.[5]
Electroless nickel plating is self-catalyzing process, the resultant nickel layer is NiP compound, with 7-11% phosphorus content. Properties of the resultant layer hardness and wear resistance are greatly altered with bath composition and deposition temperature, which should be regulated with 1 °C precision, typically at 91 °C.
During bath circulation, any particles in it will become also nickel plated, this effect is used to advantage in processes which deposit plating with particles like silicon carbide (SiC) or polytetrafluoroethylene (PTFE). While superior compared to many other plating processes, it is expensive because the process is complex. Moreover, the process is lengthy even for thin layers. When only corrosion resistance or surface treatment is of concern, very strict bath composition and temperature control is not required and the process is used for plating many tons in one bath at once.
Electroless nickel plating layers are known to provide extreme surface adhesion when plated properly. Electroless nickel plating is non-magnetic and amorphous. Electroless nickel plating layers are not easily solderable, nor do they seize with other metals or another electroless nickel plated workpiece under pressure. This effect benefits electroless nickel plated screws made out of malleable materials like titanium. Electrical resistance is higher compared to pure metal plating.
See also
References
- ^ Pushpavanam, M; Raman, V; Shenoi, B (1981). "Rhodium — Electrodeposition and applications". Surface Technology 12: 351. doi:10.1016/0376-4583(81)90029-7.
- ^ a b c "Cadmium vs. Zinc vs. Nickel Plating Comparison" Finishing.com
- ^ Cad plating letters-to-the-editor from http://www.finishing.com/136/09.shtml
- ^ Cadmium plating fact sheet from the Erie Plating Company, available http://erieplating.com/cadmium-plating (used with their permission).
- ^ http://www.schnarr.eu/en/files/SCHNARR_EN_Kanigen.pdf
External links
- Electrochemistry Encyclopedia
- New nano-ceramic coating technology brings zinc plating totally free of chromate and heavy metal ions
Categories: Coatings | Industrial processes | Metal plating | Thin film deposition
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Mon, 19 Jul 2010 02:00:39 GMT+00:00
istockAnalyst.com (press release) A scarf around her hair, she moves swiftly; plating up samosas, inspecting dishes and waving to visitors. She's been cooking Indian food out of her home for ...
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parts are copper plated then buffed again nickel and chrome plating are the final steps
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ue, 22 Jun 2010 15:54:02 GM
Funded by Guangzhou Iron and Steel Enterprise Group and Japan JFE Steel Co., Ltd., Guangzhou JFE Steel . Plate. Co., Ltd. (GJSS) was officially listed on January 15, 2004. The first phase of the project, Nansha 4000-ton hot galvanized ...
Q. Hey all, I am a full time home maker living in santa clara, ca I m interested in doing a course on food plating and presentation techniques. I dont want a degree. I just want to do it as a hobby. Any suggestions would be great. Thanq.
Asked by fhz - Mon Jul 26 01:31:38 2010 - - 1 Answers - 0 Comments
