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Electroplating , also known as electrochemical deposition or electrodeposition , is a process for producing a metal 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 (negative electrode ) of an electrolytic cell ; the electrolyte is a solution of a salt whose cation is the metal to be coated, and the anode (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 .

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100-544: The Consolidated Mine was a gold mine in Lumpkin County, Georgia , United States, just east of Dahlonega . Like most of the area around Dahlonega, the placer mining on the land on which the mine is located probably started during the Georgia Gold Rush . By 1880, the placer deposits were exhausted and the land was down to hard rock. Gold was soon discovered in a huge quartz vein system, and mined. "The richest acre"

200-399: A fault . Water often lubricates faults, filling in fractures and jogs. About 10 kilometres (6.2 mi) below the surface, under very high temperatures and pressures, the water carries high concentrations of carbon dioxide, silica, and gold. During an earthquake, the fault jog suddenly opens wider. The water inside the void instantly vaporizes, flashing to steam and forcing silica, which forms

300-483: A dilute solution of gold(III) chloride or chlorauric acid . Unlike sulfur, phosphorus reacts directly with gold at elevated temperatures to produce gold phosphide (Au 2 P 3 ). Gold readily dissolves in mercury at room temperature to form an amalgam , and forms alloys with many other metals at higher temperatures. These alloys can be produced to modify the hardness and other metallurgical properties, to control melting point or to create exotic colors. Gold

400-465: 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

500-572: A gold-from-seawater swindle in the United States in the 1890s, as did an English fraudster in the early 1900s. Fritz Haber did research on the extraction of gold from sea water in an effort to help pay Germany 's reparations following World War I . Based on the published values of 2 to 64 ppb of gold in seawater, a commercially successful extraction seemed possible. After analysis of 4,000 water samples yielding an average of 0.004 ppb, it became clear that extraction would not be possible, and he ended

600-830: A golden hue to metallic caesium . Common colored gold alloys include the distinctive eighteen-karat rose gold created by the addition of copper. Alloys containing palladium or nickel are also important in commercial jewelry as these produce white gold alloys. Fourteen-karat gold-copper alloy is nearly identical in color to certain bronze alloys, and both may be used to produce police and other badges . Fourteen- and eighteen-karat gold alloys with silver alone appear greenish-yellow and are referred to as green gold . Blue gold can be made by alloying with iron , and purple gold can be made by alloying with aluminium . Less commonly, addition of manganese , indium , and other elements can produce more unusual colors of gold for various applications. Colloidal gold , used by electron-microscopists,

700-461: A heated electroplating bath to increase the deposition rate, since the rate of most chemical reactions increases exponentially with temperature per the Arrhenius law . The anode-to-cathode gap is related to the current distribution between anode and cathode. A small gap-to-sample-area ratio may cause uneven distribution of current and affect the surface topology of the plated sample. Stirring may increase

800-552: A large alluvial deposit. The mines at Roşia Montană in Transylvania were also very large, and until very recently, still mined by opencast methods. They also exploited smaller deposits in Britain , such as placer and hard-rock deposits at Dolaucothi . The various methods they used are well described by Pliny the Elder in his encyclopedia Naturalis Historia written towards the end of

900-462: A novel type of metal-halide perovskite material consisting of Au and Au cations in its crystal structure has been found. It has been shown to be unexpectedly stable at normal conditions. Gold pentafluoride , along with its derivative anion, AuF − 6 , and its difluorine complex , gold heptafluoride , is the sole example of gold(V), the highest verified oxidation state. Some gold compounds exhibit aurophilic bonding , which describes

1000-453: A physical change is a change in the outward appearance. An example of a mechanical change is a change in tensile strength or surface hardness , which is a required attribute in the 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

1100-467: 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. Electroplating changes the chemical, physical, and mechanical properties of the workpiece. An example of a chemical change is when nickel plating improves corrosion resistance. An example of

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1200-407: A sample of the plating solution and an appropriate anode which is connected to a rectifier . 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

1300-456: 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

1400-401: A sheet of 1 square metre (11 sq ft), and an avoirdupois ounce into 28 square metres (300 sq ft). Gold leaf can be beaten thin enough to become semi-transparent. The transmitted light appears greenish-blue because gold strongly reflects yellow and red. Such semi-transparent sheets also strongly reflect infrared light, making them useful as infrared (radiant heat) shields in

1500-517: A solution of Au(OH) 3 in concentrated H 2 SO 4 produces red crystals of gold(II) sulfate , Au 2 (SO 4 ) 2 . Originally thought to be a mixed-valence compound, it has been shown to contain Au 4+ 2 cations, analogous to the better-known mercury(I) ion, Hg 2+ 2 . A gold(II) complex, the tetraxenonogold(II) cation, which contains xenon as a ligand, occurs in [AuXe 4 ](Sb 2 F 11 ) 2 . In September 2023,

1600-475: A true alloy. The true alloy is more corrosion-resistant than the as-plated mixture. Many plating baths include cyanides 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 carbonates and phosphates may be added to increase conductivity. When plating

1700-470: Is Au with a half-life of 2.27 days. Gold's least stable isomer is Au with a half-life of only 7 ns. Au has three decay paths: β decay, isomeric transition , and alpha decay. No other isomer or isotope of gold has three decay paths. The possible production of gold from a more common element, such as lead , has long been a subject of human inquiry, and the ancient and medieval discipline of alchemy often focused on it; however,

1800-696: Is Au , which decays by proton emission with a half-life of 30 μs. Most of gold's radioisotopes with atomic masses below 197 decay by some combination of proton emission , α decay , and β decay . The exceptions are Au , which decays by electron capture, and Au , which decays most often by electron capture (93%) with a minor β decay path (7%). All of gold's radioisotopes with atomic masses above 197 decay by β decay. At least 32 nuclear isomers have also been characterized, ranging in atomic mass from 170 to 200. Within that range, only Au , Au , Au , Au , and Au do not have isomers. Gold's most stable isomer

1900-417: Is a chemical element with the chemical symbol Au (from Latin aurum ) and atomic number 79. In its pure form, it is a bright , slightly orange-yellow, dense, soft, malleable , and ductile metal . Chemically, gold is a transition metal , a group 11 element , and one of the noble metals . It is one of the least reactive chemical elements, being the second-lowest in the reactivity series . It

2000-648: Is also known, an example of a mixed-valence complex . Gold does not react with oxygen at any temperature and, up to 100 °C, is resistant to attack from ozone: Au + O 2 ⟶ ( no reaction ) {\displaystyle {\ce {Au + O2 ->}}({\text{no reaction}})} Au + O 3 → t < 100 ∘ C ( no reaction ) {\displaystyle {\ce {Au{}+O3->[{} \atop {t<100^{\circ }{\text{C}}}]}}({\text{no reaction}})} Some free halogens react to form

2100-520: Is also used in infrared shielding, the production of colored glass , gold leafing , and tooth restoration . Certain gold salts are still used as anti-inflammatory agents in medicine. Gold is the most malleable of all metals. It can be drawn into a wire of single-atom width, and then stretched considerably before it breaks. Such nanowires distort via the formation, reorientation, and migration of dislocations and crystal twins without noticeable hardening. A single gram of gold can be beaten into

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2200-475: Is also used to purify metals such as copper . The aforementioned electroplating of metals uses an electroreduction process (that is, a negative or cathodic current is on the working electrode). The term "electroplating" is also used occasionally for processes that occur under electro-oxidation (i.e positive or anodic current on the working electrode), although such processes are more commonly referred to as anodizing rather than electroplating. One such example

2300-427: Is always richer at the exposed surface of gold-bearing veins, owing to the oxidation of accompanying minerals followed by weathering; and by washing of the dust into streams and rivers, where it collects and can be welded by water action to form nuggets. Gold sometimes occurs combined with tellurium as the minerals calaverite , krennerite , nagyagite , petzite and sylvanite (see telluride minerals ), and as

2400-499: Is an important parameter that provides a measure of the uniformity of electroplating current, and consequently the uniformity of the electroplated metal thickness, on regions of the part that are near the anode compared to regions that are far from it. It depends mostly on the composition and temperature of the electroplating solution. Micro throwing power refers to the extent to which a process can fill or coat small recesses such as through-holes . Throwing power can be characterized by

2500-513: Is attributed to wind-blown dust or rivers. At 10 parts per quadrillion, the Earth's oceans would hold 15,000 tonnes of gold. These figures are three orders of magnitude less than reported in the literature prior to 1988, indicating contamination problems with the earlier data. A number of people have claimed to be able to economically recover gold from sea water , but they were either mistaken or acted in an intentional deception. Prescott Jernegan ran

2600-423: Is chromium-plated to prevent dulling of the surface due to oxidation of tin. There are a number of alternative processes to produce metallic coatings on solid substrates that do not involve electrolytic reduction: Electroplating was invented by Italian chemist Luigi Valentino Brugnatelli in 1805. Brugnatelli used his colleague Alessandro Volta 's invention of five years earlier, the voltaic pile , to facilitate

2700-400: Is fabricated out of perspex or glass. 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

2800-464: Is found in ores in rock formed from the Precambrian time onward. It most often occurs as a native metal , typically in a metal solid solution with silver (i.e. as a gold/silver alloy ). Such alloys usually have a silver content of 8–10%. Electrum is elemental gold with more than 20% silver, and is commonly known as white gold . Electrum's color runs from golden-silvery to silvery, dependent upon

2900-425: Is most commonly a single metallic element , not an alloy . However, some alloys can be electrodeposited, notably brass 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

3000-465: Is most often called the oldest since this treasure is the largest and most diverse. Gold artifacts probably made their first appearance in Ancient Egypt at the very beginning of the pre-dynastic period, at the end of the fifth millennium BC and the start of the fourth, and smelting was developed during the course of the 4th millennium; gold artifacts appear in the archeology of Lower Mesopotamia during

3100-418: 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, lacquers , and waxes . 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

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3200-528: Is now questioned. The gold-bearing Witwatersrand rocks were laid down between 700 and 950 million years before the Vredefort impact. These gold-bearing rocks had furthermore been covered by a thick layer of Ventersdorp lavas and the Transvaal Supergroup of rocks before the meteor struck, and thus the gold did not actually arrive in the asteroid/meteorite. What the Vredefort impact achieved, however,

3300-427: Is red if the particles are small; larger particles of colloidal gold are blue. Gold has only one stable isotope , Au , which is also its only naturally occurring isotope, so gold is both a mononuclidic and monoisotopic element . Thirty-six radioisotopes have been synthesized, ranging in atomic mass from 169 to 205. The most stable of these is Au with a half-life of 186.1 days. The least stable

3400-553: Is resistant to most acids, though it does dissolve in aqua regia (a mixture of nitric acid and hydrochloric acid ), forming a soluble tetrachloroaurate anion . Gold is insoluble in nitric acid alone, which dissolves silver and base metals , a property long used to refine gold and confirm the presence of gold in metallic substances, giving rise to the term ' acid test '. Gold dissolves in alkaline solutions of cyanide , which are used in mining and electroplating . Gold also dissolves in mercury , forming amalgam alloys, and as

3500-484: Is similarly unaffected by most bases. It does not react with aqueous , solid , or molten sodium or potassium hydroxide . It does however, react with sodium or potassium cyanide under alkaline conditions when oxygen is present to form soluble complexes. Common oxidation states of gold include +1 (gold(I) or aurous compounds) and +3 (gold(III) or auric compounds). Gold ions in solution are readily reduced and precipitated as metal by adding any other metal as

3600-483: Is solid under standard conditions . Gold often occurs in free elemental ( native state ), as nuggets or grains, in rocks , veins , and alluvial deposits . It occurs in a solid solution series with the native element silver (as in electrum ), naturally alloyed with other metals like copper and palladium , and mineral inclusions such as within pyrite . Less commonly, it occurs in minerals as gold compounds, often with tellurium ( gold tellurides ). Gold

3700-486: 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

3800-451: Is the formation of silver chloride on silver wire in chloride solutions to make silver/silver-chloride (AgCl) electrodes . Electropolishing , a process that uses an electric current to selectively remove the outermost layer from the surface of a metal object, is the reverse of the process of electroplating. Throwing power is an important parameter that provides a measure of the uniformity of electroplating current, and consequently

3900-585: Is the soluble form of gold encountered in mining. The binary gold halides , such as AuCl , form zigzag polymeric chains, again featuring linear coordination at Au. Most drugs based on gold are Au(I) derivatives. Au(III) (referred to as auric) is a common oxidation state, and is illustrated by gold(III) chloride , Au 2 Cl 6 . The gold atom centers in Au(III) complexes, like other d compounds, are typically square planar , with chemical bonds that have both covalent and ionic character. Gold(I,III) chloride

4000-634: Is thought to have been delivered to Earth by asteroid impacts during the Late Heavy Bombardment , about 4 billion years ago. Gold which is reachable by humans has, in one case, been associated with a particular asteroid impact. The asteroid that formed Vredefort impact structure 2.020 billion years ago is often credited with seeding the Witwatersrand basin in South Africa with the richest gold deposits on earth. However, this scenario

4100-505: Is thought to have been produced in supernova nucleosynthesis , and from the collision of neutron stars , and to have been present in the dust from which the Solar System formed. Traditionally, gold in the universe is thought to have formed by the r-process (rapid neutron capture) in supernova nucleosynthesis , but more recently it has been suggested that gold and other elements heavier than iron may also be produced in quantity by

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4200-416: Is unaffected by most acids. It does not react with hydrofluoric , hydrochloric , hydrobromic , hydriodic , sulfuric , or nitric acid . It does react with selenic acid , and is dissolved by aqua regia , a 1:3 mixture of nitric acid and hydrochloric acid . Nitric acid oxidizes the metal to +3 ions, but only in minute amounts, typically undetectable in the pure acid because of the chemical equilibrium of

4300-506: Is widely used in industry and decorative arts to improve the surface qualities of objects—such as resistance to abrasion and corrosion , lubricity , reflectivity , electrical conductivity , or appearance. It is used to build up thickness on undersized or worn-out parts and 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 integrated circuits. It

4400-645: The Chu (state) circulated the Ying Yuan , one kind of square gold coin. In Roman metallurgy , new methods for extracting gold on a large scale were developed by introducing hydraulic mining methods, especially in Hispania from 25 BC onwards and in Dacia from 106 AD onwards. One of their largest mines was at Las Medulas in León , where seven long aqueducts enabled them to sluice most of

4500-583: The Old Testament , starting with Genesis 2:11 (at Havilah ), the story of the golden calf , and many parts of the temple including the Menorah and the golden altar. In the New Testament , it is included with the gifts of the magi in the first chapters of Matthew. The Book of Revelation 21:21 describes the city of New Jerusalem as having streets "made of pure gold, clear as crystal". Exploitation of gold in

4600-597: The Parthian Empire using a device resembling a Baghdad Battery , but this has since been refuted; the items were fire-gilded using mercury. Boris Jacobi in Russia not only rediscovered galvanoplastics, but developed electrotyping and galvanoplastic sculpture . Galvanoplastics quickly came into fashion in Russia, with such people as inventor Peter Bagration , scientist Heinrich Lenz , and science-fiction author Vladimir Odoyevsky all contributing to further development of

4700-641: The Varna Necropolis near Lake Varna and the Black Sea coast, thought to be the earliest "well-dated" finding of gold artifacts in history. Several prehistoric Bulgarian finds are considered no less old – the golden treasures of Hotnitsa, Durankulak , artifacts from the Kurgan settlement of Yunatsite near Pazardzhik , the golden treasure Sakar, as well as beads and gold jewelry found in the Kurgan settlement of Provadia – Solnitsata ("salt pit"). However, Varna gold

4800-470: The reducing agent . The added metal is oxidized and dissolves, allowing the gold to be displaced from solution and be recovered as a solid precipitate. Less common oxidation states of gold include −1, +2, and +5. The −1 oxidation state occurs in aurides, compounds containing the Au anion . Caesium auride (CsAu), for example, crystallizes in the caesium chloride motif; rubidium, potassium, and tetramethylammonium aurides are also known. Gold has

4900-509: The "Glory Hole" underground and pan for gold. Original cart rails, electrical lines and even an operational pneumatic drill recovered from the mine may be viewed. This mine and Crisson Mine are the two mines in the Dahlonega area that remain open for tourists. The Consolidated Mine remains the only mine in the area safe enough to take tourists into. [REDACTED] Media related to Consolidated Gold Mine at Wikimedia Commons Gold Gold

5000-642: 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 generators 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

5100-483: The Heatley throwing power 100% × ( L − M ) / ( L − 1) , and Field throwing power 100% × ( L − M ) / ( L + M − 2) . A more uniform thickness is obtained by making the throwing power larger (less negative) according to any of these definitions. Parameters that describe cell performance such as throwing power are measured in small test cells of various designs that aim to reproduce conditions similar to those found in

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5200-459: The Mining Co. folded in 1906. The mine's lower workings became flooded and lay dormant until seventy-five years later, when the site came under new ownership. There is still gold to be mined here – but the cost of extracting the gold from the mine exceeds the value of the gold, at least for the time being. Today, a part of the upper level of the mine remains open for tourists, who can tour portions of

5300-421: The 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

5400-399: The anode to the cathode. The anode may instead be made of a material that resists electrochemical oxidation, such as lead or carbon . Oxygen , hydrogen peroxide , and some other byproducts are then produced at the anode instead. In this case, ions of the metal to be plated must be replenished (continuously or periodically) in the bath as they are drawn out of the solution. The plating

5500-426: The cathode, the opposite reaction may occur at the anode, turning it into dissolved cations. For example, copper would be oxidized at the anode to Cu by losing two electrons. In this case, the rate at which the anode is dissolved will equal 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

5600-437: The coating. ASTM B322 is a standard guide for cleaning metals prior to electroplating. Cleaning includes solvent cleaning, hot alkaline detergent cleaning, electrocleaning, ultrasonic cleaning and acid treatment. 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

5700-514: 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 a high-cost, inert electrode such as platinum . Other factors that affect the pulse electroplating include temperature, anode-to-cathode gap, and stirring. Sometimes, pulse electroplating can be performed in

5800-1409: The corresponding gold halides. Gold is strongly attacked by fluorine at dull-red heat to form gold(III) fluoride AuF 3 . Powdered gold reacts with chlorine at 180 °C to form gold(III) chloride AuCl 3 . Gold reacts with bromine at 140 °C to form a combination of gold(III) bromide AuBr 3 and gold(I) bromide AuBr, but reacts very slowly with iodine to form gold(I) iodide AuI: 2 Au + 3 F 2 → Δ 2 AuF 3 {\displaystyle {\ce {2Au{}+3F2->[{} \atop \Delta ]2AuF3}}} 2 Au + 3 Cl 2 → Δ 2 AuCl 3 {\displaystyle {\ce {2Au{}+3Cl2->[{} \atop \Delta ]2AuCl3}}} 2 Au + 2 Br 2 → Δ AuBr 3 + AuBr {\displaystyle {\ce {2Au{}+2Br2->[{} \atop \Delta ]AuBr3{}+AuBr}}} 2 Au + I 2 → Δ 2 AuI {\displaystyle {\ce {2Au{}+I2->[{} \atop \Delta ]2AuI}}} Gold does not react with sulfur directly, but gold(III) sulfide can be made by passing hydrogen sulfide through

5900-424: The densest element, osmium , is 22.588 ± 0.015 g/cm . Whereas most metals are gray or silvery white, gold is slightly reddish-yellow. This color is determined by the frequency of plasma oscillations among the metal's valence electrons, in the ultraviolet range for most metals but in the visible range for gold due to relativistic effects affecting the orbitals around gold atoms. Similar effects impart

6000-450: The dimensionless Wagner number : Wa = R T κ F L α | i | , {\displaystyle {\text{Wa}}={\frac {RT\kappa }{FL\alpha |i|}},} where R is the universal gas constant , T is the operating temperature , κ is the ionic conductivity of the plating solution, F is the Faraday constant , L is

6100-664: The early 4th millennium. As of 1990, gold artifacts found at the Wadi Qana cave cemetery of the 4th millennium BC in West Bank were the earliest from the Levant. Gold artifacts such as the golden hats and the Nebra disk appeared in Central Europe from the 2nd millennium BC Bronze Age . The oldest known map of a gold mine was drawn in the 19th Dynasty of Ancient Egypt (1320–1200 BC), whereas

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6200-545: The electric current less sensitive to voltage), and raising the solution conductivity (e.g. by adding acid ). Concurrent hydrogen evolution usually improves the uniformity of electroplating by increasing | i |; however, this effect can be offset by blockage due to hydrogen bubbles and hydroxide deposits. The Wagner number is rather difficult to measure accurately; therefore, other related parameters, that are easier to obtain experimentally with standard cells, are usually used instead. These parameters are derived from two ratios:

6300-453: The equivalent size of the plated object, α is the transfer coefficient , and i the surface-averaged total (including hydrogen evolution ) current density. The Wagner number quantifies the ratio of kinetic to ohmic resistances. A higher Wagner number produces a more uniform deposition. This can be achieved in practice by decreasing the size ( L ) of the plated object, reducing the current density | i |, adding chemicals that lower α (make

6400-615: The first century AD. During Mansa Musa 's (ruler of the Mali Empire from 1312 to 1337) hajj to Mecca in 1324, he passed through Cairo in July 1324, and was reportedly accompanied by a camel train that included thousands of people and nearly a hundred camels where he gave away so much gold that it depressed the price in Egypt for over a decade, causing high inflation . A contemporary Arab historian remarked: Electroplating Electroplating

6500-508: The first electrodeposition. Brugnatelli's inventions were suppressed by the French Academy of Sciences and did not become used in general industry for the following thirty years. 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. Research from the 1930s had theorized that electroplating might have been performed in

6600-526: The first written reference to gold was recorded in the 12th Dynasty around 1900 BC. Egyptian hieroglyphs from as early as 2600 BC describe gold, which King Tushratta of the Mitanni claimed was "more plentiful than dirt" in Egypt. Egypt and especially Nubia had the resources to make them major gold-producing areas for much of history. One of the earliest known maps, known as the Turin Papyrus Map , shows

6700-403: The gold acts simply as a solute, this is not a chemical reaction . A relatively rare element, gold is a precious metal that has been used for coinage , jewelry , and other works of art throughout recorded history . In the past, a gold standard was often implemented as a monetary policy . Gold coins ceased to be minted as a circulating currency in the 1930s, and the world gold standard

6800-505: The growing aviation industry gave impetus to further developments and refinements, including such processes as hard chromium plating , bronze alloy plating, sulfamate nickel plating, and numerous other plating processes. 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

6900-563: The highest electron affinity of any metal, at 222.8 kJ/mol, making Au a stable species, analogous to the halides . Gold also has a –1 oxidation state in covalent complexes with the group 4 transition metals, such as in titanium tetraauride and the analogous zirconium and hafnium compounds. These chemicals are expected to form gold-bridged dimers in a manner similar to titanium(IV) hydride . Gold(II) compounds are usually diamagnetic with Au–Au bonds such as [ Au(CH 2 ) 2 P(C 6 H 5 ) 2 ] 2 Cl 2 . The evaporation of

7000-409: The inability to achieve as great a plate thickness. 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 a chemical bath containing dissolved ions of the metal that is to be plated onto them. The barrel is then rotated, and electrical currents are run through

7100-465: 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 electroplating can be a solution of copper(II) sulfate , which dissociates into Cu cations and SO 4 anions. At the cathode, the Cu is reduced to metallic copper by gaining two electrons. When the anode is made of the metal that is intended for coating onto

7200-542: The mineral quartz, and gold out of the fluids and onto nearby surfaces. The world's oceans contain gold. Measured concentrations of gold in the Atlantic and Northeast Pacific are 50–150 femtomol /L or 10–30 parts per quadrillion (about 10–30 g/km ). In general, gold concentrations for south Atlantic and central Pacific samples are the same (~50 femtomol/L) but less certain. Mediterranean deep waters contain slightly higher concentrations of gold (100–150 femtomol/L), which

7300-411: The noble metals, it still forms many diverse compounds. The oxidation state of gold in its compounds ranges from −1 to +5, but Au(I) and Au(III) dominate its chemistry. Au(I), referred to as the aurous ion, is the most common oxidation state with soft ligands such as thioethers , thiolates , and organophosphines . Au(I) compounds are typically linear. A good example is Au(CN) − 2 , which

7400-563: The plan of a gold mine in Nubia together with indications of the local geology . The primitive working methods are described by both Strabo and Diodorus Siculus , and included fire-setting . Large mines were also present across the Red Sea in what is now Saudi Arabia . Gold is mentioned in the Amarna letters numbered 19 and 26 from around the 14th century BC. Gold is mentioned frequently in

7500-460: The plating solution and prevents direct contact with the item being plated, is connected to the anode of a low-voltage direct-current power source, and the item to be plated is connected to the cathode . The operator dips the brush in plating solution and 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,

7600-423: The production plating bath. 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 is passed for a specific period of time. The cell

7700-459: The project. The earliest recorded metal employed by humans appears to be gold, which can be found free or " native ". Small amounts of natural gold have been found in Spanish caves used during the late Paleolithic period, c.  40,000 BC . The oldest gold artifacts in the world are from Bulgaria and are dating back to the 5th millennium BC (4,600 BC to 4,200 BC), such as those found in

7800-681: The r-process in the collision of neutron stars . In both cases, satellite spectrometers at first only indirectly detected the resulting gold. However, in August 2017, the spectroscopic signatures of heavy elements, including gold, were observed by electromagnetic observatories in the GW170817 neutron star merger event, after gravitational wave detectors confirmed the event as a neutron star merger. Current astrophysical models suggest that this single neutron star merger event generated between 3 and 13 Earth masses of gold. This amount, along with estimations of

7900-620: The rare bismuthide maldonite ( Au 2 Bi ) and antimonide aurostibite ( AuSb 2 ). Gold also occurs in rare alloys with copper , lead , and mercury : the minerals auricupride ( Cu 3 Au ), novodneprite ( AuPb 3 ) and weishanite ( (Au,Ag) 3 Hg 2 ). A 2004 research paper suggests that microbes can sometimes play an important role in forming gold deposits, transporting and precipitating gold to form grains and nuggets that collect in alluvial deposits. A 2013 study has claimed water in faults vaporizes during an earthquake, depositing gold. When an earthquake strikes, it moves along

8000-420: The rate of occurrence of these neutron star merger events, suggests that such mergers may produce enough gold to account for most of the abundance of this element in the universe. Because the Earth was molten when it was formed , almost all of the gold present in the early Earth probably sank into the planetary core . Therefore, as hypothesized in one model, most of the gold in the Earth's crust and mantle

8100-516: The ratio M = m 1 / m 2 of the plating thickness of a specified region of the cathode "close" to the anode to the thickness of a region "far" from the cathode and the ratio L = x 2 / x 1 of the distances of these regions through the electrolyte to the anode. In a Haring-Blum cell, for example, L = 5 for its two independent cathodes, and a cell yielding plating thickness ratio of M = 6 has Harring-Blum throwing power 100% × ( L − M ) / L = −20% . Other conventions include

8200-935: The reaction. However, the ions are removed from the equilibrium by hydrochloric acid, forming AuCl − 4 ions, or chloroauric acid , thereby enabling further oxidation: 2 Au + 6 H 2 SeO 4 → 200 ∘ C Au 2 ( SeO 4 ) 3 + 3 H 2 SeO 3 + 3 H 2 O {\displaystyle {\ce {2Au{}+6H2SeO4->[{} \atop {200^{\circ }{\text{C}}}]Au2(SeO4)3{}+3H2SeO3{}+3H2O}}} Au + 4 HCl + HNO 3 ⟶ HAuCl 4 + NO ↑ + 2 H 2 O {\displaystyle {\ce {Au{}+4HCl{}+HNO3->HAuCl4{}+NO\uparrow +2H2O}}} Gold

8300-464: The rest of the gold on Earth is thought to have been incorporated into the planet since its very beginning, as planetesimals formed the mantle . In 2017, an international group of scientists established that gold "came to the Earth's surface from the deepest regions of our planet", the mantle, as evidenced by their findings at Deseado Massif in the Argentinian Patagonia . On Earth, gold

8400-474: The same result and showing that the isotopes of gold produced by it were all radioactive . In 1980, Glenn Seaborg transmuted several thousand atoms of bismuth into gold at the Lawrence Berkeley Laboratory. Gold can be manufactured in a nuclear reactor, but doing so is highly impractical and would cost far more than the value of the gold that is produced. Although gold is the most noble of

8500-484: The silver content. The more silver, the lower the specific gravity . Native gold occurs as very small to microscopic particles embedded in rock, often together with quartz or sulfide minerals such as " fool's gold ", which is a pyrite . These are called lode deposits. The metal in a native state is also found in the form of free flakes, grains or larger nuggets that have been eroded from rocks and end up in alluvial deposits called placer deposits . Such free gold

8600-446: The south-east corner of the Black Sea is said to date from the time of Midas , and this gold was important in the establishment of what is probably the world's earliest coinage in Lydia around 610 BC. The legend of the golden fleece dating from eighth century BCE may refer to the use of fleeces to trap gold dust from placer deposits in the ancient world. From the 6th or 5th century BC,

8700-434: The substrate, then 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. The pulse electroplating or pulse electrodeposition (PED) process involves the swift alternating of the electrical potential or current between two different values, resulting in

8800-622: The technology. Among the most notorious cases of electroplating usage in mid-19th century Russia were the gigantic galvanoplastic sculptures of St. Isaac's Cathedral in Saint Petersburg and gold-electroplated dome of the Cathedral of Christ the Saviour in Moscow , the third tallest Orthodox church in the world . Soon after, John Wright of Birmingham , England discovered that potassium cyanide

8900-436: The tendency of gold ions to interact at distances that are too long to be a conventional Au–Au bond but shorter than van der Waals bonding . The interaction is estimated to be comparable in strength to that of a hydrogen bond . Well-defined cluster compounds are numerous. In some cases, gold has a fractional oxidation state. A representative example is the octahedral species {Au( P(C 6 H 5 ) 3 )} 2+ 6 . Gold

9000-428: The transfer/diffusion rate of metal ions from the bulk solution to the electrode surface. The ideal stirring setting varies for different metal electroplating processes. 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 an absorbent cloth material that both holds

9100-403: The transmutation of the chemical elements did not become possible until the understanding of nuclear physics in the 20th century. The first synthesis of gold was conducted by Japanese physicist Hantaro Nagaoka , who synthesized gold from mercury in 1924 by neutron bombardment. An American team, working without knowledge of Nagaoka's prior study, conducted the same experiment in 1941, achieving

9200-453: The uniformity of the electroplated metal thickness, on regions of the part that are near to the anode compared to regions that are far from it. It depends mostly on the composition and temperature of the electroplating solution, as well as on the operating current density . A higher throwing power of the plating bath results in a more uniform coating. The electrolyte in the electrolytic plating cell should contain positive ions (cations) of

9300-429: 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 is essential to successful electroplating, since molecular layers of oil can prevent adhesion of

9400-417: The visors of heat-resistant suits and in sun visors for spacesuits . Gold is a good conductor of heat and electricity . Gold has a density of 19.3 g/cm , almost identical to that of tungsten at 19.25 g/cm ; as such, tungsten has been used in the counterfeiting of gold bars , such as by plating a tungsten bar with gold. By comparison, the density of lead is 11.34 g/cm , and that of

9500-479: 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 electroplating 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. Throwing power (or macro throwing power )

9600-545: 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 from where it spread around the world. The Woolrich Electrical Generator of 1844, now in Thinktank, Birmingham Science Museum , is the earliest electrical generator used in industry. It

9700-783: Was abandoned for a fiat currency system after the Nixon shock measures of 1971. In 2020, the world's largest gold producer was China, followed by Russia and Australia. As of 2020 , a total of around 201,296 tonnes of gold exist above ground. This is equal to a cube, with each side measuring roughly 21.7 meters (71 ft). The world's consumption of new gold produced is about 50% in jewelry, 40% in investments , and 10% in industry . Gold's high malleability, ductility, resistance to corrosion and most other chemical reactions, as well as conductivity of electricity have led to its continued use in corrosion-resistant electrical connectors in all types of computerized devices (its chief industrial use). Gold

9800-611: Was mined deep into the ground, and the resulting shaft became known as the " Glory Hole .” After an interruption of operations at the mine, a group of investors purchased about 7,000 acres (28 km) of land around the discovery site and formed the Dahlonega Consolidated Gold Mining Co. in 1895. After constructing the largest stamp mill east of the Mississippi River at the Consolidated Mine property,

9900-605: Was to distort the Witwatersrand basin in such a way that the gold-bearing rocks were brought to the present erosion surface in Johannesburg , on the Witwatersrand , just inside the rim of the original 300 km (190 mi) diameter crater caused by the meteor strike. The discovery of the deposit in 1886 launched the Witwatersrand Gold Rush . Some 22% of all the gold that is ascertained to exist today on Earth has been extracted from these Witwatersrand rocks. Much of

10000-450: Was used by Elkingtons . The Norddeutsche Affinerie in Hamburg was the first modern electroplating plant starting its production in 1876. As the science of electrochemistry grew, its relationship to electroplating became understood and other types of non-decorative metal electroplating were developed. Commercial electroplating of nickel , brass , tin , and zinc were developed by

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