Copper is a chemical element with the symbol Cu (from Latin: cuprum) and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish. It is used as a conductor of heat and electricity, a building material, and a constituent of various metal alloys. The metal and its alloys have been used for thousands of years. In the Roman era, copper was principally mined on Cyprus, hence the origin of the name of the metal as сyprium (metal of Cyprus), later shortened to сuprum. Its compounds are commonly encountered as copper(II) salts, which often impart blue or green colors to minerals such as turquoise and have been widely used historically as pigments. Architectural structures built with copper corrode to give green verdigris (or patina). Decorative art prominently features copper, both by itself and as part of pigments. Copper(II) ions are water-soluble, where they function at low concentration as bacteriostatic substances, fungicides, and wood preservatives. In sufficient amounts, they are poisonous to higher organisms; at lower concentrations it is an essential trace nutrient to all higher plantand animal life. The main areas where copper is found in animals are tissues, liver, muscle and bone.
Copper, silver and gold are in group 11 of the periodic table, and they share certain attributes: they have one s-orbital electron on top of a filled d-electron shell and are characterized by high ductility and electrical conductivity. The filled d-shells in these elements do not contribute much to the interatomic interactions, which are dominated by the s-electrons through metallic bonds. Contrary to metals with incomplete d-shells, metallic bonds in copper are lacking a covalent character and are relatively weak. This explains the low hardness and high ductility of single crystals of copper. At the macroscopic scale, introduction of extended defects to the crystal lattice, such as grain boundaries, hinders flow of the material under applied stress thereby increasing its hardness. For his reason, copper is usually supplied in a fine-grained polycrystalline form, which has greater strength than monocrystalline forms. The low hardness of copper partly explains its high electrical (59.6×106 S/m) and thus also high thermal conductivity, which are the second highest among pure metals at room temperature. This is because the resistivity to electron transport in metals at room temperature mostly originates from scattering of electrons on thermal vibrations of the lattice, which are relatively weak for a soft metal. The maximum permissible current density of copper in open air is approximately 3.1×106 A/m2 of cross-sectional area, above which it begins to heat excessively. As with other metals, if copper is placed against another metal, galvanic corrosion will occur. Together with osmium (bluish), caesium (yellow) and gold (yellow), copper is one of only four elemental metals with a natural color other than gray or silver. Pure copper is orange-red and acquires a reddish tarnish when exposed to air. The characteristic color of copper results from the electronic transitions between the filled 3d and half-empty 4s atomic shells – the energy difference between these shells is such that it corresponds to orange light. The same mechanism accounts for the yellow color of gold.
Copper forms a rich variety of compounds with oxidation states +1 and +2, which are often called cuprous and cupric, respectively. It does not react with water, but it slowly reacts with atmospheric oxygen forming a layer of brown-black copper oxide. In contrast to the oxidation of iron by wet air, this oxide layer stops the further, bulk corrosion. A green layer of verdigris (copper carbonate) can often be seen on old copper constructions, such as the Statue of Liberty, the largest copper statue in the world build using repoussé and chasing. Hydrogen sulfides and sulfides react with copper to form various copper sulfides on the surface. In the latter case, the copper corrodes, as is seen when copper is exposed to air containing sulfur compounds. Oxygen-containing ammonia solutions give water-soluble complexes with copper, as do oxygen and hydrochloric acid to form copper chlorides and acidified hydrogen peroxide to form copper(II) salts. Copper(II) chloride and copper comproportionate to form copper(I) chloride.
There are 29 isotopes of copper. 63Cu and 65Cu are stable, with 63Cu comprising approximately 69% of naturally occurring copper; they both have a spin of 3/2. The other isotopes are radioactive, with the most stable being 67Cu with a half-life of 61.83 hours. Seven metastable isotopes have been characterized, with 68mCu the longest-lived with a half-life of 3.8 minutes. Isotopes with a mass number above 64 decay by β–, whereas those with a mass number below 64 decay by β+. 64Cu, which has a half-life of 12.7 hours, decays both ways. 62Cu and 64Cu have significant applications. 64Cu is a radiocontrast for X-ray imaging, and complexed with a chelate can be used for treating cancer. 62Cu is used in 62Cu-PTSM that is a radioactive tracer for positron emission tomography.
Copper can be found as either native copper or as part of minerals. Native copper is a polycrystal, with the largest single crystals found to date measuring 4.4×3.2×3.2 cm. The largest mass of elemental copper weighed 420 tonnes and was found in 1857 on the Keweenaw Peninsula in Michigan, US. There are many examples of copper-containing minerals: chalcopyrite and chalcocite are copper sulfides, azurite and malachite are copper carbonates and cuprite is a copper oxide. Copper is present in the Earth’s crust at a concentration of about 50 parts per million (ppm), and is also synthesised in massive stars.
Most copper is mined or extracted as copper sulfides from large open pit mines in porphyry copper deposits that contain 0.4 to 1.0% copper. Examples include Chuquicamata in Chile, Bingham Canyon Mine in Utah, United States and El Chino Mine in New Mexico, United States. According to the British Geological Survey, in 2005, Chile was the top mine producer of copper with at least one-third world share followed by the United States, Indonesia and Peru. The amount of copper in use is increasing and the quantity available is barely sufficient to allow all countries to reach developed world levels of usage.
Copper has been in use at least 10,000 years, but more than 95% of all copper ever mined and smelted has been extracted since 1900. As with many natural resources, the total amount of copper on Earth is vast (around 1014 tons just in the top kilometer of Earth’s crust, or about 5 million years worth at the current rate of extraction). However, only a tiny fraction of these reserves is economically viable, given present-day prices and technologies. Various estimates of existing copper reserves available for mining vary from 25 years to 60 years, depending on core assumptions such as the growth rate. Recycling is a major source of copper in the modern world. Because of these and other factors, the future of copper production and supply is the subject of much debate, including the concept of Peak copper, analogue to Peak Oil. The price of copper has historically been unstable, and it quintupled from the 60-year low of US$0.60/lb (US$1.32/kg) in June 1999 to US$3.75 per pound (US$8.27/kg) in May 2006. It dropped to US$2.40/lb (US$5.29/kg) in February 2007, then rebounded to US$3.50/lb (US$7.71/kg) in April 2007. In February 2009, weakening global demand and a steep fall in commodity prices since the previous year’s highs left copper prices at US$1.51/lb.
The concentration of copper in ores averages only 0.6%, and most commercial ores are sulfides, especially chalcopyrite (CuFeS2) and to a lesser extent chalcocite (Cu2S). These minerals are concentrated from crushed ores to the level of 10–15% copper by froth flotation or bioleaching. Heating this material with silica in flash smelting removes much of the iron as slag. The process exploits the greater ease of converting iron sulfides into its oxides, which in turn react with the silica to form the silicate slag, which floats on top of the heated mass. The resulting copper matte consisting of Cu2S is then roasted to convert all sulfides into oxides:
- 2 Cu2S + 3 O2 → 2 Cu2O + 2 SO2
The cuprous oxide is converted to blistercopper upon heating:
- 2 Cu2O → 4 Cu + O2
This step exploits the relatively easy reduction of copper oxides to copper metal. Natural gas is blown across the blister to remove most of the remaining oxygen and electrorefining is performed on the resulting material to produce pure copper:
- Cu2+ + 2 e– → Cu
Copper, like aluminium, is 100% recyclable without any loss of quality whether in a raw state or contained in a manufactured product. In volume, copper is the third most recycled metal after iron and aluminium. It is estimated that 80% of the copper ever mined is still in use today. The process of recycling copper follows roughly the same steps as is used to extract copper, but requires fewer steps. High purity scrap copper is melted in a furnace and then reduced and cast into billets and ingots; lower purity scrap is refined by electroplating in a bath of sulfuric acid.
As for other elements, the simplest compounds of copper are binary compounds, i.e. those containing only two elements. The principal ones are the oxides, sulfides and halides. Both cuprous and cupric oxides are known. Among the numerous copper sulfides, important examples include copper(I) sulfide and copper(II) sulfide. The cuprous halides with chlorine, bromine, and iodine are known, as are the cupric halides with fluorine, chlorine, and bromine. Attempts to prepare copper(II) iodide give cuprous iodide and iodine.
- 2 Cu2+ + 4 I− → 2 CuI + I2
Copper, like all metals, forms coordination complexes with ligands. In aqueous solution, copper(II) exists as [Cu(H2O)6]2+. This complex exhibits the fastest water exchange rate (speed of water ligands attaching and detaching) for any transition metal aquo complex. Adding an aqueous sodium hydroxide causes the precipitation of light blue solid copper(II) hydroxide. A simplified equation is:
- Cu2+ + 2 OH− → Cu(OH)2
- Cu(H2O)4(OH)2 + 4 NH3 → [Cu(H2O)2(NH3)4]2+ + 2 H2O + 2 OH−
Many other oxyanions form complexes; these include copper(II) acetate, copper(II) nitrate, and copper(II) carbonate. Copper(II) sulfate forms a blue crystalline pentahydrate, which is the most familiar copper compound in the laboratory. It is used in a fungicide called the Bordeaux mixture.
Polyols, compounds containing more than one alcohol functional group, generally interact with cupric salts. For example, copper salts are used to test for reducing sugars. Specifically, using Benedict’s reagent and Fehling’s solution the presence of the sugar is signaled by a color change from blue Cu(II) to reddish copper(I) oxide. Schweizer’s reagent and related complexes with ethylenediamine and other amines dissolve cellulose. Amino acids form very stable chelate complexes with copper(II). Many wet-chemical tests for copper ions exist, one involving potassium ferrocyanide, which gives a brown precipitate with copper(II) salts.
Compounds that contain a carbon-copper bond are known as organocopper compounds. They are very reactive towards oxygen to form copper(I) oxide and have many uses in chemistry. They are synthesised by treating copper(I) compounds with Grignard reagents, terminal alkynes or organolithium reagents; in particular, the last reaction described produces a Gilman reagent. These can undergo substitution with alkyl halides to form coupling products; as such, they are important in the field of organic synthesis. Copper(I) acetylide is highly shock-sensitive but is an intermediate in reactions such as the Cadiot-Chodkiewicz coupling and the Sonogashira coupling. Conjugate addition to enones and carbocupration of alkynes can also be achieved with organocopper compounds. Copper(I) forms a variety of weak complexes with alkenes and carbon monoxide, especially in the presence of amine ligands.
Copper(III) and copper(IV)
Complexes of copper(III) are frequent intermediates in reactions of organocopper compounds. Dicopper oxo complexes also feature copper(III). Fluoride ligands, being highly basic, stabilize metal ions in high oxidation states; indeed, representative copper(III) and copper(IV) complex are fluorides. These include K3CuF6 and Cs2CuF6. With di- and tripeptides, purple-colored complexes of copper(III) have been observed, this high oxidation state being stabilized by the deprotonated amide ligands.
Copper occurs naturally as native copper and was known to some of the oldest civilizations on record. It has a history of use that is at least 10,000 years old, and estimates of its discovery place it at 9000 BC in the Middle East; a copper pendant was found in northern Iraq that dates to 8700 BC. There is evidence that gold and iron were the only metals used by humans before copper. Copper smelting is known to have occurred since 5500 BC in the Balkans by a chisel from Prokuplje in Serbia. It was invented independently in other parts of the world: China before 2800 BC, the Andes around 2000 BC, Central America around 600 AD and West Africa around 900 AD. Investment casting was invented in 4500–4000 BC in Southeast Asia and carbon dating has established mining at Alderley Edge in Cheshire, UK at 2280 to 1890 BC. Ötzi the Iceman, a male dated from 3300–3200 BC, was found with an axe with a copper head 99.7% pure; high levels of arsenic in his hair suggest his involvement in copper smelting. Experience with copper has assisted the development of other metals; in particular, copper smelting led to the discovery of iron smelting. Production in the Old Copper Complex in Michigan and Wisconsin is dated between 6000 and 3000 BC.
Alloying of copper with zinc or tin to make brass and bronze was practiced soon after the discovery of copper. Bronze artifacts from Sumerian cities and Egyptian artifacts of copper and bronze alloys date to 3000 BC. The Bronze Age was from 2500 BC to 600 BC when usage of bronze was widespread in Europe; the transition between the Neolithic period and the Bronze Age is termed the Chalcolithic period (copper-stone), with copper tools being used with stone tools. Brass was known to the Greeks, but became a significant supplement to bronze during the Roman Empire.
Antiquity and Middle Ages
In Greece, copper was known by the name chalkos (χαλκός). It was an important resource for the Romans, Greeks and other ancient peoples. In Roman times, it was known as aes Cyprium, aes being the generic Latin term for copper alloys and Cyprium from Cyprus, where much copper was mined. The phrase was simplified to cuprum, hence the English copper. Aphrodite and Venus represented copper in mythology and alchemy, due to its lustrous beauty, its ancient use in producing mirrors, and its association with Cyprus, which was sacred to the goddess. The seven heavenly bodies known to the ancients were associated with the seven metals known in antiquity, and Venus was assigned to copper. Britain’s first use of brass occurred around the 3rd–2nd century BC. In North America, copper mining began with marginal workings by Native Americans. Native copper is known to have been extracted from sites on Isle Royale with primitive stone tools between 800 and 1600. Copper metallurgy was flourishing in South America, particularly in Peru around 1000 AD; it proceeded at a much slower rate on other continents. Copper burial ornamentals from the 15th century have been uncovered, but the metal’s commercial production did not start until the early 20th century. The cultural role of copper has been important, particularly in currency. Romans in the 6th through 3rd centuries BC used copper lumps as money. At first, the copper itself was valued, but gradually the shape and look of the copper became more important. Julius Caesar had his own coins made from brass, while Octavianus Augustus Caesar‘s coins were made from Cu-Pb-Sn alloys. With an estimated annual output of around 15,000 t, Roman copper mining and smelting activities reached a scale unsurpassed until the time of the Industrial Revolution; the provinces most intensely mined were those of Hispania, Cyprus and in Central Europe. The gates of the Temple of Jerusalem used Corinthian bronze made by depletion gilding. It was most prevalent in Alexandria, where alchemy is thought to have begun. In ancient India, copper was used in the holistic medical science Ayurveda for surgical instruments and other medical equipment. Ancient Egyptians (~2400 BC) used copper for sterilizing wounds and drinking water, and later on for headaches, burns, and itching. The Baghdad Battery, with copper cylinders soldered to lead, dates back to 248 BC to 226 AD and resembles a galvanic cell, leading people to believe this was the first battery; the claim has not been verified.
The Great Copper Mountain was a mine in Falun, Sweden, that operated from the 10th century to 1992. It produced two thirds of Europe’s copper demand in the 17th century and helped fund many of Sweden’s wars during that time. It was referred to as the nation’s treasury; Sweden had a copper backed currency. The uses of copper in art were not limited to currency: it was used by Renaissance sculptors, in pre-photographic technology known as the daguerreotype, and the Statue of Liberty. Copper plating and copper sheathing for ships’ hulls was widespread; the ships of Christopher Columbus were among the earliest to have this feature. The Norddeutsche Affinerie in Hamburg was the first modern electroplating plant starting its production in 1876. The German scientist Gottfried Osann invented powder metallurgy in 1830 while determining the metal’s atomic mass; around then it was discovered that the amount and type of alloying element (e.g. tin) to copper would affect bell tones. Flash smelting was developed by Outokumpu in Finland and first applied at Harjavalta in 1949; the energy-efficient process accounts for 50% of the world’s primary copper production. The Intergovernmental Council of Copper Exporting Countries, formed in 1967 with Chile, Peru, Zaire and Zambia, played a similar role for copper as OPEC does for oil. It never achieved the same influence, particularly because the second-largest producer, the United States, was never a member; it was dissolved in 1988.
The major applications of copper are in electrical wires (60%), roofing and plumbing (20%) and industrial machinery (15%). Copper is mostly used as a metal, but when a higher hardness is required it is combined with other elements to make an alloy (5% of total use) such as brass and bronze. A small part of copper supply is used in production of compounds for nutritional supplements and fungicides in agriculture. Machiningof copper is possible, although it is usually necessary to use an alloy for intricate parts to get good machinability characteristics.
The electrical properties of copper are exploited in copper wires and devices such as electromagnets. Integrated circuits and printed circuit boards increasingly feature copper in place of aluminium because of its superior electrical conductivity; heat sinks and heat exchangers use copper as a result of its superior heat dissipation capacity to aluminium. Vacuum tubes, cathode ray tubes, and the magnetrons in microwave ovens use copper, as do wave guides for microwave radiation.
Architecture and industry
Because of the waterproof nature of copper, it has been used as the roofing material of many buildings since ancient times. The green colour on these buildings is due to a long-term chemical reaction: copper is first oxidised to copper(II) oxide, then to cuprous and cupric sulfide and finally to copper(II) carbonate, also called verdigris, which is highly corrosion-resistant. The copper used in this application is phosphorus deoxidized copper (Cu-DHP). Lightning rods use copper as a means to divert electric current throughout the ground instead of destroying the main structure. Copper has excellent brazing and soldering properties and can be welded; the best results are obtained with gas metal arc welding.
Copper in alloys
Numerous copper alloys exist, many with important uses. Brass is an alloy of copper and zinc and bronze usually refers to copper-tin alloys, but can refer to any alloy of copper such as aluminium bronze. Copper is one of the most important constituents of carat silver and gold alloys and carat solders used in the jewelry industry, modifying the color, hardness and melting point of the resulting alloys. The alloy of copper and nickel, called cupronickel, is used in low-denomination statuary coins, often for the outer cladding. The US 5-cent coin called nickel consists of 75% copper and 25% nickel and has a homogeneous composition. The 90% copper/10% nickel alloy is remarkable by its resistance to corrosion and is used in various parts being exposed to seawater. Alloys of copper with aluminium (about 7%) have a pleasant golden color and are used in decorations. Copper alloys with tin are part of lead-free solders.
Copper has long been used as a biostatic surface to line parts of ships to protect against barnacles and mussels. It was originally used pure, but has since been superseded by Muntz metal. Bacteria will not grow on a copper surface because it is biostatic. Similarly, as discussed in copper alloys in aquaculture, copper alloys have become important netting materials in the aquaculture industry for the fact that they are antimicrobial and prevent biofouling even in extreme conditions and have strong structural and corrosion-resistant properties in marine environments. Copper doorknobs are used by hospitals to reduce the transfer of disease, and Legionnaires’ disease is suppressed by copper tubing in plumbing systems.
Copper compounds in liquid form are used as a wood preservative, particularly in treating original portion of structures during restoration of damage due to dry rot. Together with zinc, copper wires may be placed over non-conductive roofing materials to discourage the growth of moss. Textile fibers use copper to create antimicrobial protective fabrics, as do ceramic glazes, stained glass and musical instruments. Electroplating commonly uses copper as a base for other metals such as nickel. Copper is one of three metals, along with lead and silver, used in a museum materials testing procedure called the Oddy test. In this procedure, copper is used to detect chlorides, oxides, and sulphur compounds. Copper is also commonly found in jewelry, and folklore states that copper bracelets relieve arthritis symptoms, though this is not proven.
Copper proteins have diverse roles in biological electron transport and oxygen transportation, processes that exploit the easy interconversion of Cu(I) and Cu(II). The biological role for copper commenced with the appearance of oxygen in earth’s atmosphere. The protein hemocyanin is the oxygen carrier in most mollusks and some arthropods such as the horseshoe crab (Limulus polyphemus). Because hemocyanin is blue, these organisms have blue blood, not the red blood found in organisms that rely on hemoglobin for this purpose. Structurally related to hemocyanin are the laccases and tyrosinases. Instead of reversibly binding oxygen, these proteins hydroxylate substrates, illustrated by their role in the formation of lacquers. Copper is also a component of other proteins associated with the processing of oxygen. In cytochrome c oxidase, which is required for aerobic respiration, copper and iron cooperate in the reduction of oxygen. Copper is also found in many superoxide dismutases, proteins that detoxify superoxides, by converting it (by disproportionation) to oxygen and hydrogen peroxide:
- 2 HO2 → H2O2 + O2
Several copper proteins, such as the “blue copper proteins”, do not interact directly with substrates, hence they are not enzymes. These proteins relay electrons by the process called electron transfer.
Copper is an essential trace element in plants and animals, but not some microorganisms. The human body contains copper at a level of about 1.4 to 2.1 mg per kg of body mass. Stated differently, the RDA for copper in normal healthy adults is quoted as 0.97 mg/day and as 3.0 mg/day. Copper is absorbed in the gut, then transported to the liver bound to albumin. It enters the bloodstream via the plasma protein called ceruloplasmin, where its metabolism is controlled, and is excreted in bile.
Because of its role in facilitating iron uptake, copper deficiency can produce anemia-like symptoms, neutropenia, bone abnormalities, hypopigmentation, impaired growth, increased incidence of infections, and abnormalities in glucose and cholesterol metabolism. Conversely, an accumulation of copper in body tissues causes Wilson’s disease. Severe deficiency can be found by testing for low plasma or serum copper levels, low ceruloplasmin, and low red blood cell superoxide dismutase levels; these are not sensitive to marginal copper status. The “cytochrome c oxidase activity of leucocytes and platelets” has been stated as another factor in deficiency, but the results have not been confirmed by replication.
Copper, like silver, is antibacterial via the oligodynamic effect; for example, brass doorknobs disinfect themselves of much bacteria within a period of eight hours. It is effective against methicillin-resistant Staphylococcus aureus (MRSA), Escherichia coli and other pathogens. At lower temperatures, longer times are required to kill bacteria. On February 29, 2008, the United States EPA registered 275 alloys, containing greater than 65% nominal copper content, as antimicrobial materials. Registered alloys include pure copper, an assortment of brasses and bronzes, and additional alloys. EPA-sanctioned tests using Good Laboratory Practices were conducted in order to obtain several antimicrobial claims valid against MRSA, Enterobacter aerogenes, Escherichia coli O157: H7 and Pseudomonas aeruginosa. The EPA registration allows the manufacturers of these copper alloys to legally make public health claims as to the health effects of these materials. Several of the aforementioned bacteria are responsible for a large portion of the nearly two million hospital-acquired infections contracted each year in the United States.
Gram quantities of various copper salts have been taken in suicide attempts and produced acute copper toxicity in humans, possibly due to redox cycling and the generation of reactive oxygen species that damage DNA. Corresponding amounts of copper salts (30 mg/kg) are toxic in animals. Chronic copper toxicity does not normally occur in humans because of transport systems that regulate absorption and excretion. Autosomal recessive mutations in copper transport proteins can disable these systems, leading to Wilson’s disease with copper accumulation and cirrhosis of the liver in persons who have inherited two defective genes.
- Erosion corrosion of copper water tubes
- Metal theft
- Peak copper
- Category:Copper mining companies
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|in pure water, or acidic or alkali conditions. Copper in neutral water is more noble than hydrogen.||in water containing sulfide||in 10 M ammonia solution||in a chloride solution|
- Massaro, Edward J., ed (2002). Handbook of Copper Pharmacology and Toxicology. Humana Press. ISBN 0-89603-943-9.
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- William D. Callister (2003). Materials Science and Engineering: an Introduction, 6th Ed.. Table 6.1, p. 137: Wiley, New York. ISBN 0471736961.
- Material: Copper (Cu), bulk, MEMS and Nanotechnology Clearinghouse.
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- Copper transport disorders: an Instant insight from the Royal Society of Chemistry
|Wikimedia Commons has media related to: Copper|
|Look up copper in Wiktionary, the free dictionary.|
- National Pollutant Inventory – Copper and compounds fact sheet
- Copper Resource Page. Includes 12 PDF files detailing the material properties of various kinds of copper, as well as various guides and tools for the copper industry.
- The Copper Development Association has an extensive site of properties and uses of copper; it also maintains a web site dedicated to brass, a copper alloy.
- The Third Millennium Online page on Copper
- Price history of copper, according to the IMF