Hen copper is heated close to dull-red-hot temperature, the many small crystals of metal grow into each other and form...MORE?
1326 °C, 1599 K, 2419 °F
2000 °C, 2273 K, 3632 °F
or cupric oxide
(CuO) is the higher oxide of copper. As a mineral, it is known as tenorite.
It is a black solid with an ionic structure which melts above 1200 °C with some loss of oxygen. It can be formed by heating copper in air:
although in this case copper(I) oxide is formed as well. Pure Copper(II) oxide is better prepared by heating copper(II) nitrate, copper(II) hydroxide or copper(II) carbonate:
Copper(II) oxide is a amphoteric oxide, so it dissolves in mineral acids such as hydrochloric acid, sulfuric acid or nitric acid to give the corresponding copper(II) salts:
It reacts with concentrated alkali to form the corresponding cuprate salts:
It can also be reduced to copper metal using hydrogen or carbon monoxide:
A laboratory method for preparing copper(II) oxide is to electrolyze water containing sodium bicarbonate at a moderate voltage with a copper anode, collect the mixture of insoluble copper hydroxide, basic copper carbonate, and copper carbonate precipitates, and heat it to release the hydrogen, carbon and excess oxygen.
Copper(II) oxide belongs to the monoclinic crystal system, with a crystallographic point group of 2/m or C2h
. The space group of its unit cell is C2/c, and its lattice parameters are a
= 4.6837(5), b
= 3.4226(5), c
= 5.1288(6), α
= 90°, β
= 99.54(1)°, γ
= 90°. The copper atom is coordinated by 4 oxygen atoms in an approximately square planar configuration.
Copper(II) oxide is an irritant. It also can cause damage to the endocrine and central nervous system. Contact to the eyes or skin can cause irritation. Ingesting cupric oxide powder can result in a metallic taste, nausea, vomiting and stomach pain. In more severe cases, there may be blood in vomit or black or tarry stools, jaundice and enlarged liver. Blood cells rupture resulting in circulatory collapse and shock. Inhalation can lead to damage to the lungs and septum. Inhalation of fumes during smelting of cupric oxide powder can lead to a disease called metal fume fever, which can result in flu like symptoms. Copper (II) oxide can cause a toxic build-up of copper in a small subset of the population with Wilson's disease. Handling copper (II) oxide powder should be done in well ventilated area, and care should be taken to avoid contact with the skin or eyes. However copper is an essential trace element for the normal function of many tissues, including the nervous system, immune system, heart, skin and for the formation of capillaries as well as copper being extremely well metabolized by humans. Copper (II) oxide (Cupric oxide, not Cuprous oxide) has extremely low bioavailability (practically zero) and should not be taken in conditions of copper deficiency, especially as part of a multivitamin which also includes zinc or molybdenum. Excessive zinc or molybdenum intake eliminates copper from the body. Copper oxide is used in vitamins supplements as a safe source of copper and over-the-counter treatments. Copper oxide is also used in consumer products such as pillowcases and socks, due to its cosmetic and anti-microbial properties. The risk of dermal sensitivity to copper is considered extremely minimal.
Cupric oxide is used as a pigment in ceramics to produce blue, red, and green (and sometimes gray, pink, or black) glazes. It is also used to produce cuprammonium hydroxide solutions, used to make rayon. It is also occasionally used as a dietary supplement in animals, against copper deficiency. Copper(II) oxide has application as a p-type semiconductor, because it has a narrow band gap of 1.2 eV. It is an abrasive used to polish optical equipment. Cupric oxide can be used to produce dry cell batteries. It has also been used in wet cell batteries as the cathode, with lithium as an anode, and dioxalane mixed with lithium perchlorate as the electrolyte. Copper(II) oxide can be used to produce other copper salts. It is also used when welding with copper alloys.
Another use for cupric oxide is as a substitute for iron oxide in thermite. This can turn the thermite from an incendiary to a low explosive.
Cupric oxide can be used to safely dispose of hazardous materials such as cyanide, hydrocarbons, halogenated hydrocarbons and dioxins, through oxidation.
Here are equations depicting the decomposition of phenol and pentachlorophenol, respectively, with copper oxide:
Red copper oxide
1232 °C, 1505 K, 2250 °F
1800 °C, 2073 K, 3272 °F
or cuprous oxide
is the inorganic compound with the formula Cu2
O. It is one of the principal oxides of copper. This red-coloured solid is a component of some antifouling paints. The compound can appear either yellow or red, depending on the size of the particles. Copper(I) oxide is found as the reddish mineral cuprite.
Copper(I) oxide may be produced by several methods. Most straightforwardly, it arises via the oxidation of copper metal:
Additives such as water and acids affect the rate of this process as well as the further oxidation to copper(II) oxides. It is also produced commercially by reduction of copper(II) solutions with sulfur dioxide. Aqueous cuprous chloride solutions react with base to give the same material. In all cases, the color is highly sensitive to the procedural details.
Formation of copper(I) oxide is the basis of the Fehling's test and Benedict's test for reducing sugars. These sugars reduce an alkaline solution of a copper(II) salt, giving a bright red precipitate of Cu2
It forms on silver-plated copper parts exposed to moisture when the silver layer is porous or damaged. This kind of corrosion is known as red plague.
Little evidence exists for cuprous hydroxide, which is expected to rapidly undergo dehydration. A similar situation applies to the hydroxides of gold(I) and silver(I).
Copper(I) oxide can also be prepared by reacting a copper-ammonia complex with hydrogen peroxide.
The solid is diamagnetic. In terms of their coordination spheres, copper centres are 2-coordinated and the oxides are tetrahedral. The structure thus resembles in some sense the main polymorphs of SiO2
, and both structures feature interpenetrated lattices.
Copper(I) oxide dissolves in concentrated ammonia solution to form the colourless complex [Cu(NH3
]+, which is easily oxidized in air to the blue [Cu(NH3
]2+. It dissolves in hydrochloric acid to give solutions of CuCl2
-. Dilute sulfuric acid and nitric acid produce copper(II) sulfate and copper(II) nitrate, respectively.
O degrades to copper(II) oxide in moist air.
O crystallizes in a cubic structure with a lattice constant al
=4.2696 Å. The Cu atoms arrange in a fcc sublattice, the O atoms in a bcc sublattice. One sublattice is shifted by a quarter of the body diagonal. The space group is
, which includes the point group with full octahedral symmetry.
In the history of semiconductor physics, Cu2
O is one of the most studied materials, and many experimental observations and semiconductor applications have been demonstrated first in this material:
Today, it is still under investigation in semiconductor optics. Particularly people are trying to create a Bose-Einstein condensate of excitons in Cu2
The lowest excitons in Cu2
O are extremely long living and show a neV resonance, which is the narrowest bulk exciton resonance ever observed. The associated quadrupole polaritons have low group velocity approaching the speed of sound. Thus, light moves almost as slowly as sound in this medium, which results in high polariton densities.
Another unusual feature of the ground state excitons is that all primary scattering mechanisms are known quantitatively. Cu2
O was the first substance where an entirely parameter-free model of absorption linewidth broadening by temperature could be established, allowing the corresponding absorption coefficient to be deduced. It can be shown using Cu2
O that the Kramers–Kronig relations do not apply to polaritons.
Cuprous oxide is commonly used as a pigment, a fungicide, and an antifouling agent for marine paints. Rectifier diodes based on this material have been used industrially as early as 1924, long before silicon became the standard. Copper(I) oxide is also responsible for the pink color in a positive Benedict's Test.
Oxides are sorted by oxidation state.
Oxygen-free copper (OFC) or Oxygen-free high thermal conductivity (OFHC) copper generally refers to a group of wrought high conductivity copper alloys that have been electrolytically refined to reduce the level of oxygen to .001% or below.
Oxygen-free copper is typically specified according to the ASTM/UNS database. The UNS database includes many different compositions of high conductivity electrical copper. Of these three are widely used and two are considered oxygen-free.
Oxygen-free high thermal conductivity (OFHC) copper is widely used in cryogenics. OFHC is produced by the direct conversion of selected refined cathodes and castings under carefully controlled conditions to prevent contamination of the pure oxygen-free metal during processing. The method of producing OFHC copper ensures extra high grade of metal with a copper content of 99.99%. With so small a content of extraneous elements, the inherent properties of elemental copper are brought forth to a high degree. Characteristics are high ductility, high electrical and thermal conductivity, high impact strength, good creep resistance, ease of welding, and low relative volatility under high vacuum.
Conductivity is generally specified relative to the 1913 International Annealed Copper Standard of 58 MS/m. Advances in the refining process now yield OF and ETP copper that can meet or exceed 101% of this standard. (Ultra-pure copper has a conductivity of 58.65 MS/m, 102.75% IACS.) Note that OF and ETP coppers have identical conductivity requirements.
Oxygen plays a beneficial role for improving copper conductivity. During the copper smelting process, oxygen is deliberately injected into the melt to scavenge impurities that would otherwise degrade conductivity.
There are advanced refining processes such as Czochralski process than can be used to reduce impurity levels to below the C10100 specification by reducing copper grain density.][ At this time, there are currently no UNS/ASTM classifications for these specialty coppers and the IACS conductivity of these coppers is not readily available.
For industrial applications, oxygen-free copper is valued more for its chemical purity than its electrical conductivity. OF/OFE grade copper is used in plasma deposition (sputtering) processes, including the manufacture of semiconductors and superconductor components, as well as in high vacuum devices such as particle accelerators. In any of these applications, the release of oxygen or other impurities can cause undesirable chemical reactions with other materials in the local environment.
The high-end speaker wire industry markets oxygen-free copper as having enhanced conductivity or other electrical properties that are significantly advantageous to audio signal transmission. However, conductivity specifications for common C11000 Electrolytic-Tough-Pitch (ETP) and higher-cost C10200 Oxygen-Free (OF) coppers are identical. Much more expensive C10100, a highly refined copper with silver impurities removed and oxygen reduced to 0.0005%, has only a one percent increase in conductivity rating, insignificant in audio applications. OFC is nevertheless valued by some][ for both audio and video signals in audio playback systems and home cinema.
High electrical conductivity coppers are distinct from coppers deoxidized by the addition of phosphorus in the smelting process. Oxygen-free phosphorus-containing copper (CuOFP) is typically used for structural and thermal applications where the copper material will be subject to temperatures high enough to cause hydrogen embrittlement or more exactly steam embrittlement. Examples include welding/brazing rods and heat exchanger tubing.
Indeed, copper alloys which contain oxygen as an impurity (in the form of residual oxides present in the metal matrix) can be embrittled if exposed to hot hydrogen. The hydrogen diffuses through the copper and reacts with inclusions of O2Cu, forming H2O (water), which then forms pressurized water steam bubbles at the grain boundaries. This process can cause the grains to literally be forced away from each other, and is known as steam embrittlement (because steam is produced, not because exposure to steam causes the problem).
CuOFP has been selected as corrosion resistant material for the overpack of spent nuclear fuel in the KBS-3 concept developed in Sweden and Finland to dispose high-level radioactive waste in crystalline rock formations.
An operating temperature is the temperature at which an electrical or mechanical device operates. The device will operate effectively within a specified temperature range which varies based on the device function and application context, and ranges from the minimum operating temperature to the maximum operating temperature (or peak operating temperature). Outside this range of safe operating temperatures the device may fail. Aerospace and military-grade devices generally operate over a broader temperature range than industrial devices; commercial-grade devices generally have the lowest operating temperature range.
It is one component of reliability engineering.
Although biological systems do not have a defined operating temperature, individuals are most comfortable when body temperature fluctuations as a result of environmental factors are minimised.
Electrical and mechanical devices used in military and aerospace applications must endure greater environmental variability, including temperature range.
For example, resistors are manufactured in several grades:][
These grades ensure that a device is suitable for its application, and may withstand the environmental conditions in which it is used. In the United States, the Department of Defense has defined the United States Military Standard for all products used by the United States armed forces. A product's environmental design and test limits to the conditions that it will experience throughout its service life are specified in MIL-STD-810, the Department of Defense Test Method Standard for Environmental Engineering Considerations and Laboratory Tests.
The MIL-STD-810G standard specifies that the "operating temperature stabilization is attained when the temperature of the functioning part(s) of the test item considered to have the longest thermal lag is changing at a rate of no more than 2.0°C (3.6°F) per hour." It also specifies procedures to assess the performance of materials to extreme temperature loads.
Military engine turbine blades experience two significant deformation stresses during normal service, creep and thermal fatigue. Creep life of a material is "highly dependent on operating temperature", and creep analysis is thus an important part of design validation. Some of the effects of creep and thermal fatigue may be mitigated by integrating cooling systems into the device's design, reducing the peak temperature experienced by the metal.
In spacecraft propulsion, the performance of nuclear engines can be improved by raising the operating temperature of the fuel elements.
Commercial and retail products are manufactured to less stringent requirements than those for military and aerospace applications. For example, microprocessors produced by Intel Corporation are manufactured to three grades: commercial, industrial and extended.
Because some devices generate heat during operation, they may require thermal management to ensure they are within their specified operating temperature range; specifically, that they are operating at or below the maximum operating temperature of the device. Cooling a microprocessor mounted in a typical commercial or retail configuration requires "a heatsink properly mounted to the processor, and effective airflow through the system chassis". Systems are designed to protect the processor from unusual operating conditions, such as "higher than normal ambient air temperatures or failure of a system thermal management component (such as a system fan)", though in "a properly designed system, this feature should never become active". Cooling and other thermal management techniques may affect performance and noise level. Noise mitigation strategies may be required in residential applications to ensure that the noise level does not become uncomfortable.
Battery service life and efficacy is affected by operating temperature. Efficacy is determined by comparing the service life achieved by the battery as a percentage of its service life achieved at 20°C versus temperature. Ohmic load and operating temperature often jointly determine a battery's discharge rate. Moreover, if the expected operating temperature for a primary battery deviates from the typical 10°C to 25°C range, then operating temperature "will often have an influence on the type of battery selected for the application". Energy reclamation from partially depleted lithium sulfur dioxide battery has been shown to improve when "appropriately increasing the battery operating temperature".
Mammals attempt to maintain a comfortable body temperature under various conditions by thermoregulation, part of mammalian homeostasis. The lowest normal temperature of a mammal, the basal body temperature, is achieved during sleep. In women, it is affected by ovulation, causing a biphasic pattern which may be used as a component of fertility awareness.
In humans, the hypothalamus regulates metabolism, and hence the basal metabolic rate. Amongst its functions is the regulation of body temperature. The core body temperature is also one of the classic phase markers for measuring the timing of an individual's Circadian rhythm.
Changes to the normal human body temperature may result in discomfort. The most common form is a fever, a temporary elevation in the body's thermoregulatory set-point by about 1–2 °C (1.8–3.6 °F). Hyperthermia is an acute condition caused by the body absorbing more heat than it can dissipate, whereas hypothermia is a condition in which the core temperature drops below that required for normal metabolism and is caused by the body's inability to replenish the heat that is being lost to the environment.
Copper is a chemical element with the symbol Cu (from Latin: ) and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; a freshly exposed surface has a reddish-orange color. 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 azurite and 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 is essential to all living organisms as a trace dietary mineral because it is a key constituent of the respiratory enzyme complex cytochrome c oxidase. In molluscs and crustacea copper is a constituent of the blood pigment hemocyanin, which is replaced by the iron-complexed hemoglobin in fish and other vertebrates. The main areas where copper is found in humans are liver, muscle and bone. Copper compounds are used as bacteriostatic substances, fungicides, and wood preservatives.
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 this reason, copper is usually supplied in a fine-grained polycrystalline form, which has greater strength than monocrystalline forms.
The softness of copper partly explains its high electrical conductivity (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 caesium and gold (both yellow), and osmium (bluish), 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 and caesium.
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 built using repoussé and chasing. Copper tarnishes when exposed to hydrogen sulfides and other sulfides, which react with it to form various copper sulfides on the surface. 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. Cu64, which has a half-life of 12.7 hours, decays both ways.
62Cu and 64Cu have significant applications. 64Cu is a radiocontrast agent 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 is synthesized in massive stars and is present in the Earth's crust at a concentration of about 50 parts per million (ppm), where it occurs as native copper or in minerals such as the copper sulfides chalcopyrite and , copper carbonates azurite and malachite and the copper(I) oxide mineral cuprite. The largest mass of elemental copper discovered weighed 420 tonnes and was found in 1857 on the Keweenaw Peninsula in Michigan, US. Native copper is a polycrystal, with the largest described single crystal measuring 4.4×3.2×3.2 cm.
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. Copper can also be recovered through the In-situ leach process. Several sites in the state of Arizona are considered prime candidates for this method. 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 96% of all copper ever mined and smelted has been extracted since 1900, and more than half was extracted in only the last 24 years. 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, analogous 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:
The cuprous oxide is converted to blister copper upon heating:
The Sudbury matte process converted only half the sulfide to oxide and then used this oxide to remove the rest of the sulfur as oxide. It was then electrolytically refined and the anode mud exploited for the platinum and gold it contained. 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:
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. According to the International Resource Panel's Metal Stocks in Society report, the global per capita stock of Copper in use in society is 35–55 kg. Much of this is in more-developed countries (140–300 kg per capita) rather than less-developed countries (30–40 kg per capita).
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.
Numerous copper alloys exist, many with important uses. Brass is an alloy of copper and zinc. 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 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. Some lead-free solders consist of tin alloyed with a small proportion of copper and other metals.
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.
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 aqueous sodium hydroxide causes the precipitation of light blue solid copper(II) hydroxide. A simplified equation is:
Aqueous ammonia results in the same precipitate. Upon adding excess ammonia, the precipitate dissolves, forming tetraamminecopper(II):
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 synthesized 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) is most characteristically found in oxides. A simple example is potassium cuprate, KCuO2, a blue-black solid. The best studied copper(III) compounds are the cuprate superconductors. Yttrium barium copper oxide (YBa2Cu3O7) consists of both Cu(II) and Cu(III) centres. Like oxide, fluoride is a highly basic anion and is known to stabilize metal ions in high oxidation states. Indeed, both copper(III) and even copper(IV) fluorides are known, 6CuF3K and 6CuF2Cs, respectively.
Some copper proteins form oxo complexes, which also feature copper(III). With di- and tripeptides, purple-colored copper(III) complexes are stabilized by the deprotonated amide ligands.
Complexes of copper(III) are also observed as intermediates in reactions of organocopper compounds.
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 meteoric iron (but not iron smelting) were the only metals used by humans before copper. The history of copper metallurgy is thought to have followed the following sequence: 1) cold working of native copper, 2) annealing, 3) smelting, and 4) the lost wax method. In southeastern Anatolia, all four of these metallurgical techniques appears more or less simultaneously at the beginning of the Neolithic c. 7500 BC. However, just as agriculture was independently invented in several parts of the world (including Pakistan, China, and the Americas) copper smelting was invented locally in several different places. It was probably discovered independently in China before 2800 BC, in Central America perhaps around 600 AD, and in West Africa about the 9th or 10th century 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. Natural bronze, a type of copper made from ores rich in silicon, arsenic, and (rarely) tin, came into general use in the Balkans around 5500 BC.
Alloying copper with tin to make bronze was first practiced about 4000 years after the discovery of copper smelting, and about 2000 years after "natural bronze" had come into general use. Bronze artifacts from Sumerian cities and Egyptian artifacts of copper and bronze alloys date to 3000 BC. The Bronze Age began in Southeastern Europe around 3700–3300 BC, in Northwestern Europe about 2500 BC. It ended with the beginning of the Iron Age, 2000–1000 BC in the Near East, 600 BC in Northern Europe. The transition between the Neolithic period and the Bronze Age was formerly termed the Chalcolithic period (copper-stone), with copper tools being used with stone tools. This term has gradually fallen out of favor because in some parts of the world the Chalcolithic and Neolithic are coterminous at both ends. Brass, an alloy of copper and zinc, is of much more recent origin. It was known to the Greeks, but became a significant supplement to bronze during the Roman Empire.
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, because of 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 AD 226 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 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 pure 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. Machining of copper is possible, although it is usually necessary to use an alloy for intricate parts to get good machinability characteristics.
Despite competition from other materials, copper remains the preferred electrical conductor in nearly all categories of electrical wiring with the major exception being overhead electric power transmission where aluminium is often preferred. Copper wire is used in power generation, power transmission, power distribution, telecommunications, electronics circuitry, and countless types of electrical equipment. Electrical wiring is the most important market for the copper industry. This includes building wire, communications cable, power distribution cable, appliance wire, automotive wire and cable, and magnet wire. Roughly half of all copper mined is used to manufacture electrical wire and cable conductors. Many electrical devices rely on copper wiring because of its multitude of inherent beneficial properties, such as its high electrical conductivity, tensile strength, ductility, creep (deformation) resistance, corrosion resistance, low thermal expansion, high thermal conductivity, solderability, and ease of installation.
Integrated circuits and printed circuit boards increasingly feature copper in place of aluminium because of its superior electrical conductivity (see Copper interconnect for main article); heat sinks and heat exchangers use copper as a result of its superior heat dissipation capacity to aluminium. Electromagnets, vacuum tubes, cathode ray tubes, and magnetrons in microwave ovens use copper, as do wave guides for microwave radiation.
Copper’s greater conductivity versus other metallic materials enhances the electrical energy efficiency of motors. This is important because motors and motor-driven systems account for 43%-46% of all global electricity consumption and 69% of all electricity used by industry. Increasing the mass and cross section of copper in a coil increases the electrical energy efficiency of the motor. Copper motor rotors, a new technology designed for motor applications where energy savings are prime design objectives, are enabling general-purpose induction motors to meet and exceed National Electrical Manufacturers Association (NEMA) premium efficiency standards.
Copper has been used since ancient times as a durable, corrosion resistant, and weatherproof architectural material. Roofs, flashings, rain gutters, downspouts, domes, spires, vaults, and doors have been made from copper for hundreds or thousands of years. Copper’s architectural use has been expanded in modern times to include interior and exterior wall cladding, building expansion joints, radio frequency shielding, and antimicrobial indoor products, such as attractive handrails, bathroom fixtures, and counter tops. Some of copper’s other important benefits as an architectural material include its low thermal movement, light weight, lightning protection, and its recyclability.
The metal’s distinctive natural green patina has long been coveted by architects and designers. The final patina is a particularly durable layer that is highly resistant to atmospheric corrosion, thereby protecting the underlying metal against further weathering. It can be a mixture of carbonate and sulfate compounds in various amounts, depending upon environmental conditions such as sulfur-containing acid rain. Architectural copper and its alloys can also be 'finished' to embark a particular look, feel, and/or color. Finishes include mechanical surface treatments, chemical coloring, and coatings.
Copper has excellent brazing and soldering properties and can be welded; the best results are obtained with gas metal arc welding.
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 because of the fact that they are antimicrobial and prevent biofouling, even in extreme conditions and have strong structural and corrosion-resistant properties in marine environments.
Numerous antimicrobial efficacy studies have been conducted in the past 10 years regarding copper’s efficacy to destroy a wide range of bacteria, as well as influenza A virus, adenovirus, and fungi.
Copper-alloy touch surfaces have natural intrinsic properties to destroy a wide range of microorganisms (e.g., E. coli O157:H7, methicillin-resistant Staphylococcus aureus (MRSA), Staphylococcus, Clostridium difficile, influenza A virus, adenovirus, and fungi). Some 355 copper alloys were proven to kill more than 99.9% of disease-causing bacteria within just two hours when cleaned regularly. The United States Environmental Protection Agency (EPA) has approved the registrations of these copper alloys as “antimicrobial materials with public health benefits," which allows manufacturers to legally make claims as to the positive public health benefits of products made with registered antimicrobial copper alloys. In addition, the EPA has approved a long list of antimicrobial copper products made from these alloys, such as bedrails, handrails, over-bed tables, sinks, faucets, door knobs, toilet hardware, computer keyboards, health club equipment, shopping cart handles, etc. (for a comprehensive list of products, see: Antimicrobial copper-alloy touch surfaces#Approved products). Copper doorknobs are used by hospitals to reduce the transfer of disease, and Legionnaires' disease is suppressed by copper tubing in plumbing systems. Antimicrobial copper alloy products are now being installed in healthcare facilities in the U.K., Ireland, Japan, Korea, France, Denmark, and Brazil and in the subway transit system in Santiago, Chile, where copper-zinc alloy handrails will be installed in some 30 stations between 2011–2014.
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 sulfur compounds.
Copper is commonly used in jewelry, and folklore says that copper bracelets relieve arthritis symptoms. Copper is the principal alloying metal in sterling silver and gold alloys. It may also be used on its own, or as a constituent of brass, bronze, gilding metal and many other base metal alloys.
Copper is used as the printing plate in etching, engraving and other forms of intaglio (printmaking) printmaking
Copper oxide and carbonate is used in glassmaking and in ceramic glazes to impart green and brown colors.
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 catalyze the decomposition of superoxides, by converting it (by disproportionation) to oxygen and hydrogen peroxide:
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. After processing in the liver, copper is distributed to other tissues in a second phase. Copper transport here involves the protein ceruloplasmin, which carries the majority of copper in blood. Ceruloplasmin also carries copper that is excreted in milk, and is particularly well-absorbed as a copper source. Copper in the body normally undergoes enterohepatic circulation (about 5 mg a day, vs. about 1 mg per day absorbed in the diet and excreted from the body), and the body is able to excrete some excess copper, if needed, via bile, which carries some copper out of the liver that is not then reabsorbed by the intestine.
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, osteoporosis, hyperthyroidism, and abnormalities in glucose and cholesterol metabolism. Conversely, Wilson's disease causes an accumulation of copper in body tissues.
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.
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. A minimum dietary value for healthy growth in rabbits has been reported to be at least 3 ppm in the diet. However, higher concentrations of copper (100 ppm, 200 ppm, or 500 ppm) in the diet of rabbits may favorably influence feed conversion efficiency, growth rates, and carcass dressing percentages.
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.
Annealing, in metallurgy and materials science, is a heat treatment that alters a material to increase its ductility and to make it more workable. It involves heating material to above its critical temperature, maintaining a suitable temperature, and then cooling. Annealing can induce ductility, soften material, relieve internal stresses, refine the structure by making it homogeneous, and improve cold working properties.
In the cases of copper, steel, silver, and brass, this process is performed by heating the material (generally until glowing) for a while and then letting it cool to room temperature in still air. Copper, silver and brass can be cooled slowly in air, or quickly by quenching in water, unlike ferrous metals, such as steel, which must be cooled slowly to anneal. In this fashion, the metal is softened and prepared for further work—such as shaping, stamping, or forming.
Annealing occurs by the diffusion of atoms within a solid material, so that the material progresses towards its equilibrium state. Heat increases the rate of diffusion by providing the energy needed to break bonds. The movement of atoms has the effect of redistributing and destroying the dislocations in metals and (to a lesser extent) in ceramics. This alteration in dislocations allows metals to deform more easily, so increases their ductility.][
The amount of process-initiating Gibbs free energy in a deformed metal is also reduced by the annealing process. In practice and industry, this reduction of Gibbs free energy is termed stress relief.][
The relief of internal stresses is a thermodynamically spontaneous process; however, at room temperatures, it is a very slow process. The high temperatures at which the annealing process occurs serve to accelerate this process.][
The reaction that facilitates returning the cold-worked metal to its stress-free state has many reaction pathways, mostly involving the elimination of lattice vacancy gradients within the body of the metal. The creation of lattice vacancies is governed by the Arrhenius equation, and the migration/diffusion of lattice vacancies are governed by Fick’s laws of diffusion.
Hardness decreases and ductility increases, because dislocations are eliminated and the metal's crystal lattice is altered. On heating to a specific temperature atoms will migrate within the lattice and the adjusted grain can improve the mechanical properties.][
The three stages of the annealing process that proceed as the temperature of the material is increased are: recovery, recrystallization, and grain growth. The first stage is recovery, and it results in softening of the metal through removal of primarily linear defects called dislocations and the internal stresses they cause. Recovery occurs at the lower temperature stage of all annealing processes and before the appearance of new strain-free grains. The grain size and shape do not change. The second stage is recrystallization, where new strain-free grains nucleate and grow to replace those deformed by internal stresses. If annealing is allowed to continue once recrystallization has completed, then grain growth (the third stage) occurs. In grain growth, the microstructure starts to coarsen and may cause the metal to lose a substantial part of its original strength. This can however be regained with Hardening (metallurgy).][
The high temperature of annealing may result in oxidation of the metal’s surface, resulting in scale. If scale must be avoided, annealing is carried out in a special atmosphere, such as with endothermic gas (a mixture of carbon monoxide, hydrogen gas, and nitrogen gas). Annealing is also done in forming gas, a mixture of hydrogen and nitrogen.
The magnetic properties of mu-metal (Espey cores) are introduced by annealing the alloy in a hydrogen atmosphere.
Typically, large ovens are used for the annealing process. The inside of the oven is large enough to place the workpiece in a position to receive maximum exposure to the circulating heated air. For high volume process annealing, gas fired conveyor furnaces are often used. For large workpieces or high quantity parts, car-bottom furnaces are used so workers can easily move the parts in and out. Once the annealing process is successfully completed, workpieces are sometimes left in the oven so the parts cool in a controllable way. While some workpieces are left in the oven to cool in a controlled fashion, other materials and alloys are removed from the oven. Once removed from the oven, the workpieces are often quickly cooled off in a process known as quench hardening. Typical methods of quench hardening materials involve media such as air, water, oil, or salt. Salt is used as a medium for quenching usually in the form of brine (salt water). Brine provides faster cooling rates than water. This is because when an object is quenched in water air bubbles form on the surface of the object reducing the surface area the water is in contact with. The salt in the brine reduces the formation of air bubbles on the objects surface, meaning there is a larger surface area of the object in contact with the water, providing faster cooling rates.][ Quench hardening is generally applicable to some ferrous alloys, but not copper alloys.
In the semiconductor industry, silicon wafers are annealed, so that dopant atoms, usually boron, phosphorus or arsenic, can diffuse into substitutional positions in the crystal lattice, resulting in drastic changes in the electrical properties of the semiconducting material.
Normalization is an annealing process applied to ferrous alloys to give the material a uniform fine grained structure and make it less brittle. It is used on steels of less than 0.4% carbon to transform austinite into ferrite, pearlite and sorbite. It involves heating the steel to 20-50 kelvin above its upper critical point. It is soaked for a short period at that temperature and then allowed to cool in air. Smaller grains form that produce a tougher, more ductile material. It eliminates columnar grains and dendritic segregation that sometimes occurs during casting. Normalizing improves machinability of a component and provides dimensional stability if subjected to further heat treatment processes.
Process annealing, also called intermediate annealing, subcritical annealing, or in-process annealing, is a heat treatment cycle that restores some of the ductility to a product during the process of cold working, so it can be worked further without breaking. Ductility is important in shaping and creating a more refined piece of work through processes such as rolling, drawing, forging, spinning, extruding and heading. The piece is heated to a temperature typically below the austenizing temperature, and held there long enough to relieve stresses in the metal. The piece is then furnace cooled. It can then be subjected to additional cold working. This can also be used to ensure there is reduced risk of distortion of the work piece during machining, welding, or further heat treatment cycles.
The temperature range for process annealing ranges from 260 °C(500 °F) to 760 °C(1400 °F), depending on the alloy in question.
A full anneal typically results in the second most ductile state a metal can assume for metal alloy. It creates an entirely new uniform microstructure with good dynamic properties. To perform a full anneal on steel for example, steel is heated to 50°C above the austenic temperature and held for sufficient time to allow the material to fully form austenite or austenite-cementite grain structure. The material is then allowed to cool slowly so that the equilibrium microstructure is obtained. In some cases this means the material is allowed to air cool. In other cases the material is allowed to furnace cool. The details of the process depend on the type of metal and the precise alloy involved. In any case the result is a more ductile material but a lower yield strength and a lower tensile strength. This process is also called LP annealing for lamellar pearlite in the steel industry as opposed to a process anneal, which does not specify a microstructure and only has the goal of softening the material. Often the material to be machined is annealed, and then subject to further heat treatment to achieve the final desired properties.
Short cycle annealing is used for turning normal ferrite into malleable ferrite. It consists of heating, cooling, and then heating again from 4 to 8 hours.
Resistive heating can be used to efficiently anneal copper wire; the heating system employs a controlled electrical short circuit. It can be advantageous because it does not require a temperature-regulated furnace like other methods of annealing.
The process consists of two conductive pulleys (step pulleys), which the wire passes across after it is drawn. The two pulleys have an electrical potential across them, which causes the wire to form a short circuit. The Joule effect causes the temperature of the wire to rise to approximately 400 °C. This temperature is affected by the rotational speed of the pulleys, the ambient temperature, and the voltage applied. Where t is the temperature of the wire, K is a constant, V is the voltage applied, r is the number of rotations of the pulleys per minute, and ta is the ambient temperature:
t = ((KV ²)/(r))+ta
The constant K depends on the diameter of the pulleys and the resistivity of the copper.
Purely in terms of the temperature of the copper wire, an increase in the speed of the wire through the pulley system has the same effect as an increase in resistance. Therefore, the speed of the wire can be varied quadratically as the voltage is applied.
is a unit of measurement for temperature. It is one of the seven base units in the International System of Units (SI) and is assigned the unit symbol K
. The Kelvin scale
is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all thermal motion ceases in the classical description of thermodynamics. The kelvin is defined as the fraction of the thermodynamic temperature of the triple point of water (exactly 0.01 °C or 32.018 °F).
The Kelvin scale is named after the Belfast-born, Glasgow University engineer and physicist William Thomson, 1st Baron Kelvin (1824–1907), who wrote of the need for an "absolute thermometric scale
". Unlike the degree Fahrenheit and degree Celsius, the kelvin is not referred to or typeset as a degree. The kelvin is the primary unit of measurement in the physical sciences, but is often used in conjunction with the degree Celsius, which has the same magnitude. Subtracting 273.16 K from the temperature of the triple point of water (0.01 °C) makes absolute zero (0 K) equivalent to .
In 1848 Lord Kelvin (William Thomson), wrote in his paper, On an Absolute Thermometric Scale
, of the need for a scale whereby "infinite cold" (absolute zero) was the scale's null point, and which used the degree Celsius for its unit increment. Thomson calculated that absolute zero was equivalent to −273 °C on the air thermometers of the time. This absolute scale is known today as the Kelvin thermodynamic temperature scale. Thomson's value of "−273" was the reciprocal of 0.00366—the accepted expansion coefficient of gas per degree Celsius relative to the ice point, giving a remarkable consistency to the currently accepted value.
In 1954, the Resolution 3 of the 10th CGPM gave the Kelvin scale its modern definition by designating the triple point of water as its second defining point and assigned its temperature to exactly 273.16 kelvin.
In 1967/1968 Resolution 3 of the 13th CGPM renamed the unit increment of thermodynamic temperature "kelvin", symbol K, replacing "degree absolute", symbol °K. Furthermore, feeling it useful to more explicitly define the magnitude of the unit increment, the 13th CGPM also held in Resolution 4 that "The kelvin, unit of thermodynamic temperature, is equal to the fraction of the thermodynamic temperature of the triple point of water."
In 2005 The Comité International des Poids et Mesures (CIPM), a committee of the CGPM, affirmed that for the purposes of delineating the temperature of the triple point of water, the definition of the Kelvin thermodynamic temperature scale would refer to water having an isotopic composition specified as VSMOW
This SI unit is named after William Thomson, 1st Baron Kelvin. As with every International System of Units (SI) unit whose name is derived from the proper name of a person, the first letter of its symbol is upper case (K). However, when an SI unit is spelled out in English, it should always begin with a lower case letter (kelvin
), except in a situation where any
word in that position would be capitalized, such as at the beginning of a sentence or in capitalized material such as a title. Note that "degree Celsius" conforms to this rule because the "d" is lowercase. —Based on The International System of Units
, section 5.2. When spelled out or spoken, the unit is pluralised using the same grammatical rules as for other SI units such as the volt or ohm (e.g., "the triple point of water is exactly 273.16 kelvins" ). When reference is made to the "Kelvin scale
", the word "kelvin"—which is normally a noun—functions adjectivally to modify the noun "scale" and is capitalized. As with most other SI unit symbols (angle symbols, e.g. 45°3′4″, are the exception) there is a space between the numeric value and the kelvin symbol (e.g., "99.987 K").
Before the 13th General Conference on Weights and Measures (CGPM) in 1967–1968, the unit kelvin was called a "degree", the same as with the other temperature scales at the time. It was distinguished from the other scales with either the adjective suffix "Kelvin" ("degree Kelvin") or with "absolute" ("degree absolute") and its symbol was °K. The latter (degree absolute), which was the unit's official name from 1948 until 1954, was rather ambiguous since it could also be interpreted as referring to the Rankine scale. Before the 13th CGPM, the plural form was "degrees absolute". The 13th CGPM changed the unit name to simply "kelvin" (symbol K). The omission of "degree" indicates that it is not relative to an arbitrary reference point like the Celsius and Fahrenheit scales (although the Rankine scale continued to use "degree Rankine"), but rather an absolute unit of measure which can be manipulated algebraically (e.g., multiplied by two to indicate twice the amount of "mean energy" available among elementary degrees of freedom of the system).
In science and in engineering, degrees Celsius and kelvin are often used simultaneously in the same article (e.g., "...its measured value was 0.01028 °C with an uncertainty of 60 µK..."). This practice is permissible because the degree Celsius is a special name for the kelvin for use in expressing Celsius temperatures and the magnitude of the degree Celsius is exactly equal to that of the kelvin. Notwithstanding that the official endorsement provided by Resolution 3 of the 13th CGPM states, "a temperature interval may also be expressed in degrees Celsius", the practice of simultaneously using both "°C" and "K" remains widespread throughout the scientific world as the use of SI prefixed forms of the degree Celsius (such as "µ°C" or "microdegrees Celsius") to express a temperature interval has not been widely adopted.
In 2005 the CIPM embarked on a program to redefine, amongst others, the kelvin using a more rigorous basis than was in use. The current (2010) definition is unsatisfactory for temperatures below 20 K and above 1300 K. The committee proposes defining the kelvin as the temperature scale for which Boltzmann's constant is exactly. The committee hoped that the program will be completed in time for its adoption by the CGPM at its 2011 meeting, but at to 2011 meeting the decision was postponed to the 2014 meeting when it would be considered as part of a larger program.
From a scientific point of view, this will link temperature to the rest of SI and result in a stable definition that is independent of any particular substance. From a practical point of view, the redefinition will pass unnoticed; water will still freeze at 0 °C (32 °F, 273.15 K).
The kelvin is often used in the measure of the colour temperature of light sources. Colour temperature is based upon the principle that a black body radiator emits light of which the colour depends on the temperature of the radiator. Black bodies with temperatures below about 4000 K appear reddish whereas those above about 7500 K appear bluish. Colour temperature is important in the fields of image projection and photography where a colour temperature of approximately 5600 K is required to match "daylight" film emulsions. In astronomy, the stellar classification of stars and their place on the Hertzsprung–Russell diagram are based, in part, upon their surface temperature, known as effective temperature. The photosphere of the Sun, for instance, has an effective temperature of 5778 K.
In electronics, the kelvin is used as an indicator of how noisy a circuit is in relation to an ultimate noise floor, i.e. the noise temperature. The so-called Johnson–Nyquist noise of discrete resistors and capacitors is a type of thermal noise derived from the Boltzmann constant and can be used to determine the noise temperature of a circuit using the Friis formulas for noise.
Blue vitriol (pentahydrate)
Bonattite (trihydrate mineral)
Boothite (heptahydrate mineral)
Chalcanthite (pentahydrate mineral)
Glass-to-metal seals are a very important element of the construction of vacuum tubes, electric discharge tubes, incandescent light bulbs, glass encapsulated semiconductor diodes, reed switches, pressure tight glass windows in metal cases, and metal or ceramic packages of electronic components.
Properly done, such a seal is hermetic. To achieve such a seal, two properties must hold: Technology Internet
Dietary minerals (also known as mineral nutrients) are the chemical elements required by living organisms, other than the four elements carbon, hydrogen, nitrogen, and oxygen present in common organic molecules. The term is archaic, as it describes chemical elements rather than actual minerals.
Minerals in order of abundance in the human body include the seven major minerals calcium, phosphorus, potassium, sulfur, sodium, chlorine, and magnesium. Important "trace" or minor minerals, necessary for mammalian life, include iron, cobalt, copper, zinc, molybdenum, iodine, and selenium (see below for detailed discussion).