Cadmium is a chemical element with symbol Cd and atomic number 48. This soft, bluish-white metal is chemically similar to the two other stable metals in group 12, zinc and mercury. Like zinc, it demonstrates oxidation state +2 in most of its compounds, and like mercury, it has a lower melting point than the transition metals in groups 3 through 11. Cadmium and its congeners in group 12 are often not considered transition metals, in that they do not have partly filled d or f electron shells in the elemental or common oxidation states. The average concentration of cadmium in Earth's crust is between 0.1 and 0.5 parts per million (ppm). It was discovered in 1817 simultaneously by Stromeyer and Hermann, both in Germany, as an impurity in zinc carbonate.
Cadmium occurs as a minor component in most zinc ores and is a byproduct of zinc production. Cadmium was used for a long time as a corrosion-resistant plating on steel, and cadmium compounds are used as red, orange and yellow pigments, to color glass, and to stabilize plastic. Cadmium use is generally decreasing because it is toxic (it is specifically listed in the European Restriction of Hazardous Substances) and nickel-cadmium batteries have been replaced with nickel-metal hydride and lithium-ion batteries. One of its few new uses is cadmium telluride solar panels.
|Appearance||silvery bluish-gray metallic|
|Standard atomic weight Ar, std(Cd)||112.414(4)|
|Cadmium in the periodic table|
|Atomic number (Z)||48|
|Element category||post-transition metal, alternatively considered a transition metal|
|Electron configuration||[Kr] 4d10 5s2|
Electrons per shell
|2, 8, 18, 18, 2|
|Phase at STP||solid|
|Melting point||594.22 K (321.07 °C, 609.93 °F)|
|Boiling point||1040 K (767 °C, 1413 °F)|
|Density (near r.t.)||8.65 g/cm3|
|when liquid (at m.p.)||7.996 g/cm3|
|Heat of fusion||6.21 kJ/mol|
|Heat of vaporization||99.87 kJ/mol|
|Molar heat capacity||26.020 J/(mol·K)|
|Oxidation states||−2, +1, +2 (a mildly basic oxide)|
|Electronegativity||Pauling scale: 1.69|
|Atomic radius||empirical: 151 pm|
|Covalent radius||144±9 pm|
|Van der Waals radius||158 pm|
Spectral lines of cadmium
|Crystal structure|| hexagonal close-packed (hcp)|
|Speed of sound thin rod||2310 m/s (at 20 °C)|
|Thermal expansion||30.8 µm/(m·K) (at 25 °C)|
|Thermal conductivity||96.6 W/(m·K)|
|Electrical resistivity||72.7 nΩ·m (at 22 °C)|
|Magnetic susceptibility||−19.8·10−6 cm3/mol|
|Young's modulus||50 GPa|
|Shear modulus||19 GPa|
|Bulk modulus||42 GPa|
|Brinell hardness||203–220 MPa|
|Discovery and first isolation||Karl Samuel Leberecht Hermann and Friedrich Stromeyer (1817)|
|Named by||Friedrich Stromeyer (1817)|
|Main isotopes of cadmium|
Cadmium is a soft, malleable, ductile, bluish-white divalent metal. It is similar in many respects to zinc but forms complex compounds. Unlike most other metals, cadmium is resistant to corrosion and is used as a protective plate on other metals. As a bulk metal, cadmium is insoluble in water and is not flammable; however, in its powdered form it may burn and release toxic fumes.
Although cadmium usually has an oxidation state of +2, it also exists in the +1 state. Cadmium and its congeners are not always considered transition metals, in that they do not have partly filled d or f electron shells in the elemental or common oxidation states. Cadmium burns in air to form brown amorphous cadmium oxide (CdO); the crystalline form of this compound is a dark red which changes color when heated, similar to zinc oxide. Hydrochloric acid, sulfuric acid, and nitric acid dissolve cadmium by forming cadmium chloride (CdCl2), cadmium sulfate (CdSO4), or cadmium nitrate (Cd(NO3)2). The oxidation state +1 can be produced by dissolving cadmium in a mixture of cadmium chloride and aluminium chloride, forming the Cd22+ cation, which is similar to the Hg22+ cation in mercury(I) chloride.
Naturally occurring cadmium is composed of 8 isotopes. Two of them are radioactive, and three are expected to decay but have not done so under laboratory conditions. The two natural radioactive isotopes are 113Cd (beta decay, half-life is 7.7 × 1015 years) and 116Cd (two-neutrino double beta decay, half-life is 2.9 × 1019 years). The other three are 106Cd, 108Cd (both double electron capture), and 114Cd (double beta decay); only lower limits on these half-lives have been determined. At least three isotopes – 110Cd, 111Cd, and 112Cd – are stable. Among the isotopes that do not occur naturally, the most long-lived are 109Cd with a half-life of 462.6 days, and 115Cd with a half-life of 53.46 hours. All of the remaining radioactive isotopes have half-lives of less than 2.5 hours, and the majority have half-lives of less than 5 minutes. Cadmium has 8 known meta states, with the most stable being 113mCd (t1⁄2 = 14.1 years), 115mCd (t1⁄2 = 44.6 days), and 117mCd (t1⁄2 = 3.36 hours).
The known isotopes of cadmium range in atomic mass from 94.950 u (95Cd) to 131.946 u (132Cd). For isotopes lighter than 112 u, the primary decay mode is electron capture and the dominant decay product is element 47 (silver). Heavier isotopes decay mostly through beta emission producing element 49 (indium).
One isotope of cadmium, 113Cd, absorbs neutrons with high selectivity: With very high probability, neutrons with energy below the cadmium cut-off will be absorbed; those higher than the cut-off will be transmitted. The cadmium cut-off is about 0.5 eV, and neutrons below that level are deemed slow neutrons, distinct from intermediate and fast neutrons.
Cadmium is created via the s-process in low- to medium-mass stars with masses of 0.6 to 10 solar masses, over thousands of years. In that process, a silver atom captures a neutron and then undergoes beta decay.
Cadmium (Latin cadmia, Greek καδμεία meaning "calamine", a cadmium-bearing mixture of minerals that was named after the Greek mythological character Κάδμος, Cadmus, the founder of Thebes) was discovered simultaneously in 1817 by Friedrich Stromeyer and Karl Samuel Leberecht Hermann, both in Germany, as an impurity in zinc carbonate. Stromeyer found the new element as an impurity in zinc carbonate (calamine), and, for 100 years, Germany remained the only important producer of the metal. The metal was named after the Latin word for calamine, because it was found in this zinc ore. Stromeyer noted that some impure samples of calamine changed color when heated but pure calamine did not. He was persistent in studying these results and eventually isolated cadmium metal by roasting and reducing the sulfide. The potential for cadmium yellow as pigment was recognized in the 1840s, but the lack of cadmium limited this application.
Even though cadmium and its compounds are toxic in certain forms and concentrations, the British Pharmaceutical Codex from 1907 states that cadmium iodide was used as a medication to treat "enlarged joints, scrofulous glands, and chilblains".
In 1907, the International Astronomical Union defined the international ångström in terms of a red cadmium spectral line (1 wavelength = 6438.46963 Å). This was adopted by the 7th General Conference on Weights and Measures in 1927. In 1960, the definitions of both the metre and ångström were changed to use krypton.
After the industrial scale production of cadmium started in the 1930s and 1940s, the major application of cadmium was the coating of iron and steel to prevent corrosion; in 1944, 62% and in 1956, 59% of the cadmium in the United States was used for plating. In 1956, 24% of the cadmium in the United States was used for a second application in red, orange and yellow pigments from sulfides and selenides of cadmium.
The stabilizing effect of cadmium chemicals like the carboxylates cadmium laurate and cadmium stearate on PVC led to an increased use of those compounds in the 1970s and 1980s. The demand for cadmium in pigments, coatings, stabilizers, and alloys declined as a result of environmental and health regulations in the 1980s and 1990s; in 2006, only 7% of to total cadmium consumption was used for plating, and only 10% was used for pigments. At the same time, these decreases in consumption were compensated by a growing demand for cadmium for nickel-cadmium batteries, which accounted for 81% of the cadmium consumption in the United States in 2006.
Cadmium makes up about 0.1 ppm of Earth's crust. It is much rarer than zinc, which makes up about 65 ppm. No significant deposits of cadmium-containing ores are known. The only cadmium mineral of importance, greenockite (CdS), is nearly always associated with sphalerite (ZnS). This association is caused by geochemical similarity between zinc and cadmium, with no geological process likely to separate them. Thus, cadmium is produced mainly as a byproduct of mining, smelting, and refining sulfidic ores of zinc, and, to a lesser degree, lead and copper. Small amounts of cadmium, about 10% of consumption, are produced from secondary sources, mainly from dust generated by recycling iron and steel scrap. Production in the United States began in 1907, but wide use began after World War I.
Rocks mined for phosphate fertilizers contain varying amounts of cadmium, resulting in a cadmium concentration of as much as 300 mg/kg in the fertilizers and a high cadmium content in agricultural soils. Coal can contain significant amounts of cadmium, which ends up mostly in flue dust. Cadmium in soil can be absorbed by crops such as rice. Chinese ministry of agriculture measured in 2002 that 28% of rice it sampled had excess lead and 10% had excess cadmium above limits defined by law. Some plants such as willow trees and poplars have been found to clean both lead and cadmium from soil.
Typical background concentrations of cadmium do not exceed 5 ng/m3 in the atmosphere; 2 mg/kg in soil; 1 μg/L in freshwater and 50 ng/L in seawater.
Cadmium is a common impurity in zinc ores, and it is most often isolated during the production of zinc. Some zinc ores concentrates from sulfidic zinc ores contain up to 1.4% of cadmium. In the 1970s, the output of cadmium was 6.5 pounds per ton of zinc. Zinc sulfide ores are roasted in the presence of oxygen, converting the zinc sulfide to the oxide. Zinc metal is produced either by smelting the oxide with carbon or by electrolysis in sulfuric acid. Cadmium is isolated from the zinc metal by vacuum distillation if the zinc is smelted, or cadmium sulfate is precipitated from the electrolysis solution.
In 2009, 86% of cadmium was used in batteries, predominantly in rechargeable nickel-cadmium batteries. Nickel-cadmium cells have a nominal cell potential of 1.2 V. The cell consists of a positive nickel hydroxide electrode and a negative cadmium electrode plate separated by an alkaline electrolyte (potassium hydroxide). The European Union put a limit on cadmium in electronics in 2004 of 0.01%, with some exceptions, and reduced the limit on cadmium content to 0.002%. Another type of battery based on cadmium is the silver-cadmium battery.
Cadmium electroplating, consuming 6% of the global production, is used in the aircraft industry to reduce corrosion of steel components. This coating is passivated by chromate salts. A limitation of cadmium plating is hydrogen embrittlement of high-strength steels from the electroplating process. Therefore, steel parts heat-treated to tensile strength above 1300 MPa (200 ksi) should be coated by an alternative method (such as special low-embrittlement cadmium electroplating processes or physical vapor deposition).
Titanium embrittlement from cadmium-plated tool residues resulted in banishment of those tools (and the implementation of routine tool testing to detect cadmium contamination) in the A-12/SR-71, U-2, and subsequent aircraft programs that use titanium.
Cadmium is used in the control rods of nuclear reactors, acting as a very effective "neutron poison" to control neutron flux in nuclear fission. When cadmium rods are inserted in the core of a nuclear reactor, cadmium absorbs neutrons, preventing them from creating additional fission events, thus controlling the amount of reactivity. The pressurized water reactor designed by Westinghouse Electric Company uses an alloy consisting of 80% silver, 15% indium, and 5% cadmium.
QLED TVs have been starting to include cadmium in construction. Some companies have been looking to reduce the environmental impact of human exposure and pollution of the material in televisions during production.
Cadmium oxide was used in black and white television phosphors and in the blue and green phosphors of color television cathode ray tubes. Cadmium sulfide (CdS) is used as a photoconductive surface coating for photocopier drums.
Various cadmium salts are used in paint pigments, with CdS as a yellow pigment being the most common. Cadmium selenide is a red pigment, commonly called cadmium red. To painters who work with the pigment, cadmium provides the most brilliant and durable yellows, oranges, and reds — so much so that during production, these colors are significantly toned down before they are ground with oils and binders or blended into watercolors, gouaches, acrylics, and other paint and pigment formulations. Because these pigments are potentially toxic, users should use a barrier cream on the hands to prevent absorption through the skin even though the amount of cadmium absorbed into the body through the skin is reported to be less than 1%.
In PVC, cadmium was used as heat, light, and weathering stabilizers. Currently, cadmium stabilizers have been completely replaced with barium-zinc, calcium-zinc and organo-tin stabilizers. Cadmium is used in many kinds of solder and bearing alloys, because it has a low coefficient of friction and fatigue resistance. It is also found in some of the lowest-melting alloys, such as Wood's metal.
Helium–cadmium lasers are a common source of blue-ultraviolet laser light. They operate at either 325 or 422 nm in fluorescence microscopes and various laboratory experiments. Cadmium selenide quantum dots emit bright luminescence under UV excitation (He-Cd laser, for example). The color of this luminescence can be green, yellow or red depending on the particle size. Colloidal solutions of those particles are used for imaging of biological tissues and solutions with a fluorescence microscope.
Cadmium is a component of some compound semiconductors, such as cadmium sulfide, cadmium selenide, and cadmium telluride, used for light detection and solar cells. HgCdTe is sensitive to infrared light and can be used as an infrared detector, motion detector, or switch in remote control devices.
In molecular biology, cadmium is used to block voltage-dependent calcium channels from fluxing calcium ions, as well as in hypoxia research to stimulate proteasome-dependent degradation of Hif-1α.
Cadmium-selective sensors based on the fluorophore BODIPY have been developed for imaging and sensing of cadmium in cells. One of the most popular way to monitor cadmium in aqueous environments is the use of electrochemistry, one example is by attaching a self-assembled monolayer that can help obtain a cadmium selective electrode with a ppt-level sensitivity.
Cadmium has no known function in higher organisms, but a cadmium-dependent carbonic anhydrase has been found in some marine diatoms. The diatoms live in environments with very low zinc concentrations and cadmium performs the function normally carried out by zinc in other anhydrases. This was discovered with X-ray absorption fluorescence spectroscopy (XAFS).
The highest concentration of cadmium is absorbed in the kidneys of humans, and up to about 30 mg of cadmium is commonly inhaled throughout human childhood and adolescence. Cadmium is under preliminary research for its toxicity in humans, potentially affecting mechanisms and risks of cancer, cardiovascular disease, and osteoporosis.
Cadmium is a common contaminant of fluoridation chemicals used as water additives.  Fluoride additives are sourced from both the phosphate fertilizer industry and metal industry.
|GHS signal word||Danger|
|P201, P202, P260, P264, P270, P271, P273, P280, P284, P304, P340, P310, P308, P313, P403, P233, P405, P501|
Individuals and organizations have been reviewing cadmium's bioinorganic aspects for its toxicity. The most dangerous form of occupational exposure to cadmium is inhalation of fine dust and fumes, or ingestion of highly soluble cadmium compounds. Inhalation of cadmium fumes can result initially in metal fume fever but may progress to chemical pneumonitis, pulmonary edema, and death.
Cadmium is also an environmental hazard. Human exposure is primarily from fossil fuel combustion, phosphate fertilizers, natural sources, iron and steel production, cement production and related activities, nonferrous metals production, and municipal solid waste incineration. Bread, root crops, and vegetables also contribute to the cadmium in modern populations.
There have been a few instances of general population poisoning as the result of long-term exposure to cadmium in contaminated food and water, and research into an estrogen mimicry that may induce breast cancer is ongoing. In the decades leading up to World War II, mining operations contaminated the Jinzū River in Japan with cadmium and traces of other toxic metals. As a consequence, cadmium accumulated in the rice crops along the riverbanks downstream of the mines. Some members of the local agricultural communities consumed the contaminated rice and developed itai-itai disease and renal abnormalities, including proteinuria and glucosuria. The victims of this poisoning were almost exclusively post-menopausal women with low iron and other mineral body stores. Similar general population cadmium exposures in other parts of the world have not resulted in the same health problems because the populations maintained sufficient iron and other mineral levels. Thus, although cadmium is a major factor in the itai-itai disease in Japan, most researchers have concluded that it was one of several factors.
Cadmium is one of six substances banned by the European Union's Restriction on Hazardous Substances (RoHS) directive, which regulates hazardous substances in electrical and electronic equipment but allows for certain exemptions and exclusions from the scope of the law. The International Agency for Research on Cancer has classified cadmium and cadmium compounds as carcinogenic to humans. Although occupational exposure to cadmium is linked to lung and prostate cancer, there is still a substantial controversy about the carcinogenicity of cadmium in low environmental exposure. Recent data from epidemiological studies suggest that intake of cadmium through diet associates to higher risk of endometrial, breast and prostate cancer as well as to osteoporosis in humans. A recent study has demonstrated that endometrial tissue is characterized by higher levels of cadmium in current and former smoking females.
Cadmium exposure is a risk factor associated with a large number of illnesses including kidney disease, early atherosclerosis, hypertension, and cardiovascular diseases. Although studies show a significant correlation between cadmium exposure and occurrence of disease in human populations, a necessary molecular mechanism has not been identified. One hypothesis holds that cadmium is an endocrine disruptor and some experimental studies have shown that it can interact with different hormonal signaling pathways. For example, cadmium can bind to the estrogen receptor alpha, and affect signal transduction along the estrogen and MAPK signaling pathways at low doses.
The tobacco plant readily absorbs and accumulates heavy metals, such as cadmium from the surrounding soil into its leaves. These are readily absorbed into the user's body following smoke inhalation. Tobacco smoking is the most important single source of cadmium exposure in the general population. An estimated 10% of the cadmium content of a cigarette is inhaled through smoking. Absorption of cadmium through the lungs is more effective than through the gut, and as much as 50% of the cadmium inhaled in cigarette smoke may be absorbed. On average, cadmium concentrations in the blood of smokers is 4 times 5 times greater and in the kidney, 2–3 times greater than non-smokers. Despite the high cadmium content in cigarette smoke, there seems to be little exposure to cadmium from passive smoking.
In a non-smoking population, food is the greatest source of exposure. High quantities of cadmium can be found in crustaceans, mollusks, offal, and algae products. However, grains, vegetables, and starchy roots and tubers are consumed in much greater quantity in the US, and are the source of the greatest dietary exposure. Most plants bio-accumulate metal toxins like Cd, and when composted to form organic fertilizers yield a product which can often contain high amounts (e.g., over 0.5 mg) of metal toxins for every kilo of fertilizer. Fertilizers made from animal dung (e.g., cow dung) or urban waste can contain similar amounts of Cd. The Cd added to the soil from fertilizers (rock phosphates or organic fertilizers) become bio-available and toxic only if the soil pH is low (i.e., acidic soils). Zinc is chemically similar to cadmium and some evidence indicates the presence of Zn ions reduces cadmium toxicity.
Zinc, Cu, Ca, and Fe ions, and selenium with vitamin C are used to treat Cd intoxication, though it is not easily reversed.
The EFSA Panel on Contaminants in the Food Chain specifies that 2.5 μg/kg body weight is a tolerable weekly intake for humans. The Joint FAO/WHO Expert Committee on Food Additives has declared 7 μg/kg bw to be the provisional tolerable weekly intake level.
The US Occupational Safety and Health Administration (OSHA) has set the permissible exposure limit (PEL) for cadmium at a time-weighted average (TWA) of 0.005 ppm. The National Institute for Occupational Safety and Health (NIOSH) has not set a recommended exposure limit (REL) and has designated cadmium as a known human carcinogen. The IDLH (immediately dangerous to life and health) level for cadmium is 9 mg/m3.
|LD50: 225 mg/kg||rat||oral||n/a|
|LD50: 890 mg/kg||mouse||oral||n/a|
|LC50: 25 mg/m3||rat||n/a||30 min|
In May 2006, a sale of the seats from Arsenal F.C.'s old stadium, Highbury in London, England was cancelled when the seats were discovered to contain trace amounts of cadmium. Reports of high levels of cadmium use in children's jewelry in 2010 led to a US Consumer Product Safety Commission investigation. The U.S. CPSC issued specific recall notices for cadmium content in jewelry sold by Claire's and Wal-Mart stores.
In June 2010, McDonald's voluntarily recalled more than 12 million promotional "Shrek Forever After 3D" Collectable Drinking Glasses because of the cadmium levels in paint pigments on the glassware. The glasses were manufactured by Arc International, of Millville, NJ, USA.
Cadmium bromide is a cream-coloured crystalline ionic cadmium salt of hydrobromic acid that is soluble in water. It is very toxic, along with other cadmium compounds.Cadmium chloride
Cadmium chloride is a white crystalline compound of cadmium and chlorine, with the formula CdCl2. It is a hygroscopic solid that is highly soluble in water and slightly soluble in alcohol. Although it is considered to be ionic, it has considerable covalent character to its bonding. The crystal structure of cadmium chloride (described below), composed of two-dimensional layers of ions, is a reference for describing other crystal structures. Also known are CdCl2•H2O and CdCl2•5H2O.Cadmium fluoride
Cadmium fluoride (CdF2) is a mostly water-insoluble source of cadmium used in oxygen-sensitive applications, such as the production of metallic alloys. In extremely low concentrations (ppm), this and other fluoride compounds are used in limited medical treatment protocols. Fluoride compounds also have significant uses in synthetic organic chemistry. The standard enthalpy has been found to be -167.39 kcal. mole−1 and the Gibbs energy of formation has been found to be -155.4 kcal. mole−1, and the heat of sublimation was determined to be 76 kcal. mole−1.Cadmium hydride
Cadmium hydride (systematically named cadmium dihydride) is an inorganic compound with the chemical formula (CdH2)n (also written as ([CdH2])n or CdH2). It is a solid, known only as a thermally unstable, insoluble white powder.Cadmium oxide
Cadmium oxide is an inorganic compound with the formula CdO. It is one of the main precursors to other cadmium compounds. It crystallizes in a cubic rocksalt lattice like sodium chloride, with octahedral cation and anion centers. It occurs naturally as the rare mineral monteponite. Cadmium oxide can be found as a colorless amorphous powder or as brown or red crystals. Cadmium oxide is an n-type semiconductor with a band gap of 2.18 eV (2.31 eV) at room temperature (298 K).Cadmium poisoning
Cadmium is a naturally occurring toxic heavy metal with common exposure in industrial workplaces, plant soils, and from smoking. Due to its low permissible exposure in humans, overexposure may occur even in situations where trace quantities of cadmium are found. Cadmium is used extensively in electroplating, although the nature of the operation does not generally lead to overexposure. Cadmium is also found in some industrial paints and may represent a hazard when sprayed. Operations involving removal of cadmium paints by scraping or blasting may pose a significant hazard. The primary use of cadmium is in the manufacturing of NiCd rechargeable batteries. The primary source for cadmium is as a byproduct of refining zinc metal. Exposures to cadmium are addressed in specific standards for the general industry, shipyard employment, the construction industry, and the agricultural industry.Cadmium selenide
Cadmium selenide is an inorganic compound with the formula CdSe. It is a black to red-black solid that is classified as a II-VI semiconductor of the n-type. Much of the current research on cadmium selenide is focused on its nanoparticles.Cadmium sulfide
Cadmium sulfide is the inorganic compound with the formula CdS. Cadmium sulfide is a green solid. It occurs in nature with two different crystal structures as the rare minerals greenockite and hawleyite, but is more prevalent as an impurity substituent in the similarly structured zinc ores sphalerite and wurtzite, which are the major economic sources of cadmium. As a compound that is easy to isolate and purify, it is the principal source of cadmium for all commercial applications. Its vivid green color led to its adoption as a pigment for the green paint "cadmium green" in the 18th century.Cadmium telluride
Cadmium telluride (CdTe) is a stable crystalline compound formed from cadmium and tellurium. It is mainly used as the semiconducting material in cadmium telluride photovoltaics and an infrared optical window. It is usually sandwiched with cadmium sulfide to form a p-n junction solar PV cell. Typically, CdTe PV cells use a n-i-p structure.Cadmium telluride photovoltaics
Cadmium telluride (CdTe) photovoltaics describes a photovoltaic (PV) technology that is based on the use of cadmium telluride, a thin semiconductor layer designed to absorb and convert sunlight into electricity. Cadmium telluride PV is the only thin film technology with lower costs than conventional solar cells made of crystalline silicon in multi-kilowatt systems.On a lifecycle basis, CdTe PV has the smallest carbon footprint, lowest water use and shortest energy payback time of all solar technologies. CdTe's energy payback time of less than a year allows for faster carbon reductions without short-term energy deficits.
The toxicity of cadmium is an environmental concern mitigated by the recycling of CdTe modules at the end of their life time, though there are still uncertainties and the public opinion is skeptical towards this technology. The usage of rare materials may also become a limiting factor to the industrial scalability of CdTe technology in the mid-term future. The abundance of tellurium—of which telluride is the anionic form—is comparable to that of platinum in the earth's crust and contributes significantly to the module's cost.CdTe photovoltaics are used in some of the world's largest photovoltaic power stations, such as the Topaz Solar Farm. With a share of 5.1% of worldwide PV production, CdTe technology accounted for more than half of the thin film market in 2013. A prominent manufacturer of CdTe thin film technology is the company First Solar, based in Tempe, Arizona.Carbonic anhydrase
The carbonic anhydrases (or carbonate dehydratases) from a family of enzymes that catalyze the interconversion between carbon dioxide and water and the dissociated ions of carbonic acid (i.e. bicarbonate and hydrogen ions). The active site of most carbonic anhydrases contains a zinc ion. They are therefore classified as metalloenzymes.
The enzyme maintains acid-base balance and helps transport carbon dioxide.Carbonic anhydrase helps regulate pH and fluid balance. Depending on its location, the role of the enzyme changes slightly. For example, carbonic anhydrase produces acid in the stomach lining. In the kidney, the control of bicarbonate ions influences the water content of the cell. The control of bicarbonate ions also influences the water content in the eyes, and if the enzyme does not work properly, a buildup of fluid can lead to glaucoma.Cocoa solids
Dry cocoa solids are the components of cocoa beans remaining after cocoa butter, the fat component, is extracted from chocolate liquor, roasted cocoa beans that have been ground into a liquid state. Cocoa butter is 50% to 57% of the weight of cocoa beans and gives chocolate its characteristic melting properties. Cocoa powder is the powdered form of the solids sold as an end product.
Cocoa powder contains flavanol antioxidants, amounts of which are reduced if the cocoa is subjected to acid-reducing alkalization. Health benefits have been attributed to cocoa flavonoids.Control rod
Control rods are used in nuclear reactors to control the fission rate of uranium and plutonium. They are composed of chemical elements such as boron, silver, indium and cadmium that are capable of absorbing many neutrons without themselves fissioning. Because these elements have different capture cross sections for neutrons of varying energies, the composition of the control rods must be designed for the reactor's neutron spectrum. Boiling water reactors (BWR), pressurized water reactors (PWR) and heavy water reactors (HWR) operate with thermal neutrons, while breeder reactors operate with fast neutrons.Group 12 element
Group 12, by modern IUPAC numbering, is a group of chemical elements in the periodic table. It includes zinc (Zn), cadmium (Cd) and mercury (Hg). The further inclusion of copernicium (Cn) in group 12 is supported by recent experiments on individual copernicium atoms. Formerly this group was named IIB (pronounced as "group two B", as the "II" is a Roman numeral) by CAS and old IUPAC system.The three group 12 elements that occur naturally are zinc, cadmium and mercury. They are all widely used in electric and electronic applications, as well as in various alloys. The first two members of the group share similar properties as they are solid metals under standard conditions. Mercury is the only metal that is a liquid at room temperature. While zinc is very important in the biochemistry of living organisms, cadmium and mercury are both highly toxic. As copernicium does not occur in nature, it has to be synthesized in the laboratory.Isotopes of cadmium
Naturally occurring cadmium (48Cd) is composed of 8 isotopes. For two of them, natural radioactivity was observed, and three others are predicted to be radioactive but their decays were never observed, due to extremely long half-lives. The two natural radioactive isotopes are 113Cd (beta decay, half-life is 8.04 × 1015 years) and 116Cd (two-neutrino double beta decay, half-life is 2.8 × 1019 years). The other three are 106Cd, 108Cd (double electron capture), and 114Cd (double beta decay); only lower limits on their half-life times have been set. At least three isotopes—110Cd, 111Cd, and 112Cd—are absolutely stable. Among the isotopes absent in the natural cadmium, the most long-lived are 109Cd with a half-life of 462.6 days, and 115Cd with a half-life of 53.46 hours. All of the remaining radioactive isotopes have half-lives that are less than 2.5 hours and the majority of these have half-lives that are less than 5 minutes. This element also has 12 known meta states, with the most stable being 113mCd (t1/2 14.1 years), 115mCd (t1/2 44.6 days) and 117mCd (t1/2 3.36 hours).
The known isotopes of cadmium range in atomic mass from 94.950 u (95Cd) to 131.946 u (132Cd). The primary decay mode before the second most abundant stable isotope, 112Cd, is electron capture and the primary modes after are beta emission and electron capture. The primary decay product before 112Cd is element 47 (silver) and the primary product after is element 49 (indium).Metalloestrogen
Metalloestrogens are a class of inorganic xenoestrogens which can affect the gene expression of human cells responding to estrogen. Effects are related to the physiologic function of estrogen because metalloestrogens have shown affinity for estrogen receptors. Because they can mimic estrogen thus activating the receptor, they are considered harmful and potentially linked with breast cancer.
List of metalloestrogens include aluminium, antimony, arsenite, barium, cadmium, chromium (Cr(II)), cobalt, copper, lead, mercury, nickel, selenite, tin and vanadate.Nickel–cadmium battery
The nickel–cadmium battery (NiCd battery or NiCad battery) is a type of rechargeable battery using nickel oxide hydroxide and metallic cadmium as electrodes. The abbreviation NiCd is derived from the chemical symbols of nickel (Ni) and cadmium (Cd): the abbreviation NiCad is a registered trademark of SAFT Corporation, although this brand name is commonly used to describe all Ni–Cd batteries.
Wet-cell nickel-cadmium batteries were invented in 1899. Among rechargeable battery technologies, NiCd rapidly lost market share in the 1990s, to NiMH and Li-ion batteries; market share dropped by 80%. A NiCd battery has a terminal voltage during discharge of around 1.2 volts which decreases little until nearly the end of discharge. NiCd batteries are made in a wide range of sizes and capacities, from portable sealed types interchangeable with carbon-zinc dry cells, to large ventilated cells used for standby power and motive power. Compared with other types of rechargeable cells they offer good cycle life and performance at low temperatures with a fair capacity but their significant advantage is the ability to deliver practically their full rated capacity at high discharge rates (discharging in one hour or less). However, the materials are more costly than that of the lead–acid battery, and the cells have high self-discharge rates.
Sealed NiCd cells were at one time widely used in portable power tools, photography equipment, flashlights, emergency lighting, hobby R/C, and portable electronic devices. The superior capacity of the Nickel-metal hydride batteries, and more recently their lower cost, has largely supplanted their use. Further, the environmental impact of the disposal of the toxic metal cadmium has contributed considerably to the reduction in their use. Within the European Union, NiCd batteries can now only be supplied for replacement purposes or for certain types of new equipment such as medical devices.Larger ventilated wet cell NiCd batteries are used in emergency lighting, standby power, and uninterruptible power supplies and other applications.Photoresistor
A photoresistor (or light-dependent resistor, LDR, or photo-conductive cell) is a light-controlled variable resistor. The resistance of a photoresistor decreases with increasing incident light intensity; in other words, it exhibits photoconductivity. A photoresistor can be applied in light-sensitive detector circuits, and light-activated and dark-activated switching circuits.
A photoresistor is made of a high resistance semiconductor. In the dark, a photoresistor can have a resistance as high as several megohms (MΩ), while in the light, a photoresistor can have a resistance as low as a few hundred ohms. If incident light on a photoresistor exceeds a certain frequency, photons absorbed by the semiconductor give bound electrons enough energy to jump into the conduction band. The resulting free electrons (and their hole partners) conduct electricity, thereby lowering resistance. The resistance range and sensitivity of a photoresistor can substantially differ among dissimilar devices. Moreover, unique photoresistors may react substantially differently to photons within certain wavelength bands.
A photoelectric device can be either intrinsic or extrinsic. An intrinsic semiconductor has its own charge carriers and is not an efficient semiconductor, for example, silicon. In intrinsic devices the only available electrons are in the valence band, and hence the photon must have enough energy to excite the electron across the entire bandgap. Extrinsic devices have impurities, also called dopants, added whose ground state energy is closer to the conduction band; since the electrons do not have as far to jump, lower energy photons (that is, longer wavelengths and lower frequencies) are sufficient to trigger the device. If a sample of silicon has some of its atoms replaced by phosphorus atoms (impurities), there will be extra electrons available for conduction. This is an example of an extrinsic semiconductor.Plating
Plating is a surface covering in which a metal is deposited on a conductive surface. Plating has been done for hundreds of years; it is also critical for modern technology. Plating is used to decorate objects, for corrosion inhibition, to improve solderability, to harden, to improve wearability, to reduce friction, to improve paint adhesion, to alter conductivity, to improve IR reflectivity, for radiation shielding, and for other purposes. Jewelry typically uses plating to give a silver or gold finish.
Thin-film deposition has plated objects as small as an atom, therefore plating finds uses in nanotechnology.
There are several plating methods, and many variations. In one method, a solid surface is covered with a metal sheet, and then heat and pressure are applied to fuse them (a version of this is Sheffield plate). Other plating techniques include electroplating, vapor deposition under vacuum and sputter deposition. Recently, plating often refers to using liquids. Metallizing refers to coating metal on non-metallic objects.