Difference between revisions of "Cadmium" - New World Encyclopedia
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− | '''Cadmium''' ( | + | '''Cadmium''' (chemical symbol '''Cd''', [[atomic number]]* 48) is a relatively rare, soft, bluish-white [[metal]] that occurs with [[zinc]] ores. |
− | == | + | * [[transition metal]] |
− | Cadmium is a | + | * cadmium is known to cause cancer. |
+ | * Cadmium is used largely in batteries. | ||
+ | |||
+ | == Occurrence and production == | ||
+ | [[Image:CadmiumMetalUSGOV.jpg|thumb|left|Cadmium metal]] | ||
+ | |||
+ | Cadmium-containing ores are rare. The only cadmium [[mineral]] of importance is [[Greenockite]]* (cadmium sulfide, CdS), which is nearly always associated with [[sphalerite]]* (zinc sulfide, ZnS). Consequently, cadmium is produced mainly as a byproduct from mining, smelting, and refining the [[sulfide]]* ores of zinc. To a lesser degree, it is obtained from the ores of [[lead]] and [[copper]]. | ||
+ | |||
+ | Zinc sulfide ores are roasted in the presence of oxygen, thereby converting the sulfide to zinc oxide. To produce zinc metal, the oxide is either smelted with carbon or subjected to electrolysis in sulfuric acid. If the smelting process is used, cadmium is isolated from metallic zinc by vacuum distillation. If the electrolytic process is used, cadmium sulfate is precipitated out of the solution.<ref>[http://www.webelements.com/webelements/elements/text/Cd/key.html Cadmium] at WebElements.com</ref> | ||
+ | |||
+ | Small amounts of cadmium, about 10% of consumption, are produced from secondary sources—mainly from dust generated when recycling [[iron]] and [[steel]] scrap. Production in the [[United States]] began in 1907, but it was not until after [[World War I]] that cadmium came into wide use. | ||
+ | |||
+ | == History == | ||
+ | |||
+ | Cadmium ([[Latin]] ''cadmia'', [[Greek language|Greek]] ''kadmeia'' meaning "[[calamine]]*") was [[discovery of the chemical elements|discovered]]* in [[Germany]] in 1817 by [[Friedrich Strohmeyer]]*. Strohmeyer found the new element as an impurity in [[zinc carbonate]]* (calamine), after he noticed that some impure samples of calamine changed color when heated, but pure calamine did not. The element was named after the Latin word for calamine, having been found in this zinc compound. For about 100 years, Germany remained the only important producer of the metal. | ||
+ | |||
+ | Although cadmium and its compounds are highly toxic, the [[British Pharmaceutical Codex]]* from 1907 states that [[cadmium iodide]]* was used as a [[medicine]] to treat "enlarged joints, scrofulous glands, and chilblains." | ||
+ | |||
+ | In 1927, the [[International Conference on Weights and Measures]]* redefined the [[metre|meter]]* in terms of a red cadmium spectral line (1 m = 1,553,164.13 wavelengths). This definition has since been changed (see [[krypton]]). | ||
== Notable characteristics == | == Notable characteristics == | ||
− | Cadmium is a soft, malleable, ductile, bluish-white | + | |
+ | Cadmium is a soft, malleable, ductile, bluish-white [[metal]] that can be easily cut with a knife. It is similar in many respects to [[zinc]] but reacts to form more complex compounds. | ||
The most common [[oxidation state]] of cadmium is +2, though rare examples of +1 can be found. | The most common [[oxidation state]] of cadmium is +2, though rare examples of +1 can be found. | ||
+ | |||
+ | === Isotopes === | ||
+ | [[Image:HeCd laser.jpg|thumb|left|150px|Image of the violet light from a [[helium]] [[cadmium]] metal vapor [[laser]]. The highly [[monochromatic]] color arises from the 441.563 nm transition [[spectral line|line]] of cadmium.]] | ||
+ | |||
+ | Naturally occurring cadmium is composed of 8 [[isotope]]s. For two of them, natural [[radioactivity]] was observed, and other three are predicted to be [[radioactive]] but their decays were never observed, due to extremely long [[half-life]] times. The two natural radioactive isotopes are <sup>113</sup>Cd ([[beta decay]], [[half-life]] is 7.7 X 10<sup>15</sup> years) and <sup>116</sup>Cd (two-neutrino [[double beta decay]], [[half-life]] is 2.9 X 10<sup>19</sup> years). Other three ones are <sup>106</sup>Cd, <sup>108</sup>Cd ([[double electron capture]]), and <sup>114</sup>Cd ([[double beta decay]]); only lower limits on their [[half-life]] times have been set. At least three isotopes - <sup>110</sup>Cd, <sup>111</sup>Cd, and <sup>112</sup>Cd - are absolutely stable. Among the isotopes absent in the natural cadmium, the most long-lived are <sup>109</sup>Cd with a half-life of 462.6 days, and <sup>115</sup>Cd with a half-life of 53.46 hours. All of the remaining [[radioactive]] isotopes have half-lifes that are less than 2.5 hours and the majority of these have half-lifes that are less than 5 minutes. This element also has 8 known [[meta state]]s with the most stable being <sup>113m</sup>Cd (t<sub>½</sub> 14.1 years), <sup>115m</sup>Cd (t<sub>½</sub> 44.6 days) and <sup>117m</sup>Cd (t<sub>½</sub> 3.36 hours). | ||
+ | |||
+ | The known isotopes of cadmium range in [[atomic weight]] from 96.935 [[atomic mass unit|u]] (<sup>97</sup>Cd) to 129.934 amu (<sup>138</sup>Cd). The primary [[decay mode]] before the second most abundant stable isotope, <sup>112</sup>Cd, is [[electron capture]] and the primary modes after are [[beta emission]] and [[electron capture]]. The primary [[decay product]] before <sup>112</sup>Cd is element 47 ([[silver]]) and the primary product after is element 49 ([[indium]]). | ||
== Applications == | == Applications == | ||
+ | |||
About three-fourths of cadmium is used in [[Battery (electricity)|batteries]] (especially [[nickel-cadmium battery|Ni-Cd]] batteries) and most of the remaining one-fourth is used mainly for [[Cadmium pigments|pigments]], coatings and plating, and as stabilizers for [[plastic]]s. Other uses; | About three-fourths of cadmium is used in [[Battery (electricity)|batteries]] (especially [[nickel-cadmium battery|Ni-Cd]] batteries) and most of the remaining one-fourth is used mainly for [[Cadmium pigments|pigments]], coatings and plating, and as stabilizers for [[plastic]]s. Other uses; | ||
*Used in some of the lowest melting [[alloy]]s. | *Used in some of the lowest melting [[alloy]]s. | ||
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''See also [[:Category:Cadmium compounds|Cadmium compounds]].'' | ''See also [[:Category:Cadmium compounds|Cadmium compounds]].'' | ||
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== Precautions == | == Precautions == | ||
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While working with cadmium it is important to do so under a [[fume hood]] to protect against dangerous fumes. [[Silver (element)|Silver]] [[solder]], for example, which contains cadmium, should be handled with care. Serious toxicity problems have resulted from long-term exposure to cadmium plating baths. | While working with cadmium it is important to do so under a [[fume hood]] to protect against dangerous fumes. [[Silver (element)|Silver]] [[solder]], for example, which contains cadmium, should be handled with care. Serious toxicity problems have resulted from long-term exposure to cadmium plating baths. | ||
− | + | ==Footnotes== | |
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<references/> | <references/> | ||
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*[http://periodic.lanl.gov/elements/48.html Los Alamos National Laboratory – Cadmium] | *[http://periodic.lanl.gov/elements/48.html Los Alamos National Laboratory – Cadmium] | ||
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Revision as of 16:59, 14 November 2006
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General | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Name, Symbol, Number | cadmium, Cd, 48 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Chemical series | transition metals | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Group, Period, Block | 12, 5, d | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Appearance | silvery gray metallic | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Atomic mass | 112.411(8) g/mol | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Electron configuration | [Kr] 4d10 5s2 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Electrons per shell | 2, 8, 18, 18, 2 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Physical properties | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Phase | solid | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Density (near r.t.) | 8.65 g/cm³ | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Liquid density at m.p. | 7.996 g/cm³ | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Melting point | 594.22 K (321.07 °C, 609.93 °F) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Boiling point | 1040 K (767 °C, 1413 °F) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Heat of fusion | 6.21 kJ/mol | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Heat of vaporization | 99.87 kJ/mol | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Heat capacity | (25 °C) 26.020 J/(mol·K) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Atomic properties | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Crystal structure | hexagonal | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Oxidation states | 2 (mildly basic oxide) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Electronegativity | 1.69 (Pauling scale) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Ionization energies | 1st: 867.8 kJ/mol | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
2nd: 1631.4 kJ/mol | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
3rd: 3616 kJ/mol | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Atomic radius | 155 pm | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Atomic radius (calc.) | 161 pm | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Covalent radius | 148 pm | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Van der Waals radius | 158 pm | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Miscellaneous | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Magnetic ordering | no data | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Electrical resistivity | (22 °C) 72.7 nΩ·m | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Thermal conductivity | (300 K) 96.6 W/(m·K) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Thermal expansion | (25 °C) 30.8 µm/(m·K) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Speed of sound (thin rod) | (20 °C) 2310 m/s | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Speed of sound (thin rod) | (r.t.) 50 m/s | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Shear modulus | 19 GPa | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Bulk modulus | 42 GPa | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Poisson ratio | 0.30 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Mohs hardness | 2.0 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Brinell hardness | 203 MPa | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
CAS registry number | 7440-43-9 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Notable isotopes | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Cadmium (chemical symbol Cd, atomic number 48) is a relatively rare, soft, bluish-white metal that occurs with zinc ores.
- transition metal
- cadmium is known to cause cancer.
- Cadmium is used largely in batteries.
Occurrence and production
Cadmium-containing ores are rare. The only cadmium mineral of importance is Greenockite (cadmium sulfide, CdS), which is nearly always associated with sphalerite (zinc sulfide, ZnS). Consequently, cadmium is produced mainly as a byproduct from mining, smelting, and refining the sulfide ores of zinc. To a lesser degree, it is obtained from the ores of lead and copper.
Zinc sulfide ores are roasted in the presence of oxygen, thereby converting the sulfide to zinc oxide. To produce zinc metal, the oxide is either smelted with carbon or subjected to electrolysis in sulfuric acid. If the smelting process is used, cadmium is isolated from metallic zinc by vacuum distillation. If the electrolytic process is used, cadmium sulfate is precipitated out of the solution.[1]
Small amounts of cadmium, about 10% of consumption, are produced from secondary sources—mainly from dust generated when recycling iron and steel scrap. Production in the United States began in 1907, but it was not until after World War I that cadmium came into wide use.
History
Cadmium (Latin cadmia, Greek kadmeia meaning "calamine") was discovered in Germany in 1817 by Friedrich Strohmeyer. Strohmeyer found the new element as an impurity in zinc carbonate (calamine), after he noticed that some impure samples of calamine changed color when heated, but pure calamine did not. The element was named after the Latin word for calamine, having been found in this zinc compound. For about 100 years, Germany remained the only important producer of the metal.
Although cadmium and its compounds are highly toxic, the British Pharmaceutical Codex from 1907 states that cadmium iodide was used as a medicine to treat "enlarged joints, scrofulous glands, and chilblains."
In 1927, the International Conference on Weights and Measures redefined the meter in terms of a red cadmium spectral line (1 m = 1,553,164.13 wavelengths). This definition has since been changed (see krypton).
Notable characteristics
Cadmium is a soft, malleable, ductile, bluish-white metal that can be easily cut with a knife. It is similar in many respects to zinc but reacts to form more complex compounds.
The most common oxidation state of cadmium is +2, though rare examples of +1 can be found.
Isotopes
Naturally occurring cadmium is composed of 8 isotopes. For two of them, natural radioactivity was observed, and other three are predicted to be radioactive but their decays were never observed, due to extremely long half-life times. The two natural radioactive isotopes are 113Cd (beta decay, half-life is 7.7 X 1015 years) and 116Cd (two-neutrino double beta decay, half-life is 2.9 X 1019 years). Other three ones 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-lifes that are less than 2.5 hours and the majority of these have half-lifes that are less than 5 minutes. This element also has 8 known meta states with the most stable being 113mCd (t½ 14.1 years), 115mCd (t½ 44.6 days) and 117mCd (t½ 3.36 hours).
The known isotopes of cadmium range in atomic weight from 96.935 u (97Cd) to 129.934 amu (138Cd). 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).
Applications
About three-fourths of cadmium is used in batteries (especially Ni-Cd batteries) and most of the remaining one-fourth is used mainly for pigments, coatings and plating, and as stabilizers for plastics. Other uses;
- Used in some of the lowest melting alloys.
- Due to a low coefficient of friction and very good fatigue resistance, it is used in bearing alloys.
- 6% of cadmium finds use in electroplating.
- Many kinds of solder contain this metal.
- As a barrier to control nuclear fission.
- Compounds containing cadmium are used in black and white television phosphors and also in the blue and green phosphors for color television picture tubes.
- Cadmium forms various salts, with cadmium sulfide being the most common. This sulfide is used as a yellow pigment. Cadmium selenide can be used as red pigment, commonly called cadmium red. To painters who work with the pigment, Cadmium yellows, oranges and reds are the most potent colours to use. In fact,during production these colours are significantly toned down before they are ground with oils and binders, or blended into watercolours, gouaches, casesin, acrylics and other paint and pigment formulations. These pigments are toxic and it is recommended to use a barrier cream on your hands to prevent absorption through the skin when working with them. There is no such thing as cadmium blue, green or violet.
- Used in some semiconductors such as cadmium sulfide, cadmium selenide, and cadmium telluride, which can be used for light detection or solar cells. HgCdTe is sensitive to infrared.
- Some cadmium compounds are employed in PVC as stabilizers.
- Used in the first neutrino detector.
- Used to block voltage-dependent calcium channels from fluxing calcium ions in molecular biology.
See also Cadmium compounds.
Precautions
Cadmium has no constructive purpose in the human body. This element and solutions of its compounds are toxic even in low concentrations, and will bioaccumulate in organisms and ecosystems. One possible reason for its toxicity is that it interferes with the action of zinc-containing enzymes. Zinc is an important element in biological systems, but cadmium, although similar to zinc chemically in many ways, apparently does not substitute or "stand in" for it well at all. Cadmium may also interfere with biological processes containing magnesium and calcium in a similar fashion. Pathways of human contact include soil contamination from industrial releases or landfill and associated leachate processes.
Inhaling cadmium laden dust quickly leads to respiratory tract infection and kidney problems which can be fatal (often from renal failure). Ingestion of any significant amount of cadmium causes immediate poisoning and damage to the liver and the kidneys.
Compounds containing cadmium are also carcinogenic [2], and can induce many types of cancer [3].
Cadmium poisoning is the cause of the itai-itai disease, which literally means "ouch ouch" in Japanese. In addition to kidney damage, patients suffered from osteoporosis and osteomalacia.
While working with cadmium it is important to do so under a fume hood to protect against dangerous fumes. Silver solder, for example, which contains cadmium, should be handled with care. Serious toxicity problems have resulted from long-term exposure to cadmium plating baths.
Footnotes
External links
- IARC Monograph "Cadmium and Cadmium Compounds"
- National Pollutant Inventory - Cadmium and compounds
- WebElements.com – Cadmium
- Los Alamos National Laboratory – Cadmium
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