Zinc

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30 copper ← zinc → gallium - ↑ Zn ↓ Cd Periodic table - Extended periodic table
General
Name, symbol, number	zinc, Zn, 30
Chemical series	transition metals
Group, period, block	12, 4, d
Appearance	bluish pale gray
Standard atomic weight	65.409(4) g·mol−1
Electron configuration	Ar 3d10 4s2
Electrons per shell	2, 8, 18, 2
Physical properties
Phase	solid
Density (near r.t.)	7.14 g·cm−3
Liquid density at m.p.	6.57 g·cm−3
Melting point	692.68 K (419.53 °C, 787.15 °F)
Boiling point	1180 K (907 °C, 1665 °F)
Heat of fusion	7.32 kJ·mol−1
Heat of vaporization	123.6 kJ·mol−1
Specific heat capacity	(25 °C) 25.470 J·mol−1·K−1
Vapor pressure P/Pa 1 10 100 1 k 10 k 100 k at T/K 610 670 750 852 990 (1185)
Atomic properties
Crystal structure	hexagonal
Oxidation states	+1(rare) +2 (amphoteric oxide)
Electronegativity	1.65 (Pauling scale)
Ionization energies (more)	1st: 906.4 kJ·mol−1
	2nd: 1733.3 kJ·mol−1
	3rd: 3833 kJ·mol−1
Atomic radius	135 pm
Atomic radius (calc.)	142 pm
Covalent radius	131 pm
Van der Waals radius	139 pm
Miscellaneous
Magnetic ordering	diamagnetic
Electrical resistivity	(20 °C) 59.0 nΩ·m
Thermal conductivity	(300 K) 116 W·m−1·K−1
Thermal expansion	(25 °C) 30.2 µm·m−1·K−1
Speed of sound (thin rod)	(r.t.) (rolled) 3850 m·s−1
Young's modulus	108 GPa
Shear modulus	43 GPa
Bulk modulus	70 GPa
Poisson ratio	0.25
Mohs hardness	2.5
Brinell hardness	412 MPa
CAS registry number	7440-66-6
Selected isotopes
Main article: Isotopes of zinc iso NA half-life DM DE (MeV) DP 64Zn 48.6% 64Zn is stable with 34 neutrons 65Zn syn 244.26 d ε - 65Cu γ 1.1155 - 66Zn 27.9% 66Zn is stable with 36 neutrons 67Zn 4.1% 67Zn is stable with 37 neutrons 68Zn 18.8% 68Zn is stable with 38 neutrons 69Zn syn 56.4 min β− 0.906 69Ga 70Zn 0.6% 70Zn is stable with 40 neutrons
References
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Zinc (pronounced /ˈzɪŋk/, from German: Zink) is a metallic chemical element with the symbol Zn and atomic number 30. In nonscientific context it is sometimes called spelter.^[1] Commercially pure zinc is known as Special High Grade, often abbreviated SHG, and is 99.995% pure.^[2]

Notable characteristics

Zinc is a moderately reactive bluish grey metal that tarnishes in moist air and burns in air with a bright bluish-green flame, giving off fumes of zinc oxide. It reacts with acids, alkalis and other non-metals. If not completely pure, zinc reacts with dilute acids to release hydrogen. The one common oxidation state of zinc is +2. From 100 °C to 210 °C (212 °F to 410 °F) zinc metal is malleable and can easily be beaten into various shapes. Above 210 °C (410 °F), the metal becomes brittle and will be pulverized by beating. Zinc is nonmagnetic.

Applications

• Zinc is used to galvanize steel to prevent corrosion

• Zinc is used to Parkerize steel to prevent rust and corrosion

• Zinc is used in alloys such as brass, nickelled silver, typewriter metal, various soldering formulas and German silver

• Zinc is the primary metal used in making American one cent coins since 1982

• Zinc is used in die casting notably in the automobile industry

• Zinc is used as part of the containers of batteries. The most widespread such use is as the anode in alkaline batteries

• Zinc is used as the anode or fuel of the zinc-air battery/fuel cell providing the basis of the theorised zinc economy

• Zinc is used as a sacrificial anode on boats and ships that use cathodic protection to prevent corrosion of metals that are exposed to sea water

• Zinc is used in contemporary pipe organs as a substitute for the lead/tin alloy in pipes

• Zinc sheet metal is used in making contemporary zinc bars.^[3]

• Zinc oxide is used as a white pigment in watercolours or paints, and as an activator in the rubber industry. As an over-the-counter ointment, it is applied as a thin coating on the exposed skin of the face or nose to prevent dehydration of the area of skin. It can protect against sunburn in the summer and windburn in the winter. Applied thinly to a baby's diaper area (perineum) with each diaper change, it can protect against rash. As determined in the Age-Related Eye Disease Study, it is part of an effective treatment for age-related macular degeneration in some cases

• Zinc chloride is used as a deodorant and can also be used as a wood preservative

• Zinc sulphide is used in luminescent pigments such as on the hands of clocks and other items that glow in the dark.

• Zinc methyl (Zn(CH₃)₂) is used in a number of organic syntheses.

• Zinc stearate is a lubricative plastic additive.

• Lotions made of calamine, a mix of Zn-(hydroxy-)carbonates and silicates, are used to treat skin rash.

• Zinc metal is included in most single tablet over-the-counter daily vitamin and mineral supplements. It is believed to possess anti-oxidant properties, which protect against premature aging of the skin and muscles of the body. In larger amounts, taken as zinc alone in other proprietaries, it is believed by some to speed up the healing process after an injury. Preparations include zinc acetate and zinc gluconate.

• Zinc gluconate glycine and zinc acetate are also used in throat lozenges or tablets to reduce the duration and the severity of cold symptoms.^[4]

• Zinc lactate is used in toothpaste to prevent malodour.

• Zinc pyrithione is widely applied in shampoo's because of its anti-dandruff function.

History

Zinc

The name of the metal zinc is unusual and, while vague in origin, was probably first used by Paracelsus, a Swiss-born German chemist, who referred to the metal as "Zincum", in the 16th century.^[5] These words in German apparently mean "tooth-like, pointed or jagged part" and, as zinc metallic crystals are needle-like, the derivation appears plausible.

In ancient India the production of zinc metal was very common. Many mine sites of Zawar Mines, near Udaipur, Rajasthan, were active even during 1300–1000 BC. There are references of medicinal uses of zinc in the Charaka Samhita (300 BC). The Rasaratna Samuccaya (800 AD) explains the existence of two types of ores for zinc metal, one of which is ideal for metal extraction while the other is used for medicinal purpose.^[6] Zinc alloys have been used for centuries, as brass goods dating to 1400–1000 BC have been found in Israel and zinc objects with 87% zinc have been found in prehistoric Transylvania. Because of the low boiling point and high chemical reactivity of this metal (isolated zinc would tend to go up the chimney rather than be captured), the true nature of this metal was not understood in ancient times.

The manufacture of brass was known to the Ebi by about 30 BC, using a technique where calamine and copper were heated together in a crucible. The zinc oxides in calamine were reduced, and the free zinc metal was trapped by the copper, forming an alloy. The resulting calamine brass was either cast or hammered into shape.

Smelting and extraction of impure forms of zinc was accomplished around 1200 AD in India.^[5] China did not learn of the technique until 17th Century AD.^[5] In the West, impure zinc as a remnant in melting ovens was known since antiquity, but usually discarded as worthless. Strabo mentions it as pseudo-arguros — "mock silver". The Berne zinc tablet is a votive plaque dating to Roman Gaul, probably made from such zinc remnants.

Pure zinc in the West

The metallurgist Andreas Libavius received in 1597 a quantity of zinc metal in its pure form, which was unknown in the West before then. Libavius called it Indian/Malabar lead. It was regularly imported to Europe from the orient in the 17th and first half of the 18th century,^[5] but was at times very expensive.

The isolation of metallic zinc in the West may have been achieved independently by several people:

• Traders from the Orient were bringing zinc to England in the early 1700s. It is suggested that they also brought the secret of its smelting,^[7] but evidence of this is lacking.

• Dr. John Lane is said to have carried out experiments, probably at Landore, prior to his bankruptcy in 1726.^[8] Postlewayt's Universal Dictionary, a contemporary source giving technological information in Europe, did not mention zinc before 1751.^[9]

• In 1738, William Champion patented in Great Britain a process to extract zinc from calamine in a vertical retort style smelter, using a technology somewhat similar to that used at Zawar zinc mines in Rajasthan. However, there is no evidence that he visited the orient.^[10] Champion's process was used through 1851.^[5]

• In 1742, the Swedish chemist Anton von Swab distilled zinc from calamine.^[5]

• The discovery of pure metallic zinc is often credited to the German Andreas Marggraf in 1746.^[5]

In 1758, William's brother, John, developed a new process for calcining zinc sulfide into an oxide for use in the retort process. Prior to this only calamine could be used to produce zinc. This process was then used into the 20th century. In 1798, Johann Ruberg built the first horizontal retort smelter in Upper Silesia. This was much more fuel efficient and less labor intensive than the vertical retort process. Jean-Jacques Daniel Dony built a different kind of horizontal zinc smelter in Belgium, which processes more.^[5]

Biological role

Foods and spices that contain the essential mineral zinc

Zinc is an essential element, necessary for sustaining all life. It is estimated that 3,000 of the hundreds of thousands of proteins in the human body contain zinc prosthetic groups, one type of which is the so-called zinc finger. In addition, there are over a dozen types of cells in the human body that secrete zinc ions, and the roles of these secreted zinc signals in medicine and health are now being actively studied. Zinc ions are now considered to be neurotransmitters. Cells in the salivary gland, prostate, immune system and intestine use zinc signalling.^[11]

Zinc is also involved in olfaction: the olfactory receptors contain zinc binding sites and a deficiency in zinc causes anosmia.

Zinc is an activator of certain enzymes, such as carbonic anhydrase. Carbonic anhydrase is important in the transport of carbon dioxide in vertebrate blood. It is also required in plants for leaf formation, the synthesis of indole acetic acid (auxin) and anaerobic respiration (alcoholic fermentation).^[12]

Food sources

Zinc is found in oysters, and to a far lesser degree in most animal proteins, beans, nuts, almonds, whole grains, pumpkin seeds and sunflower seeds.^[13] A turkey's neck and beef's chuck or shank also contain good amounts of zinc. Phytates, which are found in whole grain breads, cereals, legumes and other products, have been known to decrease zinc absorption. Clinical studies have found that zinc, combined with antioxidants, may delay progression of age-related macular degeneration.^[14] Significant dietary intake of zinc has also recently been shown to impede the onset of flu.^[15] Soil conservation analyzes the vegetative uptake of naturally occurring zinc in many soil types.

The US recommended dietary allowance of zinc from puberty on is 11mg for males and 8mg for females, with higher amounts recommended during pregnancy and lactation.

Zinc deficiency

Main article: Zinc deficiency

Zinc deficiency occurs where insufficient zinc is available for metabolic needs. It is usually nutritional, but can also be associated with malabsorption, acrodermatitis enteropathica, chronic liver disease, chronic renal disease, sickle cell disease, diabetes, malignancy, and other chronic illnesses.

Zinc toxicity

Even though zinc is an essential requirement for a healthy body, too much zinc can be harmful. Excessive absorption of zinc can also suppress copper and iron absorption. The free zinc ion in solution is highly toxic to plants, invertebrates, and even vertebrate fish. The Free Ion Activity Model (FIAM) is well-established in the literature, and shows that just micromolar amounts of the free ion kills some organisms. A recent example showed 6 micromolar killing 93% of all Daphnia in water.^[16]

The free zinc ion is also a powerful Lewis acid up to the point of being corrosive. Stomach acid contains hydrochloric acid, in which metallic zinc dissolves readily to give corrosive zinc chloride. Swallowing a post 1982 American one cent piece (97.5% zinc) can cause damage to the stomach lining due to the high solubility of the zinc ion in the acidic stomach.^[17] Zinc toxicity, mostly in the form of the ingestion of US pennies minted after 1982, is commonly fatal in dogs where it causes a severe hemolytic anemia.^[18] In pet parrots zinc is highly toxic and poisoning can often be fatal^[19].

There is evidence of induced copper deficiency at low intakes of 100–300 mg Zn/d. The USDA RDA is 15 mg Zn/d. Even lower levels, closer to the RDA, may interfere with the utilization of copper and iron or to adversely affect cholesterol.^[20].

There is also a condition called the zinc shakes or "zinc chills" that can be induced by the inhalation of freshly formed zinc oxide formed during the welding of galvanized materials.

Immune system

See also: Zinc gluconate

Zinc salts are effective against pathogens in direct application. Gastroenteritis is strongly attenuated by ingestion of zinc, and this effect could be due to direct antimicrobial action of the zinc ions in the GI tract, or to absorption of the zinc and re-release from immune cells (all granulocytes secrete zinc), or both.^[21][22]

In clinical trials, both zinc gluconate and zinc gluconate glycine (the formulation used in lozenges) have been shown to shorten the duration of symptoms of the common cold.^[23] The amount of glycine can vary from two to twenty moles per mole of zinc gluconate. It should be known that there have been clinical trials that both support the use of zinc for the common cold, and are inconclusive of its effectiveness. All clinical trials have their critics, including the dosage amount used, and the highly subjective format of patient self-reporting the results of their trials.^[24]

Abundance

See also: Zinc minerals

Zinc is the 23rd most abundant element in the Earth's crust. The most heavily mined ores (sphalerite) tend to contain roughly 10% iron as well as 40–50% zinc. Minerals from which zinc is extracted include sphalerite (zinc sulfide), smithsonite (zinc carbonate), hemimorphite (zinc silicate), and franklinite (a zinc spinel).

The earth has been estimated to have 46 years supply of zinc.^[25] A chemist estimated in 2007 that at the current rate of usage, the world's supply of zinc would be exhausted by about the year 2037.^[26]

Zinc mining and processing

Zinc output in 2005

Main article: Zinc smelting

See also: List of countries by zinc production

Zinc is the fourth most common metal in use, trailing only iron, aluminium, and copper in annual production.^{citation needed}

There are zinc mines throughout the world, with the largest producers being China, Australia and Peru. In 2005, China produced almost one-fourth of the global zinc output, reports the British Geological Survey. Mines and refineries in Europe include Umicore in Belgium, Tara, Galmoy and Lisheen in Ireland and Zinkgruvan in Sweden. Zinc metal is produced using extractive metallurgy.

Alloys

The most widely used alloy of zinc is brass, in which copper is alloyed with anywhere from 9% to 45% zinc, depending upon the type of brass, along with much smaller amounts of lead and tin. Alloys of 85–88% zinc, 4–10% copper, and 2–8% aluminium find limited use in certain types of machine bearings. Alloys of primarily zinc with small amounts of copper, aluminium, and magnesium are useful in die casting as well as spin casting. An example of this is zinc aluminium. Similar alloys with the addition of a small amount of lead can be cold-rolled into sheets. An alloy of 96% zinc and 4% aluminium is used to make stamping dies for low production run applications where ferrous metal dies would be too expensive.^[27]

Compounds

See also: Zinc compounds

Zinc oxide is perhaps the best known and most widely used zinc compound, as it makes a good base for white pigments in paint. It also finds industrial use in the rubber industry, and is sold as opaque sunscreen. A variety of other zinc compounds find use industrially, such as zinc chloride (in deodorants), zinc pyrithione (anti-dandruff shampoos), zinc sulfide (in luminescent paints), and zinc methyl or zinc diethyl in the organic laboratory. Roughly one quarter of all zinc output is consumed in the form of zinc compounds.

Isotopes

Main article: Isotopes of zinc

Naturally occurring zinc is composed of the 5 stable isotopes ⁶⁴Zn, ⁶⁶Zn, ⁶⁷Zn, ⁶⁸Zn, and ⁷⁰Zn with ⁶⁴Zn being the most abundant (48.6% natural abundance). Twenty-one radioisotopes have been characterised with the most abundant and stable being ⁶⁵Zn with a half-life of 244.26 days, and ⁷²Zn with a half-life of 46.5 hours. All of the remaining radioactive isotopes have half-lives that are less than 14 hours and the majority of these have half lives that are less than 1 second. This element also has 4 meta states.

Zinc has been proposed as a "salting" material for nuclear weapons (cobalt is another, better-known salting material). A jacket of isotopically enriched ⁶⁴Zn, irradiated by the intense high-energy neutron flux from an exploding thermonuclear weapon, would transmute into the radioactive isotope Zn-65 with a half-life of 244 days and produce approximately 2.27 MeV of gamma radiation, significantly increasing the radioactivity of the weapon's fallout for several days. Such a weapon is not known to have ever been built, tested, or used.

References

• Los Alamos National Laboratory - Zinc
• WebElements.com – Zinc

External links

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Zinc

Look up zinc in
Wiktionary, the free dictionary.

• History & Etymology of Zinc
• Statistics and Information from the U.S. Geological Survey
• Reducing Agents > Zinc
• American Zinc Association Information about the uses and properties of zinc.
• Outline safety data for zinc