THC Science

Zinc (from German zink) is a chemical element in the periodic table that has the symbol Zn and atomic number 30.

Notable characteristics

Zinc is a moderately reactive metal that will combine with oxygen and other non-metals, and will react with dilute acids to release hydrogen. The one common oxidation state of zinc is +2.

Applications

Zinc is the fourth most common metal in use, trailing only iron, aluminium, and copper in annual production.

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 pennies since 1982.
Zinc is used in die casting notably in the automobile industry.
Zinc is used as part of the containers of batteries.
Zinc is used in contemporary pipe organ building as a substitute for the classic lead/tin alloy in pipes sounding the lowest (pedal) tones, as it is tonally almost indistinguishable from lead/tin at those pitches, and has the added advantages of being much more economical and lighter in weight. Even the best organ builders will use zinc in this capacity.
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's part of an effective treatment for age-related macular degeneration in some cases.
Zinc is the fourth common material used in metal wall tiles, and is used for its germicidal properties in kitchens[1].
Zinc chloride is used as a deodorant and can also be used as a wood preservative.
Zinc sulfide 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 in an attempt to remedy the common cold.[2]
Zinc is used as the anode or fuel of the Zinc-air battery/Fuel Cell providing the basis of the Zinc Economy.

Popular misconceptions

The highly characteristic metal counters of traditional French bars are often referred to as zinc bars or vaguely zinc, but actually zinc has never been used for this purpose and the counters are really made of an alloy of lead and tin.

In Argentina some people wrongly believe that zinc is a deadly poison, and some of them are not eating food which is known to contain zinc. In 1997 a municipality north of the centre of Buenos Aires posted commercial advertisements in popular magazines and other text explaining the usefulness of zinc in the entire human body.

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Biological role

Zinc is an essential element, necessary for sustaining all life. It is estimated that 3000 of the hundreds of thousands of proteins in the human body contain zinc. 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. Intriguingly, brain cells in the mammalian forebrain are one type of cell that secretes zinc, along with its other neuronal messenger substances. Cells in the salivary gland, prostate, immune system and intestine are other types that secrete zinc.

Food sources

Zinc is found in oysters, and to a far lesser degree in most animal proteins, beans, nuts, whole grains, pumpkin seeds and sunflower seeds. 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, but the effect is extremely small and not likely to be clinically important. Significant dietry intake of zinc has also recently been shown to impede the onset of flu. Soil conservation analyzes the vegetative uptake of naturally occurring zinc in many soil types.

Zinc deficiency

Zinc deficiency results from inadequate intake of zinc, or inadequate absorption of zinc into the body. Signs of zinc deficiency includes hair loss, skin lesions, diarrhea, wasting of body tissues, and, eventually, death. Eyesight, taste, smell and memory are also connected with zinc and a deficiency in zinc can cause malfunctions of these organs and functions. Congenital abnormalities causing Zinc deficiency may lead to a disease called Acrodermatitis enteropathica.

Obtaining a sufficient zinc intake during pregnancy and in young children is a very real problem, especially among those who cannot afford a good and varied diet. Brain development is stunted by zinc insufficiency in utero and in youth. Teenage boys require 11 milligrams of zinc.

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. On the other hand, 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 of 6 micromolar killing 93% of all daphnia in water is in Muyssen et al., (Aquat Toxicol. 2006). Swallowing an American one cent piece (98% zinc) can also cause damage to the stomach lining due to the high solubility of the zinc ion in the acidic stomach (Bothwell and Mair, PEDIATRICS 2003) whereas the British penny is made from copper-plated steel.

Immune system

Zinc salts are effective against pathogens in direct application. Gastrointestinal infections are also 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.

The direct effect of zinc (as in lozenges) on bacteria and viruses is also well-established, and has been used since at least 2000 BC, from when zinc salts in palliative salves are documented. However, exactly how to deliver zinc salts against pathogens without injuring one's own tissues is still being investigated.

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).

Zinc production

There are zinc mines throughout the world, with the largest producers being Australia, Canada, China, Peru and the U.S.A. Mines in Europe include Vieille Montagne in Belgium, Tara, Galmoy and Lisheen in Ireland, and Zinkgruvan in Sweden. Zinc metal is produced using extractive metallurgy. Zinc sulfide (sphalerite) minerals are concentrated using the froth flotation method and then usually roasted using pyrometallurgy to oxidise the zinc sulfide to zinc oxide. The zinc oxide is leached in sulfuric acid and the resulting solution is purified using zinc dust. The metal is then extracted by electrowinning as cathodic deposits. Zinc cathodes can be directly cast or alloyed with aluminium.

Another process to produce zinc is flash smelting, a pyrometallurgical process. Then zinc oxide is obtained, usually producing zinc of lesser quality than the hydrometallurgical process. Zinc oxide treatment has much fewer applications, but high grade deposits have been successful in producing zinc from zinc oxides and zinc carbonates using hydrometallurgy.

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 sulfide (in luminescent paints), and zinc methyl in the organic laboratory. Roughly one quarter of all zinc output is consumed in the form of zinc compounds.

Isotopes

Naturally occurring zinc is composed of the 5 stable isotopes ⁶⁴Zn,⁶⁶ Zn, ⁶⁷Zn, ⁶⁸Zn, and ⁷⁰Zn with ⁶⁴Zn being the most abundant (48.6% natural abundance). 21 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.

Precautions

Metallic zinc is not considered to be toxic, but free zinc ions in solution (like copper or iron ions) are highly toxic. There is also a condition called zinc shakes or zinc chills (see metal fume fever) that can be induced by the inhalation of freshly formed zinc oxide formed during the welding of galvanized materials. Excessive intake of zinc can promote deficiency in other dietary minerals.

References

Los Alamos National Laboratory - Zinc

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 In [[Argentina]] some people wrongly believe that zinc is a deadly [[poison]], and some of them are not eating food which is known to contain zinc. In [[1997]] a municipality north of the centre of [[Buenos Aires]] posted commercial advertisements in popular magazines and other text explaining the usefulness of zinc in the entire [[human body]].
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-==History==
-[[Image:ZincMetalUSGOV.jpg|thumb|left|Zinc]]
-Zinc alloys have been used for centuries, as brass goods dating to [[1000s BC|1000]]–[[1400s BC|1400 BC]] have been found in [[Israel (region)|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 [[Ancient Rome|Romans]] by about [[30 BC]], using a technique where [[calamine]] and [[copper]] were heated together in a crucible. The [[zinc oxide]]s 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 being accomplished as early as [[1000]] AD in [[India]] and [[China]]. By the end of the [[14th century]], the [[Hindus]] were aware of the existence of zinc as a metal separate from the seven known to the ancients. In the West, impure zinc as a remnant in melting ovens was  known since Antiquity, but usually thrown away 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. The discovery of pure metallic zinc is most often credited to the German [[Andreas Sigismund Marggraf|Andreas Marggraf]], in the year [[1746]], though the whole story is considerably more involved.
-Descriptions of brass manufacture are found in Western Europe in the writings of Albertus Magnus, c. [[1248]], and by the [[16th century]], the understanding and awareness of the new metal broadened considerably. [[Georg Agricola]] observed, in [[1546]], that a white metal could be condensed and scraped off the walls of a furnace when zinc ores were smelted. He added in his notes that a similar metal called "zincum" was being produced in Silesia. [[Paracelsus]] (died [[1541]]) was the first in the West to say that "zincum" was a new metal and that it had a separate set of chemical properties from other known metals.
-The upshot is that zinc was known by the time Marggraf made his discoveries and in fact zinc had been isolated two years earlier by another chemist, Anton von Swab. However, Marggraf's reports were exhaustive and methodical and the quality of his research cemented his reputation as the discoverer of zinc.
-In [[1738]], [[William Champion (metallurgist)]] is credited with patenting in [[Britain]] a process to extract zinc from calamine in a smelter. The metallic zinc is captured by an iron tube into water.
-Before the discovery of the [[zinc sulfide]] [[flotation]] technique, [[calamine]] was the mineral source of zinc metal.
-[[Image:Foodstuff-containing-Zinc.jpg|thumb|250px|Foods and spices that contain the essential mineral zinc]]
 == Biological role ==