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Zinc

2007 Schools Wikipedia Selection. Related subjects: Chemical elements


                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
                                              Atomic mass 65.409 (4) g/mol
                                    Electron configuration [Ar] 3d^10 4s^2
                                           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
                         Heat capacity (25 °C) 25.390 J·mol^−1·K^−1

   CAPTION: 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 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

                   CAPTION: Main article: Isotopes of zinc

                                  iso   NA   half-life DM  DE ( MeV)  DP
                                 ^64Zn 48.6% Zn is stable with 34 neutrons
                                 ^65Zn syn   244.26 d  ε   -         ^65Cu
                                                       γ   1.1155    -
                                 ^66Zn 27.9% Zn is stable with 36 neutrons
                                 ^67Zn 4.1%  Zn is stable with 37 neutrons
                                 ^68Zn 18.8% Zn is stable with 38 neutrons
                                 ^69Zn syn   56.4 min  β^− 0.906     ^69Ga
                                 ^70Zn 0.6%  Zn is stable with 40 neutrons

                                                                References

   Zinc ( IPA: /ˈzɪŋk/, 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 bluish-white metal that tarnishes in
   moist air and burns in air with a bright greenish flame, giving off
   plumes of zinc oxide. It reacts with acids and 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 zinc metal is malleable and can easily be beaten into
   various shapes. Above 210 °C, the metal becomes brittle and will be
   pulverized by beating.

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 cents 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 is part of an effective treatment
       for age-related macular degeneration in some cases.
     * Zinc is the fourth most common material used in metal wall tiles,
       and is used for its germicidal properties in kitchens.
     * 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(CH[3])[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.
     * 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.

History

   Zinc
   Enlarge
   Zinc

   In ancient India the production of zinc metal was very common. Many
   mine sites of Zawarmaala were active even during 1300-1000 BC. There
   are references of medicinal uses of zinc in the Charaka Samhita (300
   BC). The Rasa Ratna 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. Zinc alloys
   have been used for centuries, as brass goods dating to 1000– 1400 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 Romans 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 as
   early as 1000 AD in India and China. 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. The discovery of pure metallic
   zinc is most often credited to the German Andreas Marggraf, in the year
   1746, though the whole story is disputed.

   The English metallurgist Libavius received in 1597 a quantity of zinc
   metal in its pure form, which was unknown in the West before then.
   Libavius identified it as Indian/Malabar lead. Paracelsus ( 1616) was
   credited with the name "zinc". Postlewayt's Universal Dictionary, the
   most authentic source of all technological information in Europe, did
   not mention zinc before 1751.

   In 1738, William Champion is credited with patenting in Britain a
   process to extract zinc from calamine in a smelter, a technology he
   acquired after visiting Zawar zinc mines in Rajasthan. His first patent
   was rejected by the patent court on grounds of plagiarising the
   technology common in India. However he was granted the patent on his
   second submission of patent approval.

   Before the discovery of the zinc sulfide flotation technique, calamine
   was the mineral source of zinc metal.
   Foods and spices that contain the essential mineral zinc
   Enlarge
   Foods and spices that contain the essential mineral zinc

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 prosthetic groups. 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.

   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).

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. 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.

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. 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. 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 anaemia.

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

   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 and refiners
   in Europe include Umicore 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 several stages of increasingly stronger
   sulfuric acid (H[2]SO[4]). Iron is usually rejected as Jarosite or
   goethite, removing other impurities at the same time. The final
   purification uses zinc dust to remove copper, cadmium and cobalt. The
   metal is then extracted from the solution by electrowinning as cathodic
   deposits. Zinc cathodes can be directly cast or alloyed with aluminium.

   Electrolyte solutions must be very pure for electrowinning to be at all
   efficient. Impurities can change the decomposition voltage enough to
   where the electrolysis cell produces largely hydrogen gas rather than
   zinc metal.

   There are two common processes for electrowinning the metal, the low
   current density process, and the Tainton high current density process.
   The former uses a 10% sulfuric acid solution as the electolyte, with
   current density of 270–325 amperes per square meter. The latter uses
   22-28% sulfuric acid solution as the electrolyte with current density
   of about 1000 amperes per square meter. The latter gives better purity
   and has higher production capacity per volume of electrolyte, but has
   the disadvantage of running hotter and being more corrosive to the
   vessel in which it is done. In either of the electrolytic processes,
   each metric ton of zinc production expends about 3900 kW·h (14 MJ) of
   electric power.

   There are also several pyrometallurgical processes that reduce zinc
   oxide using carbon, then distill the metallic zinc from the resulting
   mix in an atmosphere of carbon monoxide. These include the Belgian-type
   horizontal-retort process, the New Jersey Zinc continuous
   vertical-retort process, and the St. Joseph Lead Company's
   electrothermal process. The Belgian process requires redistillation to
   remove impurities of lead, cadmium, iron, copper, and arsenic. The New
   Jersey process employs a fractionating column, which is absent in the
   Belgian process, that separates the individual impurities, where they
   can be sold as byproducts. The St. Joseph Lead Company process heats
   the zinc oxide/coke mixture by passing an electric current through it
   rather than by coal or gas fire.

   Another pyrometallurgical process is flash smelting. 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.

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% aluminum find limited use in certain types of
   machine bearings. Alloys of primarily zinc with small amounts of
   copper, aluminum, and magnesium are useful in die-casting. 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.

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 or zinc diethyl 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,
   ^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.

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.
   Retrieved from " http://en.wikipedia.org/wiki/Zinc"
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   with only minor checks and changes (see www.wikipedia.org for details
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