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Zinc oxide

    Zinc oxide
    General
    Other names Zinc white,
    Molecular formulaZnO
    Molar mass 81.4084 g/mol
    Appearance White solid
    Crystal Structure wurtzite (hexagonal)
    CAS numberCAS=1314-13-2}}
    Properties
    Density and phase 5.606 g/cm3, solid
    Solubility in water Insoluble
    Melting point 1975°C (decomposes)
    Boiling point
    Mohs hardness 5
    a, c Lattice constants 3.249Å, 5.201Å
    Thermodynamic data
    Standard enthalpy change of formation|Standard enthalpy
    fH°solid
    −348.0 kJ/mol
    Standard molar entropysolid 43.9 J.K−1.mol−1
    Hazards
    EU classification Dangerous for
    N)
    R-phrases , , .
    S-phrases , .
    NFPA 704
    Supplementary data page
    Structure and
    n, εr, etc.
    Thermodynamic
    Phase behaviour
    Spectral data UV, IR, NMR, MS
    Regulatory data Flash point,
    Related compounds
    Other anion Zinc sulfide
    Other cation Cadmium oxide
    Except where noted otherwise, data are given for
    materials in their standard state

    Zinc oxide is a chemical compound with formula ZnO. It is nearly insoluble in water but soluble in acids or alkalis. It occurs as white hexagonal crystals or a white powder commonly known as zinc white. It remains white when exposed to hydrogen sulfide or ultraviolet light. Crystalline zinc oxide exhibits the piezoelectric effect and is thermochromic (it will change colour from white to yellow when heated, and back again when cooled down). Zinc oxide decomposes into zinc vapor and oxygen at around 1975°C. High-quality single-crystalline ZnO is almost transparent. Fumes of zinc oxide are generated when melting brass, because the melting point of brass is close to the boiling point of zinc.[1] Exposure to zinc oxide in the air (also while welding) can result in a nervous malady called metal fume fever[2].
    Zinc oxide occurs in nature as the mineral zincite.
    Zincum Oxydatum is the latin name for Zinc Oxide commonly listed on homeopathic medicines.

    Applications

    Zinc oxide in a mixture with about 0.5% iron oxide (Fe2O3) is called calamine and is used in calamine lotion. There are also two minerals, smithsonite and hemimorphite, which have been called calamine historically (see: calamine .
    Zinc peroxide, ZnO2 .½ H2O, is a white to yellow powder that is used in antiseptic ointments.
    Zinc white is used as a pigment in paints and is more opaque than lithopone, but less opaque than titanium dioxide. It is also used in coatings for paper. Chinese white is a special grade of zinc white used in artists' pigments. Because it reflects both UVA and UVB rays of ultraviolet light, zinc oxide can be used in ointments, creams, and lotions to protect against sunburn and other damage to the skin caused by ultraviolet light (see sunscreen).
    Zinc oxide and stearic acid are important ingredients in the commercial manufacture of rubber goods. A proper mixture of these two compounds allows a quicker and more controllable rubber cure. Zinc oxide can also be used as a filler in some rubber mixtures.
    Zinc oxide is a semiconductor with a direct band gap of 3.37 eV (368 nm at room temperature, deep violet/borderline UV). A common application is in gas sensors. As of 2003, it has been utilized in recent research to build blue LEDs and transparent TFT.
    n-type doped films are often used in thin film technology, where zinc oxide serves as a TCO (transparent conducting oxide). n-type doping is possible by introduction of aluminum, indium, or excess zinc Acc. Chem. Res. 1985, 18, pp. 228-234, Zinc Oxide: An Outstanding Example of a Binary Compound Semiconductor,Hirschwald, Wolfgang H.. Oxygen vacancies generate states in the band gap and hence also cause an increase in conductivity."Oxygen Vacancies in ZnO", A. Janotti and C. G. Van de Walle, Appl. Phys. Lett. 87, 122102 (2005). p-type doping is difficult and is currently an active area of research, with arsenic as the leading candidate dopantPhys. Lett. 87, 192103 (2005) p type doping of zinc oxide by arsenic ion implantation by G. Braunstein, A. Muraviev, H. Saxena, N. Dhere, V. Richter and R. Kalish. Thin-film solar cells, LCD and flat panel displays are typical applications of this material. Appropriately doped Zinc oxide may be transparent and conductive, and can therefore be used as a transparent electrode. Indium tin oxide (ITO) is another transparent conducting oxide often used in microelectronics.
    ZnO has also been considered for spintronics applications because of theoretical predictions of room temperature ferromagnetism. Unsubstantiated reports of ferromagnetism have been made, but presence of dilute magnetic semiconductors remains a large unanswered question in physics.
    ZnO layers are mainly deposited by sputter deposition and chemical vapor deposition (CVD). The latter method allows the growth of a rough layer, which can diffuse the incoming light by scattering, increasing the efficiency of solar cells.
    Recently, ZnO has been observed to act as a chemical reagent for Friedel-Craft Acylation Reaction.
    Zinc oxide – recognized as a mild antimicrobial, wound healing and sunscreen agent. Primarily absorbs UVA light rather than scattering or reflecting, non-irritating, non-comedogenic, and micronized by forming many small micro particles for cosmetic use.
    Zinc oxide has been studied as a treatment for cold sores and appears to shorten their duration.[3]

    Pyroelectric coefficient

    • Primary pyroelectric coefficient: -6.8 μC/m2·K
    • Secondary pyroelectric coefficient: -2.5 μC/m2·K
    • Total pyroelectric coefficient: -9.4 μC/m2·K

    Production Methods

    Zinc oxide is produced by oxidation of metallic zinc vapor at elevated temperatures. There are two methods. Direct method and indirect method.

    Indirect method

    Metallic zinc is vaporized in suitable containers. Zinc vapor reacts with oxygen that is in the air to form zinc oxide.

    Direct method

    Zinc ores or roasted sulfide concentrates are mixed with coal. In a reduction furnace, ore is reduced to metallic zinc and vaporized zinc reacts with oxygen to form zinc oxide.
    For more information and specifications
    zinc oxide

    Use in pop culture

    Zinc Oxide and You is a spoof of a high school science film, in Kentucky Fried Movie. The plot is straightforward - as the announcer intones "without zinc oxide, you would not have ...", then there is a "ding" and the noted object disappears, with successively more disastrous results. The results can be guessed at from the title of the next film (introduced but not shown), which is "Rebuilding your Home". An online version of this sketch can be found at the Frankin-Sterling Hill web site.
    In one episode of SpongeBob SquarePants, SpongeBob rubs Zinc Oxide on his nose to achieve the "life guard look".

    External links


    References

    • Physics Today, volume 58, No. 8, p.33, August 2005.
    • "Introduction and recovery of point defects in electron-irradiated ZnO", Tuomisto, F., Saarinen, K., Look, D.C., and Farlow, G.C., Physical Review B 72, 085206 (2005).