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! {{chembox header}} | Zinc oxide
|-
| align="center" colspan="2" | [[Image:Zinc oxide.jpg|200px|Zinc oxide]]<br>[[Image:Zincite-3D-balls.png|200px]]
|-
! {{chembox header}} | General
|-
| Other names
| Zinc white,<br />calamine
|-
| [[Chemical formula|Molecular formula]]
|ZnO
|-
| [[Molar mass]]
| 81.4084 g/mol
|-
| Appearance
| White solid
|-
| [[Crystal Structure]]
| wurtzite (hexagonal)
|-
| [[CAS registry number|CAS number]]
| {{CASREF|CAS=1314-13-2}}
|-
! {{chembox header}} | Properties
|-
| [[Density]] and [[Phase (matter)|phase]]
| 5.606 g/cm<sup>3</sup>, solid
|-
| [[Soluble|Solubility]] in [[Water (molecule)|water]]
| Insoluble
|-
<!-- | [[Soluble|Solubility]] in other solvents e.g. [[ethanol]], [[acetone]] -->
<!-- | ? -->
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| [[Melting point]]
| 1975 °C (decomposes)
|-
| [[Boiling point]]
|
|-
| [[Mohs hardness]]
| 5
|-
| a, c [[Lattice constants]]
| 3.249Å, 5.201Å
|-
! {{chembox header}} | Thermodynamic data
|-
| [[Standard enthalpy change of formation|Standard enthalpy<br /> of
formation]] Δ<sub>f</sub>''H''°<sub>solid</sub>
| −348.0 kJ/mol
|-
| [[Standard molar entropy]]<br/>''S''°<sub>solid</sub>
| 43.9 J.K<sup>−1</sup>.mol<sup>−1</sup>
|-
! {{chembox header}} | '''Hazards''' <!-- INDEX n° 030-013-00-7 -->
|-
| [[Directive 67/548/EEC|EU classification]]
| Dangerous for<br />the environment ('''N''')
|-
| [[List of R-phrases|R-phrases]]
| {{R20}}, {{R36}}, {{R37}}.
|-
| [[List of S-phrases|S-phrases]]
| {{S60}}, {{S61}}.
|-
| [[NFPA 704]]
| {{NFPA 704 | Health = 1 | Flammability = 0 | Reactivity = 0}}
|-
! {{chembox header}} | [[Zinc oxide (data page)|Supplementary data page]]
|-
| [[Zinc oxide (data page)#Structure and properties|Structure and<br />properties]]
| [[Refractive index|''n'']], [[Dielectric constant|''ε<sub>r</sub>'']], etc.
|-
| [[Zinc oxide (data page)#Thermodynamic properties|Thermodynamic<br />data]]
| Phase behaviour<br />Solid, liquid, gas
|-
| [[Zinc oxide (data page)#Spectral data|Spectral data]]
| [[UV/VIS spectroscopy|UV]], [[Infrared spectroscopy|IR]], [[NMR spectroscopy|NMR]], [[Mass spectrometry|MS]]
|-
| [[Zinc oxide (data page)#Regulatory data|Regulatory data]]
| [[Flash point]],<br />[[RTECS|RTECS number]], etc.
|-
! {{chembox header}} | Related compounds
|-
| Other [[Ion|anion]]s
| [[Zinc sulfide]]<br />[[Zinc selenide]]<br/>[[Zinc telluride]]
|-
| Other [[Ion|cation]]s
| [[Cadmium oxide]]<br />[[Mercury oxide]]
|-
| {{chembox header}} | <small>Except where noted otherwise, data are given for<br> materials in their [[standard state|standard state (at 25 °C, 100 kPa)]]<br />[[wikipedia:Chemical infobox|Infobox disclaimer and references]]</small>
|-
|}
'''Zinc oxide''' is a [[chemical compound]] with formula '''ZnO'''. It is nearly [[solubility|insoluble]] in water but soluble in [[acid]]s or [[alkali]]s. It occurs as white [[hexagon]]al [[crystal]]s 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 [[thermochromism|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.[http://www.theodoregray.com/PeriodicTable/ZincSafety.html] Exposure to zinc oxide in the air (also while welding) can result in a nervous malady called [[metal fume fever]][http://www.du.edu/~jcalvert/phys/zinc.htm].
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(III) oxide]] (Fe<sub>2</sub>O<sub>3</sub>) 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 (mineral)]].
Zinc [[peroxide]], ZnO<sub>2</sub> .½ H<sub>2</sub>O, is a white to yellow powder that is used in [[antiseptic]] ointments.
Zinc white is used as a pigment in [[paint]]s 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 [[artist]]s' [[pigment]]s. Because it absorbs both UVA and UVB rays of [[ultraviolet light]], zinc oxide can be used in ointments, creams, and [[lotion]]s to protect against [[sunburn]] and other damage to the skin caused by [[ultraviolet light]] (see [[sunscreen]]). It is the broadest spectrum UVA and UVB absorber that is approved for use as a sunscreen by FDA, and is completely photostable. Additionally, since zinc oxide has antimicrobial and antifungal activities, it is the number one active ingredient recommended by pediatricians for the treatment of diaper rash.
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]] [[sensor]]s. [[As of 2003]], it has been utilized in recent research to build blue [[LED]]s and transparent [[Thin-film transistor|TFT]]s.
[[n-type|''n''-type]] [[doping (semiconductors)|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]] <ref>Acc. Chem. Res. 1985, 18, pp. 228-234, ''Zinc Oxide: An Outstanding Example of a Binary Compound Semiconductor'',
Hirschwald, Wolfgang H.</ref>. [[Oxygen]] vacancies generate states in the band gap and hence also cause an increase in conductivity.<ref>"Oxygen Vacancies in ZnO", A. Janotti and C. G. Van de Walle, Appl. Phys. Lett. 87, 122102 (2005).</ref> [[p-type |''p''-type]] doping is difficult and is currently an active area of research, with [[arsenic]] as the leading candidate dopant<ref>Phys. 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</ref>. Thin-film [[solar cell]]s, [[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|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 semiconductor |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 has been 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.<ref>[http://www.uhseast.com/121274.cfm]</ref>
When mixed with [[eugenol]], [[zinc oxide eugenol]] forms which has [[dental restoration|restorative]] and [[prosthodontics|prosthodontic]] applications in [[dentistry]].
== Pyroelectric coefficient ==
* Primary [[Pyroelectricity|pyroelectric]] coefficient: -6.8 µC/m<sup>2</sup>·K
* Secondary pyroelectric coefficient: -2.5 µC/m<sup>2</sup>·K
* Total pyroelectric coefficient: -9.4 µC/m<sup>2</sup>·K
== Production Methods ==
Zinc Oxide is produced by two main processes:-
1. French Process<br />
In this process, metallic zinc (Zinc Dross) is heated to a vapour form, the metallic zinc vapour is allowed to auto oxidize to form Zinc Oxide.
Higher purity of Zinc Oxide (Up to 99.9%) can be obtained by this method.
2. American Process<br />
In this process ore of zinc (Zinc Ash) is dissolved (as ZnCl2) then goes through a precipitation process using alkali. Then it is filtered off, dried and micronised to obtain the powdered form.
Zinc oxide made from this process is known as "Active Zinc Oxide"
== Indirect method ==
Metallic zinc is melted at 419.5 deg C in a graphite crucible and vaporized above 907 deg C. Zinc vapor instantaneously reacts with the oxygen in the air to become zinc oxide accompanied by a sudden drop in its temperature and also bright luminescence. Zinc oxide particles are transported into a cooling duct and collected in a bag house. This indirect method is commonly known as the French process (FP) which was popularised by LeClaire (France) in 1844. A typical FP zinc oxide normally consists of agglomerated zinc oxide particles with an average size of 0.1 micron to a few microns. By tonnage, most of the world's zinc oxide is manufactured via French process and major applications involve industries related to rubber, varistors, suncreens, paints, healthcare and poultry nutrients. Recent developments involve acicular nanostructures (rods, wires, tripods, tetrapods, plates) synthesized using a modified French process known as catalyst-free combust-oxidized mesh (CFCOM) process. Acicular nanostructures usually have micron-length nanorods with nanometric diameters (below 100 nm).
More details on new developments here [http://uk.geocities.com/shahromx/nano.html NanoZnO]
<!-- Unsourced image removed: [[Image:FPzincoxidefurnaces1.jpg]] --><!-- Unsourced image removed: [[Image:FPzincoxide2.jpg]] --><!-- Unsourced image removed: [[Image:ZincOxideRods3.jpg]] -->
== 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.
== 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 [http://franklin-sterlinghill.com/franklinminerals/zno.stm Frankin-Sterling Hill web site].
In one episode of ''[[SpongeBob SquarePants]]'', SpongeBob rubs Zinc Oxide on his nose to achieve the "lifeguard look".
In the series Gundam SEED and Gundam SEED Destiny, there is a mass-produced unit called the ZnO which is an underwater type mobile suit.
== External links ==
* [http://www.ilo.org/public/english/protection/safework/cis/products/icsc/dtasht/_icsc02/icsc0208.htm International Chemical Safety Card 0208].
* [http://www.cdc.gov/niosh/npg/npgd0675.html NIOSH Pocket Guide to Chemical Hazards].
* [http://www.navbharat.co.in/clients.htm Nav Bharat Metallic Oxide Industries]. (uses of zinc oxide)
* [http://physchem.ox.ac.uk/MSDS/ZI/zinc_oxide.html External MSDS].
== References ==
<!--See http://en.wikipedia.org/wiki/Wikipedia:Footnotes for an explanation of how to generate footnotes using the <ref> and </ref> tags and the tag below -->
<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).
* "Nanostructure of ZnO fabricated via French Process and its correlation to electrical properties of semiconducting varistors", S.Mahmud, M.J.Abdullah, J.Chong, A.K.Mohamad, M.Z.Zakaria, J. Syn. React. Inorg., Met-org. and Nano-metal Chem., 36, pp155-159 (2006).
[[Category:Oxides]]
[[Category:Zinc compounds]]
[[Category:Inorganic pigments]]
[[Category:Inorganic compounds]]
[[Category:Semiconductor materials]]
[[Category:Sunscreening agents]]
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