View source for Chemistry:Zinc oxide

{{Short description|White powder insoluble in water}}
{{Chembox
| Verifiedfields = changed
| Watchedfields = changed
| verifiedrevid = 477003077
| ImageFile = Zinc oxide.jpg
| Name = Zinc oxide
| OtherNames = Zinc white, calamine, philosopher's wool, Chinese white, flowers of zinc
|Section1={{Chembox Identifiers
| CASNo = 1314-13-2
| CASNo_Ref = {{cascite|correct|CAS}}
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = SOI2LOH54Z
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 14122
| ChEBI_Ref = {{ebicite|correct|EBI}}
| ChEBI = 36560
| SMILES = [Zn]=O
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChI = 1S/O.Zn
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = XLOMVQKBTHCTTD-UHFFFAOYSA-N
| PubChem = 14806
| ChEMBL_Ref = {{ebicite|changed|EBI}}
| ChEMBL = 3988900
| RTECS = ZH4810000
| EINECS = 215-222-5
| UNNumber = 3077
| Gmelin = 13738
| KEGG = C12570
| DrugBank = DB09321
}}
|Section2={{Chembox Properties
| Formula = {{chem|[[Chemistry:Zinc|Zn]]|[[Chemistry:Oxygen|O]]}}
| MolarMass = 81.406 g/mol<ref name=h1>Haynes, pp. 4.95, 12.80</ref>
| Appearance = White solid<ref name=h1/>
| Odor = Odorless
| Density = 5.6 g/cm<sup>3</sup><ref name=h1/>
| Solubility = 0.0004% (17.8°C)<ref name=PGCH/>
| MeltingPtC = 1974
| MeltingPt_notes = (decomposes)<ref name=h1/><ref name="melt"/>
| BoilingPtC = 2360
| BoilingPt_notes = (decomposes)
| BandGap = 3.2 eV ([[Physics:Direct and indirect band gaps|direct]])<ref name=h1285>Haynes, pp. 12.85, 12.89</ref>
| ElectronMobility =180 cm<sup>2</sup>/(V·s)<ref name=h1285/>
| RefractIndex = n<sub>1</sub>=2.013, n<sub>2</sub>=2.029<ref>Haynes, pp. 4.138, 10.251</ref>
| MagSus = −27.2·10<sup>−6</sup> cm<sup>3</sup>/mol<ref>Haynes, p. 4.131</ref>
| ThermalConductivity = 0.6 W/(cm·K)<ref>Haynes, p. 12.80</ref>
}}
|Section3={{Chembox Structure
| Structure_ref =<ref>Haynes, p. 4.145</ref>
| CrystalStruct = [[Chemistry:Wurtzite (crystal structure)|Wurtzite]]
| SpaceGroup = ''C''<sub>6v</sub><sup>4</sup>-''P''6<sub>3</sub>''mc''
| Coordination = Tetrahedral
| UnitCellFormulas = 2
| LattConst_a = 3.2495 Å 
| LattConst_c = 5.2069 Å
}}
|Section5={{Chembox Thermochemistry
| Thermochemistry_ref =<ref>Haynes, pp. 5.2, 5.42, 6.163</ref>
| DeltaHf = -350.46±0.27 kJ mol<sup>−1</sup>
| Entropy = 43.65±0.40 J·K<sup>−1</sup>mol<sup>−1</sup>
| HeatCapacity = 40.3 J·K<sup>−1</sup>mol<sup>−1</sup>
| DeltaGf = -320.5 kJ mol<sup>−1</sup>
| DeltaHfus = 70 kJ/mol
}}
|Section6={{Chembox Pharmacology
| ATCvet = yes
| ATCCode_prefix = A07
| ATCCode_suffix = XA91
}}
|Section7={{Chembox Hazards
| ExternalSDS = [http://www.inchem.org/documents/icsc/icsc/eics0208.htm ICSC 0208]
| GHSPictograms = {{GHS09}}
| GHSSignalWord = Warning
| HPhrases = {{H-phrases|400|401}}
| PPhrases = {{P-phrases|273|391|501}}
| NFPA-H = 2
| NFPA-F = 0
| NFPA-R = 0
| NFPA-S = 
| FlashPtC = 1436
| LD50 = 240 mg/kg (intraperitoneal, rat)<ref>[https://chem.nlm.nih.gov/chemidplus/rn/1314-13-2 Zinc oxide]. Chem.sis.nlm.nih.gov. Retrieved on 2015-11-17.</ref><br/>7950 mg/kg (rat, oral)<ref name=IDLH/>
| IDLH = 500 mg/m<sup>3</sup><ref name=PGCH>{{PGCH|0675}}</ref>
| LC50 = 2500 mg/m<sup>3</sup> (mouse)<ref name=IDLH>{{IDLH|1314132|Zinc oxide}}</ref>
| REL = Dust: TWA 5 mg/m<sup>3</sup> C 15 mg/m<sup>3</sup><br/>
Fume: TWA 5 mg/m<sup>3</sup> ST 10 mg/m<sup>3</sup><ref name=PGCH/>
| PEL = TWA 5 mg/m<sup>3</sup> (fume) TWA 15 mg/m<sup>3</sup> (total dust) TWA 5 mg/m<sup>3</sup> (resp dust)<ref name=PGCH/>
| LCLo = 2500 mg/m<sup>3</sup> (guinea pig, 3–4 h)<ref name=IDLH/>
}}
|Section8={{Chembox Related
| OtherAnions = [[Chemistry:Zinc sulfide|Zinc sulfide]]<br/>[[Chemistry:Zinc selenide|Zinc selenide]]<br/>[[Chemistry:Zinc telluride|Zinc telluride]]
| OtherCations = [[Chemistry:Cadmium oxide|Cadmium oxide]]<br/>[[Chemistry:Mercury(II) oxide|Mercury(II) oxide]]
}}
}}
'''Zinc oxide''' is an [[Chemistry:Inorganic compound|inorganic compound]] with the [[Chemistry:Chemical formula|formula]] {{chem|[[Chemistry:Zinc|Zn]]|[[Chemistry:Oxygen|O]]}}. It is a white powder that is insoluble in water. ZnO is used as an additive in numerous materials and products including cosmetics, food supplements, rubbers, plastics, ceramics, glass, cement, lubricants,<ref name="wear"/> paints, sunscreens, ointments, adhesives, sealants, pigments, foods, batteries, ferrites, fire retardants, semi conductors,<ref name="ozgur">{{cite journal |vauthors=Özgür Ü, Alivov YI, Liu C, Teke A, Reshchikov M, Doğan S, Avrutin VC, Cho SJ, Morkoç AH |year=2005 |title=A comprehensive review of ZnO materials and devices |url=https://scholarscompass.vcu.edu/cgi/viewcontent.cgi?article=1158&context=egre_pubs |journal=Journal of Applied Physics |volume=98 |issue=4 |pages=041301–041301–103 |bibcode=2005JAP....98d1301O |doi=10.1063/1.1992666}}</ref> and first-aid tapes. Although it occurs naturally as the mineral [[Chemistry:Zincite|zincite]], most zinc oxide is produced synthetically.<ref name=Ullmann>{{cite book | last = De Liedekerke | first = Marcel | name-list-style = vanc | date = 2006 | chapter = 2.3. Zinc Oxide (Zinc White): Pigments, Inorganic, 1 | title = Ullmann's Encyclopedia of Industrial Chemistry | publisher = Wiley-VCH | location = Weinheim | doi = 10.1002/14356007.a20_243.pub2 }}</ref>

==History==
Zinc compounds were probably used by early humans, in processed<ref name="Ullmann" /> and unprocessed forms, as a paint or medicinal ointment, but their composition is uncertain. The use of ''pushpanjan'', probably zinc oxide, as a salve for eyes and open wounds, is mentioned in the Indian medical text the [[Religion:Charaka Samhita|Charaka Samhita]], thought to date from 500 BC or before.<ref>{{cite book |title=2000 years of zinc and brass |vauthors=Craddock PT |publisher=British Museum |year=1998 |isbn=978-0-86159-124-4 |page=27 |chapter=Zinc in India}}</ref> Zinc oxide ointment is also mentioned by the Greek physician Dioscorides (1st century AD).<ref name="c111">{{cite book |title=The Oxford Handbook of Engineering and Technology in the Classical World |vauthors=Craddock PT |publisher=Oxford University Press |year=2008 |isbn=978-0-19-518731-1 |editor-last=Oleson |editor-first=John Peter |pages=111–112 |chapter=Mining and Metallurgy, chapter 4 |chapter-url=https://books.google.com/books?id=OPOdZaIElRkC&pg=PA111}}</ref> [[Biography:Galen|Galen]] suggested treating ulcerating cancers with zinc oxide,<ref>{{cite book |last1=Winchester |first1=David J. |title=Breast Cancer (Atlas of Clinical Oncology) |last2=Winchester |first2=David P. |last3=Hudis |first3=Clifford A. |last4=Norton |first4=Larry |publisher=PMPH USA |year=2005 |isbn=978-1550092721 |page=3 |name-list-style=vanc}}</ref> as did [[Biography:Avicenna|Avicenna]] in his ''The Canon of Medicine''. It is used as an ingredient in products such as [[Chemistry:Baby powder|baby powder]] and creams against diaper rashes, [[Chemistry:Calamine|calamine]] cream, anti-[[Medicine:Dandruff|dandruff]] [[Medicine:Shampoo|shampoo]]s, and [[Chemistry:Antiseptic|antiseptic]] ointments.<ref name="Harding">{{Cite book |last=Harding |first=Fred John |url=https://books.google.com/books?id=0h2gDLv3MOEC&pg=PT83 |title=Breast Cancer: Cause – Prevention – Cure |publisher=Tekline Publishing |year=2007 |isbn=978-0-9554221-0-2 |page=83 |name-list-style=vanc}}</ref>

The Romans produced considerable quantities of [[Chemistry:Brass|brass]] (an alloy of [[Chemistry:Zinc|zinc]] and [[Chemistry:Copper|copper]]) as early as 200 BC by a cementation process where copper was reacted with zinc oxide.<ref>{{cite book |url=http://www.britannica.com/EBchecked/topic/657264/zinc |title=Encyclopædia Britannica |date=10 March 2009 |chapter=Zinc}}</ref> The zinc oxide is thought to have been produced by heating zinc ore in a shaft furnace. This liberated metallic zinc as a vapor, which then ascended the flue and condensed as the oxide. This process was described by Dioscorides in the 1st century AD.<ref>{{cite journal |last1=Craddock |first1=Paul Terence |name-list-style=vanc |year=2009 |title=The origins and inspirations of zinc smelting |journal=Journal of Materials Science |volume=44 |issue=9 |pages=2181–2191 |bibcode=2009JMatS..44.2181C |doi=10.1007/s10853-008-2942-1 |s2cid=135523239}}</ref> Zinc oxide has also been recovered from zinc mines at Zawar in {{wipe|India}}, dating from the second half of the first millennium BC.<ref name="c111" />

From the 12th to the 16th century zinc and zinc oxide were recognized and produced in India using a primitive form of the direct synthesis process. From India, zinc manufacture moved to China in the 17th century. In 1743, the first European zinc smelter was established in Bristol, United Kingdom.<ref>[http://chinese-school.netfirms.com/Zinc-information.html General Information of Zinc from the National Institute of Health, WHO, and International Zinc Association]. Retrieved 10 March 2009</ref> Around 1782 Louis-Bernard Guyton de Morveau proposed replacing [[Lead white|lead white]] pigment with zinc oxide.<ref>{{Cite web |title=Zinc White |url=https://www.matisse.com.au/zinc-white}}</ref>

The main usage of zinc oxide (zinc white) was in paints and as an additive to ointments. Zinc white was accepted as a pigment in oil paintings by 1834 but it did not mix well with oil. This problem was solved by optimizing the synthesis of ZnO. In 1845, Edme-Jean Leclaire in Paris was producing the oil paint on a large scale, and by 1850, zinc white was being manufactured throughout Europe. The success of zinc white paint was due to its advantages over the traditional white lead: zinc white is essentially permanent in sunlight, it is not blackened by sulfur-bearing air, it is non-toxic and more economical. Because zinc white is so "clean" it is valuable for making tints with other colors, but it makes a rather brittle dry film when unmixed with other colors. For example, during the late 1890s and early 1900s, some artists used zinc white as a ground for their oil paintings. All those paintings developed cracks over the years.<ref>{{cite web |title=Zinc white: History of use |url=http://www.webexhibits.org/pigments/indiv/history/zincwhite.html |work=Pigments through the ages |publisher=webexhibits.org}}</ref>

In recent times, most zinc oxide was used in the [[Chemistry:Rubber|rubber]] industry to resist [[Chemistry:Corrosion|corrosion]]. In the 1970s, the second largest application of ZnO was photocopying. High-quality ZnO produced by the "French process" was added to photocopying paper as a filler. This application was soon displaced by [[Chemistry:Titanium|titanium]].<ref name="porter" />

==Chemical properties==
Pure ZnO is a white powder, but in nature it occurs as the rare mineral [[Chemistry:Zincite|zincite]], which usually contains [[Chemistry:Manganese|manganese]] and other impurities that confer a yellow to red color.<ref name="k1">{{cite journal | vauthors = Klingshirn C |url=https://scholar.google.com/scholar?hl=en&as_sdt=0%2C5&q=ZnO%3A+Material%2C+Physics+and+Applications&btnG= | title = ZnO: material, physics and applications | journal = ChemPhysChem | volume = 8 | issue = 6 | pages = 782–803 | date = April 2007 | pmid = 17429819 | doi = 10.1002/cphc.200700002 }}</ref>

Crystalline zinc oxide is [[Chemistry:Thermochromism|thermochromic]], changing from white to yellow when heated in air and reverting to white on cooling.<ref name="Wiberg&Holleman">{{cite book| vauthors = Wiberg E, Holleman AF |year=2001|title=Inorganic Chemistry|publisher=Elsevier|isbn=978-0-12-352651-9}}</ref> This color change is caused by a small loss of oxygen to the environment at high temperatures to form the non-stoichiometric Zn<sub>1+x</sub>O, where at 800&nbsp;°C, x = 0.00007.<ref name = "Wiberg&Holleman"/>

Zinc oxide is an amphoteric oxide. It is nearly [[Chemistry:Solubility|insoluble]] in water, but it will dissolve in most [[Chemistry:Acid|acid]]s, such as hydrochloric acid:<ref name = "Greenwood_1997">{{Greenwood&Earnshaw2nd|name-list-style = vanc }}</ref>
:ZnO  +  2 HCl   →   ZnCl<sub>2</sub>  +  H<sub>2</sub>O
Solid zinc oxide will also dissolve in alkalis to give soluble zincates:
:ZnO  +  2 NaOH  +  H<sub>2</sub>O   →   Na<sub>2</sub>[Zn(OH)<sub>4</sub>]

ZnO reacts slowly with fatty acids in oils to produce the corresponding [[Chemistry:Carboxylate|carboxylate]]s, such as oleate or [[Chemistry:Zinc stearate|stearate]]. When mixed with a strong aqueous solution of [[Chemistry:Zinc chloride|zinc chloride]], ZnO forms cement-like products best described as zinc hydroxy chlorides.<ref>{{cite journal|doi=10.1023/A:1004327018497|title=The chemistry of cements formed between zinc oxide and aqueous zinc chloride|year=1998| vauthors = Nicholson JW |journal=Journal of Materials Science|volume=33|pages=2251–2254 |issue=9|bibcode = 1998JMatS..33.2251N |s2cid=94700819}}</ref> This cement was used in dentistry.<ref name = "Ferracane">{{cite book| vauthors = Ferracane JL |title=Materials in Dentistry: Principles and Applications|year=2001|publisher=Lippincott Williams & Wilkins|isbn=978-0-7817-2733-4|url=https://books.google.com/books?id=5uvuvNKpIkQC&pg=PA143|pages=70, 143}}</ref>

[[File:Hopeite.jpg|thumb|150px|left|Hopeite]]
ZnO also forms cement-like material when treated with [[Chemistry:Phosphoric acid|phosphoric acid]]; related materials are used in dentistry.<ref name = "Ferracane"/> A major component of zinc phosphate cement produced by this reaction is [[Chemistry:Hopeite|hopeite]], Zn<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub>·4H<sub>2</sub>O.<ref>{{cite journal|title=Setting reaction and resultant structure of zinc phosphate cement in various orthophosphoric acid cement-forming liquids| vauthors = Park CK, Silsbee MR, Roy DM |journal=Cement and Concrete Research|year=1998|volume=28|issue=1|pages=141–150|doi=10.1016/S0008-8846(97)00223-8}}</ref>

ZnO decomposes into zinc vapor and oxygen at around 1975&nbsp;°C with a standard oxygen pressure. In a [[Chemistry:Carbothermic reaction|carbothermic reaction]], heating with carbon converts the oxide into zinc vapor at a much lower temperature (around 950&nbsp;°C).<ref name = "Greenwood_1997" />
:ZnO  +  C   →   Zn<sub>(Vapor)</sub>  +  CO

==Physical properties==
[[File:Wurtzite polyhedra.png|thumb|150px|right|Wurtzite structure]]
[[Image:Sphalerite-unit-cell-depth-fade-3D-balls.png|150px|thumb|right|A zincblende unit cell]]

=== Structure ===
Zinc oxide crystallizes in two main [[Physics:Polymorphism (materials science)|forms]], hexagonal [[Physics:Wurtzite crystal structure|wurtzite]]<ref name=fierro>{{cite book| vauthors = Fierro JL |title=Metal Oxides: Chemistry & Applications|year=2006|publisher=CRC Press|page= 182|isbn=978-0824723712}}</ref> and cubic zincblende.  The wurtzite structure is most stable at ambient conditions and thus most common. The zincblende form can be stabilized by growing ZnO on substrates with cubic lattice structure. In both cases, the zinc and oxide centers are [[Physics:Tetrahedral molecular geometry|tetrahedral]], the most characteristic geometry for Zn(II).  ZnO converts to the [[Chemistry:Sodium chloride|rocksalt]] motif at relatively high pressures about 10 GPa.<ref name="ozgur"/>

Hexagonal and zincblende polymorphs have no [[Reflection symmetry|inversion symmetry]] (reflection of a crystal relative to any given point does not transform it into itself). This and other lattice symmetry properties result in [[Physics:Piezoelectricity|piezoelectricity]] of the hexagonal and zincblende ZnO, and [[Physics:Pyroelectricity|pyroelectricity]] of hexagonal ZnO.

The hexagonal structure has a point group 6&nbsp;mm ([[Chemistry:Hermann–Mauguin notation|Hermann–Mauguin notation]]) or C<sub>6v</sub> ([[Physics:Schoenflies notation|Schoenflies notation]]), and the [[Space group|space group]] is P6<sub>3</sub>mc or C<sub>6v</sub><sup>4</sup>. The lattice constants are ''a'' = 3.25 Å and ''c'' = 5.2 Å; their ratio ''c/a'' ~ 1.60 is close to the ideal value for hexagonal cell ''c/a'' = 1.633.<ref>{{cite book|title=Landolt-Bornstein, New Series, Group III|volume=17B, 22, 41B| veditors = Rossler U |publisher=Springer, Heidelberg|year=1999}}</ref> As in most [[Chemistry:Group (periodic table)|group II-VI]] materials, the bonding in ZnO is largely ionic (Zn<sup>2+</sup>O<sup>2−</sup>) with the corresponding radii of 0.074&nbsp;nm for Zn<sup>2+</sup> and 0.140&nbsp;nm for O<sup>2−</sup>. This property accounts for the preferential formation of wurtzite rather than zinc blende structure,<ref>{{cite book| vauthors = Klingshirn CF, Waag A, Hoffmann A, Geurts J |title=Zinc Oxide: From Fundamental Properties Towards Novel Applications|url=https://books.google.com/books?id=TYXinw6pKk4C&pg=PA9|date=2010|publisher=Springer|isbn=978-3-642-10576-0|pages=9–10}}</ref> as well as the strong [[Physics:Piezoelectricity|piezoelectricity]] of ZnO. Because of the polar Zn−O bonds, zinc and oxygen planes are electrically charged. To maintain electrical neutrality, those planes reconstruct at atomic level in most relative materials, but not in ZnO – its surfaces are atomically flat, stable and exhibit no reconstruction.<ref name="dutta">{{cite journal | vauthors = Baruah S, Dutta J | title = Hydrothermal growth of ZnO nanostructures | journal = Science and Technology of Advanced Materials | volume = 10 | issue = 1 | pages = 013001 | date = February 2009 | pmid = 27877250 | pmc = 5109597 | doi = 10.1088/1468-6996/10/1/013001 | bibcode = 2009STAdM..10a3001B }}</ref> However, studies using wurtzoid structures explained the origin of surface flatness and the absence of reconstruction at ZnO wurtzite surfaces<ref>{{cite journal|doi=10.1016/j.spmi.2015.07.015|title=Capped ZnO (3, 0) nanotubes as building blocks of bare and H passivated wurtzite ZnO nanocrystals|journal=Superlattices and Microstructures|volume=85|pages=813–819|year=2015|last1=Abdulsattar|first1=Mudar Ahmed | name-list-style = vanc |bibcode=2015SuMi...85..813A}}</ref> in addition to the origin of charges on ZnO planes.

===Mechanical properties===
ZnO is a wide-band gap semiconductor of the II-VI semiconductor group. The native [[Physics:Doping (semiconductor)|doping]] of the semiconductor due to oxygen vacancies or zinc interstitials is n-type.<ref name="ozgur" />

ZnO is a relatively soft material with approximate hardness of 4.5 on the [[Physics:Mohs scale|Mohs scale]].<ref name="wear">{{cite journal | vauthors = Battez AH, González R, Viesca JL, Fernández JE, Fernández JD, Machado A, Chou R, Riba J |doi=10.1016/j.wear.2007.11.013|title=CuO, ZrO2 and ZnO nanoparticles as antiwear additive in oil lubricants|year=2008 |journal=Wear|volume=265|pages=422–428 |issue=3–4}}</ref> Its elastic constants are smaller than those of relevant III-V semiconductors, such as GaN. The high heat capacity and heat conductivity, low thermal expansion and high melting temperature of ZnO are beneficial for ceramics.<ref name="porter" /> The E2 optical phonon in ZnO exhibits an unusually long lifetime of 133&nbsp;ps at 10&nbsp;K.<ref>{{Cite journal | vauthors = Millot M, Tena-Zaera R, Munoz-Sanjose V, Broto JM, Gonzalez J | title = Anharmonic effects in ZnO optical phonons probed by Raman spectroscopy | doi = 10.1063/1.3387843 | journal = Applied Physics Letters | volume = 96 | issue = 15 | page = 152103 | year = 2010 |bibcode = 2010ApPhL..96o2103M | hdl = 10902/23620 | hdl-access = free }}</ref>

Among the tetrahedrally bonded semiconductors, it has been stated that ZnO has the highest piezoelectric tensor, or at least one comparable to that of GaN and AlN.<ref>{{cite journal | vauthors = Posternak M, Resta R, Baldereschi A | title = Ab initio study of piezoelectricity and spontaneous polarization in ZnO | journal = Physical Review B | volume = 50 | issue = 15 | pages = 10715–10721 | date = October 1994 | pmid = 9975171 | doi = 10.1103/PhysRevB.50.10715 | bibcode = 1994PhRvB..5010715D }}</ref> This property makes it a technologically important material for many [[Physics:Piezoelectricity|piezoelectrical]] applications, which require a large electromechanical coupling. Therefore, ZnO in the form of [[Physics:Thin film|thin film]] has been one of the most studied resonator materials for [[Physics:Thin-film bulk acoustic resonator|thin-film bulk acoustic resonator]]s.

===Electrical and optical properties===
Favourable properties of zinc oxide include good transparency, high [[Physics:Electron mobility|electron mobility]], wide [[Physics:Band gap|band gap]], and strong room-temperature [[Physics:Luminescence|luminescence]]. Those properties make ZnO valuable for a variety of emerging applications: transparent [[Physics:Electrode|electrode]]s in liquid crystal displays, energy-saving or heat-protecting windows, and electronics as thin-film [[Engineering:Transistor|transistor]]s and [[Engineering:Light-emitting diode|light-emitting diode]]s.

ZnO has a relatively wide [[Physics:Direct and indirect band gaps|direct]] [[Physics:Band gap|band gap]] of ~3.3&nbsp;eV at room temperature. Advantages associated with a wide band gap include higher [[Physics:Breakdown voltage|breakdown voltages]], ability to sustain large electric fields, lower electronic noise, and high-temperature and high-power operation. The band gap of ZnO can further be tuned to ~3–4&nbsp;eV by its alloying with [[Chemistry:Magnesium oxide|magnesium oxide]] or [[Chemistry:Cadmium oxide|cadmium oxide]].<ref name="ozgur" /> Due to this large band gap, there have been efforts to create visibly transparent solar cells utilising ZnO as a light absorbing layer. However, these solar cells have so far proven highly inefficient. <ref>{{cite journal |doi=10.7567/1347-4065/ab532a |title=Fabrication of ZnO/NiO transparent solar cells by electrochemical deposition |date=2019 |last1=Koyama |first1=Miki |last2=Ichimura |first2=Masaya |journal=Japanese Journal of Applied Physics |volume=58 |issue=12 |bibcode=2019JaJAP..58l8003K |s2cid=209935734 }}</ref>

Most ZnO has ''n''-type character, even in the absence of intentional [[Physics:Doping (semiconductor)|doping]]. Nonstoichiometry is typically the origin of n-type character, but the subject remains controversial.<ref name=Look1999>{{cite journal | vauthors = Look DC, Hemsky JW, Sizelove JR | year = 1999 | title = Residual Native Shallow Donor in ZnO | journal = Physical Review Letters | volume = 82 | pages = 2552–2555 | doi = 10.1103/PhysRevLett.82.2552 | bibcode = 1999PhRvL..82.2552L | issue = 12 | s2cid = 53476471 | url = https://corescholar.libraries.wright.edu/physics/216 }}</ref> An alternative explanation has been proposed, based on theoretical calculations, that unintentional substitutional hydrogen impurities are responsible.<ref name=Janotti2007>{{cite journal | vauthors = Janotti A, Van de Walle CG | title = Hydrogen multicentre bonds | journal = Nature Materials | volume = 6 | issue = 1 | pages = 44–7 | date = January 2007 | pmid = 17143265 | doi = 10.1038/nmat1795 | bibcode = 2007NatMa...6...44J }}</ref> Controllable n-type doping is easily achieved by substituting Zn with group-III elements such as Al, Ga, In or by substituting oxygen with group-VII elements [[Chemistry:Chlorine|chlorine]] or [[Chemistry:Iodine|iodine]].<ref>{{cite journal | vauthors = Kato H, Sano M, Miyamoto K, Yao T |doi=10.1016/S0022-0248(01)01972-8|title=Growth and characterization of Ga-doped ZnO layers on a-plane sapphire substrates grown by molecular beam epitaxy|year=2002 |journal=Journal of Crystal Growth|volume=237–239|pages=538–543|bibcode=2002JCrGr.237..538K |doi-access=free}}</ref>

Reliable p-type doping of ZnO remains difficult. This problem originates from low solubility of p-type dopants and their compensation by abundant n-type impurities. This problem is observed with GaN and ZnSe. Measurement of p-type in "intrinsically" n-type material is complicated by the inhomogeneity of samples.<ref>{{cite journal | vauthors = Ohgaki T, Ohashi N, Sugimura S, Ryoken H, Sakaguchi I, Adachi Y, Haneda H |doi=10.1557/JMR.2008.0300|title=Positive Hall coefficients obtained from contact misplacement on evident ''n''-type ZnO films and crystals|year=2008 |journal=Journal of Materials Research|volume=23|pages=2293–2295 |issue=9|bibcode = 2008JMatR..23.2293O |s2cid=137944281 }}</ref>

Current limitations to p-doping limit electronic and optoelectronic applications of ZnO, which usually require junctions of n-type and p-type material. Known p-type dopants include group-I elements Li, Na, K; group-V elements N, P and As; as well as copper and silver. However, many of these form deep acceptors and do not produce significant p-type conduction at room temperature.<ref name="ozgur"/><!--what is this doing here? - this one is a proper reference here-->

[[Physics:Electron mobility|Electron mobility]] of ZnO strongly varies with temperature and has a maximum of ~2000&nbsp;cm<sup>2</sup>/(V·s) at 80 K.<ref>{{cite journal | vauthors = Wagner P, Helbig R |doi=10.1016/S0022-3697(74)80026-0|title=Halleffekt und anisotropie der beweglichkeit der elektronen in ZnO|year=1974 |journal=Journal of Physics and Chemistry of Solids|volume=35|pages=327–335 |bibcode=1974JPCS...35..327W|issue=3}}</ref> Data on hole mobility are scarce with values in the range 5–30&nbsp;cm<sup>2</sup>/(V·s).<ref>{{cite journal | vauthors = Ryu YR, Lee TS, White HW |doi=10.1063/1.1590423|title=Properties of arsenic-doped p-type ZnO grown by hybrid beam deposition|year=2003 |journal=Applied Physics Letters|volume=83|issue=1|page=87 |bibcode = 2003ApPhL..83...87R }}</ref>

ZnO discs, acting as a  [[Engineering:Varistor|varistor]], are the active material in most [[Physics:Surge arrester|surge arrester]]s.<ref>
René Smeets, Lou van der Sluis, Mirsad Kapetanovic, David F. Peelo, Anton Janssen.
[https://books.google.com/books?id=NVUzBAAAQBAJ "Switching in Electrical Transmission and Distribution Systems"].
2014.
p. 316.
</ref><ref>
Mukund R. Patel.
[https://books.google.com/books?id=Am5CI32itwAC "Introduction to Electrical Power and Power Electronics"].
2012.
p. 247.
</ref>

Zinc oxide is noted for its strongly nonlinear optical properties, especially in bulk. The nonlinearity of ZnO nanoparticles can be fine-tuned according to their size.<ref>{{cite journal | title = Size-dependent enhancement of nonlinear optical properties in nanocolloids of ZnO | url = http://dyuthi.cusat.ac.in/xmlui/bitstream/purl/2586/1/Dyuthi-P0146.pdf| year = 2008 | journal = Journal of Applied Physics | pages = 033105–033105–7 | volume = 103 | vauthors = Irimpan L, Krishnan Deepthy BA, ((Nampoori VPN)), Radhakrishnan P | doi = 10.1063/1.2838178 |bibcode = 2008JAP...103c3105I | issue = 3 }}</ref>

==Production==
For industrial use, ZnO is produced at levels of 10<sup>5</sup> tons per year<ref name="k1"/> by three main processes:<ref name=porter>{{cite book| vauthors = Porter F |title=Zinc Handbook: Properties, Processing, and Use in Design|publisher=CRC Press|year=1991|isbn=978-0-8247-8340-2}}</ref>

===Indirect process===
In the indirect or French process, metallic zinc is melted in a graphite crucible and vaporized at temperatures above 907&nbsp;°C (typically around 1000&nbsp;°C). Zinc vapor reacts with the oxygen in the air to give ZnO, accompanied by a drop in its temperature and bright luminescence. Zinc oxide particles are transported into a cooling duct and collected in a bag house. This indirect method was popularized by Edme Jean LeClaire of  Paris in 1844 and therefore is commonly known as the French process. Its product normally consists of agglomerated zinc oxide particles with an average size of 0.1 to a few micrometers. By weight, most of the world's zinc oxide is manufactured via French process.

===Direct process===
The direct or American process starts with diverse contaminated zinc composites, such as [[Chemistry:Calamine (mineral)|zinc ores]] or smelter by-products. The zinc precursors are reduced (carbothermal reduction) by heating with a source of carbon such as [[Chemistry:Anthracite|anthracite]] to produce zinc vapor, which is then oxidized as in the indirect process. Because of the lower purity of the source material, the final product is also of lower quality in the direct process as compared to the indirect one. 

===Wet chemical process===
A small amount of industrial production involves wet chemical processes, which start with aqueous solutions of zinc salts, from which [[Chemistry:Zinc carbonate|zinc carbonate]] or [[Chemistry:Zinc hydroxide|zinc hydroxide]] is precipitated. The solid precipitate is then calcined at temperatures around 800&nbsp;°C.

===Laboratory synthesis===
[[File:Synthetic Zincite Crystals.jpg|thumb|The red and green colors of these synthetic ZnO crystals result from different concentrations of oxygen vacancies.<ref name=growth/>]]
Numerous specialised methods exist for producing ZnO for scientific studies and niche applications. These methods can be classified by the resulting ZnO form (bulk, thin film, [[Physics:Nanowire|nanowire]]), temperature ("low", that is close to room temperature or "high", that is T&nbsp;~&nbsp;1000&nbsp;°C), process type (vapor deposition or growth from solution) and other parameters.

Large single crystals (many cubic centimeters) can be grown by the gas transport (vapor-phase deposition), [[Physics:Hydrothermal synthesis|hydrothermal synthesis]],<ref name="dutta"/><ref name=growth>{{cite journal | vauthors = Schulz D, Ganschow S, Klimm D, Struve K |journal = Journal of Crystal Growth|volume = 310|year =2008|pages= 1832–1835|title = Inductively heated Bridgman method for the growth of zinc oxide single crystals |doi = 10.1016/j.jcrysgro.2007.11.050|issue = 7–9|bibcode = 2008JCrGr.310.1832S }}</ref><ref>{{cite journal | vauthors = Baruah S, Thanachayanont C, Dutta J | title = Growth of ZnO nanowires on nonwoven polyethylene fibers | journal = Science and Technology of Advanced Materials | volume = 9 | issue = 2 | pages = 025009 | date = April 2008 | pmid = 27877984 | pmc = 5099741 | doi = 10.1088/1468-6996/9/2/025009 | bibcode = 2008STAdM...9b5009B }}</ref> or melt growth.<ref name=melt>{{cite book|url=https://books.google.com/books?id=j_HEazhVxoMC&pg=PA357|page=357|title=Wide bandgap semiconductors: fundamental properties and modern photonic and electronic devices| last1 = Takahashi | first1 = Kiyoshi | last2 = Yoshikawa | first2 = Akihiko | last3 = Sandhu | first3 = Adarsh | name-list-style = vanc |publisher=Springer|year=2007|isbn=978-3-540-47234-6}}</ref> However, because of the high [[Physics:Vapor pressure|vapor pressure]] of ZnO, growth from the melt is problematic. Growth by gas transport is difficult to control, leaving the hydrothermal method as a preference.<ref name=melt/> Thin films can be produced by [[Chemistry:Chemical vapor deposition|chemical vapor deposition]], metalorganic vapour phase epitaxy, [[Engineering:Electrophoretic deposition|electrodeposition]], [[Physics:Pulsed laser deposition|pulsed laser deposition]], [[Physics:Sputtering|sputtering]], [[Physics:Sol–gel process|sol–gel]] synthesis, [[Physics:Atomic layer deposition|atomic layer deposition]], spray pyrolysis, etc.

Ordinary white powdered zinc oxide can be produced in the laboratory by electrolyzing a solution of sodium bicarbonate with a zinc anode. Zinc hydroxide and hydrogen gas are produced. The zinc hydroxide upon heating decomposes to zinc oxide:

: Zn + 2 H<sub>2</sub>O → Zn(OH)<sub>2</sub> + H<sub>2</sub>

: Zn(OH)<sub>2</sub> → ZnO + H<sub>2</sub>O

===ZnO nanostructures===
Nanostructures of ZnO can be synthesized into a variety of morphologies including nanowires, nanorods, tetrapods, nanobelts, nanoflowers, nanoparticles etc. Nanostructures can be obtained with most above-mentioned techniques, at certain conditions, and also with the [[Physics:Vapor–liquid–solid method|vapor–liquid–solid method]].<ref name="dutta"/><ref>{{cite journal | vauthors = Miao L, Ieda Y, Tanemura S, Cao YG, Tanemura M, Hayashi Y, Toh S, Kaneko K |doi=10.1016/j.stam.2007.02.012 |title=Synthesis, microstructure and photoluminescence of well-aligned ZnO nanorods on Si substrate|year=2007 |journal=Science and Technology of Advanced Materials|volume=8|pages=443–447 |issue=6|bibcode = 2007STAdM...8..443M |doi-access=free}}</ref><ref>{{cite journal|vauthors = Xu S, Wang ZL |journal=Nano Res.|volume=4|year=2011|pages=1013–1098|title=One-dimensional ZnO nanostructures: Solution growth and functional properties|doi=10.1007/s12274-011-0160-7|issue=11|citeseerx=10.1.1.654.3359 |s2cid=137014543}}</ref> The synthesis is typically carried out at temperatures of about 90&nbsp;°C, in an equimolar aqueous solution of [[Chemistry:Zinc nitrate|zinc nitrate]] and hexamine, the latter providing the basic environment. Certain additives, such as polyethylene glycol or polyethylenimine, can improve the aspect ratio of the ZnO nanowires.<ref>{{cite journal | vauthors = Zhou Y, Wu W, Hu G, Wu H, Cui S |journal=Materials Research Bulletin|volume=43|year=2008|pages= 2113–2118|title=Hydrothermal synthesis of ZnO nanorod arrays with the addition of polyethyleneimine|doi=10.1016/j.materresbull.2007.09.024|issue=8–9 }}</ref> Doping of the ZnO nanowires has been achieved by adding other metal nitrates to the growth solution.<ref>{{cite journal | vauthors = Cui J, Zeng Q, Gibson UJ | title=Synthesis and magnetic properties of Co-doped ZnO nanowires | journal=Journal of Applied Physics | volume=99 | issue=8 | date=2006-04-15 | doi=10.1063/1.2169411 | page=08M113 |bibcode = 2006JAP....99hM113C }}</ref> The morphology of the resulting nanostructures can be tuned by changing the parameters relating to the precursor composition (such as the zinc concentration and pH) or to the thermal treatment (such as the temperature and heating rate).<ref>{{cite journal | vauthors = Elen K, Van den Rul H, Hardy A, Van Bael MK, D'Haen J, Peeters R, Franco D, Mullens J | display-authors = 6 | title = Hydrothermal synthesis of ZnO nanorods: a statistical determination of the significant parameters in view of reducing the diameter | journal = Nanotechnology | volume = 20 | issue = 5 | pages = 055608 | date = February 2009 | pmid = 19417355 | doi = 10.1088/0957-4484/20/5/055608 | bibcode = 2009Nanot..20e5608E | s2cid = 206056816 }}</ref>

Aligned ZnO nanowires on pre-seeded [[Chemistry:Silicon|silicon]], [[Chemistry:Glass|glass]], and [[Chemistry:Gallium nitride|gallium nitride]] substrates have been grown using aqueous zinc salts such as zinc nitrate and [[Chemistry:Zinc acetate|zinc acetate]] in basic environments.<ref>{{cite journal | vauthors = Greene LE, Law M, Goldberger J, Kim F, Johnson JC, Zhang Y, Saykally RJ, Yang P | display-authors = 6 | title = Low-temperature wafer-scale production of ZnO nanowire arrays | journal = Angewandte Chemie | volume = 42 | issue = 26 | pages = 3031–4 | date = July 2003 | pmid = 12851963 | doi = 10.1002/anie.200351461 }}</ref> Pre-seeding substrates with ZnO creates sites for homogeneous nucleation of ZnO crystal during the synthesis. Common pre-seeding methods include in-situ thermal decomposition of [[Chemistry:Zinc acetate|zinc acetate]] crystallites, spincoating of ZnO nanoparticles and the use of [[Physics:Physical vapor deposition|physical vapor deposition]] methods to deposit ZnO thin films.<ref>{{cite journal| last = Wu | first = Wan-Yu | name-list-style = vanc |journal= Journal of the American Ceramic Society|volume=92|issue=11|pages=2718–2723|title=Effects of Seed Layer Characteristics on the Synthesis of ZnO Nanowires|doi=10.1111/j.1551-2916.2009.03022.x|year=2009  }}</ref><ref>{{cite journal | vauthors = Greene LE, Law M, Tan DH, Montano M, Goldberger J, Somorjai G, Yang P | title = General route to vertical ZnO nanowire arrays using textured ZnO seeds | journal = Nano Letters | volume = 5 | issue = 7 | pages = 1231–6 | date = July 2005 | pmid = 16178216 | doi = 10.1021/nl050788p | bibcode = 2005NanoL...5.1231G }}</ref> Pre-seeding can be performed in conjunction with top down patterning methods such as electron beam lithography and nanosphere lithography to designate nucleation sites prior to growth. Aligned ZnO nanowires can be used in [[Physics:Dye-sensitized solar cell|dye-sensitized solar cell]]s and field emission devices.<ref>{{cite journal| last = Hua | first = Guomin | name-list-style = vanc |journal=Materials Letters|volume= 62|year=2008|pages=4109–4111|title=Fabrication of ZnO nanowire arrays by cycle growth in surfactantless aqueous solution and their applications on dye-sensitized solar cells|doi=10.1016/j.matlet.2008.06.018|issue=25 }}</ref><ref>{{cite journal | vauthors = Lee JH, Chung YW, Hon MH, Leu C | title=Density-controlled growth and field emission property of aligned ZnO nanorod arrays | journal=Applied Physics A | volume=97 | issue=2 | date=2009-05-07 | doi=10.1007/s00339-009-5226-y | pages=403–408 | bibcode = 2009ApPhA..97..403L| s2cid=97205678 }}</ref>

==Applications==
The applications of zinc oxide powder are numerous, and the principal ones are summarized below. Most applications exploit the reactivity of the oxide as a precursor to other zinc compounds. For material science applications, zinc oxide has high [[Physics:Refractive index|refractive index]], high thermal conductivity, binding, antibacterial and UV-protection properties. Consequently, it is added into materials and products including plastics, ceramics, glass, cement,<ref>{{cite journal | vauthors = Sanchez-Pescador R, Brown JT, Roberts M, Urdea MS | title = The nucleotide sequence of the tetracycline resistance determinant tetM from Ureaplasma urealyticum | journal = Nucleic Acids Research | volume = 16 | issue = 3 | pages = 1216–7 | date = February 1988 | pmid = 3344217 | pmc = 334766 | doi = 10.1093/nar/16.3.1216 }}</ref> rubber, lubricants,<ref name="wear"/> paints, ointments, adhesive, sealants, [[Chemistry:Concrete|concrete]] manufacturing, pigments, foods, batteries, ferrites, fire retardants, etc.<ref name="ap2">Ambica Dhatu Private Limited. [http://ambicaindia.in/products/zinc-oxide-manufacturer/ Applications of ZnO.] {{webarchive|url=https://web.archive.org/web/20191219104817/http://ambicaindia.in/products/zinc-oxide-manufacturer/|date=December 19, 2019|title=}} Access date January 25, 2009.</ref>

===Rubber industry===
Between 50% and 60% of ZnO use is in the rubber industry.<ref name="Moezzi 2012 1–22">{{cite journal| vauthors = Moezzi A, McDonagh AM, Cortie MB |title=Review: Zinc oxide particles: Synthesis, properties and applications|journal=Chemical Engineering Journal|year=2012|volume=185–186|pages=1–22|doi=10.1016/j.cej.2012.01.076}}</ref> Zinc oxide along with [[Chemistry:Stearic acid|stearic acid]] is used in the [[Chemistry:Sulfur vulcanization|sulfur vulcanization]] of rubber.<ref name=porter/><ref name="ap1">{{cite book| vauthors = Brown HE |title=Zinc Oxide Rediscovered|publisher=The New Jersey Zinc Company|location=New York|year=1957}}</ref> ZnO additives also protect rubber from fungi (see medical applications) and UV light.

===Ceramic industry===
Ceramic industry consumes a significant amount of zinc oxide, in particular in ceramic glaze and frit compositions. The relatively high heat capacity, thermal conductivity and high temperature stability of ZnO coupled with a comparatively low coefficient of expansion are desirable properties in the production of ceramics. ZnO affects the melting point and optical properties of the glazes, enamels, and ceramic formulations. Zinc oxide as a low expansion, secondary flux improves the elasticity of glazes by reducing the change in viscosity as a function of temperature and helps prevent crazing and shivering. By substituting ZnO for BaO and PbO, the heat capacity is decreased and the thermal conductivity is increased. Zinc in small amounts improves the development of glossy and brilliant surfaces. However, in moderate to high amounts, it produces matte and crystalline surfaces. With regard to color, zinc has a complicated influence.<ref name="Moezzi 2012 1–22"/>

===Medicine===
====Skin treatment====
Zinc oxide as a mixture with about 0.5% [[Chemistry:Iron(III) oxide|iron(III) oxide]] (Fe<sub>2</sub>O<sub>3</sub>) is called [[Chemistry:Calamine|calamine]] and is used in calamine lotion. Historically the mineral [[Chemistry:Calamine (mineral)|calamine]] is a mixture of the oxides [[Chemistry:Zincite|zincite]] and [[Chemistry:Hemimorphite|hemimorphite]]. 

Zinc oxide is widely used to treat a variety of skin conditions, including [[Medicine:Atopic dermatitis|atopic dermatitis]], contact dermatitis, itching due to eczema, diaper rash and [[Engineering:Acne|acne]].<ref name="Gupta 2014">{{cite journal |last1=Gupta |first1=Mrinal |last2=Mahajan |first2=Vikram K. |last3=Mehta |first3=Karaninder S. |last4=Chauhan |first4=Pushpinder S. |title=Zinc Therapy in Dermatology: A Review |journal=Dermatology Research and Practice |date=2014 |volume=2014 |page=709152 |doi=10.1155/2014/709152|pmid=25120566 |pmc=4120804 |doi-access=free }}</ref> It is used in products such as [[Chemistry:Baby powder|baby powder]] and barrier creams to treat diaper rashes, [[Chemistry:Calamine|calamine]] cream, anti-[[Medicine:Dandruff|dandruff]] [[Medicine:Shampoo|shampoo]]s, and [[Chemistry:Antiseptic|antiseptic]] ointments.<ref name=Harding/><ref>British National Formulary (2008). [https://web.archive.org/web/20120506044856/http://www.evidence.nhs.uk/formulary/bnf/current/13-skin/132-emollient-and-barrier-preparations/1322-barrier-preparations "Section 13.2.2 Barrier Preparations"].</ref> It is often combined with [[Chemistry:Castor oil|castor oil]] to form an emollient and astringent, zinc and castor oil cream, commonly used to treat infants.<ref>{{cite book |last1=Williams |first1=Cheryll |title=Medicinal Plants in Australia Volume 3: Plants, Potions and Poisons |date=1 July 2012 |publisher=Rosenberg Publishing |isbn=978-1-925078-07-7 |page=309 |url=https://books.google.com/books?id=ieVUAQAAQBAJ&dq=zinc+and+castor+oil+cream&pg=PA309 |access-date=8 March 2023 |language=en}}</ref><ref>{{cite book |last1=Nathan |first1=Alan |title=Non-prescription Medicines |date=2010 |publisher=Pharmaceutical Press |isbn=978-0-85369-886-9 |page=206 |url=https://books.google.com/books?id=lW-0IoSYMBYC&dq=zinc+and+castor+oil+cream&pg=PA206 |access-date=8 March 2023 |language=en}}</ref>

It is also a component in tape (called "zinc oxide tape") used by athletes as a bandage to prevent soft tissue damage during workouts.<ref>{{cite journal | vauthors = Hughes G, McLean NR | title = Zinc oxide tape: a useful dressing for the recalcitrant finger-tip and soft-tissue injury | journal = Archives of Emergency Medicine | volume = 5 | issue = 4 | pages = 223–7 | date = December 1988 | pmid = 3233136 | pmc = 1285538 | doi = 10.1136/emj.5.4.223 }}</ref> 

====Antibacterial====
Zinc oxide is used in [[Medicine:Mouthwash|mouthwash]] products and [[Medicine:Toothpaste|toothpaste]]s as an anti-bacterial agent proposed to prevent plaque and tartar formation,<ref>{{cite journal |last1=Lynch |first1=Richard J.M. |title=Zinc in the mouth, its interactions with dental enamel and possible effects on caries; a review of the literature |journal=International Dental Journal |date=August 2011 |volume=61 |issue=Suppl 3 |pages=46–54 |doi=10.1111/j.1875-595X.2011.00049.x|pmid=21762155 |pmc=9374993 |doi-access=free }}</ref> and to control [[Medicine:Bad breath|bad breath]] by reducing the [[Chemistry:Volatility|volatile]] gases and volatile sulfur compounds (VSC) in the mouth.<ref>{{cite journal |last1=Cortelli |first1=José Roberto |last2=Barbosa |first2=Mônica Dourado Silva |last3=Westphal |first3=Miriam Ardigó |title=Halitosis: a review of associated factors and therapeutic approach |journal=Brazilian Oral Research |date=August 2008 |volume=22 |issue=suppl 1 |pages=44–54 |doi=10.1590/S1806-83242008000500007|pmid=19838550 |doi-access=free }}</ref> Along with zinc oxide or zinc salts, these products also commonly contain other active ingredients, such as [[Chemistry:Cetylpyridinium chloride|cetylpyridinium chloride]],<ref>{{cite web |title=SmartMouth Clinical DDS Activated Mouthwash |url=https://smartmouth.com/products/clinical-mouthwash/#toggle-id-1 |website=smartmouth.com}}</ref> [[Chemistry:Xylitol|xylitol]],<ref>{{cite web |title=Oxyfresh |url=https://oxyfresh.com/products/patented-zinc-mouthwash-with-fresh-mint |website=Oxyfresh.com |language=en}}</ref> [[Chemistry:Hinokitiol|hinokitiol]],<ref>{{cite web |title=Dr ZinX |url=https://www.drzinx.com/ingredients |website=drzinx.com |language=en}}</ref> essential oils and [[Biology:Medicinal plants|plant]] [[Chemistry:Extract|extract]]s.<ref>{{cite journal |last1=Steenberghe |first1=Daniel Van |last2=Avontroodt |first2=Pieter |last3=Peeters |first3=Wouter |last4=Pauwels |first4=Martine |last5=Coucke |first5=Wim |last6=Lijnen |first6=An |last7=Quirynen |first7=Marc |title=Effect of Different Mouthrinses on Morning Breath |journal=Journal of Periodontology |date=September 2001 |volume=72 |issue=9 |pages=1183–1191 |doi=10.1902/jop.2000.72.9.1183|pmid=11577950 }}</ref><ref>{{cite journal |last1=Harper |first1=D. Scott |last2=Mueller |first2=Laura J. |last3=Fine |first3=James B. |last4=Gordon |first4=Jeffrey |last5=Laster |first5=Larry L. |title=Clinical Efficacy of a Dentifrice and Oral Rinse Containing Sanguinaria Extract and Zinc Chloride During 6 Months of Use |journal=Journal of Periodontology |date=June 1990 |volume=61 |issue=6 |pages=352–358 |doi=10.1902/jop.1990.61.6.352|pmid=2195152 }}</ref>
Powdered zinc oxide has deodorizing and antibacterial properties.<ref>{{cite journal | vauthors = Padmavathy N, Vijayaraghavan R | title = Enhanced bioactivity of ZnO nanoparticles-an antimicrobial study | journal = Science and Technology of Advanced Materials | volume = 9 | issue = 3 | pages = 035004 | date = July 2008 | pmid = 27878001 | pmc = 5099658 | doi = 10.1088/1468-6996/9/3/035004 | bibcode = 2008STAdM...9c5004P }}</ref> 

ZnO is added to cotton fabric, rubber, oral care products,<ref>{{cite journal | vauthors = ten Cate JM | title = Contemporary perspective on the use of fluoride products in caries prevention | journal = British Dental Journal | volume = 214 | issue = 4 | pages = 161–7 | date = February 2013 | pmid = 23429124 | doi = 10.1038/sj.bdj.2013.162 | doi-access = free }}</ref><ref>{{cite journal | vauthors = Rošin-Grget K, Peroš K, Sutej I, Bašić K | title = The cariostatic mechanisms of fluoride | journal = Acta Medica Academica | volume = 42 | issue = 2 | pages = 179–88 | date = November 2013 | pmid = 24308397 | doi = 10.5644/ama2006-124.85 | doi-access = free }}</ref> and food packaging.<ref>{{cite journal |doi=10.1002/app.24866 |title=Durability of nano ZnO antibacterial cotton fabric to sweat|year=2007| last1 = Li | first1 =  Qun |last2=Chen|first2=Shui-Lin|last3=Jiang|first3=Wan-Chao | name-list-style = vanc |journal=Journal of Applied Polymer Science |volume=103 |pages=412–416 }}</ref><ref>{{cite journal|doi=10.1177/152808379302300205 |title=Antibacterial, Deodorizing, and UV Absorbing Materials Obtained with Zinc Oxide (ZnO) Coated Fabrics|year=1993| vauthors = Saito M |journal=Journal of Industrial Textiles|volume=23|pages=150–164|issue=2|s2cid=97726945}}</ref> Enhanced antibacterial action of fine particles compared to bulk material is not exclusive to ZnO and is observed for other materials, such as [[Chemistry:Silver|silver]].<ref>{{cite journal | vauthors = Akhavan O, Ghaderi E | title = Enhancement of antibacterial properties of Ag nanorods by electric field | journal = Science and Technology of Advanced Materials | volume = 10 | issue = 1 | pages = 015003 | date = February 2009 | pmid = 27877266 | pmc = 5109610 | doi = 10.1088/1468-6996/10/1/015003 | bibcode = 2009STAdM..10a5003A }}</ref> This property results from the increased surface area of the fine particles.

====Sunscreen====
Zinc oxide is used in [[Chemistry:Sunscreen|sunscreen]] to absorb [[Physics:Ultraviolet|ultraviolet light]].<ref name="Gupta 2014"/> It is the broadest spectrum UVA and UVB absorber<ref>{{cite web|url=https://mycpss.com/skin/sunscreens/critical-wavelength-broad-spectrum-uv-protection/|title=Critical Wavelength & Broad Spectrum UV Protection |website=mycpss.com|access-date=15 April 2018}}</ref><ref>{{cite journal | vauthors = More BD | title = Physical sunscreens: on the comeback trail | journal = Indian Journal of Dermatology, Venereology and Leprology | volume = 73 | issue = 2 | pages = 80–5 | year = 2007 | pmid = 17456911 | doi = 10.4103/0378-6323.31890 | url = http://www.bioline.org.br/pdf?dv07029 | doi-access = free | hdl = 1807/47877 | hdl-access = free }}</ref> that is approved for use as a sunscreen by the U.S. [[Organization:Food and Drug Administration|Food and Drug Administration]] (FDA),<ref>{{cite news|title=Sunscreen|url=https://www.fda.gov/Radiation-EmittingProducts/RadiationEmittingProductsandProcedures/Tanning/ucm116445.htm|publisher=U.S. Food and Drug Administration}}</ref> and is completely photostable.<ref>{{cite journal | vauthors = Mitchnick MA, Fairhurst D, Pinnell SR | title = Microfine zinc oxide (Z-cote) as a photostable UVA/UVB sunblock agent | journal = Journal of the American Academy of Dermatology | volume = 40 | issue = 1 | pages = 85–90 | date = January 1999 | pmid = 9922017 | doi = 10.1016/S0190-9622(99)70532-3 }}</ref> When used as an ingredient in sunscreen, zinc oxide blocks both UVA (320–400&nbsp;nm) and UVB (280–320&nbsp;nm) rays of ultraviolet light. Zinc oxide and the other most common physical sunscreen, [[Chemistry:Titanium dioxide|titanium dioxide]], are considered to be nonirritating, nonallergenic, and non-comedogenic.<ref>{{cite news|url=http://consults.blogs.nytimes.com/2009/06/10/what-to-look-for-in-a-sunscreen/|date= June 10, 2009|title=What to Look for in a Sunscreen|work=The New York Times}}</ref> Zinc from zinc oxide is, however, slightly absorbed into the skin.<ref>{{cite journal | vauthors = Agren MS | title = Percutaneous absorption of zinc from zinc oxide applied topically to intact skin in man | journal = Dermatologica | volume = 180 | issue = 1 | pages = 36–9 | year = 2009 | pmid = 2307275 | doi = 10.1159/000247982 }}</ref>

Many sunscreens use nanoparticles of zinc oxide (along with nanoparticles of titanium dioxide) because such small particles do not scatter light and therefore do not appear white. The nanoparticles are not absorbed into the skin more than regular-sized zinc oxide particles are,<ref name=":0">{{cite journal|vauthors=Burnett ME, Wang SQ|date=April 2011|title=Current sunscreen controversies: a critical review|journal=Photodermatology, Photoimmunology & Photomedicine|volume=27|issue=2|pages=58–67|doi=10.1111/j.1600-0781.2011.00557.x|pmid=21392107|doi-access=free|s2cid=29173997}}</ref> and are only absorbed into the [[Biology:Stratum corneum|outermost layer]] of the skin but not into the body.<ref name=":0" />

====Dental restoration====
When mixed with [[Chemistry:Eugenol|eugenol]], [[Chemistry:Zinc oxide eugenol|zinc oxide eugenol]] is formed, which has applications as a [[Medicine:Dental restoration|restorative]] and prosthodontic in [[Medicine:Dentistry|dentistry]].<ref name = "Ferracane"/><ref>{{cite book| last = van Noort | first = Richard | name-list-style = vanc |year=2002|title=Introduction to Dental Materials|edition=2d|publisher=Elsevier Health Sciences|isbn=978-0-7234-3215-9}}</ref>

===Food additive===
Zinc oxide is added to many food products, including [[Engineering:Breakfast cereal|breakfast cereal]]s, as a source of zinc,<ref>[https://web.archive.org/web/20090228200301/http://www.quakeroats.com/products/oat-cereals/life-cereal/regular.aspx Quaker cereals content]. quakeroats.com</ref> a necessary [[Earth:Nutrient|nutrient]]. [[Chemistry:Zinc sulfate|Zinc sulfate]] is also used for the same purpose. Some prepackaged foods also include trace amounts of ZnO even if it is not intended as a nutrient.

===Pigment===
{{Main|Zinc white}}

Zinc oxide (zinc white) is used as a pigment in [[Engineering:Paint|paint]]s and is more opaque than [[Chemistry:Lithopone|lithopone]], but less opaque than [[Chemistry:Titanium dioxide|titanium dioxide]].<ref name=Ullmann/> It is also used in coatings for paper. Chinese white is a special grade of zinc white used in artists' pigments.<ref>{{Cite book|title=The Secret Lives of Colour|last=St. Clair|first=Kassia | name-list-style = vanc |publisher=John Murray|year=2016|isbn=9781473630819|location=London|page=40|oclc=936144129}}</ref> The use of zinc white as a pigment in oil painting started in the middle of 18th century.<ref>Kuhn, H. (1986) "Zinc White", pp. 169–186 in ''Artists’ Pigments. A Handbook of Their History and Characteristics'', Vol. 1. L. Feller (ed.). Cambridge University Press, London. {{ISBN|978-0521303743}}</ref> It has partly replaced the poisonous [[Lead white|lead white]] and was used by painters such as Böcklin, Van Gogh,<ref>[http://colourlex.com/project/van-gogh-wheatfield-cypresses/ Vincent van Gogh, 'Wheatfield with Cypresses, 1889], pigment analysis at ColourLex</ref> Manet, Munch and others. It is also a main ingredient of mineral makeup (CI 77947).<ref>{{cite journal| last = Bouchez | first = Colette | name-list-style = vanc |title=The Lowdown on Mineral Makeup|url=http://www.webmd.com/skin-beauty/features/the-lowdown-on-mineral-makeup|journal =[[Company:WebMD|WebMD]]|access-date= January 25, 2009}}</ref>

===UV absorber===
Micronized and nano-scale zinc oxide provides strong protection against UVA and UVB ultraviolet radiation, and are consequently used in [[Chemistry:Sunscreen|sunscreens]],<ref>[http://www.epa.gov/sunwise/doc/sunscreen.pdf US Environment Protection Agency: Sunscreen] What are the active Ingredients in Sunscreen – Physical Ingredients:"The physical compounds titanium dioxide and zinc oxide reflect, scatter, and absorb both UVA and UVB rays." A table lists them as providing extensive physical protection against UVA and UVB</ref> and also in UV-blocking [[Astronomy:Sunglasses#Space|sunglasses]] for use in space and for protection when [[Chemistry:Welding|welding]], following research by scientists at Jet Propulsion Laboratory ([[Organization:JPL|JPL]]).<ref>[https://web.archive.org/web/20071115152916/http://www.sti.nasa.gov/tto/Spinoff2006/ch_6.html Look Sharp While Seeing Sharp]. NASA Scientific and Technical Information (2006). Retrieved 17 October 2009. JPL scientists developed UV-protective sunglasses using dyes and "zinc oxide, which absorbs ultraviolet light"</ref>

===Coatings===
Paints containing zinc oxide powder have long been utilized as anticorrosive coatings for metals. They are especially effective for galvanized iron. Iron is difficult to protect because its reactivity with organic coatings leads to brittleness and lack of adhesion. Zinc oxide paints retain their flexibility and adherence on such surfaces for many years.<ref name="ap2"/>

ZnO highly n-type doped with [[Chemistry:Aluminium|aluminium]], [[Chemistry:Gallium|gallium]], or [[Chemistry:Indium|indium]] is transparent and conductive (transparency ~90%, lowest resistivity ~10<sup>−4</sup> Ω·cm<ref name="mende">{{cite journal|doi=10.1016/S1369-7021(07)70078-0|title=ZnO – nanostructures, defects, and devices|year=2007| vauthors = Schmidtmende L, MacManusdriscoll J |journal=Materials Today|volume=10|pages=40–48 |issue=5|doi-access=free}}</ref>). ZnO:Al coatings are used for energy-saving or heat-protecting windows. The coating lets the visible part of the spectrum in but either reflects the infrared (IR) radiation back into the room (energy saving) or does not let the IR radiation into the room (heat protection), depending on which side of the window has the coating.<ref name="k1"/>

Plastics, such as [[Chemistry:Polyethylene naphthalate|polyethylene naphthalate]] (PEN), can be protected by applying zinc oxide coating. The coating reduces the diffusion of oxygen through PEN.<ref>{{cite journal | vauthors = Guedri-Knani L, Gardette JL, Jacquet M, Rivaton A | title=Photoprotection of poly(ethylene-naphthalate) by zinc oxide coating | journal=Surface and Coatings Technology | volume=180–181 | year=2004 | doi=10.1016/j.surfcoat.2003.10.039 | pages=71–75 }}</ref> Zinc oxide layers can also be used on [[Physics:Polycarbonate|polycarbonate]] in outdoor applications. The coating protects polycarbonate from solar radiation, and decreases its oxidation rate and photo-yellowing.<ref>{{cite journal | vauthors = Moustaghfir A, Tomasella E, Rivaton A, Mailhot B, Jacquet M, Gardette JL, Cellier J | title=Sputtered zinc oxide coatings: structural study and application to the photoprotection of the polycarbonate | journal=Surface and Coatings Technology | volume=180–181 | year=2004 | doi=10.1016/j.surfcoat.2003.10.109 | pages=642–645 }}</ref>

===Corrosion prevention in nuclear reactors===
{{Main|Physics:Depleted zinc oxide}}
Zinc oxide depleted in <sup>64</sup>Zn (the [[Physics:Isotopes of zinc|zinc isotope]] with [[Physics:Atomic mass|atomic mass]] 64) is used in corrosion prevention in nuclear [[Engineering:Pressurized water reactor|pressurized water reactor]]s. The depletion is necessary, because <sup>64</sup>Zn is [[Physics:Neutron activation|transformed]] into radioactive <sup>65</sup>Zn under irradiation by the reactor neutrons.<ref>{{cite journal|doi=10.1680/nuen.40.4.245.39338|title=BWR water chemistry?a delicate balance|year=2001| vauthors = Cowan RL |journal=Nuclear Energy|volume=40|pages=245–252|issue=4}}</ref>

===Methane reforming===
Zinc oxide (ZnO) is used as a pretreatment step to remove [[Chemistry:Hydrogen sulfide|hydrogen sulfide]] (H<sub>2</sub>S) from [[Chemistry:Natural gas|natural gas]] following [[Chemistry:Hydrogenation|hydrogenation]] of any [[Chemistry:Sulfur|sulfur]] compounds prior to a [[Chemistry:Methane reformer|methane reformer]], which can poison the catalyst.  At temperatures between about {{convert|230|-|430|C|F}}, H<sub>2</sub>S is converted to [[Chemistry:Water|water]] by the following reaction:<ref>Robinson, Victor S. (1978) "Process for desulfurization using particulate zinc oxide shapes of high surface area and improved strength" {{US Patent |4128619}}</ref>
:H<sub>2</sub>S + ZnO → H<sub>2</sub>O + ZnS

===Electronics===
[[File:ZnO laser diode.png|thumb|left|Photograph of an operating ZnO UV [[Engineering:Laser diode|laser diode]] and the corresponding device structure.<ref>{{cite journal | vauthors = Liu XY, Shan CX, Zhu H, Li BH, Jiang MM, Yu SF, Shen DZ | title = Ultraviolet Lasers Realized via Electrostatic Doping Method | journal = Scientific Reports | volume = 5 | pages = 13641 | date = September 2015 | pmid = 26324054 | pmc = 4555170 | doi = 10.1038/srep13641 | bibcode = 2015NatSR...513641L }}</ref>]]
[[File:ZnO nanorod gas sensor.jpg|thumb|Flexible gas sensor based on ZnO nanorods and its internal structure. ITO stands for indium tin oxide and PET for polyethylene terephthalate.<ref>{{cite journal | vauthors = Zheng ZQ, Yao JD, Wang B, Yang GW | title = Light-controlling, flexible and transparent ethanol gas sensor based on ZnO nanoparticles for wearable devices | journal = Scientific Reports | volume = 5 | pages = 11070 | date = June 2015 | pmid = 26076705 | pmc = 4468465 | doi = 10.1038/srep11070 | bibcode = 2015NatSR...511070Z }}</ref>]]

ZnO has wide direct band gap (3.37 eV or 375&nbsp;nm at room temperature). Therefore, its most common potential applications are in laser diodes and [[Engineering:LED|light emitting diodes]] (LEDs).<ref>{{cite journal | vauthors = Bakin A, El-Shaer A, Mofor AC, Al-Suleiman M, Schlenker E, Waag A | title=ZnMgO-ZnO quantum wells embedded in ZnO nanopillars: Towards realisation of nano-LEDs | journal=Physica Status Solidi C | volume=4 | issue=1 | year=2007 | doi=10.1002/pssc.200673557 | pages=158–161|bibcode = 2007PSSCR...4..158B }}</ref> Moreover, ultrafast nonlinearities and photoconductive functions have been reported in ZnO.<ref>{{Cite journal|last1=Torres-Torres|first1=C.|last2=Castro-Chacón|first2=J. H.|last3=Castañeda|first3=L.|last4=Rojo|first4=R. Rangel|last5=Torres-Martínez|first5=R.|last6=Tamayo-Rivera|first6=L.|last7=Khomenko|first7=A. V.|date=2011-08-15|title=Ultrafast nonlinear optical response of photoconductive ZnO films with fluorine nanoparticles|url=https://www.osapublishing.org/oe/abstract.cfm?uri=oe-19-17-16346|journal=Optics Express|language=EN|volume=19|issue=17|pages=16346–16355|doi=10.1364/OE.19.016346|pmid=21934998|bibcode=2011OExpr..1916346T|issn=1094-4087|doi-access=free}}</ref> Some optoelectronic applications of ZnO overlap with that of GaN, which has a similar band gap (~3.4 eV at room temperature). Compared to GaN, ZnO has a larger exciton binding energy (~60 meV, 2.4 times of the room-temperature thermal energy), which results in bright room-temperature emission from ZnO. ZnO can be combined with GaN for LED-applications. For instance, a transparent conducting oxide layer and ZnO nanostructures provide better light outcoupling.<ref>{{cite journal|doi=10.1109/JPROC.2009.2037444|title=ZnO – GaN Hybrid Heterostructures as Potential Cost Efficient LED Technology|year=2010| vauthors = Bakin A |journal=Proceedings of the IEEE|volume=98|pages=1281–1287|issue=7 |s2cid=20442190}}</ref> Other properties of ZnO favorable for electronic applications include its stability to high-energy radiation and its ability to be patterned by wet chemical etching.<ref>{{cite journal|doi=10.1016/S0921-5107(00)00604-8|title=Recent advances in ZnO materials and devices|year=2001| vauthors = Look D |journal=Materials Science and Engineering B|volume=80|issue=1–3|pages=383–387}}</ref> Radiation resistance<ref>{{cite journal | vauthors = Kucheyev SO, Williams JS, Jagadish C, Zou J, Evans C, Nelson AJ, Hamza AV | title=Ion-beam-produced structural defects in ZnO | journal=Physical Review B | volume=67 | issue=9 | pages=094115 | date=2003-03-31 | doi=10.1103/physrevb.67.094115 |bibcode = 2003PhRvB..67i4115K | url=http://espace.library.uq.edu.au/view/UQ:115991/UQ115991.pdf }}</ref> makes ZnO a suitable candidate for space applications. ZnO is the most promising candidate in the field of [[Physics:Random laser|random laser]]s to produce an electronically pumped UV laser source.

The pointed tips of ZnO nanorods result in a strong enhancement of an electric field. Therefore, they can be used as [[Physics:Field electron emission|field emitters]].<ref>{{cite journal | vauthors = Li YB, Bando Y, Golberg D |doi=10.1063/1.1738174|title=ZnO nanoneedles with tip surface perturbations: Excellent field emitters|year=2004 |journal=Applied Physics Letters|volume=84|page=3603|issue=18|bibcode = 2004ApPhL..84.3603L }}</ref>

Aluminium-doped ZnO layers are used as transparent [[Physics:Electrode|electrode]]s. The components Zn and Al are much cheaper and less toxic compared to the generally used [[Chemistry:Indium tin oxide|indium tin oxide]] (ITO). One application which has begun to be commercially available is the use of ZnO as the front contact for solar cells or of liquid crystal displays.<ref>{{cite journal | vauthors = Oh BY, Jeong MC, Moon TH, Lee W, Myoung JM, Hwang JY, Seo DS |doi=10.1063/1.2206417|title=Transparent conductive Al-doped ZnO films for liquid crystal displays|year=2006 |journal=Journal of Applied Physics|volume=99 |issue=12|pages=124505–124505–4|bibcode = 2006JAP....99l4505O }}</ref>

Transparent thin-film [[Engineering:Transistor|transistor]]s (TTFT) can be produced with ZnO. As field-effect transistors, they do not need a p–n junction,<ref>{{cite journal | vauthors = Nomura K, Ohta H, Ueda K, Kamiya T, Hirano M, Hosono H | title = Thin-film transistor fabricated in single-crystalline transparent oxide semiconductor | journal = Science | volume = 300 | issue = 5623 | pages = 1269–72 | date = May 2003 | pmid = 12764192 | doi = 10.1126/science.1083212 | bibcode = 2003Sci...300.1269N | s2cid = 20791905 }}</ref> thus avoiding the p-type doping problem of ZnO. Some of the field-effect transistors even use ZnO nanorods as conducting channels.<ref>{{cite journal | vauthors = Heo YW, Tien LC, Kwon Y, Norton DP, Pearton SJ, Kang BS, Ren F |doi=10.1063/1.1794351|title=Depletion-mode ZnO nanowire field-effect transistor|year=2004 |journal=Applied Physics Letters|volume=85|page=2274 |issue=12|bibcode = 2004ApPhL..85.2274H }}</ref>

===Gas sensors===
Zinc oxide is used in semiconductor [[Physics:Gas detector|gas sensor]]s for detecting airborne compounds such as [[Chemistry:Hydrogen sulfide|hydrogen sulfide]], [[Chemistry:Nitrogen dioxide|nitrogen dioxide]], and [[Earth:Volatile organic compound|volatile organic compound]]s. ZnO is a semiconductor that becomes [[Physics:Doping (semiconductor)|n-doped]] by adsorption of [[Chemistry:Reducing agent|reducing compound]]s, which reduces the detected electrical resistance through the device, in a manner similar to the widely used [[Chemistry:Tin(IV) oxide|tin oxide]] semiconductor gas sensors. It is formed into nanostructures such as thin films, [[Physics:Nanoparticle|nanoparticle]]s, [[Physics:Nanopillar|nanopillar]]s or [[Physics:Nanowire|nanowire]]s in order to provide large surface area for interaction with gasses. The sensors are made selective for specific gasses by doping or surface-attaching materials such as catalytic noble metals.<ref name="Zhou 2015">{{cite journal | last1=Zhou | first1=Xin | last2=Lee | first2=Songyi | last3=Xu | first3=Zhaochao | last4=Yoon | first4=Juyoung | title=Recent Progress on the Development of Chemosensors for Gases | journal=Chemical Reviews | volume=115 | issue=15 | date=2015 | issn=0009-2665 | doi=10.1021/cr500567r | pages=7944–8000| pmid=25651137 }}</ref><ref name="Sun 2012">{{cite journal | last1=Sun | first1=Yu-Feng | last2=Liu | first2=Shao-Bo | last3=Meng | first3=Fan-Li | last4=Liu | first4=Jin-Yun | last5=Jin | first5=Zhen | last6=Kong | first6=Ling-Tao | last7=Liu | first7=Jin-Huai | title=Metal Oxide Nanostructures and Their Gas Sensing Properties: A Review | journal=Sensors | volume=12 | issue=3 | date=2012 | issn=1424-8220 | pmid=22736968 | pmc=3376589 | doi=10.3390/s120302610 | pages=2610–2631 | bibcode=2012Senso..12.2610S | doi-access=free }}</ref>

===Piezoelectricity===
The [[Physics:Piezoelectricity|piezoelectricity]] in textile fibers coated in ZnO have been shown capable of fabricating "self-powered nanosystems" with everyday mechanical stress from wind or body movements.<ref>{{cite news| last = Keim | first = Brandon | name-list-style = vanc |title=Piezoelectric Nanowires Turn Fabric Into Power Source |url=http://blog.wired.com/wiredscience/2008/02/piezoelectric-n.html |date=February 13, 2008 |work=Wired News |publisher=CondéNet |url-status=dead |archive-url=https://web.archive.org/web/20080215001128/http://blog.wired.com/wiredscience/2008/02/piezoelectric-n.html |archive-date=February 15, 2008 }}</ref><ref>{{cite journal | vauthors = Qin Y, Wang X, Wang ZL | title = Microfibre-nanowire hybrid structure for energy scavenging | journal = Nature | volume = 451 | issue = 7180 | pages = 809–13 | date = February 2008 | pmid = 18273015 | doi = 10.1038/nature06601 | bibcode = 2008Natur.451..809Q | s2cid = 4411796 }}</ref>

In 2008 the ''Center for Nanostructure Characterization'' at the Georgia Institute of Technology reported producing an electricity generating device (called flexible charge pump generator) delivering alternating current by stretching and releasing zinc oxide nanowires. This mini-generator creates an oscillating voltage up to 45 millivolts, converting close to seven percent of the applied mechanical energy into electricity. Researchers used wires with lengths of 0.2–0.3&nbsp;mm and diameters of three to five micrometers, but the device could be scaled down to smaller size.<ref>{{cite web|title=New Small-scale Generator Produces Alternating Current By Stretching Zinc Oxide Wires|date=November 10, 2008|url=https://www.sciencedaily.com/releases/2008/11/081109193342.htm|website=Science Daily}}</ref>
[[File:ZnO Anode.jpg|thumb|ZnO as anode of Li-ion battery]]

In form of a thin film ZnO has been demonstrated in miniaturised high frequency thin film resonators, sensors and filters.

===Li-ion battery and supercapacitors===
ZnO is a promising anode material for [[Engineering:Lithium-ion battery|lithium-ion battery]] because it is cheap, biocompatible, and environmentally friendly. ZnO has a higher theoretical capacity (978 mAh g<sup>−1</sup>) than many other transition metal oxides such as CoO (715 mAh g<sup>−1</sup>), NiO (718 mAh g<sup>−1</sup>) and CuO (674 mAh g<sup>−1</sup>).<ref>{{cite journal | vauthors = Zheng X, Shen G, Wang C, Li Y, Dunphy D, Hasan T, Brinker CJ, Su BL | display-authors = 6 | title = Bio-inspired Murray materials for mass transfer and activity | journal = Nature Communications | volume = 8 | pages = 14921 | date = April 2017 | pmid = 28382972 | pmc = 5384213 | doi = 10.1038/ncomms14921 | bibcode = 2017NatCo...814921Z }}</ref> ZnO is also used as an electrode in supercapacitors.<ref>{{Cite journal|last1=Sreejesh|first1=M.|last2=Dhanush|first2=S.|last3=Rossignol|first3=F.|last4=Nagaraja|first4=H. S.|date=2017-04-15|title=Microwave assisted synthesis of rGO/ZnO composites for non-enzymatic glucose sensing and supercapacitor applications|url=https://www.sciencedirect.com/science/article/pii/S0272884216324105|journal=Ceramics International|language=en|volume=43|issue=6|pages=4895–4903|doi=10.1016/j.ceramint.2016.12.140|issn=0272-8842}}</ref>

==Safety==
As a [[Chemistry:Food additive|food additive]], zinc oxide is on the U.S. FDA's list of [[Chemistry:Generally recognized as safe|generally recognized as safe]], or GRAS, substances.<ref>{{cite web|url=http://www.accessdata.fda.gov/scripts/fcn/fcnDetailNavigation.cfm?rpt=scogsListing&id=372 | archive-url = https://web.archive.org/web/20140416175808/http://www.accessdata.fda.gov/scripts/fcn/fcnDetailNavigation.cfm?rpt=scogsListing&id=372 | archive-date = 16 April 2014 | title = Zinc oxide | work = Database of Select Committee on GRAS Substances (SCOGS) Reviews | publisher = U.S. Food and Drug Administration |access-date=2009-08-03}}</ref>

Zinc oxide itself is non-toxic; it is hazardous, however, to inhale high concentrations of zinc oxide fumes, such as generated when zinc or zinc alloys are melted and oxidized at high temperature. This problem occurs while melting alloys containing [[Chemistry:Brass|brass]] because the melting point of brass is close to the boiling point of zinc.<ref name="Gray">{{cite web |  last1 = Gray | first1 = Theodore | name-list-style = vanc |url =  http://www.theodoregray.com/PeriodicTable/ZincSafety.html | title = The Safety of Zinc Casting | work = The Wooden Periodic Table Table  }}</ref> Inhalation of zinc oxide, which may occur when welding galvanized (zinc-plated) steel, can result in a malady called [[Engineering:Metal fume fever|metal fume fever]].<ref name="Gray" />

In sunscreen formulations that combined zinc oxide with small-molecule UV absorbers, UV light caused photodegradation of the small-molecule asorbers and toxicity in embryonic zebrafish assays.<ref>{{cite journal | vauthors = Ginzburg AL, Blackburn RS, Santillan C, Truong L, Tanguay RL, Hutchison JE  | title = Zinc oxide-induced changes to sunscreen ingredient efficacy and toxicity under UV irradiation. | journal = Photochem Photobiol Sci | volume = 20 | pages = 1273–1285 | date = 2021 | issue = 10 | doi = 10.1007/s43630-021-00101-2 | pmid = 34647278 | pmc = 8550398 }}</ref>

==See also==
{{Div col|colwidth=30em}}
* [[Physics:Depleted zinc oxide|Depleted zinc oxide]]
* [[Physics:Zinc oxide nanoparticle|Zinc oxide nanoparticle]]
* Gallium(III) nitride
* [[Chemistry:List of inorganic pigments|List of inorganic pigments]]
* [[Chemistry:Zinc|Zinc]]
* [[Chemistry:Zinc oxide eugenol|Zinc oxide eugenol]]
* [[Chemistry:Zinc peroxide|Zinc peroxide]]
* [[Chemistry:Zinc smelting|Zinc smelting]]
* [[Chemistry:Zinc–air battery|Zinc–air battery]]
* [[Chemistry:Zinc–zinc oxide cycle|Zinc–zinc oxide cycle]]
* [[Physics:ZnO nanostructures|ZnO nanostructures]]
{{colend}}

==References==
{{reflist|30em}}

==Cited sources==
{{refbegin}}
*{{cite book |ref=Haynes| editor= Haynes, William M. | date = 2016| title = [[Physics:CRC Handbook of Chemistry and Physics|CRC Handbook of Chemistry and Physics]] | edition = 97th | publisher = CRC Press | isbn = 9781498754293}}
{{refend}}

==Reviews==
{{refbegin|30em}}
* {{cite journal | vauthors = Özgür Ü, Alivov YI, Liu C, Teke A, Reshchikov M, Doğan S, Avrutin VC, Cho SJ, Morkoç AH | display-authors = 6 | doi = 10.1063/1.1992666 | bibcode=2005JAP....98d1301O | volume=98 | issue=4 | title=A comprehensive review of ZnO materials and devices | year=2005 | journal=Journal of Applied Physics | pages = 041301–041301–103 | url=https://scholarscompass.vcu.edu/cgi/viewcontent.cgi?article=1158&context=egre_pubs }}
* {{cite book | vauthors = Bakin A, Waag A | chapter = ZnO Epitaxial Growth | title = Comprehensive Semiconductor Science and Technology 6 Volume Encyclopaedia | date = 29 March 2011 | publisher = Elsevier | veditors = Bhattacharya P, Fornari R, Kamimura H | isbn = 978-0-444-53143-8 }}
* {{cite journal | vauthors = Baruah S, Dutta J | title = Hydrothermal growth of ZnO nanostructures | journal = Science and Technology of Advanced Materials | volume = 10 | issue = 1 | pages = 013001 | date = February 2009 | pmid = 27877250 | pmc = 5109597 | doi = 10.1088/1468-6996/10/1/013001 | bibcode = 2009STAdM..10a3001B }}
* {{cite journal | doi = 10.1088/0953-8984/17/27/R01 | volume=17 | issue=27 | title=Transition metal-doped TiO 2 and ZnO—present status of the field | year=2005 | journal=Journal of Physics: Condensed Matter | pages=R657–R689 | last = Janisch | first = Rebecca | name-list-style = vanc | bibcode=2005JPCM...17R.657J | s2cid=118610509 }}
* {{cite journal | doi = 10.1016/j.mser.2004.09.001 | volume=47 | issue=1–2 | title=ZnO nanowire growth and devices | year=2004 | journal=Materials Science and Engineering: R: Reports | pages=1–47 | vauthors = Heo YW }}
* {{cite journal | doi = 10.1002/pssb.200743072 | volume=244 | issue=9 | title=ZnO: From basics towards applications | year=2007 | journal=Physica Status Solidi B | pages=3027–3073 | vauthors = Klingshirn C| bibcode=2007PSSBR.244.3027K | s2cid=97461963 }}
* {{cite journal | vauthors = Klingshirn C |url=https://scholar.google.com/scholar?hl=en&as_sdt=0%2C5&q=ZnO%3A+Material%2C+Physics+and+Applications&btnG= | title = ZnO: material, physics and applications | journal = ChemPhysChem | volume = 8 | issue = 6 | pages = 782–803 | date = April 2007 | pmid = 17429819 | doi = 10.1002/cphc.200700002 }}
* {{cite journal | vauthors = Lu JG, Chang P, Fan Z | doi = 10.1016/j.mser.2006.04.002 | volume=52 | issue=1–3 | title=Quasi-one-dimensional metal oxide materials—Synthesis, properties and applications | year=2006 | journal=Materials Science and Engineering: R: Reports | pages=49–91 | citeseerx=10.1.1.125.7559 }}
* {{cite journal | vauthors = Xu S, Wang ZL | doi = 10.1007/s12274-011-0160-7 | volume=4 | issue=11 | title=One-dimensional ZnO nanostructures: Solution growth and functional properties | year=2011 | journal=Nano Research | pages=1013–1098 | citeseerx=10.1.1.654.3359 | s2cid = 137014543 }}
* {{cite journal |vauthors = Xu S, Wang ZL | doi = 10.1351/PAC-CON-11-08-17 | volume=83 | issue=12 | pages=2171–2198 | title=Oxide nanowire arrays for light-emitting diodes and piezoelectric energy harvesters | year=2011 | journal=Pure and Applied Chemistry | s2cid = 18770461 | doi-access=free }}
{{refend}}

==External links==

*[http://www.webmineral.com/data/Zincite.shtml Zincite properties]
*[http://www.inchem.org/documents/icsc/icsc/eics0208.htm International Chemical Safety Card 0208].
*[https://www.cdc.gov/niosh/npg/npgd0675.html NIOSH Pocket Guide to Chemical Hazards].
*{{PPDB|1321}}
*[http://colourlex.com/project/zinc-white/ Zinc white pigment] at ColourLex

{{Zinc compounds}}
{{Sunscreening agents}}
{{Oxides}}


[[Category:Amphoteric compounds]]
[[Category:Ceramic materials]]
[[Category:Corrosion inhibitors]]
[[Category:II-VI semiconductors]]
[[Category:Inorganic pigments]]
[[Category:Nonlinear optical materials]]
[[Category:Oxides]]
[[Category:Piezoelectric materials]]
[[Category:Sunscreening agents]]
[[Category:Zinc compounds|oxide]]

{{Sourceattribution|Zinc oxide}}