View source for Magnesium oxide

{{short description|Chemical compound naturally occurring as periclase}}
{{Chembox
| Verifiedfields = changed
| Watchedfields  = changed
| verifiedrevid  = 414322178
| Name           = 
| ImageFile      = Magnesium oxide.jpg
| ImageFile2     = Magnesium-oxide-3D-vdW.png
| IUPACName      = Magnesium oxide
| OtherNames     = {{Unbulleted list|Magnesia|[[Periclase]]}}
| SystematicName = 
| Section1       = {{Chembox Identifiers
| CASNo = 1309-48-4
| CASNo_Ref = {{cascite|correct|CAS}}
| ChemSpiderID = 14108
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = 3A3U0GI71G
| EINECS = 215-171-9
| KEGG = D01167
| PubChem = 14792
| ChEMBL_Ref = {{ebicite|correct|EBI}}
| ChEMBL = 1200572
| RTECS = OM3850000
| StdInChI=1S/Mg.O
| StdInChIKey = CPLXHLVBOLITMK-UHFFFAOYSA-N
| SMILES = O=[Mg]
 }}
| Section2       = {{Chembox Properties
| Formula = MgO
| MolarMass = 40.304 g/mol<ref name="CRCPress-2011a"/>
| Appearance = White powder
| Odor = Odorless
| Density = 3.6 g/cm<sup>3</sup><ref name="CRCPress-2011a"/>
| MeltingPtC = 2852
| MeltingPt_ref=<ref name="CRCPress-2011a">{{RubberBible92nd|page=4.74}}</ref>
| BoilingPtC = 3600
| BoilingPt_ref=<ref name="CRCPress-2011a"/>
| Solubility = 
| SolubleOther = Soluble in [[acid]], [[ammonia]] <br> insoluble in [[ethanol|alcohol]]
| ThermalConductivity = 45–60&nbsp;W·m<sup>−1</sup>·K<sup>−1</sup><ref>[http://www.konoshima.co.jp/en/resdev/004.html Application of magnesium compounds to insulating heat-conductive fillers] {{webarchive|url=https://web.archive.org/web/20131230233440/http://www.konoshima.co.jp/en/resdev/004.html |date=2013-12-30 }}. konoshima.co.jp</ref>
| RefractIndex = 1.7355
| BandGap = 7.8 eV<ref>{{cite journal |journal=Solid State Communications |volume=55 |year=1985 |pages=351–5 |title=Self-consistent electronic structures of MgO and SrO |first1=O.E. |last1=Taurian |doi=10.1016/0038-1098(85)90622-2 |last2=Springborg |first2=M. |last3=Christensen |first3=N.E. |issue=4 |url=http://users-phys.au.dk/nec/Papers/necSSC/SSC55351.pdf |bibcode=1985SSCom..55..351T |access-date=2012-03-27 |archive-date=2016-03-03 |archive-url=https://web.archive.org/web/20160303213012/http://users-phys.au.dk/nec/Papers/necSSC/SSC55351.pdf |url-status=dead }}</ref>
| Dipole = 6.2 ± 0.6 D
| MagSus = −10.2·10<sup>−6</sup> cm<sup>3</sup>/mol<ref>{{RubberBible92nd|page=4.133}}</ref>
| ElectricalResistivity = [[Dielectric]]{{efn|At room temperature.<ref name="Johnson-1986" /><ref name="Subramanian-1989" /><ref name="Hornak-2018" />}}
 }}
| Section3       = {{Chembox Structure
| CrystalStruct = [[Halite]] (cubic), [[Pearson symbol|cF8]]
| SpaceGroup = Fm<u style="text-decoration:overline">3</u>m, No. 225
| Coordination = Octahedral (Mg<sup>2+</sup>); octahedral (O<sup>2−</sup>)
| LattConst_a = 4.212Å
 }}
| Section4       = 
| Section5       = {{Chembox Thermochemistry
| DeltaHf = −601.6 ± 0.3&nbsp;kJ·mol<sup>−1</sup><ref name="CRCPress-2011b">{{RubberBible92nd|page=5.2}}</ref>
| DeltaGf = -569.3 kJ/mol<ref name="CRCPress-2011c"/>
| Entropy = 26.95 ± 0.15&nbsp;J·mol<sup>−1</sup>·K<sup>−1</sup><ref name="CRCPress-2011b"/>
| HeatCapacity = 37.2 J/mol K<ref name="CRCPress-2011c">{{RubberBible92nd|page=5.15}}</ref>
 }}
| Section6       = {{Chembox Pharmacology
| ATCCode_prefix = A02
| ATCCode_suffix = AA02
| ATC_Supplemental = {{ATC|A06|AD02}}, {{ATC|A12|CC10}}
}}
| Section7       = {{Chembox Hazards
| ExternalSDS = [http://www.inchem.org/documents/icsc/icsc/eics0504.htm ICSC 0504]
| Hazards_ref=
| GHSPictograms = {{GHS07}}
| GHSSignalWord = Warning
| HPhrases = {{H-phrases|315|319|335}}
| PPhrases = {{P-phrases|261|264|271|273|280|302+352|304+340|305+351+338|312|333+313|337+313|362|363|391|403+233|405}}
| MainHazards = [[Metal fume fever]], Irritant
| NFPA-H = 1
| NFPA-F = 0
| NFPA-R = 0
| NFPA-S =
| FlashPt = Non-flammable
| LD50 =
| PEL = TWA 15 mg/m<sup>3</sup> (fume)<ref name="NIOSH"/>
| REL = None designated<ref name="NIOSH"/>
| IDLH = 750 mg/m<sup>3</sup> (fume)<ref name="NIOSH">{{PGCH|0374}}</ref>
 }}
| Section8       = {{Chembox Related
| OtherAnions = [[Magnesium sulfide]]<br/>[[Magnesium selenide]]
| OtherCations = [[Beryllium oxide]]<br/>[[Calcium oxide]]<br/>[[Strontium oxide]]<br/>[[Barium oxide]]
| OtherFunction =
| OtherFunction_label =
| OtherCompounds = [[Magnesium hydroxide]]<br/>[[Magnesium nitride]]
 }}
}}
'''Magnesium oxide''' ('''[[Magnesium|Mg]][[Oxide|O]]'''), or '''magnesia''', is a white [[hygroscopy|hygroscopic]] solid [[mineral]] that occurs naturally as [[periclase]] and is a source of [[magnesium]] (see also [[oxide]]). It has an [[empirical formula]] of MgO and consists of a [[crystal structure|lattice]] of Mg<sup>2+</sup> ions and O<sup>2−</sup> ions held together by [[ionic bond]]ing. [[Magnesium hydroxide]] forms in the presence of water (MgO + H<sub>2</sub>O → Mg(OH)<sub>2</sub>), but it can be reversed by heating it to remove moisture.

Magnesium oxide was historically known as '''magnesia alba''' (literally, the white mineral from [[Ancient Magnesia|Magnesia]]), to differentiate it from ''[[magnesia nigra]]'', a black mineral containing what is now known as [[manganese]].

==Related oxides==
While "magnesium oxide" normally refers to MgO, the compound [[magnesium peroxide]] MgO<sub>2</sub> is also known. According to evolutionary crystal structure prediction,<ref>{{cite journal| last = Zhu| first = Qiang| author2 = Oganov A.R.| author3 = Lyakhov A.O.| title = Novel stable compounds in the Mg-O system under high pressure| journal = Phys. Chem. Chem. Phys.| year = 2013| volume = 15| issue = 20| pages = 7696–7700| url = http://uspex.stonybrook.edu/pdfs/Mg-O-paper-2013.pdf| doi = 10.1039/c3cp50678a| pmid = 23595296| bibcode = 2013PCCP...15.7696Z| access-date = 2013-11-06| archive-date = 2013-12-03| archive-url = https://web.archive.org/web/20131203011451/http://uspex.stonybrook.edu/pdfs/Mg-O-paper-2013.pdf| url-status = dead}}</ref> MgO<sub>2</sub> is thermodynamically stable at pressures above 116 GPa (gigapascals), and a semiconducting [[suboxide]] Mg<sub>3</sub>O<sub>2</sub> is thermodynamically stable above 500 GPa. Because of its stability, MgO is used as a model system for investigating vibrational properties of crystals.<ref>{{cite journal| last= Mei| first = AB|author2=O. Hellman|author3=C. M. Schlepütz|author4= A. Rockett|author5= T.-C. Chiang|author6= L. Hultman|author7= I. Petrov|author-link7=Ivan Georgiev Petrov|author8= J. E. Greene|author-link8=J. E. Greene|title= Reflection Thermal Diffuse X-Ray Scattering for Quantitative Determination of Phonon Dispersion Relations.|journal=Physical Review B|volume= 92| issue = 17|year= 2015|page=174301| doi=10.1103/physrevb.92.174301|bibcode=2015PhRvB..92q4301M|doi-access= free}}</ref>

== Electric properties ==
Pure MgO is not conductive and has a high resistance to electric current at [[room temperature]]. The pure powder of MgO has a [[relative permittivity]] inbetween 3.2 to 9.9 <math>k</math> with an approximate [[dielectric loss]] of [[Dissipation factor|tan(δ)]] > 2.16x10<sup>3</sup> at 1kHz.<ref name="Johnson-1986">{{Cite thesis |last=A P |first=Johnson |date=November 1986 |title=Structural and electrical properties of magnesium oxide powders |url=http://etheses.dur.ac.uk/7037/ |publisher=Durham University|type=Masters }}</ref><ref name="Subramanian-1989">{{Cite journal |last1=Subramanian |first1=M. A. |last2=Shannon |first2=R. D. |last3=Chai |first3=B. H. T. |last4=Abraham |first4=M. M. |last5=Wintersgill |first5=M. C. |date=November 1989 |title=Dielectric constants of BeO, MgO, and CaO using the two-terminal method |url=http://link.springer.com/10.1007/BF00209695 |journal=Physics and Chemistry of Minerals |language=en |volume=16 |issue=8 |pages=741–746 |doi=10.1007/BF00209695 |bibcode=1989PCM....16..741S |s2cid=95280958 |issn=0342-1791}}</ref><ref name="Hornak-2018">{{Cite journal |last1=Hornak |first1=Jaroslav |last2=Trnka |first2=Pavel |last3=Kadlec |first3=Petr |last4=Michal |first4=Ondřej |last5=Mentlík |first5=Václav |last6=Šutta |first6=Pavol |last7=Csányi |first7=Gergely |last8=Tamus |first8=Zoltán |date=2018-05-30 |title=Magnesium Oxide Nanoparticles: Dielectric Properties, Surface Functionalization and Improvement of Epoxy-Based Composites Insulating Properties |journal=Nanomaterials |language=en |volume=8 |issue=6 |pages=381 |doi=10.3390/nano8060381 |issn=2079-4991 |pmc=6027305 |pmid=29848967|doi-access=free }}</ref>

==Production==
Magnesium oxide is produced by the [[calcination]] of [[magnesium carbonate]] or [[magnesium hydroxide]].  The latter is obtained by the treatment of [[magnesium chloride]] {{Chem|Mg|Cl|2}} solutions, typically seawater, with [[limewater]] or milk of lime.<ref name="Seeger">{{Ullmann | title = Magnesium Compounds | author1 = Margarete Seeger | author2 = Walter Otto | author3 = Wilhelm Flick | author4 = Friedrich Bickelhaupt | author5 = Otto S. Akkerman | doi = 10.1002/14356007.a15_595.pub2}}</ref>
:Mg<sup>2+</sup>  + Ca(OH)<sub>2</sub>  →  Mg(OH)<sub>2</sub>  +  Ca<sup>2+</sup>
[[Calcination|Calcining]] at different temperatures produces magnesium oxide of different reactivity. High temperatures 1500 – 2000&nbsp;°C diminish the available surface area and produces dead-burned (often called dead burnt) magnesia, an unreactive form used as a [[refractory]]. Calcining temperatures 1000 – 1500&nbsp;°C produce hard-burned magnesia, which has limited reactivity and calcining at lower temperature, (700–1000&nbsp;°C) produces light-burned magnesia, a reactive form, also known as caustic calcined magnesia.  Although some decomposition of the carbonate to oxide occurs at temperatures below 700&nbsp;°C, the resulting materials appear to reabsorb carbon dioxide from the air.{{cn|date=September 2023}}

==Applications==

===Refractory insulator===

MgO is prized as a [[Refractory|refractory material]], i.e. a solid that is physically and chemically stable at high temperatures. It has the useful attributes of high thermal conductivity and low electrical conductivity. According to a 2006 reference book:<ref name="Shand-2006">{{cite book |author=Mark A. Shand |title=The chemistry and technology of magnesia |url=https://books.google.com/books?id=0ShuV4W0V2gC |access-date=10 September 2011 |year=2006 |publisher=John Wiley and Sons |isbn=978-0-471-65603-6}}</ref> 
{{blockquote|By far the largest consumer of magnesia worldwide is the refractory industry, which consumed about 56% of the magnesia in the United States in 2004, the remaining 44% being used in agricultural, chemical, construction, environmental, and other industrial applications.}}

MgO is used as a refractory material for [[crucible]]s. It is also used as an insulator in [[Mineral-insulated copper-clad cable|heat-resistant electrical cable]].

===Biomedical===
Among metal oxide nanoparticles, magnesium oxide nanoparticles (MgO NPs) have distinct physicochemical and biological properties, including biocompatibility, biodegradability, high bioactivity, significant antibacterial properties, and good mechanical properties, which make it a good choice as a reinforcement in composites.<ref>{{cite journal |vauthors=Saberi A, Baltatu MS, Vizureanu P |title=Recent Advances in Magnesium-Magnesium Oxide Nanoparticle Composites for Biomedical Applications |journal=Bioengineering |volume=11 |issue=5 |pages=508 |date=May 2024 |pmid=38790374 |pmc=11117911 |doi=10.3390/bioengineering11050508 |doi-access=free}}</ref>

====Heating elements====
It is used extensively as an electrical insulator in tubular construction [[heating element]]s as in electric [[electric stove|stove]] and [[cooktop]] heating elements. There are several [[Mesh (scale)|mesh]] sizes available and most commonly used ones are 40 and 80&nbsp;mesh per the [[American Foundry Society]]. The extensive use is due to its high dielectric strength and average thermal conductivity. MgO is usually crushed and compacted with minimal airgaps or voids.

===Cement===
MgO is one of the components in [[Portland cement]] in [[Cement kiln#The wet process and the dry process|dry process plants]].

[[Sorel cement]] uses MgO as the main component in combination with MgCl<sub>2</sub> and water.

===Fertilizer===
MgO has an important place as a commercial plant fertilizer<ref>[https://web.archive.org/web/20160422171902/http://www.fertilizer101.org/science/?seq=10 Nutrient Science]. fertilizer101.org. Retrieved on 2017-04-26.</ref> and as animal feed.<ref>[https://web.archive.org/web/20150303043215/http://www.lehvoss.de/eng/1039.htm Magnesium oxide for the Animal Feed Industry]. lehvoss.de</ref>

===Fireproofing===
It is a principal fireproofing ingredient in construction materials. As a construction material, [[magnesium oxide wallboard]]s have several attractive characteristics: fire resistance, termite resistance, moisture resistance, mold and mildew resistance, and strength, but also a severe downside as it attracts moisture and can cause moisture damage to surrounding materials.<ref>{{Cite journal|last1=Mármol|first1=Gonzalo|last2=Savastano|first2=Holmer|date=July 2017|title=Study of the degradation of non-conventional MgO-SiO 2 cement reinforced with lignocellulosic fibers|journal=Cement and Concrete Composites|volume=80|pages=258–267|doi=10.1016/j.cemconcomp.2017.03.015}}</ref><ref name="Shand-2006"/>[https://www.building-supply.dk/article/view/227159/de_fugtige_mgoplader_en_guide_til_problemstillingen]

===Medical===
Magnesium oxide is used for relief of heartburn and indigestion, as an [[antacid]], magnesium supplement, and as a short-term [[laxative]]. It is also used to improve symptoms of [[indigestion]]. Side effects of magnesium oxide may include nausea and cramping.<ref>[https://www.nlm.nih.gov/medlineplus/druginfo/meds/a601074.html Magnesium Oxide]. MedlinePlus. Last reviewed 02/01/2009</ref> In quantities sufficient to obtain a laxative effect, side effects of long-term use may rarely cause [[enterolith]]s to form, resulting in [[bowel obstruction]].<ref>{{cite journal| author = Tatekawa Y| title = Small bowel obstruction caused by a medication bezoar: report of a case| journal = Surgery Today| volume = 26| issue = 1| pages = 68–70| year = 1996| pmid = 8680127| doi = 10.1007/BF00311997| name-list-style=vanc| author2 = Nakatani K| author3 = Ishii H| display-authors = 3| last4 = Paku| first4 = Shuuichi| last5 = Kasamatsu| first5 = Minoru| last6 = Sekiya| first6 = Nao| last7 = Nakano| first7 = Hiroshige| s2cid = 24976010}}</ref>

===Waste treatment===
Magnesium oxide is used extensively in the soil and [[groundwater remediation]], wastewater treatment, drinking water treatment, air emissions treatment, and waste treatment industries for its acid buffering capacity and related effectiveness in stabilizing dissolved heavy metal species.{{according to whom|date=December 2016}}

Many heavy metals species, such as [[lead]] and [[cadmium]], are least soluble in water at mildly basic conditions (pH in the range 8–11). Solubility of metals increases their undesired bioavailability and mobility in soil and groundwater. Granular MgO is often blended into metals-contaminating soil or waste material, which is also commonly of a low pH (acidic), in order to drive the [[pH]] into the 8–10 range. Metal-hydroxide complexes tend to [[Precipitation (chemistry)|precipitate]] out of aqueous solution in the pH range of 8–10.

MgO is packed in bags around [[transuranic waste]] in the disposal cells (panels) at the [[Waste Isolation Pilot Plant]], as a {{CO2}} getter to minimize the complexation of [[uranium]] and other [[actinide]]s by [[carbonate]] ions and so to limit the [[solubility]] of [[radionuclide]]s. The use of MgO is preferred over [[CaO]] since the resulting [[hydrate|hydration product]] ({{chem|Mg|(OH)|2}}) is less soluble and releases less [[hydration enthalpy|hydration heat]]. Another advantage is to impose a lower [[pH]] value (about 10.5) in case of accidental water ingress into the dry salt layers, in contast to the more soluble {{chem|Ca|(OH)|2}} which would create a higher pH of 12.5 (strongly [[alkaline]] conditions). The {{chem|Mg|2+}} [[cation]] being the second most abundant cation in [[seawater]] and in [[rocksalt]], the potential release of magnesium ions dissolving in [[brine]]s intruding the [[deep geological repository]] is also expected to minimize the [[geochemistry|geochemical]] disruption.<ref>[http://www.wipp.energy.gov/fctshts/wastehandling.pdf wipp.energy.gov Step-By-Step Guide for Waste Handling at WIPP]. Waste Isolation Pilot Plant. wipp.energy.gov</ref>

===Niche uses===
[[Image:MgOcrystal.JPG|thumb|left|140px|Unpolished MgO crystal]]
* As a food additive, it is used as an [[anticaking agent]]. It is known to the US [[Food and Drug Administration]] for cacao products; canned peas; and frozen dessert.<ref>{{cite web |title=Compound Summary for CID 14792 – Magnesium Oxide |url=https://pubchem.ncbi.nlm.nih.gov/compound/magnesium_oxide |publisher=PubChem}}</ref> It has an [[E number]] of E530.
* As a reagent in the installation of the carboxybenzyl (Cbz) group using [[benzyl chloroformate]] in [[ethyl acetate|EtOAc]] for the [[protecting group|N-protection]] of [[amine]]s and [[amide]]s.<ref>{{Cite journal|last=Dymicky|first=M.|date=1989-02-01|title=Preparation of Carbobenzoxy-<small>L</small>-Tyrosine Methyl and Ethyl Esters and of the Corresponding Carbobenzoxy Hydrazides|journal=Organic Preparations and Procedures International|volume=21|issue=1|pages=83–90|doi=10.1080/00304948909356350|issn=0030-4948}}</ref>
* [[Doping (semiconductor)|Doping]] MgO (about 1–5% by weight) into [[hydroxyapatite]], a [[bioceramic]] mineral, increases the [[fracture toughness]] by migrating to grain boundaries, where it reduces grain size and changes the fracture mode from [[intergranular fracture|intergranular]] to [[transgranular fracture|transgranular]].<ref>{{cite journal |doi=10.1016/j.ceramint.2013.04.098 |last1=Tan |first1=C.Y. |last2=Yaghoubi |first2=A. |last3=Ramesh |first3=S. |last4=Adzila |first4=S. |last5=Purbolaksono |first5=J. |last6=Hassan |first6=M.A. |last7=Kutty |first7=M.G. |date=December 2013 |title=Sintering and mechanical properties of MgO-doped nanocrystalline hydroxyapatite |url=http://www.aun.edu.eg/reserches_files/13211.pdf |journal=Ceramics International |volume=39 |issue=8 |pages=8979–8983 |access-date=2015-08-08 |archive-date=2017-03-12 |archive-url=https://web.archive.org/web/20170312033742/http://www.aun.edu.eg/reserches_files/13211.pdf |url-status=dead }}</ref><ref >{{cite journal | last1=Tan | first1=Chou Yong | last2=Singh | first2=Ramesh | last3=Tolouei | first3=R. | last4=Sopyan | first4=Iis | last5=Teng | first5=Wan Dung | title=Synthesis of High Fracture Toughness of Hydroxyapatite Bioceramics | journal=Advanced Materials Research | volume=264-265 | year=2011 | issn=1662-8985 | doi=10.4028/www.scientific.net/amr.264-265.1849 | pages=1849–1855| s2cid=137578750 }}</ref> 
* Pressed MgO is used as an optical material. It is transparent from 0.3 to 7&nbsp;μm. The [[refractive index]] is 1.72 at 1&nbsp;μm and the [[Abbe number]] is 53.58. It is sometimes known by the [[Eastman Kodak]] trademarked name Irtran-5, although this designation is obsolete. Crystalline pure MgO is available commercially and has a small use in infrared optics.<ref>{{cite journal|title=Index of Refraction of Magnesium Oxide|author1=Stephens, Robert E.|author2=Malitson, Irving H.|name-list-style=amp|journal=Journal of Research of the National Bureau of Standards|volume=49|issue=4|year=1952|pages=249–252|doi=10.6028/jres.049.025|doi-access=free}}</ref>
* An aerosolized solution of MgO is used in library science and collections management for the [[deacidification]] of at-risk paper items. In this process, the alkalinity of MgO (and similar compounds) neutralizes the relatively high acidity characteristic of low-quality paper, thus slowing the rate of deterioration.<ref name="LibraryofCongress">{{cite web|title=Mass Deacidification: Saving the Written Word|url=https://www.loc.gov/preservation/scientists/projects/mass_deacid.html|work=Library of Congress|access-date=26 September 2011}}</ref>
* Magnesium oxide is used as an oxide barrier in [[Spintronics|spin-tunneling devices]]. Owing to the crystalline structure of its thin films, which can be deposited by [[magnetron sputtering]], for example, it shows characteristics superior to those of the commonly used amorphous Al<sub>2</sub>O<sub>3</sub>. In particular, [[spin polarization]] of about 85% has been achieved with MgO<ref>{{Cite journal 
| last1 = Parkin | first1 = S. S. P. 
| last2 = Kaiser | first2 = C. 
| last3 = Panchula | first3 = A. 
| last4 = Rice | first4 = P. M. 
| last5 = Hughes | first5 = B. 
| last6 = Samant | first6 = M. 
| last7 = Yang | first7 = S. H. 
| doi = 10.1038/nmat1256 
| title = Giant tunnelling magnetoresistance at room temperature with MgO (100) tunnel barriers 
| journal = Nature Materials 
| volume = 3 
| issue = 12 
| pages = 862–867 
| year = 2004 
| pmid = 15516928 
| bibcode = 2004NatMa...3..862P | s2cid = 33709206 
}}</ref> versus 40–60&nbsp;% with aluminium oxide.<ref>{{Cite journal | last1 = Monsma | first1 = D. J. | last2 = Parkin | first2 = S. S. P. | doi = 10.1063/1.127097 | title = Spin polarization of tunneling current from ferromagnet/Al<sub>2</sub>O<sub>3</sub> interfaces using copper-doped aluminum superconducting films | journal = Applied Physics Letters | volume = 77 | issue = 5 | page = 720 | year = 2000 |bibcode = 2000ApPhL..77..720M }}</ref> The value of [[tunnel magnetoresistance]] is also significantly higher for MgO (600% at room temperature and 1,100&nbsp;% at 4.2 K<ref>{{Cite journal | last1 = Ikeda | first1 = S. | last2 = Hayakawa | first2 = J. | last3 = Ashizawa | first3 = Y. | last4 = Lee | first4 = Y. M. | last5 = Miura | first5 = K. | last6 = Hasegawa | first6 = H. | last7 = Tsunoda | first7 = M. | last8 = Matsukura | first8 = F. | last9 = Ohno | first9 = H. | doi = 10.1063/1.2976435 | title = Tunnel magnetoresistance of 604% at 300 K by suppression of Ta diffusion in CoFeB/MgO/CoFeB pseudo-spin-valves annealed at high temperature | journal = Applied Physics Letters | volume = 93 | issue = 8 | page = 082508 | year = 2008 |bibcode = 2008ApPhL..93h2508I | s2cid = 122271110 }}</ref>) than Al<sub>2</sub>O<sub>3</sub> (ca. 70% at room temperature<ref>{{Cite journal | last1 = Wang | first1 = D. | last2 = Nordman | first2 = C. | last3 = Daughton | first3 = J. M. | last4 = Qian | first4 = Z. | last5 = Fink | first5 = J. | doi = 10.1109/TMAG.2004.830219 | title = 70% TMR at Room Temperature for SDT Sandwich Junctions with CoFeB as Free and Reference Layers | journal = IEEE Transactions on Magnetics | volume = 40 | issue = 4 | page = 2269 | year = 2004 | citeseerx = 10.1.1.476.8544 | bibcode = 2004ITM....40.2269W | s2cid = 20439632 }}</ref>).
* MgO is a common pressure transmitting medium used in high pressure apparatuses like the [[multi-anvil press]].<ref>{{Cite journal |last1=Wang |first1=Haikuo |last2=He |first2=Duanwei |last3=Yan |first3=Xiaozhi |last4=Xu |first4=Chao |last5=Guan |first5=Junwei |last6=Tan |first6=Ning |last7=Wang |first7=Wendan |date=December 2011 |title=Quantitative measurements of pressure gradients for the pyrophyllite and magnesium oxide pressure-transmitting mediums to 8 GPa in a large-volume cubic cell |url=http://www.tandfonline.com/doi/abs/10.1080/08957959.2011.614238 |journal=High Pressure Research |language=en |volume=31 |issue=4 |pages=581–591 |doi=10.1080/08957959.2011.614238 |bibcode=2011HPR....31..581W |issn=0895-7959}}</ref>

===Brake lining===
Magnesia is used in [[brake linings]] for its heat conductivity and intermediate hardness.<ref>{{cite web |url=https://www.preciseceramic.com/blog/magnesium-oxide-ceramic-materials-an-overview.html |title=Magnesium Oxide Ceramic Materials - An Overview |date=Aug 8, 2024 |website=Advanced Ceramic Materials |access-date=Sep 15, 2024}}</ref> It helps dissipate heat from friction surfaces, preventing overheating, while minimizing wear on metal components.<ref>{{cite patent |country=CN |number=105087849A |status=patent}}</ref> Its stability under high temperatures ensures reliable and durable braking performance in [[Automotive industry|automotive]] and industrial applications.<ref>{{cite patent |country=WO |number=2020122684A1 |status=patent}}</ref>

=== Thin film transistors ===
In [[thin film transistors|thin film transistors(TFTs)]], MgO is often used as a dielectric material or an insulator due to its high thermal stability, excellent insulating properties, and wide [[bandgap]].<ref>{{cite web |url=https://www.sputtertargets.net/blog/magnesium-oxide-target-in-the-production-of-thin-film-transistors.html |title=Magnesium Oxide Target in Thin-Film Transistors Production |last=Green |first=Julissa |date=Apr 24, 2024 |publisher=Stanford Advanced Materials |website=Sputter Targets |access-date=Oct 30, 2024}}</ref> Optimized IGZO/MgO TFTs demonstrated an [[electron mobility]] of 1.63 cm²/Vs, an on/off current ratio of 10⁶, and a subthreshold swing of 0.50 V/decade at −0.11 V.<ref>{{cite journal |last1=Su |first1=Zhan |last2=Zhang |first2=Xiao |year=2024 |title=Effect of substrate temperature on growth mechanism and properties of PEALD-MgO dielectric films for amorphous-IGZO TFTs |journal=Surface and Coatings Technology |volume=483 |page=130819 |doi=10.1016/j.surfcoat.2024.130819}}</ref> These TFTs are integral to low-power applications, wearable devices, and radiation-hardened electronics, contributing to enhanced efficiency and durability across diverse domains.<ref>{{cite journal |last1=Yu |first1=Fangzhou |last2=Hong |first2=Wen |year=2021 |title=MgZnO-Based Negative Capacitance Transparent Thin-Film Transistor Built on Glass |journal=IEEE Journal of the Electron Devices Society |volume=9 |pages=798–803 |doi=10.1109/JEDS.2021.3108904 |doi-access=free}}</ref><ref>{{cite journal |last1=Zhao |first1=Cheng |last2=Li |first2=Jun |year=2017 |title=Mg Doping to Simultaneously Improve the Electrical Performance and Stability of MgInO Thin-Film Transistors |journal=IEEE Transactions on Electron Devices |volume=64 |issue=5 |pages=2216–2220 |doi=10.1109/TED.2017.2678544|bibcode=2017ITED...64.2216Z }}</ref>

===Historical uses===
* It was historically used as a reference white color in [[colorimetry]], owing to its good [[diffuser (optics)|diffusing]] and [[reflectivity]] properties.<ref>{{cite journal|title=Reflectance of Magnesium Oxide|first=Peter A.|last=Tellex|author2=Waldron, Jack R.|journal=JOSA|year=1955|volume=45|issue=1|doi=10.1364/JOSA.45.000019|page=19|bibcode=1955JOSA...45...19T }}</ref> It may be smoked onto the surface of an opaque material to form an [[integrating sphere]].
* Early [[gas mantle]] designs for lighting, such as the [[Clamond basket]], consisted mainly of magnesium oxide.

==Precautions==
Inhalation of magnesium oxide fumes can cause [[metal fume fever]].<ref>[http://www.npi.gov.au/substances/magnesium-oxide-fume/index.html Magnesium Oxide]. National Pollutant Inventory, Government of Australia.</ref>

==See also==
* {{annotated link|Calcium oxide}}
* {{annotated link|Barium oxide}}
* {{Annotated link|Calcium silicate}}
* {{annotated link|Magnesium sulfide}}
* {{annotated link|Reactive magnesia}}

==Notes==
{{notelist}}

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

==External links==
*[https://web.archive.org/web/20060526045620/http://www.cmmp.ucl.ac.uk/~ahh/research/crystal/mgo.htm Data page at UCL]
*[https://web.archive.org/web/20060628083148/http://www.ceramics.nist.gov/srd/summary/ftgmgo.htm Ceramic data page at NIST]
*[https://www.cdc.gov/niosh/npg/npgd0374.html NIOSH Pocket Guide to Chemical Hazards at CDC]

{{Magnesium compounds}}
{{Antacids}}
{{oxides}}
{{oxygen compounds}}
{{Authority control}}

{{DEFAULTSORT:Magnesium Oxide}}
[[Category:Magnesium minerals]]
[[Category:Magnesium compounds]]
[[Category:Oxides]]
[[Category:Refractory materials]]
[[Category:Optical materials]]
[[Category:Ceramic materials]]
[[Category:Antacids]]
[[Category:E-number additives]]
[[Category:Rock salt crystal structure]]