Magnesium oxide (MgO), ormagnesia, is a whitehygroscopic solidmineral that occurs naturally aspericlase and is a source ofmagnesium (see alsooxide). It has anempirical formula of MgO and consists of alattice of Mg²⁺ ions and O²⁻ ions held together byionic bonding.Magnesium hydroxide forms in the presence of water (MgO + H₂O → Mg(OH)₂), but it can be reversed by heating it to remove moisture.

Magnesium oxide

Names
IUPAC name Magnesium oxide
Other names Magnesia Periclase
Identifiers
CAS Number	1309-48-4 Y
3D model (JSmol)	Interactive image
ChEMBL	ChEMBL1200572 Y
ChemSpider	14108
ECHA InfoCard	100.013.793
EC Number	215-171-9
E number	E530(acidity regulators, ...)
KEGG	D01167
PubChemCID	14792
RTECS number	OM3850000
UNII	3A3U0GI71G Y
CompTox Dashboard(EPA)	DTXSID9049665
InChI InChI=1S/Mg.O Key: CPLXHLVBOLITMK-UHFFFAOYSA-N
SMILES O=[Mg]
Properties
Chemical formula	MgO
Molar mass	40.304 g/mol[1]
Appearance	White powder
Odor	Odorless
Density	3.6 g/cm3[1]
Melting point	2,852 °C (5,166 °F; 3,125 K)[1]
Boiling point	3,600 °C (6,510 °F; 3,870 K)[1]
Solubility	Soluble inacid,ammonia insoluble inalcohol
Electrical resistivity	Dielectric[a]
Band gap	7.8 eV[2]
Magnetic susceptibility (χ)	−10.2·10−6 cm3/mol[3]
Thermal conductivity	45–60 W·m−1·K−1[4]
Refractive index (nD)	1.7355
Dipole moment	6.2 ± 0.6 D
Structure
Crystal structure	Halite (cubic),cF8
Space group	Fm3m, No. 225
Lattice constant	a = 4.212Å
Coordination geometry	Octahedral (Mg2+); octahedral (O2−)
Thermochemistry
Heat capacity(C)	37.2 J/mol K[8]
Std molar entropy(S⦵298)	26.95 ± 0.15 J·mol−1·K−1[9]
Std enthalpy of formation(ΔfH⦵298)	−601.6 ± 0.3 kJ·mol−1[9]
Gibbs free energy(ΔfG⦵)	−569.3 kJ/mol[8]
Pharmacology
ATC code	A02AA02 (WHO)A06AD02 (WHO),A12CC10 (WHO)
Hazards
Occupational safety and health (OHS/OSH):
Main hazards	Metal fume fever, Irritant
GHS labelling:
Pictograms
Signal word	Warning
Hazard statements	H315,H319,H335
Precautionary statements	P261,P264,P271,P273,P280,P302+P352,P304+P340,P305+P351+P338,P312,P333+P313,P337+P313,P362,P363,P391,P403+P233,P405
NFPA 704 (fire diamond)	1 0 0
Flash point	Non-flammable
NIOSH (US health exposure limits):
PEL (Permissible)	TWA 15 mg/m3 (fume)[10]
REL (Recommended)	None designated[10]
IDLH (Immediate danger)	750 mg/m3 (fume)[10]
Safety data sheet (SDS)	ICSC 0504
Related compounds
Otheranions	Magnesium sulfide Magnesium selenide
Othercations	Beryllium oxide Calcium oxide Strontium oxide Barium oxide
Related compounds	Magnesium hydroxide Magnesium nitride
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

Magnesium oxide was historically known asmagnesia alba (literally, the white mineral fromMagnesia), to differentiate it frommagnesia nigra, a black mineral containing what is now known asmanganese.

While "magnesium oxide" normally refers to MgO, the compoundmagnesium peroxide MgO₂ is also known. According to evolutionary crystal structure prediction,^[11] MgO₂ is thermodynamically stable at pressures above 116 GPa (gigapascals), and a semiconductingsuboxide Mg₃O₂ is thermodynamically stable above 500 GPa. Because of its stability, MgO is used as a model system for investigating vibrational properties of crystals.^[12]

Pure MgO is not conductive and has a high resistance to electric current atroom temperature. The pure powder of MgO has arelative permittivity inbetween 3.2 to 9.9${\displaystyle k}$  with an approximatedielectric loss oftan(δ) > 2.16x10³ at 1kHz.^[5][6][7]

Magnesium oxide is produced by thecalcination ofmagnesium carbonate ormagnesium hydroxide. The latter is obtained by the treatment ofmagnesium chlorideMgCl
₂ solutions, typically seawater, withlimewater or milk of lime.^[13]

Mg²⁺ + Ca(OH)₂ → Mg(OH)₂ + Ca²⁺

Calcining at different temperatures produces magnesium oxide of different reactivity. High temperatures 1500 – 2000 °C diminish the available surface area and produces dead-burned (often called dead burnt) magnesia, an unreactive form used as arefractory. Calcining temperatures 1000 – 1500 °C produce hard-burned magnesia, which has limited reactivity and calcining at lower temperature, (700–1000 °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 °C, the resulting materials appear to reabsorb carbon dioxide from the air.^{[citation needed]}

MgO is prized as arefractory 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:^[14]

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 forcrucibles. It is also used as an insulator inheat-resistant electrical cable.

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.^[15]

It is used extensively as an electrical insulator in tubular constructionheating elements as in electricstove andcooktop heating elements. There are severalmesh sizes available and most commonly used ones are 40 and 80 mesh per theAmerican 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.

MgO is one of the components inPortland cement indry process plants.

Sorel cement uses MgO as the main component in combination with MgCl₂ and water.

MgO has an important place as a commercial plant fertilizer^[16] and as animal feed.^[17]

It is a principal fireproofing ingredient in construction materials. As a construction material,magnesium oxide wallboards 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.^[18][14][1]

Magnesium oxide is used for relief of heartburn and indigestion, as anantacid, magnesium supplement, and as a short-termlaxative. It is also used to improve symptoms ofindigestion. Side effects of magnesium oxide may include nausea and cramping.^[19] In quantities sufficient to obtain a laxative effect, side effects of long-term use may rarely causeenteroliths to form, resulting inbowel obstruction.^[20]

Magnesium oxide is used extensively in the soil andgroundwater 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?]}

Many heavy metals species, such aslead andcadmium, 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 thepH into the 8–10 range. Metal-hydroxide complexes tend toprecipitate out of aqueous solution in the pH range of 8–10.

MgO is packed in bags aroundtransuranic waste in the disposal cells (panels) at theWaste Isolation Pilot Plant, as a CO₂ getter to minimize the complexation ofuranium and otheractinides bycarbonate ions and so to limit thesolubility ofradionuclides. The use of MgO is preferred overCaO since the resultinghydration product (Mg(OH)
₂) is less soluble and releases lesshydration heat. Another advantage is to impose a lowerpH value (about 10.5) in case of accidental water ingress into the dry salt layers, in contast to the more solubleCa(OH)
₂ which would create a higher pH of 12.5 (stronglyalkaline conditions). TheMg²⁺
cation being the second most abundant cation inseawater and inrocksalt, the potential release of magnesium ions dissolving inbrines intruding thedeep geological repository is also expected to minimize thegeochemical disruption.^[21]

• As a food additive, it is used as ananticaking agent. It is known to the USFood and Drug Administration for cacao products; canned peas; and frozen dessert.^[22] It has anE number of E530.
• As a reagent in the installation of the carboxybenzyl (Cbz) group usingbenzyl chloroformate inEtOAc for theN-protection ofamines andamides.^[23]
• Doping MgO (about 1–5% by weight) intohydroxyapatite, abioceramic mineral, increases thefracture toughness by migrating to grain boundaries, where it reduces grain size and changes the fracture mode fromintergranular totransgranular.^[24][25]
• Pressed MgO is used as an optical material. It is transparent from 0.3 to 7 μm. Therefractive index is 1.72 at 1 μm and theAbbe number is 53.58. It is sometimes known by theEastman Kodak trademarked name Irtran-5, although this designation is obsolete. Crystalline pure MgO is available commercially and has a small use in infrared optics.^[26]
• An aerosolized solution of MgO is used in library science and collections management for thedeacidification 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.^[27]
• Magnesium oxide is used as an oxide barrier inspin-tunneling devices. Owing to the crystalline structure of its thin films, which can be deposited bymagnetron sputtering, for example, it shows characteristics superior to those of the commonly used amorphous Al₂O₃. In particular,spin polarization of about 85% has been achieved with MgO^[28] versus 40–60 % with aluminium oxide.^[29] The value oftunnel magnetoresistance is also significantly higher for MgO (600% at room temperature and 1,100 % at 4.2 K^[30]) than Al₂O₃ (ca. 70% at room temperature^[31]).
• MgO is a common pressure transmitting medium used in high pressure apparatuses like themulti-anvil press.^[32]

Magnesia is used inbrake linings for its heat conductivity and intermediate hardness.^[33] It helps dissipate heat from friction surfaces, preventing overheating, while minimizing wear on metal components.^[34] Its stability under high temperatures ensures reliable and durable braking performance inautomotive and industrial applications.^[35]

Inthin film transistors(TFTs), MgO is often used as a dielectric material or an insulator due to its high thermal stability, excellent insulating properties, and widebandgap.^[36] Optimized IGZO/MgO TFTs demonstrated anelectron 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.^[37] These TFTs are integral to low-power applications, wearable devices, and radiation-hardened electronics, contributing to enhanced efficiency and durability across diverse domains.^[38][39]

• It was historically used as a reference white color incolorimetry, owing to its gooddiffusing andreflectivity properties.^[40] It may be smoked onto the surface of an opaque material to form anintegrating sphere.
• Earlygas mantle designs for lighting, such as theClamond basket, consisted mainly of magnesium oxide.

Inhalation of magnesium oxide fumes can causemetal fume fever.^[41]

• Calcium oxide – Chemical compound of calcium
• Barium oxide – Chemical compound used in cathode-ray tubes
• Calcium silicate – Chemical compound naturally occurring as the mineral larnite
• Magnesium sulfide – Inorganic compound generated in the production of metallic iron
• Reactive magnesia – chemical compoundPages displaying wikidata descriptions as a fallback

• Data page at UCL
• Ceramic data page at NIST
• NIOSH Pocket Guide to Chemical Hazards at CDC