Magnesium oxide (MgO), or magnesia, is a white 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 lattice of Mg2+ ions and O2− ions held together by ionic 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.
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| Names | |
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| IUPAC name
Magnesium oxide
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Other names
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| Identifiers | |
3D model (JSmol)
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| ChEMBL | |
| ChemSpider | |
| ECHA InfoCard | 100.013.793 |
| EC Number |
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| E number | E530 (acidity regulators, ...) |
| KEGG | |
PubChem CID
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| RTECS number |
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| UNII | |
CompTox Dashboard (EPA)
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| Properties | |
| 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 in acid, ammonia insoluble in alcohol |
| Electrical resistivity | Dielectric[a] |
| Band gap | 7.8 eV[2] |
| −10.2·10−6 cm3/mol[3] | |
| Thermal conductivity | 45–60 W·m−1·K−1[4] |
Refractive index (nD)
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1.7355 |
| 6.2 ± 0.6 D | |
| Structure | |
| Halite (cubic), cF8 | |
| Fm3m, No. 225 | |
a = 4.212Å
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| Octahedral (Mg2+); octahedral (O2−) | |
| Thermochemistry | |
Heat capacity (C)
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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⦵)
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-569.3 kJ/mol[8] |
| Pharmacology | |
| A02AA02 (WHO) A06AD02 (WHO), A12CC10 (WHO) | |
| Hazards | |
| Occupational safety and health (OHS/OSH): | |
Main hazards
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Metal fume fever, Irritant |
| GHS labelling: | |
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| Warning | |
| H315, H319, H335 | |
| 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) | |
| Flash point | Non-flammable |
| NIOSH (US health exposure limits): | |
PEL (Permissible)
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TWA 15 mg/m3 (fume)[10] |
REL (Recommended)
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None designated[10] |
IDLH (Immediate danger)
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750 mg/m3 (fume)[10] |
| Safety data sheet (SDS) | ICSC 0504 |
| Related compounds | |
Other anions
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Magnesium sulfide Magnesium selenide |
Other cations
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Beryllium oxide Calcium oxide Strontium oxide Barium oxide |
Related compounds
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Magnesium hydroxide Magnesium nitride |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Magnesium oxide was historically known as magnesia alba (literally, the white mineral from Magnesia), to differentiate it from magnesia nigra, a black mineral containing what is now known as manganese.
Related oxides
editWhile "magnesium oxide" normally refers to MgO, the compound magnesium peroxide MgO2 is also known. According to evolutionary crystal structure prediction,[11] MgO2 is thermodynamically stable at pressures above 116 GPa (gigapascals), and a semiconducting suboxide 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]
Electric properties
editPure 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 with an approximate dielectric loss of tan(δ) > 2.16x103 at 1kHz.[5][6][7]
Production
editMagnesium oxide is produced by the calcination of magnesium carbonate or magnesium hydroxide. The latter is obtained by the treatment of magnesium chloride MgCl
2 solutions, typically seawater, with limewater 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 a refractory. 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]
Applications
editRefractory insulator
editMgO is prized as a 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:[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 for crucibles. It is also used as an insulator in heat-resistant electrical cable.
Biomedical
editAmong 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]
Heating elements
editIt is used extensively as an electrical insulator in tubular construction heating elements as in electric stove and cooktop heating elements. There are several mesh sizes available and most commonly used ones are 40 and 80 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
editMgO is one of the components in Portland cement in dry process plants.
Sorel cement uses MgO as the main component in combination with MgCl2 and water.
Fertilizer
editMgO has an important place as a commercial plant fertilizer[16] and as animal feed.[17]
Fireproofing
editIt 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]
Medical
editMagnesium 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.[19] In quantities sufficient to obtain a laxative effect, side effects of long-term use may rarely cause enteroliths to form, resulting in bowel obstruction.[20]
Waste treatment
editMagnesium 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?]
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 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 actinides by carbonate ions and so to limit the solubility of radionuclides. The use of MgO is preferred over CaO since the resulting hydration product (Mg(OH)
2) is less soluble and releases less 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 Ca(OH)
2 which would create a higher pH of 12.5 (strongly alkaline conditions). The Mg2+
cation being the second most abundant cation in seawater and in rocksalt, the potential release of magnesium ions dissolving in brines intruding the deep geological repository is also expected to minimize the geochemical disruption.[21]
Niche uses
edit
- 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.[22] It has an E number of E530.
- As a reagent in the installation of the carboxybenzyl (Cbz) group using benzyl chloroformate in EtOAc for the N-protection of amines and amides.[23]
- 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 to transgranular.[24][25]
- Pressed MgO is used as an optical material. It is transparent from 0.3 to 7 μm. The refractive index is 1.72 at 1 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.[26]
- 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.[27]
- Magnesium oxide is used as an oxide barrier in 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 Al2O3. In particular, spin polarization of about 85% has been achieved with MgO[28] versus 40–60 % with aluminium oxide.[29] The value of tunnel 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 the multi-anvil press.[32]
Brake lining
editMagnesia is used in brake 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 in automotive and industrial applications.[35]
Thin film transistors
editIn 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.[36] 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.[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]
Historical uses
edit- It was historically used as a reference white color in colorimetry, owing to its good diffusing and reflectivity properties.[40] 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
editInhalation of magnesium oxide fumes can cause metal fume fever.[41]
See also
edit- 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 compound
Notes
editReferences
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- ^ Haynes, William M., ed. (2011). CRC Handbook of Chemistry and Physics (92nd ed.). Boca Raton, Florida: CRC Press. p. 4.133. ISBN 1-4398-5511-0.
- ^ Application of magnesium compounds to insulating heat-conductive fillers Archived 2013-12-30 at the Wayback Machine. konoshima.co.jp
- ^ a b A P, Johnson (November 1986). Structural and electrical properties of magnesium oxide powders (Masters). Durham University.
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- ^ Parkin, S. S. P.; Kaiser, C.; Panchula, A.; Rice, P. M.; Hughes, B.; Samant, M.; Yang, S. H. (2004). "Giant tunnelling magnetoresistance at room temperature with MgO (100) tunnel barriers". Nature Materials. 3 (12): 862–867. Bibcode:2004NatMa...3..862P. doi:10.1038/nmat1256. PMID 15516928. S2CID 33709206.
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- ^ Ikeda, S.; Hayakawa, J.; Ashizawa, Y.; Lee, Y. M.; Miura, K.; Hasegawa, H.; Tsunoda, M.; Matsukura, F.; Ohno, H. (2008). "Tunnel magnetoresistance of 604% at 300 K by suppression of Ta diffusion in CoFeB/MgO/CoFeB pseudo-spin-valves annealed at high temperature". Applied Physics Letters. 93 (8): 082508. Bibcode:2008ApPhL..93h2508I. doi:10.1063/1.2976435. S2CID 122271110.
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