Magnesium oxide was historically known as magnesia alba (literally, the white mineral from
Magnesia), to differentiate it from magnesia negra, a black mineral containing what is now known as
While "magnesium oxide" normally refers to MgO, the compound
magnesium peroxide MgO2 is also known. According to evolutionary crystal structure prediction, 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.
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.
MgO is prized as a
refractory material, i.e. a solid that is physically and chemically stable at high temperatures. It has two useful attributes: high thermal conductivity and low electrical conductivity. Filling the spiral
Calrod range top heating elements on kitchen electric stoves is a major use. "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 basic refractory material for
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.
gas mantles utilize magnesium oxide. Early iterations such as the
Clamond basket used only this. Later versions use ~60% magnesium oxide, with other components such as
lanthanum oxide or
yttrium oxide making up the rest. Another exception would be thoriated gas mantles.
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?]
Many heavy metals species, such as
cadmium are most soluble in water at acidic pH (below 6) as well as high pH (above 11). Solubility of metals affects bioavailability of the species and mobility soil and groundwater systems. Most metal species are toxic to humans at certain concentrations, therefore it is imperative to minimize metal bioavailability and mobility.
Granular MgO is often blended into metals-contaminated soil or waste material, which is also commonly of a low pH (acidic), in order to drive the
pH into the 8–10 range where most metals are at their lowest solubilities (
basic). Metal-hydroxide complexes have a tendency to
precipitate out of aqueous solution in the pH range of 8–10. MgO is widely regarded as the most effective metals stabilization compound when compared to Portland cement, lime,
kiln dust products, power generation waste products, and various proprietary products due to MgO's superior buffering capacity, cost effectiveness, and ease/safety of handling.
Most, if not all products that are marketed as metals stabilization technologies create very high pH conditions in aquifers whereas MgO creates an ideal aquifer condition with a pH of 8–10. Additionally, magnesium, an essential element to most biological systems, is provided to soil and groundwater microbial populations during MgO-assisted metals remediation as an added benefit.
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. In quantities sufficient to obtain a laxative effect, side effects of long-term use may rarely cause
enteroliths to form, resulting in
It is used extensively as an electrical insulator in tubular construction
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. The electrical heating industry also experimented with
aluminium oxide, but it is not used anymore.
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.
MgO has an important place as a commercial plant fertilizer  and as animal feed.
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.
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 versus 40–60 % with aluminium oxide. The value of
tunnel magnetoresistance is also significantly higher for MgO (600% at room temperature and 1,100 % at 4.2 K) than Al2O3 (ca. 70% at room temperature).
^Dymicky, M. (1989-02-01). "Preparation of Carbobenzoxy-L-Tyrosine Methyl and Ethyl Esters and of the Corresponding Carbobenzoxy Hydrazides". Organic Preparations and Procedures International. 21 (1): 83–90.
^Monsma, D. J.; Parkin, S. S. P. (2000). "Spin polarization of tunneling current from ferromagnet/Al2O3 interfaces using copper-doped aluminum superconducting films". Applied Physics Letters. 77 (5): 720.
^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.