Magnesium oxide ( MgO ), or magnesia , is a white hygroscopic solid mineral that occurs naturally as a periclase and is a source of magnesium (see also oxide). It has an empirical formula MgO and consists of lattice ion Mg 2 and O 2 - which is united by ionic bonds. Magnesium hydroxide is formed in the presence of water (MgO H 2 O -> Mg (OH) 2 ), but can be reversed by heating it to separate moisture.
Magnesium oxide is historically known as magnesia alba (literally, white minerals from magnesia - other sources give magnesia alba as MgCO 3 ), to distinguish it from magnesia negra , black minerals contain what is now known as manganese.
While "magnesium oxide" usually refers to MgO, magnesium peroxide MgO 2 is also known as a compound. According to the prediction of the evolutionary crystal structure, MgO 2 is thermodynamically stable at pressures above 116 GPa (gigapascals), and Mg suboxide semiconductor 3 O 2 stable thermodynamically above 500 GPa. Due to its stability, MgO is used as a model system to investigate the vibrational properties of crystals.
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Magnesium oxide is produced by calcining magnesium carbonate or magnesium hydroxide. The latter is obtained by treatment of magnesium chloride solution, usually sea water, with lime.
- Mg 2 Ca (OH) 2 -> Mg (OH) 2 Ca 2
Calcination at different temperatures produces magnesium oxide with different reactivity. The high temperature of 1500 - 2000 Â ° C reduces the available surface area and produces burnt dead magnesia (often called burning), a non-reactive form used as a refractory. Calcination of temperature 1000 - 1500 ° C produces hard-burning magnesia, which has limited reactivity and calcination at lower temperatures, (700-1000 ° C) produces a light-burning magnesia, a reactive form, also known as Caustic calcined magnesia. Although some decomposition from carbonate to oxide occurs at temperatures below 700 ° C, the resulting material appears to reabsorb the carbon dioxide from the air.
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MgO is valued as a refractory material, ie solids that are physically and chemically stable at high temperatures. It has two useful attributes: high thermal conductivity and low electrical conductivity. "By far the largest consumer of magnesia worldwide is the refractory industry, which consumes about 56% of magnesia in the United States in 2004, the remaining 44% is used in agricultural, chemical, construction, environmental, and other industrial applications." MgO is used as a basic refractory material for crucibles.
It is a major fireproofing material in construction materials. As a construction material, the magnesium oxide wallboard has some interesting characteristics: fireproof, termite resistant, moisture resistant, mold and mushroom resistance, and strength.
Niche uses
MgO is one of the components in Portland cement in a dry process plant.
Magnesium oxide is widely used in soil and groundwater remediation, wastewater treatment, drinking water treatment, air emissions processing and waste treatment industries for acid buffer capacity and related effectiveness in stabilizing dissolved heavy metals species.
Many species of heavy metals, such as lead and cadmium, are most soluble in water at acidic pH (below 6) and high pH (above 11). Metal solubility affects the bioavailability of soil species and groundwater and mobility systems. Most species of metal are toxic to humans at a certain concentration, therefore it is important to minimize bioavailability and metal mobility.
Granular MgO is often mixed into soil or metal contaminated waste materials, which are also generally low pH (acid), to push the pH to a range of 8-10 where most of the metal is at its lowest solubility. The complex metal-hydroxide has a tendency to precipitate from a solution in the pH range of 8-10. MgO is widely regarded as the most effective metal stabilization compound when compared to Portland cement products, lime, dust kilns, power generation waste products, and exclusive products due to superior MgO buffer capacity, cost effectiveness and ease of handling.
Most, if not all products marketed as metal stabilization technologies create very high pH conditions in aquifers while MgO creates ideal aquifer conditions with a pH of 8-10. In addition, magnesium, an essential element for most biological systems, is provided for ground and groundwater microbial populations during MgO-assisted metal remediation as an additional benefit.
Medical
Magnesium oxide has a poor solubility in water and is poorly absorbed from the intestine. For this reason, magnesium oxide is relatively ineffective in repairing magnesium deficiency. Magnesium oxide is used to relieve heartburn and stomach acid, as antacids, magnesium supplements, and as short-term laxatives. It is also used to improve the symptoms of indigestion. Side effects of magnesium oxide may include nausea and cramps. In sufficient quantities to obtain laxative effects, side effects of long-term use include enterolites resulting in intestinal obstruction.
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- This is used as a white color reference in colorimetry, due to its excellent dispersion and reflection properties. Can be smoked to the surface of opaque material to form a unified ball.
- These are widely used as electrical insulators in tubular construction heating elements. There are several mesh sizes available and the most commonly used are 40 and 80 mesh per American Foundry Society. Extensive use is due to high dielectric strength and average thermal conductivity. MgO is usually destroyed and compacted with airgaps or minimal voids. The electric heating industry also experimented with aluminum oxide, but was not used anymore.
- It is also used as an insulator in heat resistant heat cables. MgO doping has been shown to effectively inhibit grain growth in ceramics and increase their fracture toughness by altering the mechanism of nanoscale crack growth.
- Pressed MgO is used as an optical material. It's transparent from 0.3 to 7 Âμm. The refractive index is 1.72 at 1 Âμm and the Abbe rate is 53.58. Sometimes known by the Eastman Kodak trademark name Irtran-5 , although this title is outdated. Pure crystalline MgO is commercially available and has little use in infrared optics.
- MgO is packed around transuranic waste in the Insulation Waste Pilot Plant, to control radionuclide solubility.
- MgO has an important place as commercial plant fertilizer and as animal feed.
- The aerosol solutions from MgO are used in library science and collection management to deacidify paper items at risk. In this process, the alkalinity of MgO (and similar compounds) neutralizes the relatively high acidity properties of low quality paper, thereby slowing the rate of deterioration.
- MgO is also used as a protective layer in plasma displays.
- Magnesium oxide is used as an oxide barrier in a spin-tunneling device. Because of the crystalline structure of the thin film, which can be precipitated by magnetron sputtering, for example, it exhibits characteristics superior to those commonly used Al-amorf Al 2 O 3 . Specifically, 85% polarization spin has been achieved with MgO versus 40-60% with aluminum oxide. The value of tunnel magnetoresistance was also significantly higher for MgO (600% at room temperature and 1.100% at 4.2 K) than Al 2 O 3 (about 70% at room temperature ). MgO is thermally stable up to about 700 ° K, vs. 600 Â ° K for Al 2 O 3 .
Precautions
Inhaling the smoke of magnesium oxide can cause metal smoke fever.
See also
- Calcium oxide
- Barium oxide
- Magnesium sulfide
- Magnesia reactive
References
External links
- The data page at UCL
- Ceramic data page at NIST
- NIOSH A Pocket Guide for Chemical Hazards at CDC
Source of the article : Wikipedia
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