GF36467714
powder, max. particle size 1000
micron, weight 50 g
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 separate moisture.
Detailed description
Magnesium oxide was historically known as magnesia alba (literally, the white mineral from
magnesia – other sources give magnesia alba as MgCO3), to
differentiate it from magnesia negra, a black mineral
containing what is now known as manganese.
While "magnesium oxide" normally refers to
MgO, magnesium peroxide MgO2 is also known as a compound. According
to evolutionary crystal structure prediction,[8] MgO2 is thermodynamically stable at
pressures above 116 GPa (gigapascals), and a totally new 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.
Applications
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. "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."[12] MgO is used as a
basic refractory material for crucibles.
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.
Niche uses
MgO is one of the components in Portland cement in dry process plants.
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 lead and 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
(acidic) pH, in order to drive the pH into the 8–10 range where most metals are
at their lowest solubilities. 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.
Medical
In medicine, magnesium oxide is used for relief of
heartburn and sour stomach, 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.[13] In quantities
sufficient to obtain a laxative effect, side effects of long-term use include enteroliths resulting in bowel obstruction.[14]
Other
·
It is used as a
reference white color in colorimetry, owing to its good diffusing and reflectivity properties.[15] It may be smoked onto
the surface of an opaque material to form an integrating sphere.
·
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.
·
It is also used as an
insulator in heat-resistant
electrical cable.
·
MgO doping has been shown to effectively inhibit grain growth in ceramics and improve their fracture toughness by transforming the mechanism of crack growth at nanoscale.[16]
·
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.[17]
·
MgO is packed around transuranic waste at the Waste Isolation Pilot
Plant, to control the solubility of
radionuclides.[18]
·
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.[21]
·
MgO is also used as a
protective coating in plasma displays.
·
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[22]versus 40–60 % with
alluminium oxide.[23] The value of tunnel magnetoresistance is also significantly higher for MgO (600% at room temperature
and 1,100 % at 4.2 K[24]) than Al2O3 (ca. 70% at room temperature[25]). MgO is thermally
stable up to about 700 K, vs. 600 K for Al2O3.
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