The magnesium oxide it is a white crystalline inorganic solid also known as magnesia. Its chemical formula is MgO and it is formed by the oxidation of the metal magnesium by oxygen.
It is often found as a natural mineral called periclase. However, periclase is not a major source of MgO. In nature it is commonly found as clumps of crystals in marble.
It does not form rocks or crystal deposits because in contact with the water vapor in the atmosphere it converts into magnesium hydroxide (Mg (OH)two).
At an industrial level, it can be obtained in several ways: calcining magnesium carbonate (magnesite), calcining magnesium hydroxide, starting from dolomitic limestone, using seawater and pyrolysis of magnesium chloride, among other methods..
The production of magnesia from magnesite started just over 100 years ago in Austria. Since then, magnesia has several technical applications due to its high melting point, chemical resistance, high thermal conductivity, low electrical conductivity, and its biological activity..
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The crystal structure of MgO is cubic, face-centered, similar to the crystal lattice of sodium chloride (NaCl)..
Magnesia forms hexaoctahedral cubic crystals, which can be colorless, green or brown.
The mineral periclase is a small octahedron, less commonly being a cube-octahedron or dodecahedron..
- Magnesia.
- Periclase.
- Oxomagnesium.
It is solid, crystalline and white. Although the presence of iron impurities gives it a greenish or brown color depending on the degree of oxidation of the iron.
5.5-6.
40.304 g / mol.
2827 ºC.
3.581 g / cm3
Practically insoluble in water:
0.00062 g per 100 mL at 20 ºC.
0.0086 g per 100 mL at 30 ºC.
Insoluble in ethanol.
In saturated aqueous solution: 10.3.
Transparent. Color: colorless, greyish white, brownish yellow, colorless in transmitted light.
1.7355 at 589 nm.
1.7283 at 750 nm.
- It has high thermal conductivity and high electrical resistivity.
- It is hygroscopic, that is, it easily absorbs water from the atmosphere. In aqueous medium it combines with water to form magnesium hydroxide.
- It is stable in an oxidizing atmosphere up to 2300 ºC and up to 1700 ºC in a reducing atmosphere.
- It is compatible with most chemical compounds, except strong acids and strong oxidants, among others.
- After ignition at high temperatures, magnesium oxide is relatively inert.
- It is not toxic. However, precautions should be taken when handling it in powder form when it has a small particle size..
- Its crystals have a high reflective power both in the visible spectrum and in the near ultraviolet.
There are several grades of MgO that are supplied commercially:
It is a highly reactive form of magnesium oxide produced by calcining or burning raw magnesite (MgCO3) or magnesium hydroxide (Mg (OH)two) at relatively low temperatures, but above the decomposition temperature of these materials, between 700 and 1000ºC.
Also called calcined caustic magnesia, calcined magnesium oxide, reactive magnesium oxide, lightly burned magnesia. light-burned), among other names.
Caustic magnesia can be burned at a higher temperature to give sintered magnesia.
It is produced when magnesite is calcined at temperatures of 1000 to 1500 ºC. Its reactivity has been reduced compared to caustic magnesia.
When magnesite is calcined at temperatures between 1500 and 2000 ºC, magnesia "burned to death" is obtained (translation from English dead-burned), also called refractory magnesia or fused magnesia.
Molten magnesia is also obtained by melting caustic magnesia in an electric arc. Due to these treatments its reactivity has been almost totally eliminated..
This type of magnesia is generally shaped by pressure and temperature, without reaching the melting temperature. With this, parts of great hardness are produced, called sintered magnesia. It is essentially stable against humidity and atmospheric carbon dioxide.
MgO is used in the production of metallic magnesium.
Due to its high reactivity, its industrial applications are very varied.
It is used as a raw material to make cement and is used in the construction industry, for example, as a binder. In this case, it is mixed with concentrated solutions of magnesium salts and a small amount of sodium phosphate..
An extremely hard material is thus obtained. Although it is not a true cement, as it is not stable in water, it can be used as a mastic or protective coating.
Caustic magnesia is also used in lightweight building boards for thermal and acoustic insulation. They are made by adding magnesium sulfate as a binder and mineral wool. Highly non-flammable sheets result.
It is a weak base, so it serves as an acid neutralizer and is used in flue gas scrubbing, as an additive for lubricants and for fuels..
It serves as a filler in the plastic and rubber industry, as it allows the viscosity and rigidity of these materials to be adjusted..
It is used in the pulp and paper industry as it participates in bisulfite digestion. Also as a moisture absorber in libraries or for the preparation of cosmetics. In addition, in the pharmaceutical industry it is highly valued as an antacid, indigestion reliever and mild laxative..
Due to its narrow range of reactivity, it is used in applications where slow degradation is required. For example, in animal feed supplements. This is because, under some conditions, cattle can suffer from magnesium deficiency if fed only forage..
On the other hand, it is known that magnesium (Mg) is a constituent element of chlorophyll. For this reason, it is considered an essential nutrient of plants and used as a fertilizer. The way to add magnesium to plants is as magnesia.
This type of MgO can be used in a variety of applications: ceramics, wastewater treatment (as a cation adsorbent in metal removal), leather tanning and raw material for molten magnesia..
MgO has the highest melting point among the moderate cost oxides and is therefore a raw material for refractory bricks and other refractory ceramics. It is the only material, after zirconium oxide (ZrOtwo), which can withstand prolonged heating above 2000 ºC.
This refractory grade of MgO is used in the steel industry to make protective casings and replaceable linings for equipment handling molten steel, such as very high power furnaces..
Sintered magnesia blocks have a high heat storage capacity and high thermal conductivity (they conduct heat very well).
The heat generated by a heating element is transferred to the magnesia block and its temperature increases. For this reason they are used in hot storage devices.
It is used as an insulating material in the electrical heating industry related to household appliances. For example, for tubular heating elements for kitchen ovens, washing machines, coffee machines, electric irons or radiators, among others..
The high reflective power of MgO crystals in the visible and near UV spectrum has led to their use as a reflector in optical instruments and as single crystals in optical windows and lenses. White is also used as a standard.
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