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Magnesium oxide
IUPAC name Magnesium oxide
other names Magnesia Periclase
Identifiers
CAS number	1309-48-4 Y
PubChem	14792
RTECS number	OM3850000
ATC code	A02AA02
Properties
Molecular formula	MgO
Molar mass	40.3044 g/mol
Appearance	White powder
Odor	Odorless
Density	3.58 g/cm3
Melting point	2852 °C, 3125 K, 5166 °F
Boiling point	3600 °C, 3873 K, 6512 °F
Solubility in water	0.086 g/L[2]
Solubility	Soluble in acid, ammonia insoluble in alcohol
Band gap	7.8 eV [1]
Refractive index (nD)	1.736
Structure
Crystal structure	Halite (cubic), cF8
Space group	Fm3m, No. 225
Coordination geometry	Octahedral (Mg2+); octahedral (O2–)
Hazards
MSDS	ICSC 0504
EU Index	Not listed
Main hazards	Metal fume fever, irritant
NFPA 704	0 1 0
Flash point	Non-flammable
Related compounds
Other anions	Magnesium sulfide
Other cations	Beryllium oxide Calcium oxide Strontium oxide Barium oxide
Related compounds	Magnesium hydroxide Magnesium nitride
Y (what is this?)  (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Magnesium oxide, or magnesia, is a white solid mineral that occurs naturally as periclase and is a source of magnesium (see also oxide). It has an empirical formula of MgO. It is formed by an ionic bond between one magnesium and one oxygen atom. Magnesium oxide is hygroscopic in nature and care must be taken to protect it from moisture. Magnesium hydroxide forms in the presence of water (MgO + H₂O → Mg(OH)₂), but it can be reversed by heating it to separate moisture.

Applications

Desiccant

MgO is an efficient moisture absorbent used by many libraries for preserving books. It is also one of the raw materials for making cement in dry process plants; specifically Portland cement. If too much of MgO is added, the cement may become expansive.

Medical

In medicine, magnesium oxide is used for relief of heartburn and sore 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.^[3] In quantities sufficient to obtain a laxative effect, side effects of long-term use include enteroliths resulting in bowel obstruction.^[4]

Other

• MgO is used as an insulator in industrial cables, as a basic refractory material for crucibles and as a principal fireproofing ingredient in construction materials. As a construction material, magnesium oxide wallboards have several attractive characteristics: fire resistance, moisture resistance, mold and mildew resistance, and strength.

• It is used as a reference white color in colorimetry, owing to its good diffusing and reflectivity properties.^[5] It may be smoked onto the surface of an opaque material to form an integrating sphere.

• It is used extensively in electrical heating as a component of "CalRod"-styled 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 long since obsolete. Crystalline pure MgO is available commercially and has small use in infrared optics.^[6]

• It is packed around transuranic waste at the Waste Isolation Pilot Plant, to control the solubility of radionuclides.^[7]

Precautions

Magnesium oxide is easily made by burning magnesium ribbon which oxidizes in a bright white light, resulting in a powder. However, the bright flame is very hard to extinguish and it emits a harmful intensity of UV light. Inhalation of magnesium oxide fumes can cause metal fume fever.^[8]

Gallery

Unpolished MgO crystal

See also

• Calcium oxide
• Barium oxide
• Magnesium sulfide

References

External links

• Data page at UCL
• Ceramic data page at NIST