Magnesium oxide

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Magnesium oxide
Magnesium oxide.jpg
NaCl polyhedra.png
Identifiers
CAS number 1309-48-4 YesY
PubChem 14792
EC number 215-171-9
ChEMBL CHEMBL1200572 N
RTECS number OM3850000
ATC code A02AA02,A06AD02, A12CC10
Properties
Molecular formula MgO
Molar mass 40.3044 g/mol
Appearance White powder
Odor Odorless
Density 3.58 g/cm3
Melting point 2,852 °C (5,166 °F; 3,125 K)
Boiling point 3,600 °C (6,510 °F; 3,870 K)
Solubility in water 0.00062 g/100 mL (0 °C)
0.0086 g/100 mL (30 °C)
Solubility Soluble in acid, ammonia
insoluble in alcohol
Band gap 7.8 eV[1]
Thermal conductivity 45–60 W·m−1·K−1[2]
Refractive index (nD) 1.7355
Dipole moment 6.2 ± 0.6 D
Structure
Crystal structure Halite (cubic), cF8
Space group Fm3m, No. 225
Lattice constant a = 4.212Å
Coordination
geometry
Octahedral (Mg2+); octahedral (O2–)
Thermochemistry
Specific
heat capacity
C
37.8 J/mol K
Std molar
entropy
So298
26.9 J·mol−1·K−1[3]
Std enthalpy of
formation
ΔfHo298
−601.8 kJ·mol−1[3]
Gibbs free energy ΔG -596.6 kJ/mol
Hazards
MSDS ICSC 0504
EU Index Not listed
R-phrases R36, R37, R38
Main hazards Metal fume fever, Irritant
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 1: Exposure would cause irritation but only minor residual injury. E.g., turpentine Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
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
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 N (verify) (what is: YesY/N?)
Infobox references

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.

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 normally "magnesium oxide" means compound MgO, magnesium peroxide MgO2 is also known as a metastable compound. According to evolutionary crystal structure prediction,[4] MgO2 is thermodynamically stable at pressures above 116 GPa, and a totally new semiconducting suboxide Mg3O2 is thermodynamically stable above 500 GPa.

Production[edit]

Magnesium oxide is produced by the calcination of magnesium carbonate or magnesium hydroxide or by the treatment of magnesium chloride with lime followed by heat. Calcining at different temperatures produces magnesium oxide of with different reactivity. High temperatures 1500 - 2000 °C 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, lower temperature, (700-1000°C) calcining produces light-burned magnesia, a reactive form, which is sometimes called caustic magnesia.[5]

Applications[edit]

A refractory material is one that is physically and chemically stable at high temperatures. "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."[6]

Cement[edit]

MgO is one of the raw materials for making Portland cement in dry process plants. If too much MgO is added, the cement may become expansive.[clarification needed] Production of MgO-based cement using serpentinite and waste Carbon dioxide (CO
2
) (as opposed to conventional CaO-based cement using fossil fuels) may reduce anthropogenic emissions of CO
2
.[7]

Desiccant[edit]

MgO is a relatively poor desiccant, but because it neutralizes sulfur oxide acids created by oxidation of Kraft-processed papers, it is used by many libraries for preserving books.[8]

Medical[edit]

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.[9] In quantities sufficient to obtain a laxative effect, side effects of long-term use include enteroliths resulting in bowel obstruction.[10]

Other[edit]

  • 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 extensively in heating as a component of 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.
Unpolished MgO crystal
  • 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.[13]
  • 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.[15]
  • 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[16] versus 40–60% with alluminium oxide.[17] The value of tunnel magnetoresistance is also significantly higher for MgO (600% at room temperature and 1100% at 4.2 K[18]) than Al2O3 (ca. 70% at room temperature[19]). MgO is thermally stable up to about 700 K, vs. 600 K for Al2O3.

Precautions[edit]

Magnesium oxide is easily made by burning magnesium ribbon, which produces a very bright white light, and a powdery ash. 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.[20] When burned in open air, the magnesium gets hot enough to produce noticeable amounts of yellow magnesium nitride. Burning in a covered crucible, letting in just enough air to support combustion, will reduce the burning temperature, minimizing the production of the nitride.

See also[edit]

References[edit]

  1. ^ Taurian, O.E.; Springborg, M.; Christensen, N.E. (1985). "Self-consistent electronic structures of MgO and SrO". Solid State Communications 55 (4): 351–5. Bibcode:1985SSCom..55..351T. doi:10.1016/0038-1098(85)90622-2. 
  2. ^ Application of magnesium compounds to insulating heat-conductive fillers. konoshima.co.jp
  3. ^ a b Zumdahl, Steven S. (2009). Chemical Principles (6th ed.). Houghton Mifflin Company. p. A22. ISBN 0-618-94690-X. 
  4. ^ Zhu, Qiang; Oganov A.R.; Lyakhov A.O. (2013). "Novel stable compounds in the Mg-O system under high pressure.". Phys. Chem. Chem. Phys. 15: 7696–7700. doi:10.1039/c3cp50678a. 
  5. ^ R C Ropp Elsevier. Encyclopedia of the alkaline earth compounds. Elsevier. p. 109. ISBN 9780444595508. 
  6. ^ Mark A. Shand (2006). The chemistry and technology of magnesia. John Wiley and Sons. ISBN 978-0-471-65603-6. Retrieved 10 September 2011. 
  7. ^ McKenna, Phil (25 September 2010 (updated 1 October 2010)). "Emission control: Turning carbon trash into treasure". New Scientist 2779: 48–51. doi:10.1016/s0262-4079(10)62354-8. Retrieved 4 Oct 2010.  Check date values in: |date= (help)
  8. ^ Ferro, Shaunacy (6 January 2012). "FYI: Why Do Libraries Have That Smell?". Popular Science. Retrieved 19 Jan 2012. 
  9. ^ Magnesium Oxide. MedlinePlus. Last reviewed 02/01/2009
  10. ^ Tatekawa Y, Nakatani K, Ishii H et al. (1996). "Small bowel obstruction caused by a medication bezoar: report of a case". Surgery today 26 (1): 68–70. doi:10.1007/BF00311997. PMID 8680127. 
  11. ^ Tellex, Peter A.; Waldron, Jack R. (1955). "Reflectance of Magnesium Oxide". JOSA 45 (1): 19. doi:10.1364/JOSA.45.000019. 
  12. ^ Tan, C.Y.; Yaghoubi, A.; Ramesh, S.; Adzila, S.; Purbolaksono, J.; Hassan, M.A.; Kutty, M.G. (2013). "Sintering and mechanical properties of MgO-doped nanocrystalline hydroxyapatite". Ceramics International. doi:10.1016/j.ceramint.2013.04.098. 
  13. ^ Stephens, Robert E. and Malitson, Irving H. (1952). "Index of Refraction of Magnesium Oxide". Journal of Research of the National Bureau of Standards 49 (4): 249–252. doi:10.6028/jres.049.025. 
  14. ^ wipp.energy.gov Step-By-Step Guide for Waste Handling at WIPP. Waste Isolation Pilot Plant. wipp.energy.gov
  15. ^ "Mass Deacidification: Saving the Written Word". Library of Congress. Retrieved 26 September 2011. 
  16. ^ Parkin, S. S. P.; Kaiser, C.; Panchula, A.; Rice, P. M.; Hughes, B.; Samant, M.; Yang, S. H. (2004). "Giant tunnelling magnetoresistance at room temperature with MgO (100) tunnel barriers". Nature Materials 3 (12): 862–867. Bibcode:2004NatMa...3..862P. doi:10.1038/nmat1256. PMID 15516928.  edit
  17. ^ 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. Bibcode:2000ApPhL..77..720M. doi:10.1063/1.127097.  edit
  18. ^ 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. Bibcode:2008ApPhL..93h2508I. doi:10.1063/1.2976435.  edit
  19. ^ Wang, D.; Nordman, C.; Daughton, J. M.; Qian, Z.; Fink, J.; Wang, D.; Nordman, C.; Daughton, J. M.; Qian, Z.; Fink, J. (2004). "70% TMR at Room Temperature for SDT Sandwich Junctions with CoFeB as Free and Reference Layers". IEEE Transactions on Magnetics 40 (4): 2269. doi:10.1109/TMAG.2004.830219.  edit
  20. ^ Magnesium Oxide. National Pollutant Inventory, Government of Australia.

External links[edit]