Calcium oxide
Ionic crystal structure of calcium oxide
  Ca2+   O2-
Powder sample of white calcium oxide
Names
IUPAC name Calcium oxide
Other names
  • Lime
  • Quicklime
  • Burnt lime
  • Unslaked lime
  • Free lime (building)
  • Caustic lime
  • Pebble lime
  • Calcia
  • Oxide of calcium
Identifiers
CAS Number
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.013.763
EC Number
  • 215-138-9
E number E529 (acidity regulators, ...)
Gmelin Reference 485425
KEGG
PubChem CID
RTECS number
  • EW3100000
UNII
UN number 1910
CompTox Dashboard (EPA)
InChI
  • InChI=1S/Ca.OKey: ODINCKMPIJJUCX-UHFFFAOYSA-N
  • InChI=1/Ca.O/rCaO/c1-2Key: ODINCKMPIJJUCX-BFMVISLHAU
SMILES
  • O=[Ca]
Properties
Chemical formula CaO
Molar mass 56.0774 g/mol
Appearance White to pale yellow/brown powder
Odor Odorless
Density 3.34 g/cm3[1]
Melting point 2,613 °C (4,735 °F; 2,886 K)[1]
Boiling point 2,850 °C (5,160 °F; 3,120 K) (100 hPa)[2]
Solubility in water Reacts to form calcium hydroxide
Solubility in Methanol Insoluble (also in diethyl ether, octanol)
Acidity (pKa) 12.8
Magnetic susceptibility (χ) −15.0×10−6 cm3/mol
Structure
Crystal structure Cubic, cF8
Thermochemistry
Std molar
entropy (S⦵298) 		40 J·mol−1·K−1[3]
Std enthalpy of
formation (ΔfH⦵298) 		−635 kJ·mol−1[3]
Pharmacology
ATCvet code QP53AX18 (WHO)
Hazards
GHS labelling:
Pictograms
Signal word Danger
Hazard statements H302, H314, H315, H335
Precautionary statements P260, P264, P270, P271, P280, P301+P312, P301+P330+P331, P302+P352, P303+P361+P353, P304+P340, P305+P351+P338, P310, P312, P321, P330, P332+P313, P362, P363, P403+P233, P405, P501
NFPA 704 (fire diamond) 3 0 2W
Flash point Non-flammable[4]
Lethal dose or concentration (LD, LC):
LD50 (median dose) >2000 mg/kg oral, female rat [5]
NIOSH (US health exposure limits):
PEL (Permissible) TWA 5 mg/m3[4]
REL (Recommended) TWA 2 mg/m3[4]
IDLH (Immediate danger) 25 mg/m3[4]
Safety data sheet (SDS) ICSC 0409
Related compounds
Other anions
Other cations
  • Beryllium oxide
  • Magnesium oxide
  • Strontium oxide
  • Barium oxide
  • Radium oxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Calcium oxide (formula: CaO), commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic, alkaline, crystalline solid at room temperature. The broadly used term lime connotes calcium-containing inorganic compounds, in which carbonates, oxides, and hydroxides of calcium, silicon, magnesium, aluminium, and iron predominate. By contrast, quicklime specifically applies to the single compound calcium oxide. Calcium oxide that survives processing without reacting in building products, such as cement, is called free lime.[6]

Quicklime is relatively inexpensive. Both it and the chemical derivative calcium hydroxide (of which quicklime is the base anhydride) are important commodity chemicals.

Preparation

Calcium oxide is usually made by the thermal decomposition of materials, such as limestone or seashells, that contain calcium carbonate (CaCO3; mineral calcite) in a lime kiln. This is accomplished by heating the material to above 825 °C (1,517 °F),[7][8] a process called calcination or lime-burning, to liberate a molecule of carbon dioxide (CO2), leaving quicklime behind. This is also one of the few chemical reactions known in prehistoric times.[9]

CaCO3(s) → CaO(s) + CO2(g)

The quicklime is not stable and, when cooled, will spontaneously react with CO2 from the air until, after enough time, it will be completely converted back to calcium carbonate unless slaked with water to set as lime plaster or lime mortar.

Annual worldwide production of quicklime is around 283 million tonnes. China is by far the world's largest producer, with a total of around 170 million tonnes per year. The United States is the next largest, with around 20 million tonnes per year.[10]

Hydroxyapatite's free CaO content rises with increased calcination temperatures and longer times. It also pinpoints particular temperature cutoffs and durations that impact the production of CaO, offering information on how calcination parameters impact the composition of the material.

Uses

CaO (s) + H2O (l) ⇌ Ca(OH)2 (aq) (ΔHr = −63.7 kJ/mol of CaO)
As it hydrates, an exothermic reaction results and the solid puffs up. The hydrate can be reconverted to quicklime by removing the water by heating it to redness to reverse the hydration reaction. One litre of water combines with approximately 3.1 kilograms (6.8 lb) of quicklime to give calcium hydroxide plus 3.54 MJ of energy. This process can be used to provide a convenient portable source of heat, as for on-the-spot food warming in a self-heating can, cooking, and heating water without open flames. Several companies sell cooking kits using this heating method.[12]

Weapon

Quicklime is also thought to have been a component of Greek fire. Upon contact with water, quicklime would increase its temperature above 150 °C (302 °F) and ignite the fuel.[24]

David Hume, in his History of England, recounts that early in the reign of Henry III, the English Navy destroyed an invading French fleet by blinding the enemy fleet with quicklime.[25] Quicklime may have been used in medieval naval warfare – up to the use of "lime-mortars" to throw it at the enemy ships.[26]

Substitutes

Limestone is a substitute for lime in many applications, which include agriculture, fluxing, and sulfur removal. Limestone, which contains less reactive material, is slower to react and may have other disadvantages compared with lime, depending on the application; however, limestone is considerably less expensive than lime. Calcined gypsum is an alternative material in industrial plasters and mortars. Cement, cement kiln dust, fly ash, and lime kiln dust are potential substitutes for some construction uses of lime. Magnesium hydroxide is a substitute for lime in pH control, and magnesium oxide is a substitute for dolomitic lime as a flux in steelmaking.[27]

Safety

Because of vigorous reaction of quicklime with water, quicklime causes severe irritation when inhaled or placed in contact with moist skin or eyes. Inhalation may cause coughing, sneezing, and labored breathing. It may then evolve into burns with perforation of the nasal septum, abdominal pain, nausea and vomiting. Although quicklime is not considered a fire hazard, its reaction with water can release enough heat to ignite combustible materials.[28]

Mineral

Calcium oxide is also a separate mineral species (with the unit formula CaO), named 'Lime'.[29][30] It has an isometric crystal system, and can form a solid solution series with monteponite. The crystal is brittle, pyrometamorphic, and is unstable in moist air, quickly turning into portlandite (Ca(OH)2).[31][32]

References

  1. Haynes, William M., ed. (2011). CRC Handbook of Chemistry and Physics (92nd ed.). Boca Raton, Florida: CRC Press. p. 4.55. ISBN 1-4398-5511-0.
  2. Calciumoxid (Archived 2013-12-30 at the Wayback Machine). GESTIS database
  3. Zumdahl, Steven S. (2009). Chemical Principles 6th Ed. Houghton Mifflin Company. p. A21. ISBN 978-0-618-94690-7.
  4. NIOSH Pocket Guide to Chemical Hazards. "#0093". National Institute for Occupational Safety and Health (NIOSH).
  5. "Safety Data Sheet: Calcium Oxide". ThermoFisher Scientific. p. 5.
  6. "free lime". DictionaryOfConstruction.com. Archived from the original on 2017-12-09.
  7. Merck Index of Chemicals and Drugs, 9th edition monograph 1650
  8. Kumar, Gupta Sudhir; Ramakrishnan, Anushuya; Hung, Yung-Tse (2007), Wang, Lawrence K.; Hung, Yung-Tse; Shammas, Nazih K. (eds.), "Lime Calcination", Advanced Physicochemical Treatment Technologies, Handbook of Environmental Engineering, vol. 5, Totowa, NJ: Humana Press, pp. 611–633, doi:10.1007/978-1-59745-173-4_14, ISBN 978-1-58829-860-7{{citation}}: CS1 maint: work parameter with ISBN (link)
  9. "Lime throughout history | Lhoist - Minerals and lime producer". Lhoist.com.
  10. Miller, M. Michael (2007). "Lime". Minerals Yearbook (PDF). U.S. Geological Survey. p. 43.13. Archived from the original (PDF) on 2017-05-14.
  11. US patent 3955554, Collie, Robert L., "Solar heating system", issued May 11, 1976 
  12. Gretton, Lel. "Lime power for cooking - medieval pots to 21st century cans". Old & Interesting.
  13. "Compound Summary for CID 14778 - Calcium Oxide". PubChem.
  14. Gray, Theodore (September 2007). "Limelight in the Limelight". Popular Science: 84. Archived from the original on 2008-10-13.
  15. Tony Oates (2007), "Lime and Limestone", Ullmann's Encyclopedia of Industrial Chemistry (7th ed.), Wiley, pp. 1–32, doi:10.1002/14356007.a15_317, ISBN 978-3527306732
  16. Tel Aviv University (August 9, 2012). "Neolithic man: The first lumberjack?". phys.org.
  17. Karkanas, P.; Stratouli, G. (2011). "Neolithic Lime Plastered Floors in Drakaina Cave, Kephalonia Island, Western Greece: Evidence of the Significance of the Site". The Annual of the British School at Athens. 103: 27–41. doi:10.1017/S006824540000006X. S2CID 129562287.
  18. Connelly, Ashley Nicole (May 2012). Analysis and Interpretation of Neolithic Near Eastern Mortuary Rituals from a Community-Based Perspective (PDF) (Thesis). Texas: Baylor University. Archived from the original (PDF) on 2015-03-09.
  19. Walker, Thomas A (1888). The Severn Tunnel Its Construction and Difficulties. London: Richard Bentley and Son. p. 92.
  20. "Scientific and Industrial Notes". Manchester Times. Manchester, England: 8. 13 May 1882.
  21. US Patent 255042, issued 14 March 1882 
  22. Schotsmans, Eline M.J.; Denton, John; Dekeirsschieter, Jessica; Ivaneanu, Tatiana; Leentjes, Sarah; Janaway, Rob C.; Wilson, Andrew S. (April 2012). "Effects of hydrated lime and quicklime on the decay of buried human remains using pig cadavers as human body analogues". Forensic Science International. 217 (1–3): 50–59. doi:10.1016/j.forsciint.2011.09.025. hdl:2268/107339. PMID 22030481.
  23. "Riddle solved: Why was Roman concrete so durable?", MIT News, January 6, 2023
  24. Croddy, Eric (2002). Chemical and biological warfare: a comprehensive survey for the concerned citizen. Springer. p. 128. ISBN 0-387-95076-1.
  25. David Hume (1756). History of England. Vol. I.
  26. Sayers, W. (2006). "The Use of Quicklime in Medieval Naval Warfare". The Mariner's Mirror. 92 (3): 262–269. doi:10.1080/00253359.2006.10657001.
  27. Lime (PDF). U.S. Geological Survey, Mineral Commodity Summaries (Report). February 2019. p. 96. Archived from the original (PDF) on 2021-12-19.
  28. Mallinckrodt Baker Inc. - Strategic Services Division (December 8, 1996). "Hazards". ww25.hazard.com. Archived from the original on May 1, 2012.
  29. "List of Minerals". Ima-mineralogy.org. 21 March 2011.
  30. Fiquet, G.; Richet, P.; Montagnac, G. (Dec 1999). "High-temperature thermal expansion of lime, periclase, corundum and spinel". Physics and Chemistry of Minerals. 27 (2): 103–111. Bibcode:1999PCM....27..103F. doi:10.1007/s002690050246. S2CID 93706828.
  31. Tian, X.K.; Lin, S.C.; Yan, J.; Zhao, C.Y. (2022). "Sintering mechanism of calcium oxide/calcium carbonate during thermochemical heat storage process". Chemical Engineering Journal. 428 131229. Bibcode:2022ChEnJ.42831229T. doi:10.1016/j.cej.2021.131229.
  32. "Lime". mindat.org.
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