Calcium oxide

{{Short description|Chemical compound of calcium}} {{Redirect-distinguish|Quicklime|Quickline}} {{Chembox | verifiedrevid = 1353457675 | Name = Calcium oxide | ImageFile = Calcium-oxide-3D-vdW.png | ImageClass = bg-transparent | ImageSize = | ImageName = Calcium oxide | ImageFile1 = Calcium oxide powder.JPG | ImageCaption = Ionic crystal structure of calcium oxide {{color box|#ffffff}} Ca2+ {{color box|#ff0000}} O2- | ImageCaption1 = Powder sample of white calcium oxide | IUPACName = Calcium oxide | OtherNames = {{Unbulleted list|Lime|Quicklime|Burnt lime|Unslaked lime|Free lime ''(building)''|Caustic lime|Pebble lime|Calcia|Oxide of calcium}} | SystematicName = | Section1 = {{Chembox Identifiers | CASNo = 1305-78-8 | CASNo_Ref = {{cascite|correct|CAS}} | ChEBI = 31344 | ChEBI_Ref = {{ebicite|correct|EBI}} | ChEMBL = 5314372 | ChEMBL_Ref = {{ebicite|correct|EBI}} | ChemSpiderID = 14095 | ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}} | EC_number = 215-138-9 | Gmelin = 485425 | KEGG = C13140 | KEGG_Ref = {{keggcite|correct|kegg}} | PubChem = 14778 | RTECS = EW3100000 | UNII = C7X2M0VVNH | UNII_Ref = {{fdacite|correct|FDA}} | UNNumber = 1910 | StdInChI = 1S/Ca.O | StdInChI_Ref = {{stdinchicite|correct|chemspider}} | StdInChIKey = ODINCKMPIJJUCX-UHFFFAOYSA-N | StdInChIKey_Ref = {{stdinchicite|correct|chemspider}} | SMILES = O=[Ca] }} | Section2 = {{Chembox Properties | Formula = CaO | MolarMass = 56.0774{{nbsp}}g/mol | Appearance = White to pale yellow/brown powder | Odor = Odorless | Density = 3.34{{nbsp}}g/cm3<ref name=crc/> | Solubility = Reacts to form calcium hydroxide | MeltingPtC = 2613 | MeltingPt_ref = <ref name=crc>{{RubberBible92nd|page=4.55}}</ref> | BoilingPtC = 2850 | BoilingPt_notes = (100{{nbsp}}hPa)<ref name=r1>[http://gestis.itrust.de/nxt/gateway.dll/gestis_de/001200.xml?f=templates$fn=default.htm$3.0 Calciumoxid] ({{webarchive|url=https://web.archive.org/web/20131230232501/http://gestis.itrust.de/nxt/gateway.dll/gestis_de/001200.xml?f=templates%24fn%3Ddefault.htm%243.0 |date=2013-12-30 }}). GESTIS database</ref> | pKa = 12.8 | Solvent2 = methanol | Solubility2 = Insoluble | Solvent3 = diethyl ether | Solubility3 = Insoluble | Solvent4 = octanol | Solubility4 = Insoluble | MagSus = −15.0×10−6{{nbsp}}cm3/mol }} | Section3 = {{Chembox Structure | CrystalStruct = Cubic, cF8 }} | Section4 = | Section5 = {{Chembox Thermochemistry | DeltaHf = −635 kJ·mol−1<ref name=b1>{{cite book| author = Zumdahl, Steven S.|title =Chemical Principles 6th Ed.| publisher = Houghton Mifflin Company| year = 2009| isbn = 978-0-618-94690-7|page=A21}}</ref> | Entropy = 40 J·mol−1·K−1<ref name=b1 /> }} | Section6 = {{Chembox Pharmacology | ATCvet = yes | ATCCode_prefix = P53 | ATCCode_suffix = AX18 }} | Section7 = {{Chembox Hazards | GHSPictograms = {{GHS05}}{{GHS07}} | GHSSignalWord = Danger | HPhrases = {{H-phrases|302|314|315|335}} | PPhrases = {{P-phrases|260|264|270|271|280|301+312|301+330+331|302+352|303+361+353|304+340|305+351+338|310|312|321|330|332+313|362|363|403+233|405|501}} | ExternalSDS = [https://www.inchem.org/documents/icsc/icsc/eics0409.htm ICSC 0409] | NFPA-H = 3 | NFPA-F = 0 | NFPA-R = 2 | NFPA-S = w | FlashPt = Non-flammable | FlashPt_ref = <ref name=PGCH/> | PEL = TWA 5{{nbsp}}mg/m3<ref name=PGCH>{{PGCH|0093}}</ref> | REL = TWA 2{{nbsp}}mg/m3<ref name=PGCH/> | IDLH = 25{{nbsp}}mg/m3<ref name=PGCH/> | LD50 = >2000 mg/kg oral, female rat <ref>{{cite web |url=https://www.fishersci.com/store/msds?partNumber=AC196910025&countryCode=US&language=en |title=Safety Data Sheet: Calcium Oxide |publisher=ThermoFisher Scientific |access-date=12 September 2025 |page=5}}</ref> }} | Section8 = {{Chembox Related | OtherAnions = {{Plainlist| * Calcium sulfide * Calcium hydroxide * Calcium selenide * Calcium telluride }} | OtherCations = {{Plainlist| * Beryllium oxide * Magnesium oxide * Strontium oxide * Barium oxide * Radium oxide }} }} }}

'''Calcium oxide''' (formula: Ca O), 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'''.<ref>{{cite web |url=http://www.dictionaryofconstruction.com/definition/free-lime.html |title=free lime |publisher= DictionaryOfConstruction.com |archive-url=https://web.archive.org/web/20171209222951/http://www.dictionaryofconstruction.com/definition/free-lime.html |archive-date=2017-12-09 |url-status=usurped}}</ref>

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 ({{chem2|CaCO3}}; mineral calcite) in a lime kiln. This is accomplished by heating the material to above {{convert|825|C|F}},<ref name="merck">Merck Index of Chemicals and Drugs, 9th edition monograph 1650</ref><ref>{{Citation |last1=Kumar |first1=Gupta Sudhir |last2=Ramakrishnan |first2=Anushuya |last3=Hung |first3=Yung-Tse |editor-last=Wang |editor-first=Lawrence K. |editor2-last=Hung |editor2-first=Yung-Tse |editor3-last=Shammas |editor3-first=Nazih K. |title=Advanced Physicochemical Treatment Technologies |chapter=Lime Calcination |year=2007 |url=http://link.springer.com/10.1007/978-1-59745-173-4_14 |volume=5 |pages=611–633 |place=Totowa, NJ |publisher=Humana Press |language=en |doi=10.1007/978-1-59745-173-4_14 |isbn=978-1-58829-860-7 |access-date=2022-07-26 |series=Handbook of Environmental Engineering |url-access=subscription}}</ref> 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.<ref>{{Cite web|url=https://www.lhoist.com/lime-throughout-history|title=Lime throughout history {{pipe}} Lhoist - Minerals and lime producer|website=Lhoist.com|access-date=10 March 2022}}</ref> : {{chem2|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.<ref>{{cite book|first=M. Michael|last=Miller|chapter=Lime|title=Minerals Yearbook|page=43.13|publisher=U.S. Geological Survey|year=2007|url=https://minerals.usgs.gov/minerals/pubs/commodity/lime/myb1-2007-lime.pdf|archive-date=2017-05-14|access-date=2009-03-31|archive-url=https://web.archive.org/web/20170514092700/https://minerals.usgs.gov/minerals/pubs/commodity/lime/myb1-2007-lime.pdf|url-status=dead}}</ref>

==Uses== [[File:09. Гасење вар како силно егзотермен процес.webm|thumb|left|280px|A demonstration of slaking of quicklime as a strongly exothermic reaction. Drops of water are added to pieces of quicklime. After a while, a pronounced exothermic reaction occurs ("slaking of lime"). The temperature can reach up to some {{convert|300|C|F}}.]] * Heat: Quicklime releases thermal energy by the formation of the hydrate, calcium hydroxide, by the following equation:<ref name="patent">{{cite patent |inventor-last=Collie|inventor-first= Robert L. |title=Solar heating system |country=US |status=patent|number=3955554|gdate= May 11, 1976}}</ref> ::{{chem2|CaO (s) + H2O (l) <-> Ca(OH)2}} (aq) (ΔHr = −63.7{{nbsp}}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 {{convert|3.1|kg}} 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.<ref>{{cite web|last1=Gretton|first1=Lel|title=Lime power for cooking - medieval pots to 21st century cans|url=http://www.oldandinteresting.com/fireless-cooking-with-quicklime.aspx|website=Old & Interesting|access-date=13 February 2018}}</ref> * It is a food additive used as an acidity regulator, a flour treatment agent and a leavener.<ref>{{cite web |title=Compound Summary for CID 14778 - Calcium Oxide |url=https://pubchem.ncbi.nlm.nih.gov/compound/Lime |publisher=PubChem}}</ref> It has E number '''E529'''. * Light: When quicklime is heated to {{convert|2400|C|F}}, it emits an intense glow. This form of illumination is known as a limelight, and was used broadly in theatrical productions before the invention of electric lighting.<ref>{{cite journal |last=Gray |first=Theodore |date=September 2007 |title=Limelight in the Limelight |journal=Popular Science |page=84 |url=http://www.popsci.com/node/9652 |access-date=2009-03-31 |archive-date=2008-10-13 |archive-url=https://web.archive.org/web/20081013235058/http://www.popsci.com/node/9652 |url-status=dead }}</ref> * Cement: Calcium oxide is a key ingredient for the process of making cement. * As a cheap and widely available alkali.<ref name="a">{{citation | author=Tony Oates | contribution=Lime and Limestone | title=Ullmann's Encyclopedia of Industrial Chemistry | edition=7th | publisher=Wiley | year=2007 | pages=1–32 | doi=10.1002/14356007.a15_317| isbn=978-3527306732 }}</ref> * Petroleum industry: Water detection pastes contain a mix of calcium oxide and phenolphthalein. Should this paste come into contact with water in a fuel storage tank, the CaO reacts with the water to form calcium hydroxide. Calcium hydroxide has a high enough pH to turn the phenolphthalein a vivid purplish-pink color, thus indicating the presence of water. * Chemical pulping: Calcium oxide is used to make calcium hydroxide, which is used to regenerate sodium hydroxide from sodium carbonate in the chemical recovery at kraft pulp mills. * Plaster: There is archeological evidence that Pre-Pottery Neolithic B humans used limestone-based plaster for flooring and other uses.<ref>{{Cite news|author=Tel Aviv University|title=Neolithic man: The first lumberjack?|url=https://phys.org/news/2012-08-neolithic-lumberjack.html|date=August 9, 2012 |access-date=2023-02-02|website=phys.org|language=en}}</ref><ref>{{Cite journal | doi = 10.1017/S006824540000006X| title = Neolithic Lime Plastered Floors in Drakaina Cave, Kephalonia Island, Western Greece: Evidence of the Significance of the Site| journal = The Annual of the British School at Athens| volume = 103| pages = 27–41| year = 2011| last1 = Karkanas | first1 = P. | last2 = Stratouli | first2 = G. | s2cid = 129562287}}</ref><ref>{{cite thesis |last=Connelly|first= Ashley Nicole |date=May 2012 |url=https://beardocs.baylor.edu/xmlui/bitstream/handle/2104/8320/Ashley_Connelly_HonorsThesis.pdf?sequence=1 |title=Analysis and Interpretation of Neolithic Near Eastern Mortuary Rituals from a Community-Based Perspective |archive-url=https://web.archive.org/web/20150309143945/https://beardocs.baylor.edu/xmlui/bitstream/handle/2104/8320/Ashley_Connelly_HonorsThesis.pdf?sequence=1 |archive-date=2015-03-09 |publisher=Baylor University|location= Texas}}</ref> Such Lime-ash floor remained in use until the late nineteenth century. * Chemical or power production: Solid sprays or slurries of calcium oxide can be used to remove sulfur dioxide from exhaust streams in a process called flue-gas desulfurization. * Carbon capture and storage: Calcium oxide can be used to capture carbon dioxide from flue gases in a process called calcium looping. * Mining: ''Compressed lime cartridges'' exploit the exothermic properties of quicklime to break rock. A shot hole is drilled into the rock in the usual way and a sealed cartridge of quicklime is placed within and tamped. A quantity of water is then injected into the cartridge and the resulting release of steam, together with the greater volume of the residual hydrated solid, breaks the rock apart. The method does not work if the rock is particularly hard.<ref>{{cite book|last1=Walker|first1=Thomas A|author-link=Thomas A. Walker|title=The Severn Tunnel Its Construction and Difficulties|url=https://archive.org/details/severntunnelits01walkgoog|date=1888|publisher=Richard Bentley and Son|location=London|page=[https://archive.org/details/severntunnelits01walkgoog/page/n160 92]}}</ref><ref>{{cite journal|title=Scientific and Industrial Notes|journal=Manchester Times|date=13 May 1882|page=8|location=Manchester, England}}</ref><ref>{{cite patent |country=US |status=Patent |number=255042|gdate= 14 March 1882}}</ref> * Disposal of corpses: Historically, it was mistakenly thought that quicklime was efficacious in accelerating the decomposition of corpses. The application of quicklime can, in fact, promote preservation. Quicklime can aid in eradicating the stench of decomposition, which may have led people to the erroneous conclusion.<ref>{{cite journal |last1=Schotsmans |first1=Eline M.J. |last2=Denton |first2=John |last3=Dekeirsschieter |first3=Jessica |last4=Ivaneanu |first4=Tatiana |last5=Leentjes |first5=Sarah |last6=Janaway |first6=Rob C. |last7=Wilson |first7=Andrew S. |title=Effects of hydrated lime and quicklime on the decay of buried human remains using pig cadavers as human body analogues |url=https://www.researchgate.net/publication/51748334 |journal=Forensic Science International |date=April 2012 |volume=217 |issue=1–3 |pages=50–59 |doi=10.1016/j.forsciint.2011.09.025|pmid=22030481 |hdl=2268/107339 |hdl-access=free }}</ref> * It has been determined that the durability of ancient Roman concrete is attributed in part to the use of quicklime as an ingredient. Combined with hot mixing, the quicklime creates macro-sized lime clasts with a characteristically brittle nano-particle architecture. As cracks form in the concrete, they preferentially pass through the structurally weaker lime clasts, fracturing them. When water enters these cracks it creates a calcium-saturated solution which can recrystallize as calcium carbonate, quickly filling the crack.<ref>{{citation|url=https://news.mit.edu/2023/roman-concrete-durability-lime-casts-0106 |journal=MIT News | date=January 6, 2023|title=Riddle solved: Why was Roman concrete so durable? }}</ref> * The thermochemical heat storage mechanism is greatly impacted by the sintering of CaO and {{chem2|CaCO3}}. It demonstrates that the storage materials become less reactive and denser at increasing temperatures. It also pinpoints particular sintering processes and variables influencing the efficiency of these materials in heat storage.

===Weapon=== Quicklime is also thought to have been a component of Greek fire. Upon contact with water, quicklime would increase its temperature above {{convert|150|C|||}} and ignite the fuel.<ref>{{cite book|url=https://books.google.com/books?id=MQMGhInCvlgC&pg=PA128|page=128|title=Chemical and biological warfare: a comprehensive survey for the concerned citizen|author=Croddy, Eric |publisher=Springer|year=2002|isbn=0-387-95076-1}}</ref>

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.<ref>{{cite book|url=http://www.gutenberg.org/files/19212/19212-h/19212-h.htm#2H_4_0002|title=History of England| volume=I|author=David Hume|author-link=David Hume|year=1756}}</ref> Quicklime may have been used in medieval naval warfare – up to the use of "lime-mortars" to throw it at the enemy ships.<ref>{{cite journal |last=Sayers|first= W. |year=2006 |title=The Use of Quicklime in Medieval Naval Warfare |journal=The Mariner's Mirror |volume= 92 |issue= 3 |pages= 262–269 |doi= 10.1080/00253359.2006.10657001 }}</ref>

===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.<ref>{{cite report|url=https://prd-wret.s3-us-west-2.amazonaws.com/assets/palladium/production/atoms/files/mcs-2019-lime.pdf|title=Lime|page=96|website=U.S. Geological Survey, Mineral Commodity Summaries|date= February 2019|access-date=2022-03-10|archive-date=2021-12-19|archive-url=https://web.archive.org/web/20211219004903/https://prd-wret.s3-us-west-2.amazonaws.com/assets/palladium/production/atoms/files/mcs-2019-lime.pdf|url-status=dead}}</ref>

== 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.<ref>{{Cite web|url=http://ww25.hazard.com/msds/mf/baker/baker/files/c0462.htm?subid1=20230203-0103-092e-9982-d576d3e248aa |url-status=usurped |archive-url=https://web.archive.org/web/20120501110853/http://hazard.com/msds/mf/baker/baker/files/c0462.htm |archive-date=May 1, 2012 |access-date=2023-02-02|website=ww25.hazard.com|title=Hazards |date=December 8, 1996 |author=Mallinckrodt Baker Inc. - Strategic Services Division }}</ref>{{better source needed|date=June 2023}}

==Mineral== Calcium oxide is also a separate mineral species (with the unit formula CaO), named 'Lime'.<ref>{{cite web|url=http://cnmnc.units.it/|title=List of Minerals|website=Ima-mineralogy.org|date=21 March 2011}}</ref><ref>{{cite journal |last1=Fiquet |first1=G. |last2=Richet |first2=P. |last3=Montagnac |first3=G. |title=High-temperature thermal expansion of lime, periclase, corundum and spinel |journal=Physics and Chemistry of Minerals |date=Dec 1999 |volume=27 |issue=2 |pages=103–111 |doi=10.1007/s002690050246 |bibcode=1999PCM....27..103F |s2cid=93706828 |url=https://doi.org/10.1007/s002690050246 |access-date=9 February 2023|url-access=subscription }}</ref> 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 ({{chem2|Ca(OH)2}}).<ref>{{cite journal | last1=Tian | first1=X.K. | last2=Lin | first2=S.C. | last3=Yan | first3=J. | last4=Zhao | first4=C.Y. | title=Sintering mechanism of calcium oxide/calcium carbonate during thermochemical heat storage process | journal=Chemical Engineering Journal | volume=428 | date=2022 | doi=10.1016/j.cej.2021.131229 | article-number=131229 | bibcode=2022ChEnJ.42831229T | url=https://linkinghub.elsevier.com/retrieve/pii/S1385894721028102| url-access=subscription }}</ref><ref>{{mindat|id=2401|name=Lime}}</ref>

==References== {{Reflist}}

==External links== {{Commons category|Calcium oxide}} * [https://minerals.usgs.gov/minerals/pubs/commodity/lime/index.html#myb Lime Statistics & Information] {{Webarchive|url=https://web.archive.org/web/20130507120557/http://minerals.usgs.gov/minerals/pubs/commodity/lime/index.html#myb |date=2013-05-07 }} from the United States Geological Survey * [http://www.cheresources.com/quicklime.shtml Factors Affecting the Quality of Quicklime] * [http://www.americanscientist.org/issues/feature/dating-ancient-mortar ''American Scientist''] (discussion of 14C dating of mortar) * [https://web.archive.org/web/20080217232600/http://scifun.chem.wisc.edu/CHEMWEEK/Lime/lime.html Chemical of the Week – Lime] * [https://web.archive.org/web/20120501110853/http://hazard.com/msds/mf/baker/baker/files/c0462.htm Material Safety Data Sheet] * [https://www.cdc.gov/niosh/npg/npgd0093.html CDC – NIOSH Pocket Guide to Chemical Hazards]

Category:Alchemical substances Category:Bases (chemistry) Category:Calcium compounds Category:Cement Category:Dehydrating agents Category:Desiccants Category:Disinfectants Category:E-number additives Category:Limestone Category:Rock salt crystal structure Category:Oxides