Editing Calcium (section)

==Applications==
{{see also|Calcium supplement}}
The largest use of metallic calcium is in [[steelmaking]], due to its strong [[chemical affinity]] for oxygen and [[sulfur]]. Its oxides and sulfides, once formed, give liquid lime [[aluminate]] and sulfide inclusions in steel which float out; on treatment, these inclusions disperse throughout the steel and become small and spherical, improving castability, cleanliness and general mechanical properties. Calcium is also used in maintenance-free [[automotive battery|automotive batteries]], in which the use of 0.1% calcium–[[lead]] alloys instead of the usual [[antimony]]–lead alloys leads to lower water loss and lower self-discharging.{{sfn|Hluchan|Pomerantz|2005|pp = 485-87}}

Due to the risk of expansion and cracking, [[aluminium]] is sometimes also incorporated into these alloys. These lead–calcium alloys are also used in casting, replacing lead–antimony alloys.{{sfn|Hluchan|Pomerantz|2005|pp = 485-87}} Calcium is also used to strengthen aluminium alloys used for bearings, for the control of graphitic [[carbon]] in [[cast iron]], and to remove [[bismuth]] impurities from lead.{{sfn|Greenwood|Earnshaw|1997|p = 110}} Calcium metal is found in some drain cleaners, where it functions to generate heat and [[calcium hydroxide]] that [[Saponification|saponifies]] the fats and liquefies the proteins (for example, those in hair) that block drains.<ref name="Rumack" />

Besides metallurgy, the reactivity of calcium is exploited to remove [[nitrogen]] from high-purity [[argon]] gas and as a [[getter]] for oxygen and nitrogen. It is also used as a reducing agent in the production of [[chromium]], [[zirconium]], [[thorium]], [[vanadium]] and [[uranium]]. It can also be used to store hydrogen gas, as it reacts with hydrogen to form solid [[calcium hydride]], from which the hydrogen can easily be re-extracted.{{sfn|Greenwood|Earnshaw|1997|p = 110}}

Calcium isotope fractionation during mineral formation has led to several applications of calcium isotopes. In particular, the 1997 observation by Skulan and DePaolo<ref>{{Cite journal|last1=Skulan|first1=J.|title=Biological control of calcium isotopic abundances in the global calcium cycle|journal=Geochimica et Cosmochimica Acta |date=June 1997 | volume=61|pages=2505–10|last2=Depaolo|first2=D. J. | first3 =T. L.| last3= Owens |issue=12|doi=10.1016/S0016-7037(97)00047-1 | bibcode = 1997GeCoA..61.2505S }}</ref> that calcium minerals are isotopically lighter than the solutions from which the minerals precipitate is the basis of analogous applications in medicine and in paleoceanography. In animals with skeletons mineralized with calcium, the calcium isotopic composition of soft tissues reflects the relative rate of formation and dissolution of skeletal mineral.<ref name="ReferenceA">{{Cite journal|last1=Skulan|first1=J.|title=Natural calcium isotopic composition of urine as a marker of bone mineral balance|pmid=17463176|journal=Clinical Chemistry|date=2007|volume=53|pages=1155–58|last2=Bullen|first2=T.|last3=Anbar|first3=A. D.|last4=Puzas|first4=J. E.|last5=Shackelford|first5=L.|last6=Leblanc|first6=A.|last7=Smith|first7=S. M.|issue=6|doi=10.1373/clinchem.2006.080143|doi-access=free|bibcode=2007CChem..53.1155S }}</ref>

In humans, changes in the calcium isotopic composition of urine have been shown to be related to changes in bone mineral balance. When the rate of bone formation exceeds the rate of bone resorption, the <sup>44</sup>Ca/<sup>40</sup>Ca ratio in soft tissue rises and vice versa. Because of this relationship, calcium isotopic measurements of urine or blood may be useful in the early detection of metabolic bone diseases like [[osteoporosis]].<ref name="ReferenceA"/>

A similar system exists in seawater, where <sup>44</sup>Ca/<sup>40</sup>Ca tends to rise when the rate of removal of Ca<sup>2+</sup> by mineral precipitation exceeds the input of new calcium into the ocean. In 1997, Skulan and DePaolo presented the first evidence of change in seawater <sup>44</sup>Ca/<sup>40</sup>Ca over geologic time, along with a theoretical explanation of these changes. More recent papers have confirmed this observation, demonstrating that seawater Ca<sup>2+</sup> concentration is not constant, and that the ocean is never in a "steady state" with respect to calcium input and output. This has important climatological implications, as the marine calcium cycle is closely tied to the [[carbon cycle]].<ref>{{Cite journal|last1=Fantle|first1=M.|last2=Depaolo|first2=D.|title=Ca isotopes in carbonate sediment and pore fluid from ODP Site 807A: The Ca<sup>2+</sup>(aq)–calcite equilibrium fractionation factor and calcite recrystallization rates in Pleistocene sediments|journal=Geochim Cosmochim Acta|date=2007|volume=71|pages=2524–46|doi=10.1016/j.gca.2007.03.006|issue=10|bibcode=2007GeCoA..71.2524F}}</ref><ref>{{Cite journal|last1=Griffith|first1=Elizabeth M.|title=A Dynamic marine calcium cycle during the past 28 million years|pmid=19074345|journal=Science|date=2008|volume=322|pages=1671–74|last2= Paytan |first2= Adina |last3= Caldeira |first3= Ken|last4= Bullen |first4= Thomas |last5= Thomas |first5= Ellen |author5-link=Ellen Thomas (scientist) |s2cid=206515318|issue=12|doi=10.1126/science.1163614 |bibcode = 2008Sci...322.1671G }}</ref>

Many calcium compounds are used in food, as pharmaceuticals, and in medicine, among others. For example, calcium and phosphorus are supplemented in foods through the addition of [[calcium lactate]], [[calcium diphosphate]], and [[tricalcium phosphate]]. The last is also used as a polishing agent in [[toothpaste]] and in [[antacid]]s. [[Calcium lactobionate]] is a white powder that is used as a suspending agent for pharmaceuticals. In baking, [[calcium phosphate]] is used as a [[leavening agent]]. [[Calcium sulfite]] is used as a bleach in papermaking and as a disinfectant, [[calcium silicate]] is used as a reinforcing agent in rubber, and [[calcium acetate]] is a component of [[liming rosin]] and is used to make metallic soaps and synthetic resins.{{sfn|Hluchan|Pomerantz|2005|pp = 485-87}}

Calcium is on the [[WHO Model List of Essential Medicines|World Health Organization's List of Essential Medicines]].<ref name="WHO21st">{{cite book | vauthors = ((World Health Organization)) | title = World Health Organization model list of essential medicines: 21st list 2019 | year = 2019 | hdl = 10665/325771 | author-link = World Health Organization | publisher = World Health Organization | location = Geneva | id = WHO/MVP/EMP/IAU/2019.06. License: CC BY-NC-SA 3.0 IGO | hdl-access=free }}</ref>