spore: profile id: calcium spore_version: 0.2 family: alkali-and-alkaline-earth-metals name: Calcium abbreviation: Ca role: deoxidiser, vacuum getter and research battery anode category: metals type: magnesium summary: | Calcium is a silvery alkaline-earth metal, the fifth most abundant element in the Earth's crust, and it is never found as the free metal in nature. Its main industrial use is as a deoxidiser and desulphuriser in steelmaking, and it has been used as a getter for residual gases in vacuum tubes. It reacts with water to release flammable hydrogen, burns in air once ignited, and melts at 842 degC. Calcium metal is studied as an anode for rechargeable calcium batteries because its volumetric capacity is high, but only a handful of electrolytes have been shown to plate and strip it reversibly. best_for: Deoxidising steel and as a reactive getter for residual gases; research anodes for calcium batteries, where its theoretical volumetric capacity is 2073 mAh/cm3 weakest_at: Any contact with water or moist air, which releases flammable hydrogen (H261), and self-ignition at about 730 to 750 degC in air identity: formula: Ca cas: 7440-70-2 source: chemos-sds where: Section 1.1 Product identifier (CAS number 7440-70-2, substance Calcium) tags: environments: [] stresses: - extreme-heat applications: - batteries - structures - electronics-and-chips properties: - benchmark: density value: 1550 unit: kg/m3 scope: material conditions: basis: density of solid as printed by the source temperature: not stated by the source method: Value printed in a database element page (WebElements) status: ground source: webelements-physics where: 'Physical properties, Density properties: Density of solid' - benchmark: density value: 1.54 unit: g/cm3 scope: material conditions: temperature: 20 degC method: Value printed in a supplier safety data sheet under REACH status: ground source: chemos-sds where: Section 9, Density and/or relative density - benchmark: density label: Density used for calcium metal in an electrode model value: 1.57 unit: g/cm3 scope: material conditions: basis: density the review uses for calcium metal in its electrode model, not a measured value temperature: not stated by the source method: Table value in an open-access review of multivalent batteries status: ground source: frontiers-ca-2019 where: Table 1, row Calcium metal (conf. 1), density column - benchmark: melting_point value: 842 unit: degC scope: material conditions: basis: melting point as printed (the page also gives 1115 K) method: Value printed in a database element page (WebElements) and in a supplier safety data sheet status: ground source: webelements-thermo where: 'Thermochemistry: Melting point, 1115 [842 degC (1548 degF)] K' - benchmark: boiling_point value: 1484 unit: degC scope: material conditions: pressure: 1 atm method: Value printed in a database element page (WebElements) and in a supplier safety data sheet status: ground source: webelements-thermo where: 'Thermochemistry: Boiling point, 1757 [1484 degC (2703 degF)] K' - benchmark: enthalpy_of_fusion value: 8.54 unit: kJ/mol scope: material conditions: temperature: at the melting point method: Value printed in a database element page (WebElements) status: ground source: webelements-thermo where: 'Thermochemistry: Enthalpy of fusion' - benchmark: elastic_modulus label: Young's modulus value: 20 unit: GPa scope: material conditions: basis: polycrystalline metal as printed; temperature not stated method: Value printed in a database element page (WebElements) status: ground source: webelements-physics where: 'Physical properties, Elastic properties: Young''s modulus' - benchmark: bulk_modulus value: 17 unit: GPa scope: material conditions: basis: as printed; temperature not stated method: Value printed in a database element page (WebElements) status: ground source: webelements-physics where: 'Physical properties, Elastic properties: Bulk modulus' - benchmark: poissons_ratio value: 0.31 unit: '-' scope: material conditions: basis: as printed (no units) method: Value printed in a database element page (WebElements) status: ground source: webelements-physics where: 'Physical properties, Elastic properties: Poisson''s ratio' - benchmark: electrical_resistivity value: 3.4 unit: microohm cm scope: material conditions: unit_in_source: 3.4 x 10^-8 ohm m, printed as 3.4 x 10-8 ohm m with the alternative unit mohm cm temperature: not stated by the source method: Converted by Space Mushroom from ohm m to microohm cm (1 ohm m is 100 million microohm cm); the source prints the value in ohm m status: ground source: webelements-physics where: 'Electrical properties: Electrical resistivity' - benchmark: thermal_conductivity value: 200 unit: W/(m K) scope: material conditions: basis: as printed; temperature not stated method: Value printed in a database element page (WebElements) status: ground source: webelements-physics where: 'Heat and conduction: Thermal conductivity' - benchmark: cte value: 22.3 unit: 10^-6/K scope: material conditions: basis: linear coefficient as printed (22.3 x 10-6 per K); temperature not stated method: Value printed in a database element page (WebElements) status: ground source: webelements-physics where: 'Heat and conduction: Coefficient of linear thermal expansion' - benchmark: theoretical_capacity value: 1338 unit: mAh/g scope: material conditions: reaction: Ca to Ca2+, two electrons per calcium atom electrode: calcium metal anode (conf. 1 and conf. 2 in the source both list 1338) method: Value stated in an open-access review of multivalent batteries; no working is shown status: calculated source: frontiers-ca-2019 where: Table 1, row Calcium metal (conf. 1), capacity column - benchmark: volumetric_capacity label: Theoretical volumetric capacity value: 2073 unit: mAh/cm3 scope: material conditions: electrode: calcium metal anode comparison: graphite 850 mAh/cm3 and lithium metal 2062 mAh/cm3 as quoted in the same abstract method: Value stated in a doctoral thesis abstract; no working is shown status: calculated source: mit-calcium-thesis where: Abstract, sentence beginning 'Ca metal also offers attractive electrochemical metrics' - benchmark: auto_ignition_temperature label: Relative self-ignition temperature of solid calcium value: 730 value_high: 750 bound: range unit: degC scope: material conditions: basis: relative self-ignition temperature for solids (ECHA), printed as more than 730 and less than 750 degC method: Value printed in a supplier safety data sheet status: ground source: chemos-sds where: Section 9, Auto-ignition temperature corrosion: - environment: Liquid water headline: Calcium reacts with water to form calcium hydroxide and hydrogen. The supplier safety data sheet calls the reaction violent. effect: The metal sinks in water and after about an hour hydrogen bubbles stick to its surface (WebElements, which calls the reaction slow). The Chemos safety data sheet classifies calcium as water-reactive, category 2, with H261 (in contact with water releases flammable gases) and EUH014 (reacts violently with water). rating: severe conditions: form: calcium metal in water, form not stated by the source note: 'the two sources disagree on speed: slow in WebElements, violent in the safety data sheet' source: chemos-sds where: Section 2.1 (Water-react 2), Section 2.2 (H261, EUH014), Section 5.2 - environment: Room air at room temperature headline: A thin oxide layer protects calcium in air, though less well than the layer on magnesium. effect: The surface of calcium metal is covered with a thin oxide layer that protects it from air, but less well than the layer on magnesium. Once ignited it burns to calcium oxide and calcium nitride. No corrosion rate is given in the source. rating: moderate conditions: atmosphere: air at room temperature rate: not measured in the source source: webelements-chem where: 'Element reactions: Reaction of calcium with air' - environment: Air or oxygen when heated headline: Calcium self-ignites at about 730 to 750 degC in air. effect: The supplier safety data sheet gives a relative self-ignition temperature for solid calcium of more than 730 and less than 750 degC (ECHA). Burning calcium forms calcium oxide and calcium nitride (WebElements). rating: severe conditions: state: solid basis: relative self-ignition temperature, not a single ignition point source: chemos-sds where: Section 9, Auto-ignition temperature - environment: Halogen gases (fluorine, chlorine, bromine, iodine) headline: Calcium burns in fluorine and chlorine and reacts with bromine and iodine when heated. effect: Calcium is very reactive towards the halogens and forms calcium fluoride, chloride, bromide and iodide. The reactions with bromine and iodine need heat to start. rating: severe conditions: state: gas phase, temperature not stated by the source source: webelements-chem where: 'Element reactions: Reaction of calcium with the halogens' - environment: Dilute or concentrated hydrochloric acid headline: Calcium dissolves readily in hydrochloric acid and releases hydrogen. effect: Calcium metal dissolves readily in dilute or concentrated hydrochloric acid, forming calcium ions in solution and hydrogen gas (Ca + 2HCl gives Ca2+ + 2Cl- + H2). rating: severe conditions: acid: hydrochloric acid, dilute or concentrated source: webelements-chem where: 'Element reactions: Reaction of calcium with acids' - environment: Electrolyte in a calcium battery cell (research) headline: In battery electrolytes a passivating interphase forms on calcium and blocks calcium-ion transport. effect: 'The thesis names two key problems for calcium metal anodes: a passivating solid electrolyte interphase between calcium and the electrolyte, which inhibits Ca2+ transport to the anode, and strong Ca2+-anion interactions that suppress ionic conductivity. Only a handful of reversible electrolytes have been reported since the first plating and stripping demonstration in 2015.' rating: moderate conditions: setting: laboratory calcium-metal cells; electrolyte types not listed in the abstract source: mit-calcium-thesis where: Abstract risks: hazards: - text: 'Classified under CLP as water-reactive, category 2 (H261: in contact with water releases flammable gases). The signal word is Danger and the pictogram is GHS02 (flame).' ghs: - H261 source: chemos-sds where: Section 2.1 (Classification), Section 2.2 (Label elements) - text: 'Supplemental hazard EUH014: reacts violently with water.' ghs: - EUH014 source: chemos-sds where: Section 2.2, Supplemental hazard information - text: 'OSHA HCS classification of the granular lab-grade metal: water-reactive, category 2, with the hazard statement that in contact with water it releases flammable gases.' ghs: [] source: laballey-sds where: Section 2.1 (Classification) and Section 2.2 (Label elements) failure_risks: - mode: Hydrogen release on contact with water trigger: Water, moisture or a wet surface contacts the metal consequence: Flammable hydrogen is released and may ignite spontaneously, according to the safety data sheet. Storage at higher temperature speeds the release. severity: high source: chemos-sds where: Section 2.1, Section 5.2 - mode: Self-ignition when heated in air trigger: Heating solid calcium in air to its self-ignition range consequence: Calcium self-ignites at about 730 to 750 degC and burns to calcium oxide and calcium nitride (ECHA value in the safety data sheet; WebElements for the products). severity: high source: chemos-sds where: 'Section 9, Auto-ignition temperature; WebElements Element reactions: Reaction of calcium with air' - mode: Passivating interphase in calcium battery cells (research) trigger: Calcium metal in contact with the electrolyte during plating and stripping consequence: A passivating interphase and poor ionic conductivity stop reversible plating and stripping, so the anode cannot be recharged reliably. severity: moderate source: mit-calcium-thesis where: Abstract side_effects: - text: Product may release hydrogen gas, and storage at increased temperature accelerates this. affects: Sealed containers and storage areas source: chemos-sds where: Section 5.2 Special hazards - text: Burning calcium gives calcium oxide and calcium nitride, and reaction with water gives calcium hydroxide. affects: Nearby surfaces and equipment source: webelements-chem where: 'Element reactions: reaction with air and with water' handling: - text: Keep in an inert gas, protect from moisture and do not allow contact with water (P231+P232, P223). source: chemos-sds where: Section 7 (precautionary statements P223, P231+P232) - text: Store in a dry place in a closed container (P402+P404). source: chemos-sds where: Section 2.2 precautionary statements - text: Fire extinguishing media differ between the two safety data sheets. Chemos lists foam, dry powder and dry sand and names a water jet as unsuitable. Laboratory-grade granules from Lab Alley list extinguisher powder or CO2 and warn against a direct water stream. source: laballey-sds where: Section 5.1 Extinguishing media - text: 'Skin contact: brush off loose particles and immerse the skin in cool water (P302+P335+P334).' source: chemos-sds where: Section 2.2 precautionary statements mitigations: - text: Handle and store under inert gas, and keep the metal dry, so that it does not react with air or moisture. source: chemos-sds where: Section 7 (P231+P232) uses: - application: batteries device: Rechargeable calcium-metal battery (research stage) example: Calcium metal has a theoretical volumetric capacity of 2073 mAh/cm3, against 850 mAh/cm3 for graphite and 2062 mAh/cm3 for lithium metal, and the thesis says it is the basis of calcium battery research. Only a handful of reversible electrolytes have been reported since 2015. source: mit-calcium-thesis where: Abstract - application: electronics-and-chips device: Vacuum tubes (calcium as a getter) example: Calcium is used as a getter for residual gases in vacuum tubes, and WebElements lists it among the uses of the metal. source: webelements-uses where: Uses list, item on getter for residual gases in vacuum tubes - application: structures device: Steel and alloys (deoxidiser and desulphuriser) example: Calcium is used as a deoxidiser, desulphuriser or decarbonizer for various alloys, according to WebElements. The metal is not a common alloying element in steel because its solubility is low. source: webelements-uses where: Uses list, item on deoxidiser, desulphurizer or decarbonizer supply: - subject: Calcium (producer shares are for lime, not calcium metal, because USGS reports no calcium metal production) abundance: '41,500 ppm in the Earth''s crust (thesis abstract). WebElements: fifth in abundance in the crust, forming more than 3 per cent, and found in limestone, gypsum and fluorite but never as the free metal. Crustal rocks row: 50000000 ppb by weight.' producers: - country: China share_percent: 73.8 year: 2025 - country: India share_percent: 4 year: 2025 - country: United States share_percent: 3.6 year: 2025 - country: Russia share_percent: 2.9 year: 2025 critical_lists: - list: USGS Final 2025 List of Critical Minerals (Table 6) listed: false - list: EU critical raw materials list (RMIS, 34 materials) listed: false recycling: No recycling figure for calcium metal was found in the sources read. substitutes: [] source: usgs-mcs-2026 where: Lime chapter, World Lime Production and Reserves table (2025e; shares calculated by Space Mushroom against the 420,000 thousand t world total); Table 6 of the USGS summaries for the US list; EU RMIS page for the EU list; WebElements Geology page for abundance. media: [] documents: - title: 'Safety data sheet: Calcium (Chemos GmbH, CAS 7440-70-2, version GHS 1.0, compiled 2021-04-08)' type: sds url: https://www.chemos.de/import/data/msds/GB_en/7440-70-2-A0010604-GB-en.pdf year: 2021 - title: 'Safety data sheet: Calcium metal, granular lab grade (Lab Alley, revision 2 dated 2025-07-03)' type: sds url: https://media.laballey.com/docbuilder/calcium-metal-granular-lab-grade-safety-data-sheet-6866d1beb0d43.pdf year: 2025 - title: Calcium (WebElements periodic table, physical, thermochemistry, chemistry, geology and uses pages) type: database url: https://www.webelements.com/calcium/ year: 2026 - title: 'Multivalent Batteries: Prospects for High Energy Density, Ca Batteries (Frontiers in Chemistry, open access)' type: paper url: https://doi.org/10.3389/fchem.2019.00079 year: 2019 - title: Mineral Commodity Summaries 2026 (lime chapter and Table 6, Final 2025 Critical Minerals List) type: report url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026.pdf year: 2026 gaps: - Calcium metal production by country is not reported separately; the supply shares are for lime (quicklime and hydrated lime), which is a calcium compound, not the metal. - No recycling figure and no substitute list for calcium metal were found in the sources read. - The standard potential of the Ca2+/Ca couple (-2.868 V vs SHE) is printed on a LibreTexts table with a Unicode minus sign, so it was not entered; it can be added once a source prints an ASCII minus sign. - Auto-ignition is entered as a range under the non-canonical name auto_ignition_temperature; it is not in the canonical property list. - No vacuum, outgassing, radiation, cold or thermal-vacuum data for calcium were found. The getter use has no numbers in the sources read. - The two safety data sheets disagree on suitable fire extinguishing media (foam and dry sand in one, powder and CO2 in the other). Both are recorded; check the sheet for the product you hold. - WebElements describes the reaction with water as slow, while the Chemos safety data sheet classifies it as violent (EUH014). Both are recorded in the corrosion section. - Specific heat capacity and Brinell hardness (167 MN m-2, WebElements) are printed in the physical properties page but were not entered because no canonical name fitted the unit as printed. - Gravimetric and volumetric capacities come from a 2019 review and a thesis abstract, and no measured capacity of calcium metal in a cell was read. sources: webelements-physics: title: 'WebElements: Calcium, physical properties' id: WebElements, Mark Winter, University of Sheffield url: https://www.webelements.com/calcium/physics.html year: 2026 kind: database license: WebElements copyright (cited, not reproduced) webelements-thermo: title: 'WebElements: Calcium, thermochemistry' id: WebElements, Mark Winter, University of Sheffield url: https://www.webelements.com/calcium/thermochemistry.html year: 2026 kind: database license: WebElements copyright (cited, not reproduced) webelements-chem: title: 'WebElements: Calcium, element reactions' id: WebElements, Mark Winter, University of Sheffield url: https://www.webelements.com/calcium/chemistry.html year: 2026 kind: database license: WebElements copyright (cited, not reproduced) webelements-uses: title: 'WebElements: Calcium, uses' id: WebElements, Mark Winter, University of Sheffield url: https://www.webelements.com/calcium/uses.html year: 2026 kind: database license: WebElements copyright (cited, not reproduced) webelements-geo: title: 'WebElements: Calcium, geology' id: WebElements, Mark Winter, University of Sheffield url: https://www.webelements.com/calcium/geology.html year: 2026 kind: database license: WebElements copyright (cited, not reproduced) nist-atomic-weights: title: NIST Atomic Weights and Isotopic Compositions, element Ca id: NIST, standard atomic weight of calcium url: https://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl?ele=Ca&all=all year: 2026 kind: database license: public domain (US government work) chemos-sds: title: 'Safety Data Sheet: Calcium (Chemos GmbH and Co. KG, REACH format)' id: CAS 7440-70-2; article A0010604; version GHS 1.0 url: https://www.chemos.de/import/data/msds/GB_en/7440-70-2-A0010604-GB-en.pdf year: 2021 kind: datasheet license: supplier document, linked not reproduced laballey-sds: title: 'Safety Data Sheet: Calcium Metal Granular Lab Grade (Lab Alley)' id: Revision 2, 2025-07-03 url: https://media.laballey.com/docbuilder/calcium-metal-granular-lab-grade-safety-data-sheet-6866d1beb0d43.pdf year: 2025 kind: datasheet license: supplier document, linked not reproduced mit-calcium-thesis: title: Calcium metal battery thesis, abstract (MIT DSpace record 1721.1/159078) id: MIT DSpace handle 1721.1/159078 url: https://dspace.mit.edu/handle/1721.1/159078 kind: paper license: MIT DSpace abstract, cited frontiers-ca-2019: title: 'Multivalent Batteries: Prospects for High Energy Density, Ca Batteries (Frontiers in Chemistry)' id: doi:10.3389/fchem.2019.00079 url: https://doi.org/10.3389/fchem.2019.00079 year: 2019 kind: paper license: CC BY 4.0 usgs-mcs-2026: title: Mineral Commodity Summaries 2026 (USGS), lime chapter and Table 6 Final 2025 Critical Minerals List id: USGS MCS 2026, February 2026 url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026.pdf year: 2026 kind: report license: public domain (USGS) rmis-eu-crm: title: 'EU Raw Materials Information System: critical raw materials' id: Regulation (EU) 2024/1252 list of critical raw materials url: https://rmis.jrc.ec.europa.eu/eu-critical-raw-materials year: 2026 kind: web license: European Commission web page license: CC-BY-4.0 updated: '2026-10-26' review: status: draft method: assistant checked_values: 15 unreachable: 0 caveats: 3 note: Written by an AI assistant on 2026-10-26 from pages read in this run; values to be checked with verify-values. story: recipe: line: Calcium metal is the pure element, Ca, with one atom per formula unit. It is not an alloy in this profile. parts: - name: Calcium symbol: Ca atoms: 1 atomic_weight: 40.078 role: The only element in the metal. The NIST standard atomic weight is 40.078, as printed. risk_groups: - title: For people level: 4 verdict: Water-reactive and flammable on contact with water lead: Calcium metal is classified under CLP as water-reactive, category 2. It releases flammable hydrogen on contact with water and self-ignites at about 730 to 750 degC in air. points: - label: Classification line: The Chemos safety data sheet uses the signal word Danger and the GHS02 flame pictogram, with H261 (in contact with water releases flammable gases) and EUH014 (reacts violently with water). - label: Fire line: Fire extinguishing advice differs between the two safety data sheets, so use the sheet for the product you hold. Avoid water jets; one sheet names sand, dry powder and foam, the other powder and CO2. - label: Skin line: Brush off loose particles and immerse the skin in cool water, following the precautionary statement P302+P335+P334. - title: If the metal meets water or heat lead: These are hazard properties from the safety data sheets and reference pages, not field incidents. points: - label: Water line: Water releases flammable hydrogen, which may ignite. Storage at higher temperature speeds the release. - label: Heat in air line: Solid calcium self-ignites at about 730 to 750 degC and burns to calcium oxide and calcium nitride. - label: Halogens and acids line: Calcium burns in fluorine and chlorine, reacts with bromine and iodine when heated, and dissolves readily in hydrochloric acid with release of hydrogen. - title: Handling and storage points: - label: Storage line: Store in an inert gas, in a dry place, in a closed container, and keep away from water (P223, P231+P232, P402+P404). why: Calcium is the fifth most abundant element in the Earth's crust but is never found as the free metal. As a metal it is a strong reducing agent. Industry uses it to remove oxygen and sulphur from steel, and it has been used as a getter for residual gases in vacuum tubes. It is studied as a battery anode because its volumetric capacity is high. Its reactivity with water and air is the main problem for handling and for any cell that uses it. uses: - where: Steelmaking line: WebElements lists calcium as a deoxidiser, desulphuriser and decarbonizer for various alloys, and as a reducing agent for preparing other metals such as thorium, uranium and zirconium. - where: Vacuum tubes line: Calcium is used as a getter for residual gases in vacuum tubes, according to WebElements. The sources read give no pumping numbers. - where: Rechargeable batteries, still under research line: A thesis abstract gives calcium metal a theoretical volumetric capacity of 2073 mAh/cm3, against 850 for graphite. It also says only a handful of reversible electrolytes have been reported since 2015, so calcium metal anodes are not yet in use. can_do: - label: Capacity value: 1338 mAh/g line: A 2019 review gives 1338 mAh/g for calcium metal as an anode, with each calcium atom giving two electrons. Its volumetric capacity is 2073 mAh/cm3 in the thesis abstract. - label: Melting value: 842 degC line: Calcium melts at 842 degC and boils at 1484 degC. Its heat of fusion is 8.54 kJ/mol. - label: Stiffness value: 20 GPa line: Young's modulus is 20 GPa, bulk modulus 17 GPa and Poisson's ratio 0.31, as printed by WebElements. - label: Heat and electricity value: 200 W/(m K) line: Thermal conductivity is 200 W/(m K), and electrical resistivity is 3.4 microohm cm at a temperature the source does not state. compare: Calcium sits directly below magnesium in the periodic table, the closest metal type in this collection. WebElements describes calcium as more reactive with air and water than magnesium, which is virtually unreactive with cold water. For a battery anode, the thesis abstract gives calcium metal 2073 mAh/cm3 by volume, against 850 mAh/cm3 for graphite. compare_rows: - label: Density benchmark: density - label: Melting point benchmark: melting_point - label: Theoretical capacity as an anode benchmark: theoretical_capacity handling: - Store in an inert gas in a dry, closed container, away from water. - Protect from moisture; contact with water releases flammable hydrogen. - Choose the extinguisher from the product's own safety data sheet. Do not use a water jet. good_for: - Deoxidising steel, where it removes oxygen and sulphur. - Research anodes for calcium batteries, where its volumetric capacity is high. watch_out: - Water and moist air. Calcium releases hydrogen on contact with water, and its surface reacts with air. - Heat. Solid calcium self-ignites at about 730 to 750 degC in air. - Rechargeable cells. Electrolytes that plate and strip calcium reversibly are few, and a passivating layer forms on the metal. verdict: Calcium is a useful reactive metal for steel and getters, and a promising but unproven anode for rechargeable batteries. Handling needs inert, dry conditions.