Calcium Ca

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.