Materials/Metals and alloys/Collections
Alkali and alkaline earth metals
alkali-and-alkaline-earth-metalsAbout alkali and alkaline earth metals
Sodium, potassium, caesium, calcium and barium metals: density, melting point and reactivity data with sources.
The alkali and alkaline earth metals are soft, light and highly reactive. They are used as coolants, getters, reducing agents and in batteries, and they need careful storage because they react with air and water.
At a glance
- Highest density: Barium metal reaches 3.62 g/cm³. Lowest: K starts at 0.86 g/cm³. (4 of 5 grades have a sourced value.)
- Highest melting point: Calcium reaches 842 °C. Lowest: K starts at -12.6 °C. (5 of 5 grades have a sourced value.)
- Highest electrical resistivity: Barium metal reaches 3.4e-7 Ω·m. Lowest: Calcium starts at 3.4e-8 Ω·m. (3 of 5 grades have a sourced value.)
Ranges run across the conditions each source reports (temper, heat treatment, form), measured at room temperature where the source says so.
How they compare
The same measurements for every material in the collection. A range means the grade has values under several conditions; "at least" means the source gives a specified minimum. "no data" means no sourced value yet. For ranked tables, open a benchmark.
| Material | Density | Melting point | Electrical resistivity | Thermal conductivity | Young's modulus | Thermal expansion |
|---|---|---|---|---|---|---|
| Sodium (Na)coolant | 0.97 g/cm³ | 97.8 °C | 4.8e-8 Ω·m | 132 W/(m·K) | no data | no data |
| Kliquid-metal coolant | 0.86 g/cm³ | -12.6 to 64 °C | no data | 0.23 cal/(sec degC cm) | no data | no data |
| Caesium (Cs)atomic-clock and ion-thruster element | 1,827 to 1,892 kg/cu m | 28.4 to 28.6 °C | no data | no data | no data | no data |
| Calciumdeoxidiser, vacuum getter and research battery anode | 1.54 to 1.57 g/cm³ | 842 °C | 3.4e-8 Ω·m | 200 W/(m·K) | 20 GPa | 22.3 ppm/K |
| Barium metalgetter | 3.51 to 3.62 g/cm³ | 725 to 727 °C | 3.4e-7 Ω·m | 18.4 W/(m·K) | 13 GPa | 20.6 ppm/K |
What these materials are made of
Composition by weight, as printed in the sources for each grade (the first constituents listed).
| Material | Main constituents |
|---|---|
| Sodium (Na) | Na 100.0% |
| K | K 100.0% |
| Caesium (Cs) | Cs 100.0% |
| Calcium | Ca 100.0% |
| Barium metal | Ba 100.0% |
Where they are used
| Use | Grades |
|---|---|
| Stainless steel and sodium heat pipe, a radiator element for a nuclear electric propulsion spacecraft (test article) | Sodium (Na) |
| High-temperature sodium-sulfur battery | Sodium (Na) |
| Liquid sodium coolant of a sodium-cooled fast reactor | Sodium (Na) |
| Liquid-metal reactor coolant loop for a space fission power system | K |
| Primary test circuit for fission surface power (ground test) | K |
| Caesium contact-ionization ion thruster | Caesium (Cs) |
| Caesium fountain primary frequency standard (NIST-F2) | Caesium (Cs) |
| Atomic clocks for global positioning systems | Caesium (Cs) |
| Rechargeable calcium-metal battery (research stage) | Calcium |
| Vacuum tubes (calcium as a getter) | Calcium |
| Steel and alloys (deoxidiser and desulphuriser) | Calcium |
| Getter alloy in an electronic vacuum tube | Barium metal |
| Barium-impregnated hollow cathode in ion and Hall thrusters | Barium metal |
| Miniature reservoir dispenser cathode | Barium metal |
When each grade fits
| Material | Best for | Weakest at |
|---|---|---|
| Sodium (Na) | Heat transfer in a liquid metal at high temperature and low pressure, as in fast-reactor coolant loops | Any contact with water, moist air or oxygen. It reacts violently, may ignite and must be kept dry and under inert cover |
| K | Liquid-metal heat transport in space fission reactor loops, where NaK stays liquid at room temperature | Any contact with water or oxygen: it reacts violently with water and forms a surface crust in air |
| Caesium (Cs) | Frequency standards and atomic clocks, where the caesium-133 hyperfine transition defines the SI second | Handling: it ignites spontaneously in air and reacts violently with water, and it melts at 28 C, so it stays liquid in a warm room |
| Calcium | Deoxidising steel and as a reactive getter for residual gases; research anodes for calcium batteries, where its theoretical volumetric capacity is 2073 mAh/cm3 | Any contact with water or moist air, which releases flammable hydrogen (H261), and self-ignition at about 730 to 750 degC in air |
| Barium metal | Getter alloys and barium-impregnated electron emitters inside a sealed vacuum, where the metal is never exposed to water or air | Any contact with water or moist air: it reacts at once and releases hydrogen, and powdered barium reacts violently with air |
Materials
alkali-and-alkaline-earth-metals/ba
Heavy metals • 19 sourced entries • 10 sources • 2026
alkali-and-alkaline-earth-metals/cs
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alkali-and-alkaline-earth-metals/ca
Magnesium • 21 sourced entries • 12 sources • 2026
alkali-and-alkaline-earth-metals/k
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alkali-and-alkaline-earth-metals/na
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