What is tungsten?
1High melting point
With the highest melting point among metals, tungsten has low thermal expansion coefficient and extremely high shape stability even under a super high temperature environment.
2Large electric resistance
With its relatively large electric resistance, we offer tungsten rods for various discharge electrodes, which have improved discharge property and discharge consumption resistance.
3High hardness
Although tungsten is a metal with high hardness, its hardness is enhanced by combining it with carbon; it is used for high-grade cutting tools.
Tungsten, meaning “heavy stone” in Swedish, is a very hard and heavy silver gray rare metal. With the highest melting point among metals, tungsten has a relatively large electric resistance as a metal, so it is used for heaters and reflectors in furnaces exceeding 2000℃.
It also becomes a hard alloy when mixed with carbon, etc. Cemented carbide combined with cobalt is used for high-grade cutting tools.
In addition, tungsten, with extremely low environmental impact, has a very high radiation shielding capability compared to lead; it is also widely used as radiation shielding material in medical field such as X-ray CT.
Tungsten does not seem familiar to us in our daily life, but it is closely related to our lives for its industrial and medical uses.
| Atomic number *1 | 74 | |
|---|---|---|
| Element symbol | W | |
| Density （Mg/m3）*2 |
293K | 19.3 |
| Melting point（K）*2 | 3653 | |
| Boiling point（K）*2 | 5800 | |
| Electrical Resistance （10-8Ωm）*2 |
293K | 5.4 |
| Specific heat （J/kgK）*2 |
273-373K | 138 |
| Thermal conductivity（W/mK）*2 | 273-373K | 174 |
| Coefficient of Linear Expansion （10-6/K）*2 |
273-373K 293-2273K |
4.5 5.4 |
| Work function （eV）*2 |
4.5 | |
| Thermal neutron capture cross section area （barns/atom）*3 |
19.2±1.0 | |
*2 Fourth Edition of Metal Data Book, The Japan Institute of Metals and Materials
*3 Materials and techniques for electron Tubes,Walter H.Kohl (1960)
Chemical properties
- Tungsten is stable at room temperature but oxidizes to the extent that surface gloss is lost. It reacts mainly with O₂, CO₂, N₂, H₂O and hydrocarbon at high temperature, but not with mercury vapor and hydrogen.
- When reacting with oxygen or air, it produces elevated oxide (WO₃) via lower oxides such as W₃O, WO₂, or W₂₀O₅₈ as the temperature rises.
- Water does not corrode it, but vapor in the red heat state does, producing WO₃.
- It reacts vigorously and dissolves in a mixed solution of nitric acid and hydrofluoric acid.
- It has reducing properties under extremely hot temperature. When heated at very high temperature with sulfur, it produces the compound (WS₂); it produces the compound (W₃P₄) when phosphorus vapor is applied.
| Substance | Temperature | Reaction |
|---|---|---|
| Air | Room temperature |
No reaction |
| 400℃ | Oxidation starts | |
| 700℃ | Produces WO3 and rapidly oxidizes | |
| Oxygen | Room temperature |
No reaction |
| 530℃ | Produces WO3 even at low pressure | |
| Vapor |
≧700℃ |
Oxidation progresses rapidly |
| Nitrogen | No reaction up to 2,000℃ | |
| Three stages of absorption up to 1,700°C | ||
| Carbon monoxide |
≧1,000℃ | Produces W2C4 |
| Carbon dioxide |
1,200℃ | Oxidizes |
| Hydrocarbon | 1,200℃ | Produces carbides |
| 2,430℃ | Carbide decomposes | |
| Dry chlorine | 250℃ | Produces 6 chloride |
| Fluorine | Room temperature |
Produces sublimable fluoride |
| Bromine | Red heat | Produces bromide |
| Iodine | Red heat | Produces bromide |
| Hydrogen |
No reaction |
|
| Hydrogen sulfide |
Red heat | Surface reaction occurs |
| Sulfur dioxide |
≧700℃ | Oxide formation |
| Substance | Temperature | Reaction |
|---|---|---|
| Water | Room temperature |
No reaction |
| Hot liquid | No reaction | |
| Mercury | No reaction | |
| Hydrochloric acid | Room temperature |
No reaction for dilute/concentrated |
| Hot liquid | A little corrodes | |
| Dilute sulfuric acid | Room temperature |
Doesn't corrode |
| Hot liquid | Slightly corrodes | |
| Concentrated sulfuric acid |
Room temperature |
Slightly corrodes |
| Hot liquid | Gradually corrodes | |
| Sulfuric acid | Hot liquid | Slightly corrodes |
| Hydrofluoric acid | Hot liquid | No reaction for dilute/concentrated |
|
Sulfuric acid ＋hydrofluoric acid |
Hot liquid | Rapidly corrodes |
| Aqua regia | Hot liquid | Slightly dissolves producing oxide film |
| Sodium hydroxide |
Room temperature |
Doesn't corrode |
| Dissolved state |
Rapidly corrodes | |
| Accelerated in air by oxidation | ||
| Sodium nitrite | about 500℃ | Melts while violently generating heat |
| Ammonium hydroxide |
Not corrode | |
| Liquid ammonia | Not corrode |
| Substance | Temperature | Reaction |
|---|---|---|
| Carbon, graphite | 850 to 1,410℃ | Absorbs carbon |
| 1,410 to 1,600℃ | Produces carbides | |
| Magnesia | up to 1,500℃ | Stable |
| Zirconia | up to 1,600℃ | Stable |
| Thoria | 2,200℃ | Reduces thoria slightly |
| Alumina | up to 1,900℃ | Stable |
| Beryllia | up to 2,200℃ | Stable |