Tungsten by Wolfram Industries – an unrivalled metal
Tungsten is a metal with an extremely high density and thermal capacity. Not only does it have the highest melting point of all metals, it also exhibits the greatest mechanical strength, very high stiffness and the smallest thermal expansion coefficient. Temperatures like those on the surface of the sun are required to bring tungsten to a boil (approx. 5,900°C). With a density of 19.28 g/cm³, tungsten is also among the heaviest metals which is why it is used among other things for specific mass balancing. Tungsten takes eighth place in the electrical conductivity ranking. This means it has about 31% of the electrical conductivity of copper.
Tungsten is also a special metal in terms of its chemistry. It is extraordinarily resistant to air exposure at room temperature. Only at high temperatures does it gradually burn, forming tungsten (VI) trioxide (WO3). It is impervious to most acids and bases. Mineral acids, hydrofluoric acid and even nitrohydrochloric acid (aqua regia) only attack the metal slowly. It does however dissolve quickly in a mixture of nitric and hydrofluoric acid.
Physical properties of tungsten:
Chemical properties of tungsten:
Physical and mechanical properties
Density
18.0 – 19.25 g/cm³ (depending on the degree of deformation)
Strength
at 1.0 – 1.99 mm diameter > 1500 – 2200 MPa
at 2.0 – 3.2 mm diameter > 1300 – 2000 MPa
Expansion
< 6 %
Recrystallisation properties
Start of recrystallisation: approx. 1150 °C
Full recrystallisation: approx. 1350 °C 1 hour
Specific electrical resistance
| 300 K | 5,65 µΩcm |
| 500 K | 10,65 µΩcm |
| 1000 K | 24,93 µΩcm |
| 1500 K | 40,36 µΩcm |
| 2000 K | 56,67 µΩcm |
| 2500 K | 73,91 µΩcm |
| 3000 K | 92,04 µΩcm |
| 3500 K | 111,10 µΩcm |
Thermal conductivity at 293° K
174 W/m·K
Temperature coefficient
273 – 373 K 4,5 · 10-6 K-1
Surface
Can be ground, drawn (black/cleaned), wrought, turned, milled and eroded
Heat treatment
May be annealed or unannealed
