What Is a Tungsten Sheet?
Tungsten sheet is a flat product rolled from commercially pure tungsten, a silver-white to steel grey refractory metal with the highest melting point of all metals. It is produced by powder metallurgy: high purity tungsten powder is pressed, sintered into a dense bar or ingot, then rolled and annealed in successive passes until the required thickness and flatness are reached. Finished sheet is finally cut, ground or polished to size.
Tungsten is a heavy, hard and brittle metal at room temperature and becomes more workable only at elevated temperature, which is why sheet production is carried out hot and why the finished product is normally used in the annealed or stress relieved condition. Its combination of very high melting point, low vapour pressure, high density and good thermal conductivity makes it the standard choice for parts that must survive extreme heat.
Key Physical Properties of Tungsten Sheet
The table below collects the characteristic values used when specifying tungsten sheet. They refer to commercially pure tungsten, typically 99.95 % minimum purity.
| Property | Value |
|---|---|
| Atomic number / atomic weight | 74 / 183.84 |
| Crystal structure | Body centred cubic (bcc) |
| Density at 20 °C | 19.25 g/cm³ |
| Melting point | 3422 °C |
| Boiling point | 5555 °C |
| Mohs hardness | about 7.5 |
| Young's modulus | about 411 GPa |
| Poisson's ratio | about 0.28 |
The density of tungsten is close to that of gold and roughly two and a half times that of carbon steel, which is why the metal has been called heavy stone since ancient times and why it is used where mass must be concentrated in a small volume. Hardness and brittleness are the two properties that shape workshop practice: sheet is normally ground, sheared or machined with carbide tooling rather than bent sharply at room temperature.
Thermal and Electrical Behaviour
Tungsten conducts heat well and electricity moderately, and its thermal expansion is among the lowest of the common metals. Table values are given for room temperature.
| Property | Value |
|---|---|
| Thermal conductivity | 173 W/(m·K) |
| Coefficient of linear thermal expansion | 4.5 x 10-6 /K |
| Specific heat capacity | 0.134 J/(g·K) |
| Electrical resistivity | 5.6 x 10-8 Ω·m |
| Magnetic behaviour | Paramagnetic, permeability close to 1 |
Thermal conductivity is roughly three times that of carbon steel, so tungsten sheet spreads heat quickly and is used in components that must not develop hot spots. The low expansion coefficient reduces distortion when the metal is cycled between room temperature and incandescent temperatures, which matters in filament and high temperature furnace work.
Chemical Stability, Oxidation and Fabrication
Tungsten is stable in air at room temperature and is not attacked quickly by ordinary atmospheric exposure, which is the behaviour described as resistance to air erosion. At high temperature the situation changes: in air the metal begins to oxidize noticeably above about 400 °C, and protective atmosphere or vacuum is therefore required for any high temperature use.
At room temperature tungsten resists most mineral acids only partially; it is attacked by mixtures of hydrofluoric and nitric acid and by strong oxidizing media, and it dissolves in molten alkalis in the presence of an oxidizer. Sheet can be machined with carbide or diamond tooling, joined by brazing or by welding in an inert atmosphere, and cleaned by abrasive or electrolytic methods. Grinding is the usual route to close flatness and surface finish.
Typical Applications of Tungsten Sheet
Filaments and heating elements that operate at incandescent temperatures
High speed cutting tool steel and other alloy steels to which tungsten is added as an alloying element
Super hard moulds, dies and wear parts that must keep their shape at high temperature
Optical instruments and analytical or chemical instruments that need stable, non-magnetic internal parts
Heat shields, boats and fixtures in vacuum and protective atmosphere furnaces
Counterweights, radiation shielding and ballistic components where high density is the design driver
In instrument work the metal is chosen for its dimensional stability, low magnetic permeability and resistance to thermal cycling, while in tooling and mould applications it is chosen for hot hardness and wear resistance.
Frequently Asked Questions
Q: What is the melting point of tungsten sheet?
3422 °C, the highest melting point of any metal, which is the main reason tungsten is chosen for filaments and high temperature furnace parts.
Q: How dense is tungsten compared with steel?
Density is 19.25 g/cm³ at 20 °C, about two and a half times the density of carbon steel, so a tungsten sheet weighs considerably more than a steel sheet of the same size.
Q: Why is tungsten used for filaments and heating elements?
Because the metal combines the highest melting point with a very low vapour pressure, it can be heated to incandescence without evaporating or losing its shape.
Q: Is tungsten sheet magnetic?
Tungsten is paramagnetic with a magnetic permeability close to 1, so it behaves as a non-magnetic metal in instrument and shielding applications.
Q: How is tungsten sheet manufactured?
By powder metallurgy: pressing and sintering tungsten powder into a dense body, then hot and warm rolling with intermediate annealing to reach the final thickness, followed by cutting, grinding and inspection.
Q: Does tungsten sheet oxidize in air?
It is stable at room temperature, but oxidation becomes significant above about 400 °C, so high temperature service requires vacuum or a protective atmosphere.