Tungsten filaments are ultra-fine wire forms of high-purity tungsten engineered to operate at extremely high temperatures while maintaining mechanical integrity, dimensional stability, and consistent electrical performance. They are essential in incandescent and halogen lamps, vacuum electronics, heating elements, and scientific instrumentation.
Chemical Composition
| Element | Content (wt%) |
|---|---|
| Tungsten (W) | 99.9 – 99.99 |
| Potassium (K) | 0.001 – 0.01 |
| Silicon (Si) | Trace |
| Aluminum (Al) | Trace |
| Oxygen / Carbon / Nitrogen | Extremely low |
Potassium-doped tungsten (K-W) is the most common filament grade, providing superior creep resistance and sag control at elevated temperatures.
Key Physical Properties
| Property | Value |
|---|---|
| Density | 19.25 g/cm³ |
| Melting Point | 3422 °C |
| Working Temperature | 2000 – 3000 °C |
| Electrical Resistivity (20 °C) | 5.6 µΩ·cm |
| Thermal Conductivity | 170 – 180 W/m·K |
| Thermal Expansion | 4.5 × 10⁻⁶ /K |
| Crystal Structure | BCC |
| Vapor Pressure | Extremely low |
Key Mechanical Properties
| Property | Typical Value |
|---|---|
| Tensile Strength (RT) | 800 – 2000 MPa |
| Tensile Strength (Hot) | Retained above 2000 °C |
| Elastic Modulus | ~410 GPa |
| Creep Resistance | Outstanding |
| Sag Resistance | Excellent |
| Ductility | Low at RT, good at high temperature |
Strengthening & Metallurgical Behavior
Fiber-like grain structure from wire drawing
Dispersion strengthening via potassium bubbles
Grain boundary pinning for creep resistance
Very high recrystallization temperature (>1200 °C)
Excellent resistance to thermal fatigue
Manufacturing Process
Hydrogen reduction to tungsten powder
Pressing and sintering
Swaging and hot forging
Multi-stage heated wire drawing
K–Si–Al doping process
Final annealing and filament coiling
Available Forms
Straight filaments
Coiled filaments
Double-coiled filaments
Flat filaments
Ribbon filaments
Custom geometries
Applications
Lighting
Incandescent lamps
Halogen lamps
Projection lamps
Electronics & Vacuum Devices
Cathodes
Electron guns
Vacuum tubes
Heating & Scientific
Vacuum furnace heaters
X-ray tubes
Electron microscopes
Mass spectrometers
Advantages
✔ Highest operating temperature of any metal filament
✔ Excellent creep and sag resistance
✔ Stable electrical performance
✔ Long operational life
✔ Extremely low vapor pressure
Limitations
❌ Rapid oxidation in air at high temperature
❌ Brittle at room temperature
❌ Requires vacuum or inert atmosphere
❌ Declining use in general lighting
Why Choose Tungsten Filaments?
Choose tungsten filaments when extremely high operating temperatures, stable electron emission, precise electrical heating, and long-term reliability in vacuum or inert environments are required.