- Heating Element Definition: A heating element is a device that converts electrical energy into heat through Joule heating, commonly used in various appliances.
- Material Properties: The efficiency of heating elements depends on properties like high melting point, resistivity, and resistance to oxidation.
- Nichrome Properties and Use: Nichrome, an alloy of nickel and chromium, is valued for its high oxidation resistance and use in high-temperature applications up to 1200 °C.
- Kanthal Properties and Use: Kanthal, an iron-chromium-aluminum alloy, is suitable for even higher temperatures up to 1400 °C, forming an insulating aluminum oxide layer.
- Applications of Platinum: Platinum is used in specialized high-temperature applications and medical treatments due to its high resistivity and stability, despite its high cost.
A heating element is a device that converts electrical energy into heat through the process of Joule heating. When an electric current passes through a resistance, it produces heat. Heating elements are used in various heating equipment or appliances, such as electric furnaces, electric ovens, electric heaters, etc.
The performance and life of a heating element depend on the properties of the material used for it. The material should have the following:
- High melting point
- High resistivity
- Low-temperature coefficient of resistance
- High tensile strength
- Sufficient ductility to form wires
- High resistance to oxidation in open atmosphere
Four materials dominate heating-element manufacture: Nichrome, Kanthal, Cupronickel and Platinum. Each combines a different mix of melting point, resistivity, temperature stability and cost.
What is Nichrome?
Nichrome, an alloy of nickel and chromium with small amounts of iron, manganese and silicon, is one of the most widely used materials for resistance wire heating elements. The typical composition of Nichrome is:
| Element | Percentage |
|---|---|
| Nickel | 80% |
| Chromium | 20% |
| Iron | 0.5% |
| Manganese | 0.5% |
| Silicon | 0.5% |
Properties of Nichrome
Nichrome has the following properties:
- Resistivity: 40 µΩ-cm
- Temperature coefficient of resistance: 0.0004 / °C
- Melting point: 1400 °C
- Specific gravity: 8.4 g/cm³
- High resistance to oxidation
Applications of Nichrome
Nichrome is used for heating elements in electric heaters and furnaces, operating up to 1200 °C. When first heated, chromium in the alloy forms a protective chromium oxide layer, preventing further oxidation and wire damage.
What is Kanthal?
Kanthal is a trademark name for a family of iron-chromium-aluminum (FeCrAl) alloys. These alloys are used for a wide range of resistance and heating applications. The typical composition of Kanthal is:
| Element | Percentage |
|---|---|
| Iron | 72% |
| Chromium | 22% |
| Aluminum | 5.8% |
Properties of Kanthal
Kanthal has the following properties:
- Resistivity at 20 °C: 145 µΩ-cm
- Temperature coefficient of resistance at 20 °C: 0.000001 / °C
- Melting point: 1500 °C
- Specific gravity: 7.1 g/cm³
- High resistance to oxidation
Applications of Kanthal
Kanthal is used in heating elements for electric heaters and furnaces, operating up to 1400 °C. On first heating, aluminum in the alloy forms a tight, insulating aluminum oxide layer that protects against further oxidation and helps the element survive thermal shock. Ceramic, steel, glass and electronics industries all rely on it.
What is Cupronickel?
Cupronickel, an alloy of copper and nickel with small amounts of strengthening iron and manganese, is also known as copper-nickel or CuNi. Low-temperature heating applications use it. The typical composition of Cupronickel is:
| Element | Percentage |
|---|---|
| Copper | 75% |
| Nickel | 23% |
| Iron | 1% |
| Manganese | 1% |
Properties of Cupronickel
Cupronickel has the following properties:
- Resistivity at 20 °C: 50 µΩ-cm
- Temperature coefficient of resistance at 20-500 °C: 0.00006 / °C
- Melting point: 1280 °C
- Specific gravity: 8.86 g/cm³
- High resistance to oxidation
Applications of Cupronickel
Cupronickel is used for heating elements in electric heaters and furnaces, particularly for low-temperature applications. Its corrosion resistance and silver-like appearance also make it a favourite coinage alloy.
What is Platinum?
Platinum is a noble metal with the symbol Pt and atomic number 78, remarkable for corrosion resistance even at high temperatures and for staying highly ductile, malleable, mechanically strong and stable.
Properties of Platinum
Platinum has the following properties:
- Resistivity at 20 °C: 10.50 µΩ-cm
- Temperature coefficient of resistance at 20 °C: 0.00393 / °C
- Melting point: 1768.3 °C
- Specific gravity: 21.45 g/cm³
- High resistance to oxidation
- High ductility
- Highly malleable
- Good mechanical strength
- Good stability with temperature and mechanical stress
Applications of Platinum
Platinum, prized for stability and corrosion resistance at high temperatures, is ideal for heating elements, rheostats and resistance thermometers. Its high cost confines it to lab furnaces (up to 1300 °C), precision rheostats and thermometers.
Platinum is also a precious metal that is very popular for making jewelry.
In medicine, platinum is used in chemotherapy for the treatment of certain types of cancers.
Conclusion
Nichrome, Kanthal, Cupronickel and Platinum cover most heating-element duties, each balancing melting point, resistivity, oxidation behaviour and cost differently.
The short version:
- Nichrome is an alloy of nickel and chromium that has high resistance to oxidation and can operate up to 1200 °C.
- Kanthal is an alloy of iron-chromium-aluminum that has high resistance to oxidation and can operate up to 1400 °C.
- Cupronickel is an alloy of copper and nickel that has high resistance to oxidation and can operate up to 600 °C.
- Platinum is a noble metal that has high resistivity and melting point but very high cost.
Match the alloy to the temperature, and the element will outlast the appliance around it.
