CBSE Class 12-science Answered
The performance and life of heating coil depend on properties of the material used for heating element.
The required properties in material used for heating coils-
- High melting point.
- Free from oxidation in open atmosphere.
- High tensile strength.
- Sufficient ductility to draw the metal or alloy in the form of wire.
- High resistivity.
- Low temperature coefficient of resistance.
Following material are used for manufacturing heating coil-
- Nichrome
- Kanthal
- Cupronickel
Properties of Nichrome
- Resistivity : 40 µΩ -cm
- Temperature coefficient of resistance: 0.0004 /oC
- Melting point: 1400oC
- High resistance to oxidation
“Kantahl” is trademark name for alloys made by composing Iron-Chromium-Aluminum (Fe-Cr-Al).
These alloys are used in wide range resistance and heating applications.
Composition of Kanthal :- 70% Fe , 25% Cr and 5% Al
Properties of Kanthal
- Resistivity at 20oC: 145 µΩ -cm
- Temperature coefficient of resistance at 20oC: 0.000001/oC
- Melting point: 1500oC
- High resistance to oxidation
Cupronickel is also called as copper-nickel. It is an alloy made by composing copper, nickel and
strengthening elements such as iron and manganese.
Composition of Cupronickel :- 66% Cu , 30% Ni , 2% Fe and 2% Mn
Properties of Cupronickel
- Resistivity at 20oC: 50 µΩ -cm
- Temperature coefficient of resistance at 20-500oC : 0.00006 /oC
- Melting point: 1280oC
- High resistance to oxidation