Nichrome is basically a name given to nickel-chromium resistance wires. It is a non-magnetic alloy, which consists of 80 percent nickel and 20 percent chromium by weight, and is widely used in heating elements because of its relatively high resistivity. Out of the constituents of nichrome, nickel is an element with the chemical symbol Ni and atomic number 28, whereas chromium is an element with the symbol Cr and atomic number 24. Nickel is generally a silvery-white lustrous metal, and chromium, a steely-gray and hard metal. Nichrome, the alloy, is silvery-gray in color, resistant towards corrosion, and has a high melting point.
Physical Properties of Nichrome
The ultimate tensile strength of nichrome is 105,000 PSI (Pounds per Square Inch) and yield strength is around 50,000 PSI. Following are some of the other physical properties of nichrome.
- Electrical Resistivity at room temperature: 1.0 x 10-6 to 1.5 x 10-6 ohm m
- Thermal Conductivity: 11.3 W/moC
- Magnetic Attraction: None
- Thermal Expansion Coefficient (20oC to 100oC): 13.4 x 10-6/oC
- Temperature Coefficient of Resistivity (25oC to 100oC): 100 ppm/oC
- Specific Gravity: 8.4
- Density: 8400 kg/m3
- Melting point: 1400oC
- Specific Heat: 450 J/kgoC
- Modulus of elasticity: 2.2 x 1011
Uses of Nichrome
It is used in the explosives, fireworks, and ceramic making industry, as a heating element. The alloy is very useful in the process of ceramic making, as it can withstand the high temperatures that are generated when a clay object is fired in a kiln. It is also used in motorcycle silencers and in certain microbiological lab apparatus. The chromium present in the wire oxidizes on being heated, and forms a protective layer of chromium oxide. The alloy is expensive because of its high nickel content.
It is also used in the production of special thin films, which are ideally suited for use in hybrid assemblies. The application of these thin films also extends to integrated circuits in fields like telecommunication, power supplies, instrumentation, military, and medical equipment, where low noise and good power dissipation is required. Due to its relatively high resistivity and resistance to oxidation at high temperatures, nichrome is used in heating elements built inside hair dryers, electric ovens, and toasters. For such purposes, the wire is generally wound in coils, which when subjected to electric current, produces heat as a result of its high electrical resistance.
Nichrome is a very useful alloy because of its properties, and has found applications in many instruments which require high resistivity of the constituent material.