Properties of Nichrome Wire

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), yield strength is around 50,000 PSI, and modulus of elasticity is 31 x 10⁶ 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/m^oC
• Magnetic Attraction: None
• Thermal Expansion Coefficient (20^oC to 100^oC): 13.4 x 10^-6/^oC
• Temperature Coefficient of Resistivity (25^oC to 100^oC): 100 ppm/^oC
• Specific Gravity: 8.4
• Density: 8400 kg/m³
• Melting point: 1400^oC
• Specific Heat: 450 J/kg^oC
• Modulus of elasticity: 2.2 x 10¹¹

Uses of Nichrome

Nichrome is used in the explosives and fireworks industry, ceramic making and as a heating element. The alloy is very useful in the process of ceramic making, as it can withstand the high temperatures that occur when a clay work is fired in a kiln. Nichrome is also used in motorcycle silencers and in certain microbiological lab apparatus. The chromium present in nichrome wire oxidizes on being heated and forms a protective layer of chromium oxide. The alloy is expensive because of its high nickel content.

Nichrome is also used in the production of special nichrome 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 are 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 purpose, nichrome is generally wound in wire coils to a certain electrical resistance and current is passed through it, in order to produce heat.

Nichrome is a very useful alloy because of its properties and has found application in many instruments which require high resistivity of the constituent material.