- Nichrome
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Nichrome is a non-magnetic alloy of nickel, chromium, and often iron, usually used as a resistance wire. Patented in 1905, it is the oldest documented form of resistance heating alloy. A common alloy is 80% nickel and 20% chromium, by mass, but there are many others to accommodate various applications. It is silvery-grey in colour, is corrosion-resistant, and has a high melting point of about 1400 °C (2552 °F). Due to its relatively high electrical resistivity and resistance to oxidation at high temperatures, it is widely used in electric heating elements, such as in hair dryers, electric ovens, soldering iron, toasters, and even electronic cigarettes. Typically, Nichrome is wound in coils to a certain electrical resistance, and current is passed through to produce heat.
Contents
Uses
Nichrome is used in the explosives and fireworks industry as a bridgewire in electric ignition systems, such as electric matches and model rocket igniters.
Industrial and hobby hot wire foam cutters use nichrome wire.
Nichrome wire is commonly used in ceramics as an internal support structure to help some elements of clay sculptures hold their shape while they are still soft. Nichrome wire is used because of its ability to withstand the high temperatures that occur when clay work is fired in a kiln.
Nichrome wire is used in testing the colour of the flame in the non-luminous part of fire of a cation such as the cations of potassium, copper, calcium, sodium etc.
The alloy tends to be expensive due to its high nickel content. Distributor pricing is typically indexed to commodity market prices for nickel.
Other areas of usage include motorcycle silencers, and in certain areas in the microbiological lab apparatus.
For heating, resistance wire must be stable in air when hot. Nichrome wire forms a protective layer of chromium oxide. [1]
Properties
The properties of nichrome vary depending on its alloy. Figures given are representative of typical material and are accurate to expressed significant figures. Any variations are due to different percentages of nickel or chromium.
Material property Value Units Modulus of elasticity 2.2 × 1011 Pa Specific gravity 8.4 Dimensionless Density 8400 kg/m3 Melting point 1400 °C Electrical resistivity at room temperature 1.0 × 10−6 to 1.5 × 10−6 Ωm Specific heat 450 Jkg−1°C−1 Thermal conductivity 11.3 Wm−1°C−1 Thermal expansion 14 × 10−6 °C−1 Standard ambient temperature and pressure
used unless otherwise noted.Additional properties
Approximate current (A) to heat a straight oxidized wire to a given temperature[2] AWG DIA-IN 400F 1000F 2000F 8 .128 22.4 52 128 10 .102 16.2 37.5 92 12 .081 11.6 26.5 65 22 .0253 2.9 5.6 12.5 32 .0080 0.68 1.36 2.76 40 .0031 0.24 0.43 0.79 Ohms per foot @ 20 deg C[2] AWG DIA-IN NiCrA NiCrC 10 .102 0.06248 0.06488 12 .081 0.09907 0.1029 22 .0253 1.015 1.055 32 .0080 10.16 10.55 40 .0031 67.64 70.24 Increase in resistance with temperature[2] DEG.F DEG.C NiCrA NiCrC 68 20 0 0 600 315 3.3% 5.2% 1000 538 6.3% 8.6% 2000 1093 6.0% 10.5% - NiCrA
- Chemical Composition: 80% Ni, 20% Cr
- Approx. Melting Point: 1400 deg C
- NiCrC
- Chemical Composition: 61% Ni, 15% Cr, bal. Fe
- Approx. Melting Point: 1350 deg C
See also
References
- ^ "Advanced Topic: Oxidation Resistant Materials" (PDF). Sciences Education Foundation. General Atomics. 2002.
- ^ a b c "Nichrome 80 & Other Resistance Alloys - Technical Data & Properties". wiretron.com, Wiretronic Inc.
External links
Categories:- Nickel–chromium alloys
- Refractory metals
- Firelighting
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