Manganin

This article is about an alloy. For the antimicrobial peptides, see magainin.

Manganin is a trademarked name for an alloy of typically 84.2% copper, 12.1% manganese, and 3.7% nickel. It was first developed by Edward Weston in 1892, improving upon his Constantan (1887).

Manganin
A manganin resistor made in 1900 at the Bushy House physics laboratory.
Material type	Copper-manganese alloy
Physical properties
Density (ρ)	8.4 g/cm3
Mechanical properties
Tensile strength (σt)	300–600 MPa
Elongation (ε) at break	<50%
Izod impact strength	107 J/m
Thermal properties
Melting temperature (Tm)	1020 °C
Thermal conductivity (k) at 23 °C	22 W/(m·K)
Linear thermal expansion coefficient (α)	(14–19)×10−6 K−1
Specific heat capacity (c)	0.097 cals/gm
Electrical properties
Volume resistivity (ρ)	43–48 μΩ⋅cm
Source[1]

Manganin foil and wire is used in the manufacture of resistors, particularly ammeter shunts, because of its virtually zero temperature coefficient of resistance value^[2] and long term stability. Several Manganin resistors served as the legal standard for the ohm in the United States from 1901 to 1990.^[3] Manganin wire is also used as an electrical conductor in cryogenic systems, minimizing heat transfer between points which need electrical connections.

Manganin is also used in gauges for studies of high-pressure shock waves (such as those generated from the detonation of explosives) because it has low strain sensitivity but high hydrostatic pressure sensitivity.^[4]

History

In 1887 Edward Weston discovered that metals can have a negative temperature coefficient of resistance, inventing what he called his "Alloy No. 2." It was produced in Germany where it was renamed "Constantan".^[5] In 1888 he patented^[6] "an alloy containing from 65 to 70 parts of copper, 25 to 30 parts of ferro-manganese, and 2.5 to 10 parts of nickel" which had a nearly constant resistivity.

Manganin wire as we know it was developed by Weston's assistant John Forrest Kelly.^[7] In May 1893, Weston received a patent^{[citation needed]} for the material and its use for resistors. While Manganin represented a significant advance in technology -- the material was a conductive metal with constant resistance over a wide range of working temperatures, Weston did not receive wide recognition at the time.^[8]

Properties

Cu86/Mn12/Ni2

Electrical Properties

• Temperature coefficient: 1.5×10⁻⁵ K⁻¹

Mechanical Properties

• Modulus of elasticity: 124–159 GPa
• Maximum use temperature in air: 300 °C

Cu84/Mn12/Ni4^[9]

Temperature [°C]	coefficient of resistivity
12	+.000006
25	.000000
100	−.000042
250	−.000052
475	.000000
500	+.00011

Resistance of Wires at 20 °C^[10]

AWG	ohms per cm	ohms per ft
10	.000836	0.0255
12	.00133	0.0405
14	.00211	0.0644
16	.00336	0.102
18	.00535	0.163
20	.00850	0.259
22	.0135	0.412
24	.0215	0.655
26	.0342	1.04
27	.0431	1.31
28	.0543	1.66
30	.0864	2.63
32	.137	4.19
34	.218	6.66
36	.347	10.6
40	.878	26.8

See also

• List of named alloys