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Manganin
Manganin
Manganin
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Manganin
A manganin resistor made in 1900 at the Bushy House physics laboratory.
Material typeCopper-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 strength107 J/m
Thermal properties
Melting temperature (Tm)1020 °C
Thermal conductivity (k) at 23 °C22 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 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 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.[citation needed]

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

[edit]

Invention and early development

[edit]

In the late 19th century, the American chemist Edward Weston sought to improve the accuracy of electrical measuring instruments. At the time, the resistance of most metals changed significantly with temperature, introducing errors in precision measurements. In 1887, Weston discovered that certain alloys could possess a negative temperature coefficient of resistance. He invented "Alloy No. 2", a copper-nickel alloy which was later produced in Germany under the name Constantan.[5]

Continuing his research, Weston developed Manganin in 1892 as an improvement upon Constantan. While Constantan had a low temperature coefficient, Manganin offered a resistance value that was virtually constant near room temperature and possessed better long-term stability.[6] In May 1893, Weston received U.S. Patent 497,482 for a "Shunt for Electric Light and Power Stations," which detailed the use of his new high-resistance alloys in precision applications.[7][8]

Standardization

[edit]

Manganin was rapidly adopted by the scientific community, particularly in Germany where the Physikalisch-Technische Reichsanstalt (PTR) conducted extensive research on its properties. In 1890, K. Feussner at the PTR developed the "Reichsanstalt-type" resistor, which utilized Manganin wire wound on a metal form.[6] These resistors served as the primary reference standards for the ohm in national metrology laboratories for decades. However, the early designs were not hermetically sealed; the wire was typically insulated with shellac, which was hygroscopic. Changes in atmospheric humidity caused the shellac to swell, stressing the wire and causing the resistance to drift over time.[9]

Refinement at NBS

[edit]

To address the stability issues of the Reichsanstalt design, James L. Thomas at the U.S. National Bureau of Standards (now NIST) developed an improved standard in 1933, known as the "Thomas-type" resistor. These standards used heavy Manganin wire that was annealed at high temperatures in a vacuum to remove internal stresses. Crucially, the resistor was hermetically sealed in a double-walled container to protect it from humidity and atmospheric effects.[6]

Modern legacy

[edit]

From 1901 until 1990, Manganin resistors (first the Reichsanstalt type, then the Thomas type) served as the legal standard for the ohm in the United States and many other nations.[10] In 1990, the international standard for resistance was redefined based on the Quantum Hall effect, which provides an invariant quantum standard. Despite this, Manganin resistors remain widely used today as robust working standards and in high-precision ammeter shunts due to their proven reliability and low cost compared to quantum standards.[6]

Properties

[edit]

Cu86/Mn12/Ni2

[edit]

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[11]
Temperature [°C] coefficient of resistivity
 12 +0.000006
 25  0.000000
100 −0.000042
250 −0.000052
475  0.000000
500 +0.00011 
Resistance of Wires at 20 °C[12]
AWG [Ω/cm] [Ω/ft]
10 0.000836  0.0255
12 0.00133   0.0405
14 0.00211   0.0644
16 0.00336   0.102 
18 0.00535   0.163 
20 0.00850   0.259 
22 0.0135    0.412 
24 0.0215    0.655 
26 0.0342    1.04  
27 0.0431    1.31  
28 0.0543    1.66  
30 0.0864    2.63  
32 0.137     4.19  
34 0.218     6.66  
36 0.347    10.6   
40 0.878    26.8   

See also

[edit]

References

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Manganin

View on Grokipedia
from Grokipedia
Manganin is a trademarked name for a copper-manganese-nickel alloy, with typical compositions of approximately 84–86% copper, 11–12% manganese, and 3–4% nickel. Invented by Edward Weston in 1892, it is valued for its nearly constant electrical resistivity with temperature changes (low temperature coefficient of resistance), making it suitable for precision resistors and sensors. The alloy is used in standard resistors, current shunts, pressure gauges, and precision instrumentation where stable resistance is critical.

Composition

Standard Alloy

Manganin is a copper-based primarily composed of approximately 86% (Cu), 12% (Mn), and 2% (Ni) by weight. This specific ratio forms the standard formulation, serving as the foundational material for precision resistance applications due to its balanced elemental contributions to overall performance. Copper acts as the base element, establishing the alloy's inherent electrical conductivity while forming a matrix that integrates the other components effectively. enhances the stability of electrical resistance, helping maintain consistent properties under varying conditions. fine-tunes the of resistance, optimizing the alloy's response to thermal changes through precise compositional adjustment. The resulting physical characteristics include a of 8.4 g/cm³, directly attributable to the weighted contributions of , , and in this mix. Additionally, the alloy exhibits a of 960 °C, reflecting the thermal stability inherent to its elemental proportions. This composition enables a low of resistance, crucial for reliable performance in sensitive electrical circuits.

Variants

Manganin variants involve precise adjustments to the proportions of , , and to suit specific performance needs while maintaining the alloy's core resistance characteristics. Compositions can vary slightly by manufacturer or application, typically within 84–86% Cu, 12% Mn, and 2–4% . One common variant consists of 84% , 12% , and 4% , often used for general resistance applications. Another modification is 84.2% , 12.1% , and 3.7% . In shunt-specific variants, the alloy shifts to 87% , 9.5% , and 3.5% to optimize for high-current environments. These variations arise primarily from adjustments to content, which improves workability and mechanical strength, or to levels for optimizing the of resistance (TCR) in targeted conditions like varying or load. Such compositional tweaks result in minor alterations to fundamental physical traits, including shifts from approximately 8.19 to 8.4 g/cm³ and points ranging from 960 °C to 1020 °C, influencing processability without compromising usability.

Properties

Electrical Properties

Manganin exhibits a resistivity ranging from 43 to 48 μΩ·cm at , making it suitable for applications requiring stable electrical resistance. The of resistance (TCR) for manganin is approximately ±10 ppm/°C, equivalent to 1.0 × 10^{-5} K^{-1}, and remains nearly zero between +20°C and +50°C, ensuring minimal variation in resistance over this range. This low TCR arises because the alloy's resistance changes only slightly with , as quantified by the formula α=1RdRdT,\alpha = \frac{1}{R} \frac{dR}{dT}, where α\alpha is the TCR, RR is the resistance, and dR/dTdR/dT is the rate of change of resistance with ; for manganin, this yields a near-constant value in the specified range, minimizing drift in precision circuits. The thermal (EMF) of manganin against is low, typically less than 1 μV/°C, which prevents unwanted voltage generation in thermocouple-like setups and supports its use in accurate current devices. For electrical stability, manganin's maximum working is 140°C in air, though it can reach up to 300°C in or inert atmospheres without significant degradation.

Mechanical and Thermal Properties

Manganin exhibits a range of mechanical properties that provide moderate strength and suitable for precision components. Its typically falls between 300 and 600 MPa, depending on the wire and conditions, with thinner wires achieving higher values around 390 MPa. Elongation at break is generally less than 50%, often around 12% for fine wires and up to 25% for thicker sections, indicating good without excessive . The ranges from 124 to 159 GPa, reflecting a comparable to many copper-based alloys, which supports reliable elastic behavior under load. In terms of thermal properties, manganin has a relatively low thermal conductivity of 22 W/(m·K) at 20°C, which helps minimize heat dissipation in resistive elements and contributes to thermal stability alongside its low of resistance. The coefficient of linear is (14–19) × 10^{-6} K^{-1}, with values around 18 × 10^{-6} K^{-1} over 20–100°C and increasing slightly to 19.5 × 10^{-6} K^{-1} up to 400°C, allowing dimensional stability across moderate temperature ranges. Its of 8.4 g/cm³ and of 960°C further inform thermal processing limits, enabling use up to 140°C in air without significant degradation. Manganin demonstrates poor and oxidation resistance, readily forming a thin in air that can impair performance over time, thus necessitating protective coatings such as enamels or varnishes for prolonged exposure. The offers good workability, with excellent for shaping into wires, foils, and strips, and strong , , and brazeability, facilitating straightforward joining without specialized techniques.

History

Invention

Manganin was developed by Edward Weston in 1884 as a high-stability resistance alloy for precision electrical instruments. Motivated by the need to overcome the instability and high temperature coefficient of earlier materials like German silver, Weston sought a conductor with minimal variation in resistance under temperature changes and low thermoelectric effects when paired with copper. This effort built upon his concurrent invention of Constantan in the same year, which offered a negative temperature coefficient of resistance (TCR) but suffered from high thermal electromotive force (EMF) against copper, limiting its use in sensitive millivolt measurements. Weston's experiments involved testing over 400 combinations, focusing on a -manganese base to achieve inherent stability, with added to further reduce the TCR. The resulting manganin composition—approximately 84% , 12% , and 4% —demonstrated a TCR of nearly zero between 25°C and 55°C, with an overall value of ±0.00001 per °C, far surpassing prior . Early tests also confirmed low thermal EMF of 1.7 µV/°C against , compared to Constantan's 43 µV/°C, enabling more accurate instrument performance without significant thermoelectric errors. Weston applied for a patent on the alloy in 1885 (original U.S. Patents Nos. 381,304 and 381,305, issued April 24, 1888), which was granted as U.S. Reissue Patent No. 10,944 on , 1888, covering an composed of , , and in proportions such as 65-70 parts , 20 parts , and 10-15 parts . This patent emphasized the alloy's utility for standards of resistance and measuring instruments, marking a key advancement in materials for .

Adoption and Standards

Following its , manganin rapidly gained commercial traction in the production of precision resistors during the early , owing to its exceptional temperature stability and low resistance drift, which made it ideal for electrical instruments. By 1898, the German firm Isabellenhütte GmbH had begun large-scale manufacturing of manganin alloy under the MANGANIN®, supplying it for applications in , railroads, and , marking the alloy's transition from laboratory curiosity to industrial material. This widespread adoption stemmed from manganin's ability to maintain consistent resistivity under varying environmental conditions, surpassing earlier alloys like in reliability for shunt resistors and standard coils. Manganin played a pivotal role in establishing electrical resistance standards, particularly as the material for the U.S. legal standard of the from 1901 to 1990, maintained by the National Bureau of Standards (now NIST). Initially, non-sealed Reichsanstalt-type manganin resistors were employed starting in 1901, but these proved sensitive to , leading to their replacement by oil-sealed Rosa-type standards in 1909, which offered improved . By 1932, the superior Thomas-type resistors—featuring hermetically sealed, double-walled designs with heat-treated manganin wire—became the primary standard, demonstrating long-term stability with drifts as low as 1 μΩ/Ω over decades. These refinements, including larger wire diameters and optimized mounting to minimize thermal gradients, enhanced precision and reduced loading errors, solidifying manganin's status in . The alloy's dominance in standards waned with the advent of quantum-based measurements; on January 1, 1990, the U.S. ohm was redefined using the quantum Hall effect, leveraging the von Klitzing constant for absolute accuracy with uncertainties below 2.4 × 10⁻⁸, supplanting manganin artifacts due to their gradual drift (approximately 5.3 × 10⁻⁸ per year). Nonetheless, manganin remains in use today for high-precision resistors in calibration labs and instrumentation, valued for its enduring stability in non-quantum contexts.

Manufacturing

Alloy Production

Manganin alloy is produced using high-purity raw materials, primarily (99.99% purity oxygen-free electronic copper), (99.99% purity), and (99.92% purity), to minimize impurities that could affect its electrical stability. These elements are selected for their roles in achieving the alloy's characteristic low of resistance (TCR). The melting process employs induction melting in a , such as or , to prevent oxidation of the reactive component. This method allows for precise temperature control, typically reaching the around 960–1020°C, while avoiding contamination from crucibles or ambient air. During alloying, the elements are added in controlled proportions to target a standard composition of approximately 86% , 12% , and 2% , with electromagnetic stirring induced by the induction process ensuring homogeneity throughout the melt. Small-scale production batches, up to 20 kg, are common in pilot plants to maintain quality. The molten alloy is then cast into ingots or bar forms, often with dimensions such as 300 mm × 80 mm × 25 mm, to solidify the material while preserving uniformity. Following casting, an initial homogenization annealing is performed to stabilize the microstructure, reducing internal stresses and ensuring consistent properties across the ingot. involves compositional analysis using techniques like optical emission spectroscopy (ICP-OES) to verify the and contents within tight tolerances, confirming the alloy's potential for low TCR values around ±10 ppm/K. This step ensures the final product meets standards for precision resistance applications.

Forming and Processing

Manganin ingots undergo through rolling or to produce intermediate bars, rods, or strips, followed by processes such as and rolling to achieve final dimensions. Cold is commonly employed to form round wires with diameters ranging from 0.02 mm to 8.00 mm, while rolling produces flat strips (0.02–0.5 mm thick by 0.5–8 mm wide) and foils (0.02–0.1 mm thick by up to 50 mm wide). These processes leverage manganin's good and workability, enabling precise shaping without excessive cracking. After forming, via annealing is essential to relieve residual stresses from working and to stabilize the of resistance (TCR) for consistent performance. Annealing typically involves heating at 250–300°C for 1–2 hours, which minimizes resistance drift and enhances long-term stability in precision applications. For high-stability resistors, additional aging treatments at controlled temperatures further reduce mechanical strains, ensuring the TCR remains near zero over operational ranges. Given manganin's limited oxidation resistance in air above 140°C, surface treatments are applied to provide protection during use and handling. Common methods include enameling or applying insulating s such as , , or coverings directly onto the formed components, which prevent atmospheric degradation while maintaining electrical integrity. Prior to , any surface layer must be removed to ensure and uniform coverage. Manganin is supplied in these processed forms—primarily bare or coated round wires, flat strips, and foils—ready for integration into elements or other components. A key challenge in forming and is preserving uniformity across the , as localized strains or inconsistencies in can introduce variations in resistivity and TCR, compromising overall stability. Strict control of working parameters and post- annealing helps mitigate these issues, ensuring reliable electrical properties.

Applications

Precision Resistance Components

Manganin, a -manganese-nickel , serves as a foundational in precision resistance components due to its exceptional electrical stability, enabling accurate performance in measurement and control devices. Its low of resistance (TCR), typically around ±10 ppm/K between +20 °C and +50 °C, minimizes variations in resistance with fluctuations, making it ideal for applications requiring long-term reliability. This stability supports high accuracy over wide current ranges and reduces drift, outperforming like pure or other in demanding circuits. In precision resistors, manganin is primarily employed in wire-wound configurations, where its high resistivity (approximately 0.44 × 10⁻⁶ Ω·m) and low TCR ensure consistent performance in circuits demanding tight tolerances. Foil-type resistors also utilize manganin for enhanced precision, offering compact designs with minimal suitable for high-frequency applications. Potentiometers incorporate manganin wire or foil to provide adjustable resistance with negligible emf versus , preventing errors in DC circuits and supporting fine control in . Ammeter shunts rely on manganin for creating low-resistance paths that divert excess current, allowing safe measurement of high DC currents through a voltage drop across the shunt. The alloy's time-stable resistance and low TCR (about 20 ppm/°C) maintain accuracy in shunts rated from 1 A to over 1200 A, essential for industrial and laboratory ammeters where even small drifts could compromise readings. Manganin has historically and currently played a critical role in resistance standards for purposes, particularly in labs. Double-walled, hermetically sealed manganin resistors, such as the Thomas-type designs, exhibited resistance changes of less than 1 part in 10⁶ over decades, serving as U.S. legal standards from 1939 until the 1990 redefinition. Today, they function as working standards and verification tools for quantum-based calibrations, with NIST annually calibrating around 125 units to ensure in resistance measurements. This TCR stability enables precise scaling from low to high resistance values without significant environmental interference. Strain gauges leverage manganin's piezoresistive effects, where applied mechanical stress induces a measurable change in resistance due to its piezoresistive response, with a relative sensitivity (ΔR/R per strain) around 0.7 under uniaxial and low temperature sensitivity (<15 ppm/°C). Thin-film or foil manganin gauges, with resistances from 0.03 to 350 Ω, detect dynamic stresses with resolution, minimizing wave perturbations in the material under test. The low temperature sensitivity (<15 ppm/°C) isolates strain-induced signals from , enhancing accuracy in mechanical sensing applications like shock compression analysis. Overall, manganin's advantages in these components include superior long-term stability, with resistance drift minimized through controlled annealing and hermetic sealing, achieving accuracies better than 0.01% over extended periods. This enables reliable operation across current ranges from milliamps to kiloamps, reducing calibration frequency and maintenance in precision electrical systems.

Specialized Uses

Manganin finds specialized applications in high-pressure scientific instrumentation, particularly as piezoresistive gauges for measuring dynamic stress waves in materials under extreme conditions. These gauges exploit manganin's high sensitivity to pressure-induced resistance changes, with a relative piezoresistive typically around 0.02 GPa^{-1} (ΔR/R per GPa), while remaining largely insensitive to variations. In shock physics experiments, manganin foil gauges (5–25 µm thick) are embedded in samples to capture longitudinal and lateral stresses from 1 to 40 GPa, resolving pulses as short as 10 ns; this enables studies of phenomena such as shock-induced conduction in polymers, in metals, and pressures in explosives. Configurations include in-situ gauges for bulk property assessment and back-surface setups for wave profile analysis, often in plate-impact or explosive-driven tests. Beyond standard pressure transduction, manganin wire gauges are employed in high-temperature, large-volume presses for in-situ pressure monitoring up to 100 kbar, leveraging the in the wire for precise calibration against diffraction standards like NaCl. Thin-film manganin sensors extend this capability to microscale measurements, such as pressures in confined geometries, where traditional foil gauges are too bulky. These applications are prevalent in , , and defense research, with manganin preferred for its minimal perturbation of the stress field and established calibration protocols developed over decades. In cryogenic environments, manganin serves as a low-magnetization conductor for instrumentation wiring and sensors, exhibiting magnetic susceptibility of 1.25 × 10^{-2} emu/g·Oe at 4.2 K and magnetoresistance of about -2.8% at 10 T (4 K, transverse field). This makes it suitable for nonmagnetic cryostat leads, heater elements, and strain gauges in liquid-helium systems, where it minimizes thermal electromotive forces relative to copper (typically <1 µV/K). Manganin-based sensors have been adapted for low-temperature pressure gauging down to 55 K, maintaining a stable pressure coefficient of resistance across helium-gas setups. Such uses support precision measurements in superconductivity research and space cryogenics, as documented in NASA evaluations of metallic resistance thermometers.

References

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  10. https://nepp.nasa.gov/files/23452/S-311-S-820.pdf
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  34. https://pubs.aip.org/aip/rsi/article-abstract/78/4/046104/349994
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  37. https://ntrs.nasa.gov/api/citations/19700020667/downloads/19700020667.pdf
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