Chromel
{{Short description|Trademark for a family of chromium-nickel alloys}}
Chromel is an alloy made of approximately 90% nickel and 10% chromium by weight that is used to make the positive conductors of ANSI Type E (chromel-constantan) and K (chromel-alumel) thermocouples. It can be used at temperatures up to {{convert|1100|°C|abbr=on}} in oxidizing atmospheres. Chromel is a registered trademark of Concept Alloys, Inc.[http://conceptalloys.com/concept-alloys-intellectual-property/ Concept Alloys, Inc. Intellectual Property] retrieved 12 April 2016
| class="wikitable"
|+ Characteristics and properties of chromel (Ni, 90%; Cr, 10% by weight) |
| Characteristic
! Value |
|---|
| Temperature coefficient
| 0.00032 K−1 |
| Electrical resistivity
| 0.706 μΩ m |
| colspan=2 | Mechanical |
| Elongation at break
| <44% |
| Izod impact strength
| 108 J m−1 |
| Modulus of elasticity
| 186 GPa |
| Tensile strength
| 620–780 MPa |
| colspan=2 | Physical |
| Density
| 8.5 g cm−3 |
| Melting point
| 1420 °C |
| colspan=2 | Thermal |
| Coefficient of thermal expansion
| 12.8×10−6 K−1 at 20–1000 °C |
| Maximum use temperature in air
| 1100 °C |
| Thermal conductivity
| 19 W m−1 K−1 at 23 °C |
Chromel A
Chromel A is an alloy containing approximately 80% nickel and 20% chromium (by weight), with low-level quantities of Si (1%), Fe (0.5%), and Ni. It is used for its excellent resistance to high-temperature corrosion and oxidation. It is also commonly called Nichrome 80-20, and is used for electric heating elements.
Chromel C
Chromel C is an alloy containing 60% nickel, 16% chromium and 24% iron. It is also commonly called Nichrome 60 and is used for heating elements, resistance windings, and hot wire cutters.
Chromel-R
File:USAF Astronaut Maneuvering Unit.jpg
Chromel R has a composition of Cr 20%, Ni 80%.{{Cite book
|title=Woldman's Engineering Alloys
|editor=John P. Frick
|year=2000
|publisher=ASM International
|isbn=9780871706911
|page=264
|url=https://books.google.com/books?id=RzMOiOEQ-oMC&pg=PA264
}}
Chromel-R was also produced as a woven fabric of chromel wires.{{why|reason=unclear what material properties commended Chromel to this application|date=March 2025}} It was developed by Litton Industries for use by NASA in the Gemini and Apollo programs.{{Cite book
|title=Textile Technology and Design
|last1=Schneiderman |first1=Deborah
|last2=Winton |first2=Alexa Griffith
|publisher=Bloomsbury Publishing
|year=2016
|isbn=9781474261968
|page=177
|url=https://books.google.com/books?id=4ASrCgAAQBAJ&pg=PT177
}}
The Gemini G4C spacesuit did not use Chromel-R as standard. However the Gemini 9 mission was to test the use of the Astronaut Maneuvering Unit, a free-flying 'rocket pack'. To protect against the hot exhaust of its hydrogen peroxide engine, Gene Cernan's suit was given additional protection with an over-trouser layer of Chromel-R. The spacewalk during this flight gave a number of problems, with Cernan overheating and finding the suit difficult to move in it, with "all the flexibility of a rusty suit of armor".{{cite book
|title=The Last Man on the Moon: Astronaut Eugene Cernan and America's Race in Space
|first1=Eugene |last1=Cernan
|authorlink=Gene Cernan
|first2=Donald A. |last2=Davis
|year=2013
|publisher=St. Martin's Press |location=New York
|isbn=9781429971782
|page=134
}} The Chromel-R layer was an integral part of the spacesuit,It may be seen being worn as the astronauts travel out to the launch pad, :File:S66-34075.jpg although the confined Gemini capsule did not require much movement until the spacewalk. Once pressurised, the suit became difficult to move in.
File:Neil Armstrong's Apollo 11 Lunar EVA glove (27933065161).jpg
Smaller patches of Chromel-R formed an outer layer of the Apollo spacesuit where abrasion resistance was needed.{{Cite magazine
|title=New Apollo is to have fireproof cabin materials and spacesuits
|magazine=Popular Science
|date=November 1967
|page=98
|url=https://books.google.com/books?id=wioDAAAAMBAJ&pg=PA98
}} These patches can be seen as silver-grey areas over the white Beta cloth of the main suit. Using patches, rather than an entire garment, avoided the flexibility problems with Gemini. The upper areas of the overshoes, the gloves{{Citation
|title=Apollo Experience Report – Development of the Extra Vehicular Mobility Unit
|id=NASA TN D-8093
|publisher=NASA
|work=NASA Technical Note
|date=November 1975
|page=12
|url=https://www.hq.nasa.gov/alsj/tnD8093EMUDevelop.pdf
}} and patches beneath the life support backpack were of Chromel-R. Gold-plated open-weave Chromel-R mesh has also been used as the reflecting surface for compact-folding parabolic antenna on spacecraft.{{Cite web
|title=Deployable Antenna
|work=Jet Propulsion Laboratory 1971 Annual Report
|publisher=Jet Propulsion Laboratory
|year=1972
|url=https://www.jpl.nasa.gov/report/1971.pdf
|archive-url=https://web.archive.org/web/20140714143849/http://www.jpl.nasa.gov/report/1971.pdf
|url-status=dead
|archive-date=July 14, 2014
|page=23
}}
References and notes
{{Reflist}}
External links
- [https://web.archive.org/web/20170724022707/https://www.omega.com/temperature/Z/pdf/z016.pdf Materials properties of thermocouple wires sold by Omega Engineering, Inc.]
- [https://web.archive.org/web/20120220080318/http://www.evek.com.ua/index.php?page=Chromel_thermocouple&lang=2 Technical information on alloys at Electrovek-Steel Ltd.]
Category:Nickel–chromium alloys
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