Thermal conductivity measurements of pitch-bonded graphites at millikelvin temperatures: finding a replacement for AGOT graphite

Year: 2009

Authors: Woodcraft A. L., Barucci M., Hastings P. R., Lolli L., Martelli V., Risegari L., Ventura G.

Autors Affiliation: Univ Edinburgh, Inst Astron, SUPA, Edinburgh EH9 3HJ, Midlothian Scotland;
UK Astron Technol Ctr, Edinburgh EH9 3HJ, Midlothian Scotland;
Univ Florence, Dept Phys, I-50019 Florence, Italy

Abstract: Pitch-bonded graphites are among the best known thermal insulators at sub-kelvin temperatures, but are very good conductors at higher temperatures. This makes them ideal for mechanical supports which must provide good thermal isolation at an operating temperature below 1 K, but must have good conductance at higher temperatures to aid in initially cooling down an instrument (a \”passive heat switch\”). One type of graphite, AGOT, has been known as having the lowest thermal conductivity below 1 K not only among graphites, but also compared with any other material. It is, however, no longer available. We have carried out thermal conductivity measurements at temperatures between 60 mK and 4 K on a proposed replacement, POCO AXM-5Q graphite, as well as a sample of AGOT graphite. Our measurements show that both graphites have a difference of about six orders of magnitude in conductivity between room temperature and 100 mK, but that AGOT graphite is not as good an insulator as previously believed. We conclude that AXM-5Q graphite is not only a suitable replacement for AGOT, but in fact is somewhat superior. (C) 2009 Published by Elsevier Ltd.

Journal/Review: CRYOGENICS (GUILDF.)

Volume: 49 (5)      Pages from: 159  to: 164

KeyWords: A. Structural materials; C. Thermal conductivity; D. Instrumentation; Heat switches; Higher temperatures; Kelvin temperatures; Mechanical supports; Millikelvin temperatures; Operating temperatures; Orders of magnitudes; Room temperatures; Thermal conductivity measurements; Thermal insulators; Thermal isolations, Building materials; Electric conductivity measurement; Instruments; Measurements; Thermal conductivity; Thermal insulating materials; Thermoanalysis; Thermoelectricity, Graphite
DOI: 10.1016/j.cryogenics.2008.10.024

Citations: 23
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