International Journal of Thermophysics

, Volume 27, Issue 6, pp 1826–1843 | Cite as

Thermal Conductivity of Carbon Aerogels as a Function of Pyrolysis Temperature

  • M. Wiener
  • G. Reichenauer
  • F. Hemberger
  • H. -P. Ebert

Amorphous carbon samples with a total porosity of about 85% were synthesized via pyrolysis of sol–gel derived resin precursors. Since the pores in the samples investigated have dimensions of a few tens of nanometers only, the gaseous contribution to the thermal conductivity is largely suppressed at ambient pressure. Values for the total thermal conductivity as low as 0.054 W·m−1·K−1 at 300°C are detected. However, the pyrolysis temperature has a great impact on the contribution of the solid backbone to the total thermal conductivity. From the same precursor a series of samples was prepared via pyrolysis at temperatures ranging from 800 to 2500°C. The thermal conductivity of this series of carbons at 300°cC under vacuum increases by a factor of about 8 if the pyrolysis temperature is shifted from 800 to 2500°C. To elucidate the reason for this strong increase, the infrared radiative properties, the electrical conductivity, the macroscopic density, the microcrystallite size, the sound velocity, and the inner surface of the samples were determined. Evaluation of the experimental data yields only a negligible contribution from radiative heat transfer and electronic transport to the total thermal conductivity. The main part of the increasing thermal conductivity therefore has to be attributed to an increasing phonon mean free path in the carbons prepared at higher pyrolysis temperatures. However, the phonon mean free path does not match directly the in-plane microcrystallite size of the amorphous carbon. Rather, the in-plane microcrystallite size represents an upper limit for the phonon mean free path. Hence, the limiting factor for the heat transport via phonons has to be defects swithin the carbon microcrystallites which are partially cured at higher temperatures.


aerogels amorphous carbon mean free path microcrystallites pyrolysis temperature thermal conductivity 


Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.


  1. 1.
    Pekala R.W. and Kong F.M., “A Synthetic Route to Organic Aerogels – Mechanism, Structure, and Properties,” 2nd Int. Symp. on Aerogels (ISA 2), Montpellier. France, C4, 33–40Google Scholar
  2. 2.
    Saliger R., Carbon Aerogels for Application in Electrochemical Double Layer Capacitors (Ph.D. Thesis, University of Würzburg, Germany, Report E21 – 1099 −1, 1999).Google Scholar
  3. 3.
    H. Pröbstle, Kohlenstoffaerogele für den Einsatz in Superkondensatoren (Ph.D. Thesis, University of Würzburg, Germany, Report E21 – 1001 – 1, 2001).Google Scholar
  4. 4.
    Wiener M., Elektroden aus Kohlenstoffaerogel für PEM-Brennstoffzellen (Diploma Thesis, University of Würzburg, Germany, Report E21 – 1200 – 1 , 2000).Google Scholar
  5. 5.
    Glora M., Charakterisierung von Gasdiffusionsschichten auf der Basis von Kohlenstoff-Aerogelen für PEM-Brennstoffzellen (Ph.D. Thesis, University of Würzburg, Germany, Report E21 – 0502 – 1, 2002).Google Scholar
  6. 6.
    Hanzawa Y., Hatori H., Yoshizawa N., Yamada Y., (2002) . Carbon 40:575CrossRefGoogle Scholar
  7. 7.
    Soukup L., Gregora I., Jastrabik L., (1992) . Mater. Sci. Eng. B11:355CrossRefGoogle Scholar
  8. 8.
    Lu X., Nilsson O., Fricke J., Pekala R.W., (1993) . J. Appl. Phys. 73:583ADSGoogle Scholar
  9. 9.
    Nilsson O., Bock V., Caps R., and Fricke J., “High Temperature Thermal Properties of Carbon Aerogels,” Thermal Conductivity 22, Proc. Twenty-Second Int. Conf. Therm. Conduct., T.W. Tong, ed. (1994), pp. 878–887.Google Scholar
  10. 10.
    Bock V., Nilsson O., Blumm J., Fricke J., (1995) . J. Non-Cryst. Solids 185:233CrossRefGoogle Scholar
  11. 11.
    Wiener M., Reichenauer G., Scherb T., Fricke J., (2004) . J. Non-Cryst. Solids 350:126CrossRefGoogle Scholar
  12. 12.
    McCreery R.L., “Carbon Electrodes: Structural Effects on Electron Transfer Kinetics,” in Electroanalytical Chemistry, A Series of Advances, Vol. 17, Bard A.J., ed. (Marcel Dekker, New York, 1991), p. 221.Google Scholar
  13. 13.
    Knight D.S., White W.B., (1989) . J. Mater. Res. 4:385ADSGoogle Scholar
  14. 14.
    Reynolds G.A.M., Fung A.W.P., Wang Z.H., Dresselhaus M.S., Pekala R.W., (1995) . J. Non-Cryst. Solids 188:27CrossRefGoogle Scholar
  15. 15.
    Manara J., Caps R., Rather F., Fricke J., (1999) . Optics Commun. 168:237CrossRefADSGoogle Scholar
  16. 16.
    Brunauer S., Emmett P.H., Teller E., (1938) . J. Am. Ceram. Soc. 60:309ADSGoogle Scholar
  17. 17.
    Nilsson O., Mehling H., Horn R., Fricke J., Hofmann R., Müller S.G., Eckstein R.,Hofmann D., (1997) . High Temps. - High Press. 29:73CrossRefGoogle Scholar
  18. 18.
    Cowan R.D., (1963) . J. Appl. Phys.34:926CrossRefADSGoogle Scholar
  19. 19.
    National Bureau of Standards, Special Publication 260–89 (1984).Google Scholar
  20. 20.
    P. G. Klemens, in Thermal Conductivity 1, R. P. Tye, ed. (Academic, London, 1969), p. 1.Google Scholar
  21. 21.
    Debye P., in Vorträge über die Kinetische Theorie der Materie und der Elektrizität (B. G. Teubner, Berlin, 1914), p. 43.Google Scholar
  22. 22.
    Reichenauer G., Emmerling A., Fricke J., Pekala R.W., (1998) . J. Non-Cryst. Solids 255:210CrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media, Inc. 2006

Authors and Affiliations

  • M. Wiener
    • 1
  • G. Reichenauer
    • 1
    • 2
  • F. Hemberger
    • 2
  • H. -P. Ebert
    • 2
  1. 1.Physics DepartmentWürzburg UniversityWürzburgGermany
  2. 2.Bavarian Center for Applied Energy ResearchWürzburgGermany

Personalised recommendations