Thermal diffusivity of aligned multi-walled carbon nanotubes measured by the flash method

Thermal diffusivity of freestanding catalytic chemical vapor deposition (CCVD) grown multi-walled carbon nanotube (MWCNT) forests (height of 1.5 and 1.9 mm) was characterized in the temperature range between 25 and 200 degrees C. Copper and Al-alloy metal blocks were used as references for validation of the experimental setup. The measurements were carried out along the MWCNT alignment direction with a thermal property analyzer that uses the flash method. The thermal diffusivities measured at room temperature for as-grown and post-annealed (2 h at 480 degrees C in open air) samples were found to be similar to 0.45 and similar to 0.23 cm(2)/s, respectively. In both cases, the thermal diffusivity values were slightly decreasing with increasing temperature. The observed decrease in diffusivity after annealing is most probably due to the loss of amorphous carbon in the specimens and also because of the increased defect density in the nanotube walls resulting in a more pronounced phonon scattering in the lattice. The measured thermal diffusivities for as-grown samples agree with data reported elsewhere for similar MWCNT materials [W. Yi et al., Rev. B 59, 9015 (1999) and T. Borca-Tasciuc et al., J. Appl. Phys. 98, 054309 (2005)]. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei