Thermal and electrical conductivity of tall, vertically aligned carbon nanotube arrays

Vertically aligned multi-walled carbon nanotube (MWCNT) arrays up to ∼6 mm high with an array density of 0.06 g cm−3 have been grown by chemical vapor deposition. Thermal conductivities (κ) and electrical conductivities (σ) were determined from 5 K to 390 K. The range for κ at 300 K is 0.5–1.2 W m−1 K−1 along the tube growth direction, with the shortest array having the highest κ, and an order of magnitude lower in the direction perpendicular to the tubes. The same trends also were evident for electrical conductivity, i.e., decreasing values with increasing array height and conductivity an order of magnitude lower in the perpendicular direction. Values of σ ranged from 7 to 14 S cm−1 along the array at 300 K. The Seebeck coefficient is ∼20 μV K−1 at 300 K. The effective Lorentz number indicates that thermal conductivity in the carbon nanotube arrays is phonon dominated over the full temperature range.