Radial thermal expansion of pure and Xe-saturated bundles of single-walled carbon nanotubes at low temperatures

Abstract

The radial thermal expansion coefficient α r of pure and Xe-saturated bundles of singlewalled carbon nanotubes has been measured in the interval 2.2-120 K. The coefficient is positive above T = 5.5 K and negative at lower temperatures. The experiment was made using a low temperature capacitance dilatometer with a sensitivity of 2·10 -9 cm and the sample was prepared by compacting a CNT powder such that the pressure applied oriented the nanotube axes perpendicular to the axis of the cylindrical sample. The data show that individual nanotubes have a negative thermal expansion while the solid compacted material has a positive expansion coefficient due to expansion of the intertube volume in the bundles. Doping the nanotubes with Xe caused a sharp increase in the magnitude of α r in the whole range of temperatures used, and a peak in the dependence α r (T) in the interval 50-65 K. A subsequent decrease in the Xe concentration lowered the peak considerably but had little effect on the thermal expansion coefficient of the sample outside the region of the peak. The features revealed have been explained qualitatively.

Low-temperature radial thermal expansion of single-walled carbon nanotube bundles saturated with nitrogen

“…It is found in [2] that the air-oxidative treatment applied to open the CNT ends enhanced the Xe sorption. However, our comparative experiments on saturating o-SWNT and c-SWNT bundles with H 2 [4] showed that the c-SWNTs absorbed more hydrogen than the oxidated ones.…”

“…Its design and the experimental technique are detailed elsewhere [2]. According to the manufacturer, the starting CNT powder (CCVD method, Cheap Tubes, USA) contained over 90% of SWNTs, the average outer diameter of the tubes being 1.1 nm.…”

“…According to the manufacturer, the starting CNT powder (CCVD method, Cheap Tubes, USA) contained over 90% of SWNTs, the average outer diameter of the tubes being 1.1 nm. Two samples were used: the starting CNT powder (c-SWNT) and a CNT powder after an oxidative treatment applied to open the CNT ends (o-SWNT) (see [2] for details). It should be noted that an o-SWNT sample was used only in the investigation of desorption.…”

“…Nevertheless, some properties of carbon nanotubes (CNTs) and their bundles, the low temperature thermal expansion among them, still remain obscure. Dilatometric measurements of the radial thermal expansion coefficient α r on singlewalled carbon nanotube (SWNT) bundles at T = 2-120 K [1,2] show that α r is positive above 5.5 K and negative at lower temperatures. The negative α r values can be attributed to the low-frequency vibrations of individual nanotubes at liquid helium temperatures.…”

“…A controlled desorption of the impurities from the doped samples showed that the α r (T) peaks decreased with the impurity concentration. It was interesting to extend the investigations mentioned [1,2,4] and to find out how the radial thermal expansion of SWNT bundles could be influenced by gases consisting of nonspherical molecules. In this study the radial thermal expansion of N 2 -saturated SWNT bundles was measured in the temperature interval 2.2-43 K. To interpret the results obtained, we needed information about the concentration and the spatial distribution of the N 2 molecules in SWNT bundles.…”