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تسجيل مستخدم جديدRadial thermal expansion of single-walled carbon nanotube bundles at low temperatures
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A.V. Dolbin
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The linear coefficient of the radial thermal expansion has been measured on a system of SWNT bundles in an interval of 2.2 - 120K. The measurement was performed using a dilatometer with a sensitivity of 2*10-9 cm. The cylindrical sample 7 mm high and 10 mm in diameter was obtained by compressing powder. The resulting bundles of the nanotubes were oriented perpendicular to the sample axis. The starting powder contained over 90% of SWNTs with the outer diameter 1.1 nm, the length varying within 5-30 um.
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The radial thermal expansion coefficient (a)r of pure and Xe-saturated bundles of single-walled 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 experime
nt was made using a low temperature capacitance dilatometer with a sensitivity of 2x10-9 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 (a)r in the whole range of temperatures used, and a peak in the dependence (a)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.
The effect of a normal H2 impurity upon the radial thermal expansion (Ar) of SWNT bundles has been investigated in the interval T = 2.2-27 K using the dilatometric method. It is found that H2 saturation of SWNT bundles causes a shift of the temperatu
re interval of the negative thermal expansion towards lower (as compared to pure CNTs) temperatures and a sharp increase in the magnitude of (Ar) in the whole range of temperatures investigated. The low temperature desorption of H2 from a powder consisting of bundles of SWNTs, open and closed at the ends, has been investigated.
The effect of a N2 impurity on the radial thermal expansion coefficient (ar) of single-walled carbon nanotube bundles has been investigated in the temperature interval 2.2 - 43 K by the dilatometric method. Saturation of nanotube bundles with N2 caus
ed a sharp increase in the positive magnitudes of ar in the whole range of temperatures used and a very high and wide maximum in the thermal expansion coefficient (ar)(T) at T about 28 K. The low temperature desorption of the impurity from the N2-saturated powder of bundles of single-walled carbon nanotubes with open and closed ends has been investigated.
The effect of oxygen impurities upon the radial thermal expansion (ar) of bundles of closed single-walled carbon nanotubes has been investigated in the temperature interval 2.2-48 K by the dilatometric method. Saturation of bundles of nanotubes with
oxygen caused an increase in the positive ar-values in the whole interval of temperatures used. Also, several peaks appeared in the temperature dependence ar(T) above 20 K. The low temperature desorption of oxygen from powders consisting of bundles of single-walled nanotubes with open and closed ends has been investigated
The radial thermal expansion (ar) of bundles of single-walled carbon nanotubes saturated with 4He impurities to the molar concentration 9.4% has been investigated in the interval 2.5-9.5 K using the dilatometric method. In the interval 2.1-3.7 K (ar)
is negative and is several times higher than the negative (ar) for pure nanotube bundles. This most likely points to 4He atom tunneling between different positions in the nanotube bundle system. The excess expansion was reduced with decreasing 4He concentration.
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