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We tried to unwrap single-walled carbon nanotubes (SWCNTs) by reducing the oxidized SWCNTs. A transmission electron microscope (TEM) observation revealed that the unwrapped SWCNTs were transformed from a pristine nanotube structure to a sheet-like (graphene-like) structure. Electrochemical measurements demonstrated that the electric double layer capacitance (EDLC) of SWCNTs increases significantly due to the unwrapping treatment. For example, the EDLC (199 F/g) of the unwrapped SWCNTs in 1 M H2SO4 electrolyte at a current rate of 50 mA/g is about four times greater than that (51.9 F/g) of pristine SWCNTs.

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A simple method was proposed for estimation of the temperature of the hot wire of the thermal diffusion column. The method is based on Boyle-Charle's law between the pressure change before and after turning on electricity and the radial temperature distribution which is determined by the thermal conductivity of the charged gas. The hot wire temperatures estimated by the present method agree well with those measured directly by the thermocouple and those measured through the glass window by the radiation pyrometer whose correction dial of emissivity was calibrated by the thermocouple. Separative analyses incorporated with the present temperature of the hot wire temperature predicted well experiments for nitrogen isotope separation. The present method is applicable for experiments with continuous feed and draw-offs, if the temperature distribution in the radial direction is not effectively affected by the feed and draw-offs.

The effect of cold wall temperature on separative performances for 14 N 15 N-14 N 2 separation was studied with the thermal diffusion column of an effective height of 950 mm, a hot wire of 0.15 mm in radius and a cold wall of 5.0 mm in radius. The column was maintained at a constant pressure 0.1 MPa with feed flow rate of 10 cm 3 -min-1 (at 0.1 MPa and 298.15 K). The temperature of the cold wall was changed from 223 to 283 K by 20 K keeping at the same temperature difference 235 K between the hot and cold walls. The total separation factor became larger as the cold wall temperature decreased, but had almost the same value at 223 K and 243 K. The experimentally obtained separation factors were compared with the results of the numerical analyses of a convection-diffusion equation. The solutions of numerical analyses with thermal diffusion factor incorporated with inelastic effect gave a good reproduction of dependence of separation factors on cut and cold wall temperature rather than those without inelastic effect. The discrepancy between experimental and analytical results, however, became larger as the cold wall temperature decreased.