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Novel syntheses of high-quality double-walled carbon nanotubes (DWNTs) have been realized by the high-temperature pulsed arc discharge method with Y/Ni alloy catalysts at 1250 °C. The optimum conditions of the DWNT synthesis are almost the same as those of single-walled carbon nanotubes (SWNTs), indicating that the growth processes of DWNTs and SWNTs are closely related to each other. High-resolution TEM and Raman spectroscopy have revealed that the present DWNTs have an inner and an outer diameter of 0.8−1.2 and 1.6−2.0 nm, respectively, which correspond to the smallest diameters and the narrowest diameter distribution of mass produced DWNTs ever reported. The purification of the so-produced DWNTs can be achieved by oxidation in air at 500 °C as a result of the remarkable chemical resistance of the current DWNTs compared with that of SWNTs.
Sugai et al. (Sat,) studied this question.