Carbon nanotubes(CNT)s are interesting carbon nanomaterials due to their unique properties which cannot be expected in conventional materials. For practical application, however, several problems should be overcome such as s strong tendenct of agglomeration and a poor wettability with other metallic or ceramic materials. In the present work, thus, we have studied the structural modification of multi-wall carbon nanotubes (MWCNTs) by ball-milling and/or by thermal expansion. For this, various processing parameters were examined.

First, MWCNTs were ball-milled and examined the effect of various milling variables on structural modification: milling atmosphere, milling methods, milling mode and the addition of additive materials. The result showed that liquid-state process control agents (PCAs) decrease the agglutination of nanotubes. The most pronounced structural changes were observed in MWCNTs which were ball-milled in dry ice. The milling efficiency was better in a friction mode milling than an impact mode milling.
Second, we have attempted for the first time the thermal expansion of nanotubes. For this, MWCNTs were immersed in the solution of H2SO4 or H2O2 (MWCNT : H2SO4: H2O2 = 6g : 100ml : 15ml) for 90 min. This resulted in the formtion of MWCNTs with intercalation compounds. The resulting materials were washed until pH=5-7 and dried at 150C for 10 h. Heating these materials resulted in expansion of MWCNTs whose outer diameters increased with increasing temperature. These results were confirmed by XRD analysis (lattice constance) and Raman spectroscopy.
In conclusion, both ball milling and/or thermal expansion could be effectively employed for the structural changes and the morphological modification of carbonnaotubes. These materials could be possibly used for MWCNT-based composite materials and energy storage purpose.