This study demonstrates the ability to fabricate lightweight, ductile but mechanically strong magnesium alloy (AZ91D) composites by introducing a small number of high crystalline multi-walled carbon nanotubes. It is demonstrated that 1 % of relatively short and straight carbon nanotubes distributed homogeneously on the outer surface of magnesium powders act as an effective reinforcing filler to prevent deformation, thereby contributing to the enhanced tensile strength of magnesium alloy composites (e.g., from 315 to 388 MPa).Keywords: Carbon nanotubes; Magnesium alloy; Powder processing; Mechanical property There has been strong recent interest in developing lightweight and high-strength materials to improve the energy-efficiency through the weight reduction of automobiles and aircrafts. For these purposes, magnesium alloys have attracted a lot of attention [1-3], as they have low density in its purest form, and in addition, they have been proved to have good mechanical properties through the incorporation of structural filler (e.g., silicon carbide whisker, aluminum and graphite particles, and carbon fibers) [4][5][6][7]. Within this context, the dimensionally nano-sized, mechanically strong, electrically and thermally conductive carbon nanotubes [8][9][10][11], considered to be the ideal reinforcing filler in various composite systems [12][13][14][15], have been incorporated into magnesium matrix [16][17][18][19]. Recently, Goh et al. [19] reported a simple way of preparing nanotube-reinforced magnesium composite by powder-powder mixing and subsequent hot extrusion processes. However, low enhancement (only 5 %), or even a decrease in, tensile strengths in nanotube-reinforced magnesium composites (see Table 3 in ref. 19) could be explained by the presence of aggregated carbon nanotubes within a magnesium matrix. To exploit carbon nanotubes fully as a mechanical reinforcing filler in a magnesium matrix, optimized fabrication processes including homogeneous dispersion of carbon nanotubes must be 1

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High-speed agitation by a mixing blade has efficiently achieved the cutting of a large diameter (100-150 nm) of multi-walled carbon nanotubes. The cutting process is caused by an inter-collision of the nanotubes with high transfer energy. The collision-induced cutting allows for the shortening of the nanotubes without serious damage of the sidewalls due to the cutting effect being limited to the collision points. Furthermore, the operation under ambient atmosphere introduces oxygen-containing functional groups to the cut nanotubes. The estimated length distribution has indicated that high-speed agitation achieves a large cutting effect during a short duration of several minutes.

Nitrogen-doped porous activated carbon monoliths (NDP-ACMs) have long been the most desirable materials for supercapacitors. Unique to the conventional template based Lewis acid/base activation methods, herein, we report on a simple yet practicable novel approach to production of the three-dimensional NDP-ACMs (3D-NDP-ACMs). Polyacrylonitrile (PAN) contained carbon nanotubes (CNTs), being pre-dispersed into a tubular level of dispersions, were used as the starting material and the 3D-NDP-ACMs were obtained via a template-free process. First, a continuous mesoporous PAN/CNT based 3D monolith was established by using a template-free temperature-induced phase separation (TTPS). Second, a nitrogen-doped 3D-ACM with a surface area of 613.8 m2/g and a pore volume 0.366 cm3/g was obtained. A typical supercapacitor with our 3D-NDP-ACMs as the functioning electrodes gave a specific capacitance stabilized at 216 F/g even after 3000 cycles, demonstrating the advantageous performance of the PAN/CNT based 3D-NDP-ACMs.