(492b) Synthesis of Boron Nanotube and Magnisium Boride Nanostructure

Synthesis of pure boron single-wall nanotubes by reaction of BCl3 with H2 over 1%Mg-MCM-41 and Mg-Ni co-incorporated MCM-41 at room pressure was previously reported by our group. Laboratory controllable parameters including catalyst nature, reaction pressure and temperature, boron precursors, are observed to significantly affect the boron nanostructures yield. Different reaction condition will result in various boron nanostructures, such as nanotubes, nanowires, and nanocapsules. A mechanism involving the physical templating of boron nanotubes is proposed. The boron nanotubes with diameter within 5nm are achieved from MCM-41 template with uniform diameter cylindrical pores. Boron nanowires (along with some nanopipes) with uniform 20nm diameter are achieved from Mg incorporated mesoporous alumina which has comparatively larger pores and less uniformity in porous structure. To further utilize the physical templating idea, surface modified single-wall carbon nanotubes were tested as the catalyst support for the synthesis of boron nanotubes by introducing active Mg such as Reike-Mg on the single-wall carbon nanotubes surface.

By doping Mg on to the as-synthesized boron nanotubes at high temperature in a sealed inert environment, magnesium boride nanotubes are obtained, as well as other nanostructures. TEM, EELS and Raman are used to confirm the existence of boron nanotubes and magnesium boride nanotubes. SEM with EDX is utilized to characterized larger nanostructure. NEXAFS of boron K-edge suggests the local coordination of boron nanostructure differs from the bulk phase boron compound. DC magnetization tests suggest the superconductive transition temperature of the different boron nanostructures range from about 35K, which is the same as bulk phase MgB2 transition temperature, to roughly 100K. Magnesium boride nanotubes shows higher transition temperature compare to nanowire structures.