Heat-Induced Transformation between Nanospheres and Nanofibers of Boehmite

Two opposite shape transformation processes are observed during the synthesis of alumina nanofibers. In liquid phase alumina hydrate nanospheres are assembled into nanofibers by hydrolysis of aluminum alkoxide, while in vacuum state the nanofibers are disassembled into nanospheres by electron beam irradiation. A number of parameters which dominate the processes are investigated, including the aging time of sample, the concentration of precursor, exposure time, and electron energy. It is found that the aging time of boehmite in liquid phase plays a crucial role for the formation and crystallization of nanofibers. At a given temperature, the longer the aging time, the higher the electron beam energy is needed for the disassembling of the nanofibers.