Growth mechanism of single-crystal alpha-Al2O3 nanofibers fabricated by electrospinning techniques

Crystal-growth-related microstructures and the length-to-diameter ratio of a single-crystal-type α-Al 2 O 3 nanofiber were examined using HR-TEM techniques. The fibers exhibited diameters ranging from 50 to 100nm and lengths of several tens of micrometers. During thermal treatments, the alumina fiber went through phase transformations similar to boehmite. Therefore, the phase evolution, especially the final θ- to α-Al 2 O 3 stage of the phase transformation, may be the determining factor in the microstructural evolution of the nanofibers. HR-TEM techniques were utilized to demonstrate that the single crystals were formed by the coalescence of well-elongated α-Al 2 O 3 colonies. The fibers grew in the [110] or [112] direction instead of [001]. A thermodynamic analysis revealed that if the α-Al 2 O 3 nanofiber that transformed from θ-Al 2 O 3 behaved in a stable manner, there could be a size ratio limit for the length and diameter of each α-Al 2 O 3 colony. The smallest potential diameter was calculated to be around 17nm.We thank Miss Liang-Chu Wang and Mr. Shu-Hau Hsu for assistance in HR-TEM and SEM operations. This study was supported by the National Science Council, ROC under Contract No. NSC 096-2917-I-006-014 and the Ministry of Economic Affairs, ROC under Contract No. 97-EC-17–A-08-S1-023