Phase transformation and morphological evolution of electrospun zirconia nanofibers during thermal annealing

Pure zirconia nanofibers were fabricated by electrospinning zirconia-polymer precursor and subsequent annealing. Fiber properties such as polymer decomposition, crystallization formation, phase transformation, surface morphologies, etc., were investigated by various techniques, including thermogravimetric analysis (TGA) and differential thermal analysis (DTA), high temperature differential scanning calorimeter (HTDSC), powder X-ray diffractometer (XRD), field emission scanning electron microscopy (FESEM), etc. It was found that the crystallization of as-spun fibers started at 450 degrees C and the initial crystallized zirconia phase was tetragonal (t), which began transforming to monoclinic (in) phase at 650 degrees C as evidenced by XRD; HTDSC showed at different thermal circles, the m-to-t transformation temperatures remained virtually unchanged while the reverse t-to-m temperatures systematically shifted from 924.9 to 978.6 degrees C as the progress of thermal circles; FESEM examinations revealed that fibers calcined to 1000 degrees C went through thermal grooving due to surface diffusion during heat treatment; fibers heated to 1370 degrees C formed the so-called bamboo wires, where volume diffusion was the dominant driving force. (C) 2009 Elsevier Ltd and Techna Group S.r.l. Elsevier B.V. All rights reserved.