Preparation, characterization and mechanical properties of continuous mullite fibers derived from the diphasic sol-gel route

In the present work, continuous mullite fibers were fabricated through the diphasic sol-gel route using aluminum isopropoxide (AIP) and aluminum nitrate (AN) as the alumina sources and colloidal silica as the silica source. Fiber processing was achieved via draw-spinning method. Amorphous inorganic mullite fibers with smooth and dense features, as well as designed chemical composition and uniform elemental distribution, were obtained by pyrolysis of the continuous precursor fibers at the ending temperature of 800 °C in air. The microstructure and mechanical properties of the samples sintered at elevated temperatures were investigated. Differential thermal analysis (DTA) showed two exothermic peaks at 978 and 1271 °C assigned to the crystallization of γ-Al2O3 and mullite phase, respectively. X-ray powder diffraction (XRD) results verified the typical phase transformation route of diphasic mullite while sintering. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) showed a rapid grain growth after the mullite phase had formed. As the sintering temperatures increased, the filament tensile strength of the mullite fibers first increased and then decreased, reaching a maximum value of 934 MPa at 1000 °C.