Thermal behavior of zirconia-dop ed mullite gel fibers

The zirconia-doped mullite gel fibers were prepared via a sol–gel method. The thermal behaviors of the gel fibers during pyrolysis were investigated by means of thermal gravity-differential scanning calorimetry (TG-DSC), in-situ fourier transform infrared spectroscopy (in-situ FTIR), X-ray diffraction (XRD) and transmission electron microscope (TEM). It was found that the mass loss during calcination can be divided into two stages, i.e. ～50% below 400 °C and ～3% during 550–700 °C. The three exothermic peaks in DSC curves were attributed to the burning of organics, decomposition of nitrates and mullite transformation, respectively. H₂O, CO₂ and NO₂ were generated during the pyrolysis of mullite gel fibers, and the concentration of NO₂ was higher than CO₂. The activation energy (E_a) of mullite transformation was calculated by a non-isothermal method, which was the smallest for the 1% ZrO₂-doped gel fiber (1145 kJ/mol).