Thermal behavior of zirconia-doped 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 (Ea) of mullite transformation was calculated by a non-isothermal method, which was the smallest for the 1% ZrO2-doped gel fiber (1145 kJ/mol).