Structure evolution and thermal stability of La2O3-doped mullite fibers via sol-gel method

The lanthana-doped mullite fibers were prepared via a sol-gel method from the aluminum isopropoxide-aluminum nitrate-tetraethyl orthosilicate system. The structure evolution and thermal stability of the mullite fibers were investigated by means of X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that the fibers obtained after calcination at 1000°C was in the form of Al2O3-rich mullite, which tended to transform to stoichiometric mullite with the lanthana content increasing. The lattice parameter a exhibited a decline trend with the lanthana content increasing, while b showed an upward tendency. Correspondingly, the redshift of Si–O–Si bond from 1255 to 1245 cm−1 was observed. The grain growth was inhibited for the doped fibers, among which the 5% La2O3-doped sample presented a minimum crystallite size (17.2 nm) after calcination at 1000 °C for 1 h.