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 trans-mission electron microscopy （TEM）. The results showed that the fibers obtained after calcination at 1000℃ 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 mini-mum crystallite size （17.2 nm） after calcination at 1000 ℃ for 1 h.