Preparation by pyrolysis of aerosols and structural characterization of Fe-doped mullite powders

Amorphous Fe-doped 2SiO2·3Al2O3 powders were prepared by pyrolysis of aerosols generated from solutions of TEOS, Al(III) nitrate, and Fe(III) nitrate in methanol. The study of the thermal evolution of these powders revealed that the presence of Fe(III) promotes mullite formation and that these cations enter into the mullite lattice at the first stages of crystallization at ∼900°C. It was also found that the amount of Fe(III) in solid solution with mullite increased as increasing temperature from 900 to 1400°C. The limit of Fe(III) incorporation into mullite in the as-prepared powders was in the range previously reported for samples prepared by the ceramic procedure (∼11 Fe2O3 wt%). The additional iron phase appearing in samples with an iron content above this limit consisted of an iron oxide spinel, which probably contained some Al(III) cations in solid solution. Finally, the analysis of the EXAFS spectra of the heated samples showed that the iron cations incorporated into the mullite lattice are mainly located at octahedral positions.