The Isothermal and Non-Isothermal Crystallization Kinetics La2O3 Doped, Sol-Gel Derived Mullite
The crystallization kinetic parameters of mullite formation from gels doped with La2O3 in 0.99, 1.96 and 2.91 mol% were determined by differential thermal analysis (DTA) under isothermal and non-isothermal conditions. The gels were prepared by sol-gel process from aluminum and lanthanum nitrate precursors and TEOS dissolved in ethanol (molar ratio Al/Si=3:1) Powder X-ray diffraction (XRD) and electron microscopy analysis methods (SEM, EDS) were used to characterize the present phases. Lanthanum forms no separate crystal phases and its incorporation ability in mullite lattice is neglectable, yet by promoting amorphous phase formation lanthanum evidently influences the mullite composition by making it rich in Al2O3. The obtained activation energies for the mullite crystallization process in non-doped sample are higher than 1300 kJmol-1. The increase of doping level brings the activation energies below 1100 kJmol-1 for the sample with highest amount of lanthanum, i.e. with the greatest deviation from stoichiometric mullite composition.
Pietro VINCENZINI and Jean-François BAUMARD
V. Mandić et al., "The Isothermal and Non-Isothermal Crystallization Kinetics La2O3 Doped, Sol-Gel Derived Mullite", Advances in Science and Technology, Vol. 62, pp. 107-112, 2010