Influence of iron on the mullite formation

Influence of iron on the crystallization mechanism of mullite obtained from the hybrid gels and doped with different concentrations of iron was examined. DTA analysis showed that iron addition had a beneficial effect on the mullite formation leading to the temperature decreasing as the amount of iron increased. X-ray diffraction and M?ssbauer spectroscopy confirmed the increased iron content in the mullite lattice, which led to an increase in the unit parameter and was related to the higher iron content in regular octahedra, disordered octahedra, and tetrahedra with oxygen vacancies. Plate-like morphology observed by SEM suggests the two-dimensional crystal growth (n = 2). The most prominent kinetic models were used to estimate n and Ea from the DTA curves. Ea values increases as iron content increase, indicating that mullitization slows down due to iron incorporation. The Ea values for the undoped mullite sample ranged from 820 to 860 kJ/mol, from 820 to 890 kJ/mol for the irondoped mullite sample containing 6.0 wt% of Fe2O3, and from 960 to 1060 kJ/mol for the irondoped mullite sample containing 12 wt% of Fe2O3.