Mullítízacíón de geles de mullita conteniendo NiO o TÍO2

The effect of NiO and TiO 2 on the mullite formation from monophasic gels at 980°C was studied. Gels were prepared by replacement of Al by Ti or Ni in 3:2 stoichiometric mullite. The transformations during thermal processing were followed by infrared spectroscopy, ultraviolet-visible spectroscopy, X-ray diffraction and scanning and transmission electron microscopies. Mullite was the only crystalline phase detected at 900°C in Ni-containing samples both in isothermal and nonisothermal treatments. Conversely, Al-Si spinel formation was favoured in Ti-containing samples and mullite formation was only completed at temperatures above 1100°C. The formation of mullite at low temperature and the morphology of doped mullites at high temperature were evidenced by SEM and TEM.