Y. Wang et Wj. Thomson, MULLITE FORMATION FROM NONSTOICHIOMETRIC SLOW HYDROLYZED SINGLE-PHASEGELS, Journal of materials research, 10(4), 1995, pp. 912-917
A comparative dynamic x-ray diffraction (DXRD) and differential therma
l analysis (DTA) study was performed in the investigation of mullite a
nd spinel formation from slowly hydrolyzed single phase gels with Al/S
i ratios ranging from 1/1 to 14/1. Both metastable tetragonal mullite
and spinel were observed to form at temperatures <1000 degrees C in th
e gels with Al/Si ratios <8/1 and mullite transformed to the orthorhom
bic structure at similar to 1250 degrees C. However, at higher Al/Si r
atios, spinel was the only crystalline phase detected at <1000 degrees
C and orthorhombic mullite formed directly at temperatures >1250 degr
ees C. As the Al/Si ratio increases, both the tetragonal mullite and s
pinel formation temperatures decrease while the orthorhombic mullite f
ormation temperature increases. Based on the Al/Si composition where t
he formation extents of tetragonal mullite and spinel were maximum, th
eir compositions are estimated to be 2Al(2)O(3) . SiO2 and 6Al(2)O(3)
. SiO2, respectively.