High-temperature behaviour of mullites:: Study by means of X-Ray Diffraction

Results on thermal behaviour of several sol-gel chromium doped mullites (3Al(2)O(3).2SiO(2) with Cr contents of 1, 3, 6 and 9 wt.%. Cr2O3) by means of high-temperature X-ray diffraction are exposed in this work. Chromium additions make possible to obtain glass-free materials with Very homogeneous microstructures, which is highly convenient as the presence of glass in these materials provides a certain degradation on their mechanical properties, especially at high temperature operations. This study reveals that the chromium introduction in the mullite lattice promotes in effective reduction of its linear thermal expansion coefficient, although also an increase in the anisotropy with which this expansion takes place. Only with the 6 wt.%, Cr2O3 content the anisotropy for the lattice expansion is similar to the non-doped mullite.