Low-temperature formation of alpha-alumina by doping of an alumina-sol

In our present study, the phase transition behavior of gamma-alumina doped by an alumina-sol was explored using X-ray powder diffraction and transmiss ion electron microscopy. It was found that the addition of an alumina-sol i nto gamma-alumina enabled the onset of the gamma- to alpha-alumina transfor mation at temperatures as low as 600 degrees C. This phenomenon was designa ted as the "sol-effect." Although the onset temperature of the phase transf ormation was very low, the transformation was completed at 1100 degrees C w hich is the same as that observed with the seeding method. Further investig ation revealed that the transformation was composed of two steps. One occur s over the temperature region from 600 to 950 degrees C where a slow increa se in the content of alpha-alumina is observed. The other is the region fro m 950 to 1100 degrees C where a rapid increase of alpha-alumina occurs due to "self-seeding." The "sol-effect" produces powders with very fine alpha-a lumina particle sizes and little agglomeration. (C) 1999 Academic Press.