PHASE-TRANSFORMATION KINETICS OF PRECURSOR GEL TO ALPHA-ALUMINA

The kinetic analysis of the transformation of gels to alpha-alumina in the Al (OPr(i))3-Al(NO3)3-(citric acid) system, was studied; the relationship between alpha-alumina and the gel structure, presumed from the solution structure and the transformation to alpha-alumina by calcination, was also investigated. It was shown that the gel structure effects the formation of alpha-alumina nuclei and their growth. The former was confirmed by the apparent activation energy obtained from incubation time, namely the gel obtained from the spinnable solution showed a smaller apparent activation energy than that from the unspinnable solution. Evidence for the latter was derived from the apparent activation energy, obtained from annealing time. That is, contrary to above, the gel obtained from the spinnable solution showed a larger apparent activation energy. However, the gel structure did not affect the manner of crystal growth. These phenomena can be explained by the difference in gel structure, i.e. by the kind of Al-O structure it is composed of, and by the conditions of formation of the alpha-alumina grains in the first place.