caa a22 4500 463230787 CHVBK 20180405153241.0 cr unu---uuuuu 170326e20070401xx s 000 0 eng 10.1007/s10853-006-1364-1 doi (NATIONALLICENCE)springer-10.1007/s10853-006-1364-1 Kinetics of the γ → α-alumina phase transformation by quantitative X-ray diffraction [Elektronische Daten] [Maria Macêdo, Celso Bertran, Carla Osawa] This work reports the kinetics of α-alumina transformation from γ-alumina, prepared by the sol-gel method from a solution of saturated aluminum nitrate and urea. The γ-alumina phase transformed directly into α-alumina at 750, 800, 850 and 900oC, without any intermediate phases, such as θ- or δ-alumina. The kinetics of γ → α-alumina phase transformation was monitored by determination of α-alumina fraction formed through quantitative X-ray diffraction (XRD), with calcium fluoride added as an internal standard. The crystallised fractions of α-alumina increased sigmoidally with time, indicating that the γ → α-alumina phase transformation had a nucleation and growth mechanism. The kinetic parameters for this transformation were determined through the Kolmogorov-Johnson-Mehl-Avrami (KJMA) model and the Arrhenius' law. The apparent activation energy, the Avrami exponent, n, and the t 0.75/t 0.25 ratio determined for the transformation were, respectively, of (201±4)kJmol−1 (2.1±0.2) and (2.1±0.1). The apparent activation energy is lower than the values previously reported for the γ → α-alumina transformation, as a consequence of the high surface area (425m2/g) of γ-alumina. The t 0.75/t 0.25 ratio of (2.1±0.1) suggested that the α-alumina growth was plate-like, which was confirmed by the SEM micrograph of α-alumina. Springer Science+Business Media, LLC, 2007 Macêdo Maria Chemistry Institute, Federal University of Rio de Janeiro (UFRJ), Centro de Tecnologia, Bloco A, Cidade Universitária, CEP 21945-970, Rio de Janeiro, RJ, Brazil aut Bertran Celso Chemistry Institute, State University of Campinas (UNICAMP), P.O. Box 6154, 13084-871, Campinas, SP, Brazil aut Osawa Carla Chemistry Institute, State University of Campinas (UNICAMP), P.O. Box 6154, 13084-871, Campinas, SP, Brazil aut Journal of Materials Science Kluwer Academic Publishers-Plenum Publishers; http://www.springer-ny.com 42/8(2007-04-01), 2830-2836 0022-2461 42:8<2830 2007 42 10853 https://doi.org/10.1007/s10853-006-1364-1 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/s10853-006-1364-1 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Macêdo Maria Chemistry Institute, Federal University of Rio de Janeiro (UFRJ), Centro de Tecnologia, Bloco A, Cidade Universitária, CEP 21945-970, Rio de Janeiro, RJ, Brazil aut NATIONALLICENCE 700 1- Bertran Celso Chemistry Institute, State University of Campinas (UNICAMP), P.O. Box 6154, 13084-871, Campinas, SP, Brazil aut NATIONALLICENCE 700 1- Osawa Carla Chemistry Institute, State University of Campinas (UNICAMP), P.O. Box 6154, 13084-871, Campinas, SP, Brazil aut NATIONALLICENCE 773 0- Journal of Materials Science Kluwer Academic Publishers-Plenum Publishers; http://www.springer-ny.com 42/8(2007-04-01), 2830-2836 0022-2461 42:8<2830 2007 42 10853 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer