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Journal of Materials Science

, Volume 42, Issue 8, pp 2830–2836 | Cite as

Kinetics of the γ → α-alumina phase transformation by quantitative X-ray diffraction

  • Maria Iaponeide Fernandes Macêdo
  • Celso Aparecido BertranEmail author
  • Carla Cristiane Osawa
Article

Abstract

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 900 oC, 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 t0.75/t0.25 ratio determined for the transformation were, respectively, of (201 ± 4) kJ mol−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 (425 m2/g) of γ-alumina. The t0.75/t0.25 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.

Keywords

Apparent Activation Energy Gibbsite Aluminum Nitrate Calcium Fluoride Avrami Exponent 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Notes

Acknowledgements

The authors would like to thank CNPq and CAPES for financial support.

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Copyright information

© Springer Science+Business Media, LLC 2007

Authors and Affiliations

  • Maria Iaponeide Fernandes Macêdo
    • 1
  • Celso Aparecido Bertran
    • 2
    Email author
  • Carla Cristiane Osawa
    • 2
  1. 1.Chemistry InstituteFederal University of Rio de Janeiro (UFRJ), Centro de Tecnologia, Bloco A, Cidade UniversitáriaRio de JaneiroBrazil
  2. 2.Chemistry InstituteState University of Campinas (UNICAMP)CampinasBrazil

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