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首页> 外文期刊>Journal of Materials Science >Kinetics of the γ → α-alumina phase transformation by quantitative X-ray diffraction
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Kinetics of the γ → α-alumina phase transformation by quantitative X-ray diffraction

机译：定量X射线衍射分析γ→α-氧化铝相变的动力学

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摘要

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 t 0.75/t 0.25 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 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.
机译：这项工作报道了通过溶胶-凝胶法从饱和硝酸铝和尿素溶液制备的从γ-氧化铝转化为α-氧化铝的动力学。 γ-氧化铝相在750、800、850和900℃下直接转变成α-氧化铝，而没有任何中间相，例如θ-或δ-氧化铝。通过确定通过定量X射线衍射（XRD）形成的α-氧化铝分数，并添加氟化钙作为内标物，可以监测γ→α-氧化铝相变的动力学。 α-氧化铝的结晶分数随时间呈S形增加，表明γ→α-氧化铝相变具有成核和生长机理。通过Kolmogorov–Johnson–Mehl–Avrami（KJMA）模型和Arrhenius定律确定了该转化的动力学参数。表观活化能，Avrami指数n和转化的t 0.75 / t 0.25 比率分别为（201±4）kJ mol？1 （ 2.1±0.2）和（2.1±0.1）。由于γ-氧化铝的高表面积（425 m2 / g），表观活化能低于先前报道的γ→α-氧化铝转变的值。 （2.1±0.1）的t 0.75 / t 0.25 比表明α-氧化铝的生长呈板状，这由α-氧化铝的SEM显微照片证实。

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