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首页> 外文期刊>Crystal growth & design >Transformation of Gibbsite to Boehmite in Caustic Aqueous Solution at Hydrothermal Conditions
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Transformation of Gibbsite to Boehmite in Caustic Aqueous Solution at Hydrothermal Conditions

机译：水热条件下腐蚀性水溶液中Gibbsite转化

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摘要

Phase transformations among aluminum (oxyhydr)oxide minerals play important roles across a wide range of natural and industrial settings. In highly caustic aqueous solutions, uncertainty persists regarding whether solid-state or dissolution-reprecipitation pathways dominate. We explored the transformation of gibbsite [alpha-Al(OH)(3)] to boehmite (gamma-AlOOH) in caustic NaOH solution at hydrothermal conditions as a function of temperature, Al(III) and NaOH concentrations, and reaction time. Comparison of detailed structural and morphological solids characterization by X-ray diffraction, scanning electron microscopy/transmission electron microscopy, atomic force microscopy, Raman spectroscopy, and high-field Al-27 MAS NMR to predictions from equilibrium thermodynamics calculations suggests the critical importance of dissolution-reprecipitation across our range of system conditions. The yield and physical properties of the boehmite product were found to be sensitive to the hydrothermal treatment temperature and the Al/OH- ratio, controlled by the loading of gibbsite with respect to NaOH. Experiments at lower Al/OH- ratios (e.g., 0.64) indicate that the dissolution of the gibbsite reaches an aqueous aluminate saturation state sufficient to overcome the nucleation barrier for boehmite. Higher Al/OH- ratios (e.g., 3.2) are found to slow the phase transformation, leaving residual unreacted gibbsite in the final product. Higher temperatures appear to improve the phase transformation rate but also typically yield smaller-sized boehmite particles. Particle morphological analyses compared to thermodynamic expectations suggest an important role of kinetics at mineral/solution interfaces, both in the gibbsite dissolution rate as well as the growth rate of boehmite nanocrystals.
机译：铝（Oxyhydr）氧化物矿物之间的相变在各种自然和工业环境中起重要作用。在高苛性苛性水溶液中，关于固态或溶解 - 再沉淀途径是否占主导地位的不确定性。我们探讨了在水热条件下的苛性NaOH溶液中Gibbsiteα（γ-AlOOH）的转化为温度，Al（III）和NaOH浓度和反应时间。通过X射线衍射进行详细的结构和形态固体的比较，扫描电子显微镜/透射电子显微镜，原子力显微镜，拉曼光谱和高场Al-27 Mas NMR从平衡热力学计算的预测表明溶解的关键重要性 - 跨越我们的系统条件范围。发现勃姆石产物的产量和物理性质对水热处理温度和Al / OH-比敏感，通过对NaOH的加载荷钛矿的负载来控制。下Al / OH-比（例如，0.64）的实验表明，Gibbsite的溶解率足以克服勃姆石的成核屏障。发现较高的Al / OH-比（例如，3.2）减缓相变减缓，在最终产品中留下残留的未反应的Gibbsite。较高的温度似乎改善相变率，但通常也产生较小的勃姆石颗粒。颗粒形态分析与热力学期望相比表明动力学在矿物/溶液界面中的重要作用，无论是Gibbsite溶解速率还是勃姆石纳米晶体的生长速率。

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