Alumina Hydrate Polymorphism Control in Al–Water Reaction Crystallization by Seeding to Change the Metastable Zone Width

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• 作者：Hongqi Wang ; Zhi Wang ; Ling Liu ; Xuzhong Gong ; Mingyong Wang
• 刊名：Crystal Growth & Design
• 出版年：2016
• 出版时间：February 3, 2016
• 年：2016
• 卷：16
• 期：2
• 页码：1056-1062
• 全文大小：486K
• ISSN：1528-7505

文摘

The polymorph of alumina hydrate from Al–H₂O reaction crystallization is hard to control due to its complexity. In this study, seeding is adopted to control the polymorphism by changing the metastable zone width (MSZW) which provides the easiest way to quantify the system stability. First, the influence of seed amount on the MSZW and polymorph was investigated. The MSZW declines with the increase of seed loading, and the critical seed loading for obtaining single gibbsite phase products is determined to be 15 g/L. Then the effect of seeding time on the polymorph indicates that the seed should be added before nucleation occurrence in order to control polymorphism effectively. The MSZW and polymorph of both seed-free and seeded Al–H₂O reaction crystallization is controlled by changing the temperature and alkali concentration. It is found that if the critical concentration is lower than the saturation solubility curve of bayerite in the diagram, single gibbsite phase crystals can be obtained. Besides, the mechanism for polymorph control by changing the MSZW mainly includes the epitaxial growth and secondary nucleation which dominates the process under 90 and 60 °C, respectively.