Two-Step Process in Homogeneous Nucleation of Alumina in Supersaturated Vapor

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• 作者：Shinnosuke Ishizuka ; Yuki Kimura ; Tomoya Yamazaki ; Tetsuya Hama ; Naoki Watanabe ; Akira Kouchi
• 刊名：Chemistry of Materials
• 出版年：2016
• 出版时间：December 13, 2016
• 年：2016
• 卷：28
• 期：23
• 页码：8732-8741
• 全文大小：698K
• ISSN：1520-5002

文摘

Multiple pathways in crystal nucleation are now known to be more common than previously predicted; it is, therefore, crucial to understand the early stages of crystallization. Even in relatively simple vapor-phase homogeneous nucleation, the process has significant potential diversity. Here, we experimentally show crystalline Al₂O₃ nanoparticles forming via precisely two steps in the nucleation process from supersaturated vapor with a moderate cooling rate. In situ FT-IR measurement of nucleation allowed us to observe the formation of Al₂O₃ nanoparticles. Liquid-like particles first nucleated from the vapor before crystallizing. The crystalline phase was preserved by quenching without further transformation into the most stable α-Al₂O₃ polymorph. The precipitated phase changed from δ-Al₂O₃ for pure Al₂O₃ to γ-Al₂O₃ or θ-Al₂O₃ by adding Sb or Cr, respectively. We demonstrate that a two-step process occurs in homogeneous nucleation of refractory materials from supersaturated vapor, which may facilitate polymorphic control in industry and improve understanding of cosmic dust formation in space.