Size and Size Distribution Control of 纬-Fe2O3 Nanocrystallites: An in Situ Study

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• 作者：Henrik L. Andersen ; Kirsten M. 脴. Jensen ; Christoffer Tyrsted ; Espen D. B酶jesen ; Mogens Christensen
• 刊名：Crystal Growth & Design
• 出版年：2014
• 出版时间：March 5, 2014
• 年：2014
• 卷：14
• 期：3
• 页码：1307-1313
• 全文大小：511K
• 年卷期：v.14,no.3(March 5, 2014)
• ISSN：1528-7505

文摘

The formation and growth of maghemite (纬-Fe₂O₃) nanocrystals during the hydrothermal synthesis from aqueous solutions of ammonium iron(III) citrate (C₆H₈O₇路xFe(III)路yNH₃) have been studied by in situ powder X-ray diffraction (PXRD). Data analysis by Rietveld refinement and whole powder pattern modeling (WPPM) reveals that the crystallite size and size distribution can be precisely tuned through simple adjustments of the reaction temperature and time. Increasing the reaction temperature causes faster growth and results in larger crystallites while the size distribution broaden as reaction times increase, regardless of temperature. The crystallization kinetics were investigated by fitting the Johnson鈥揗ehl鈥揂vrami鈥揔olmogorov (JMAK) kinetic model to the growth curves. The activation energy was found to be 67(15) kJ/mol, and the limiting mechanisms of crystallite formation were determined. The growth was studied with various precursor compositions of ammonium iron(III) citrate and Fe(NO₃)₃路9H₂O or FeCl₃路6H₂O. Increasing the fraction of Fe(NO₃)₃路9H₂O in the precursor results in larger maghemite nanocrystallites. The addition of Fe(NO₃)₃路9H₂O also results in the formation of the thermodynamically more stable hematite (伪-Fe₂O₃) phase as a byproduct.