Microstructural behavior of γ-Fe₂O₃ formation in reactions between layered iron oxychloride and sodium n-pentoxide

Microstructural behavior of γ-Fe₂O₃ formation in reactions between FeOCl and n-C₅H₁₁ONa was thoroughly investigated. Reactions were conducted at 50-150 °C for 3 days in an autoclave using n-C₅H₁₁OH as a solvent. X-ray diffraction (XRD) patterns and infrared (IR) spectra of the products suggested the crystallization of γ-Fe₂O₃ besides the formation of n-pentoxy derivatives of FeOCl. Scanning electron microscopic observation revealed that the FeOCl particles were divided into thin sheets upon reaction. The selected area electron diffractions (SAED) of the sheets revealed the crystallization of γ-Fe₂O₃ at even 80 °C, apparently due to the fact that the γ-Fe₂O₃ crystallization process involved a collapse from n-pentoxide derivatives with large separations between two adjacent layers. In the reaction at 150 °C, a part of the sheets was converted into highly oriented polycrystalline γ-Fe₂O₃ in improved crystallinity, and the SAED clearly showed that an oriented transformation with a crystallographic relationship of FeOCl (010)//γ-Fe₂O₃ (110) occurred. The reaction at 120 °C, on the contrary, led to the formation of randomly oriented γ-Fe₂O₃ crystallites within a sheet.