Effect of calcination temperature on structure evolution of hematite nanoparticles

Abstract

The objective of this study is to investigate the transition structure of iron oxide, specifically the change from magnetite to hematite, as well as the influence of calcination temperature on the structural growth of hematite nanoparticles. The magnetite was extracted from the native iron sand in Indonesia using the coprecipitation procedure. To generate hematite, magnetite was calcined at various temperatures (350, 500, 650, and 800 °C). The structural changes resulting from the effect of calcination temperature were investigated by combining a number of characterisation methods. The crystal structure was examined using synchrotron x-ray diffraction (SRD) and the local structure was examined using x-ray absorption spectroscopy (XAS). Crystallite size was calculated using the Debye-Schrerrer equation at the most dominant SRD peak. Surface morphology was investigated using scanning electron microscopy (SEM). SRD data revealed that the sample calcined at 350 °C displayed both the Fe3O4 and α-Fe2O3 phases, while higher temperatures revealed the single-phase α-Fe2O3. Furthermore, an increase in calcination temperature was shown to be associated with an increase in crystallinity and crystallite size. For the samples H350 and H800, the crystallinity increased from 95.56 to 98.17%. In the magnetite, H350, H500, H650, and H800 samples, the crystallite size increased from 9.57 to 29.55, 16.40, 28,48, 29.26, and 29.55 nm. Higher calcination temperatures, on the other hand, increase the interatomic distance while decreasing the Debye–Waller factor, according to XAS fitting data. It can be inferred that around 500 °C, the transition from Fe3O4 to single-phase α-Fe2O3 was observed. While a greater calcination temperature of at least 800 °C would alter the structural parameters, it would not affect the phase.