Kinetics of Thermal Transformation of Synthetic Al-Maghemites into Al-Hematites

Abstract

) may largely influence this process. We analyzed the kinetics of thermal transformation of Al-maghemites into Al-hematites and some of its mineralogical aspects. Synthetic substituted maghemites with different degrees of Al-substitution (0.0, 1.0, 2.0, 2.9, 3.8, 5.6, 6.7, 10.0, 12.0, and 17.1 mol% Al) were subjected to a temperature of 500±10 °C for 0, 5, 10, 16, 64, 128, 192, 360, 720, 2160, 3600, 5040, and 6480 min. After thermal treatment, samples were characterized by X ray diffraction (XRD), differential thermal analysis (DTA), specific surface area (SSA) measurement, and total chemical analysis. XRD patterns were analyzed by Rietveld refinement, and maghemite and hematite contents were calculated using Rietveld refinement and the method proposed by Sidhu. Isomorphic substitution of Fe by Al increased the critical temperature of transformation and the time necessary for maghemite to hematite transformation. Rietveld refinement data showed a better fit than the data adjusted by the Sidhu method. Increasing isomorphic substitution also decreased lattice parameters and mean crystallite dimension (MCD) values in maghemite; but only c-dimension and MCD decreased with increasing Al-substitution in hematite. For maghemite, the SSA increased with isomorphic substitution, rising up to 5.9 mol% Al; for hematite, SSA increased linearly. SSA decreased with heating time, regardless of isomorphic substitution.

Microwave-Assisted Sol–Gel Preparation of the Nanostructured Magnetic System for Solid-Phase Synthesis

“…The MW-NPS-1 sample shows the lowest mass loss, with the volatile or easily oxidizable substances already being removed by the calcination process. No color change or changes of magnetic properties were observed for any of the resulting residues after TGA analysis of MW-NPS, proving the presence of the silica secondary shell, and also sustained by the absence of specific physical transformation of maghemite-hematite in the range of 500-700 • C [21].…”

Study the Effect of Reaction Time on Preparation of Iron Oxide Nanoparticles by Hydrothermal Technique

“…Any particular peaks other than Fe2O3 peaks do not appear in XRD that's means the main phase is Fe2O3 nanoparticles. Adriele et al [11] also showed that when the reaction time increased the magnetite phase decreased with an increase in the hematite phase and the Peak intensities are seen to increase due to the increase in crystallinity and particle size. With hydrothermal synthesis, variations in reaction time can influence the size and crystallinity of the nanoparticles [12].…”

Structure and magnetic properties of SiO2−FeOoskoui1, rezvani2 2023Heliyon8000View full textAdd to dashboardCite

“…In the DTA curve two apparent crystallization peaks can be observed: The first crystallization peak ( ) at about 500–780 °C is attributable to the crystallization of the maghemite (γ - sodium-calcium silicate, and maghemite to hematite ( - ) transformation. The thermal transformation from maghemite to hematite due to the stability of the hexagonal phase than the cubic phase in 570–690 °C [ [27] , [28] , [29] ]. The second crystallization peak ( ) at about 790–940 °C is assigned to the crystallization of the wollastonite phase, as confirmed with the aid of the XRD patterns.…”