Thermal Behavior, Apparent Kinetics, and High-Temperature Evolution of Fe 3 O 4 Nanoparticles

Thermal desorption and high-temperature phase evolution of iron-oxide nanoparticles are well-established phenomena. The incremental contribution of this study is an integrated evaluation, for the same Fe3O4 nanopowder, of XRD/SEM characterization, TGA and DTA under argon, multi-rate DSC, and a separate air-annealing experiment. TGA and DTA were recorded under argon at 20°C min−1, while a separate sample was annealed in air at 750°C for 10 min. XRD confirmed spinel-type Fe3O4 with an average lattice parameter of 8.294 ± 0.035 Å calculated from six reflections, and the XRD coherent crystallite size was approximately 10 nm; the 30–200 nm features visible by SEM are apparent particle/agglomerate dimensions rather than XRD crystallite sizes. Two TGA mass-loss regions (4.1% at 50–230°C and 1.5% at 230–510 °C) are discussed as plausible surface-related processes because evolved gases were not analyzed. Coats–Redfern analysis of these broad regions gave apparent activation energies of 9.1 and 48.9 kJ mol−1, whereas Kissinger analysis of two DSC peak shifts gave 28.7 and 144.1 kJ mol−1. The difference reflects the distinct observables, process breadth, and kinetic assumptions of the methods rather than equivalent barriers for identical processes. DTA showed an exothermic event at 621.7°C under argon; the available measurements do not establish a γ-Fe2O3 → α-Fe2O3 mechanism. The air-annealed sample formed α-Fe2O3, demonstrating susceptibility to hematite formation under oxidative high-temperature conditions without assigning the argon DTA event.