Growth Mechanism and Stability of Magnetite Nanoparticles Synthesized by the Hydrothermal Method

Abstract

Magnetite (Fe 3 O 4 nanoparticles were synthesized using FeCl 3 , FeSO 4 (initial molar ratio Fe 2+ /Fe 3+ is fixed at 1/1) and KOH as raw materials by the hydrothermal method. The crystallographic and microstructures, thermal and magnetic properties of Fe 3 O 4 were characterized by X-ray powder diffraction, scanning electron microscopy, thermogravimetric analyses and vibrating sample magnetometer. The results show that by controlling the reaction temperature and time, Fe 3 O 4 nanocrystals with homogeneous morphology and nanometer grain sizes can be obtained. The Fe 3 O 4 nanocrystals are stable up to temperature of 115 C in air then undergo allotropic transformation to maghetite and hematite. The kinetics of the grain growth of Fe 3 O 4 nanocrystals during the hydrothermal process were investigated. Based on the experimental data, the radius of the initial Fe 3 O 4 particles in the hydrothermal synthesis was found to be 23 nm. The average particle radius increases linearly with the reaction time in agreement with the Lifshitz-Slyozov-Wagner model for coarsening and the rate constant for the coarsening increases with the temperature of the hydrothermal reaction.

Identification and Classification of Archeological Materials From Bronze Age Gold Mining Site Ada Tepe (Bulgaria) Using Rock Magnetism

“…The magnetic signature of the materials classified in cluster #1 is distinguished from the others by the presence of a magnetic component with very low coercivity (Figures 5a and Table S2) which can be attributed to the submicron magnetic fraction consisting of unstable grains at the SP/SD domain boundary produced during firing of soils at the various archeological structures. Taking into account that prolonged firing produces larger grains than shorter and/or single burning (Long et al, 2016), it can be supposed that heap materials from mining operations with fire settings (classified in cluster #3) were treated by prolonged firing. In addition, possible presence of ε-Fe 2 O 3 ( Figure 4c) supports such assumption because this mineral phase forms upon heating to temperatures above ∼900°C (Tadić et al, 2008).…”

Hydrothermal Production of H2 and Magnetite From Steel Slags: A Geo-Inspired Approach Based on Olivine Serpentinization

“…The opposite effect of temperature and pH may potentially explain why magnetite in the same size range is obtained under the contrasted conditions recalled above for the experiments of Crouzet et al (2017a,b). Long et al (2016) investigated the coarsening kinetics of magnetite nanoparticles produced by the co-precipitation method in the 100-200 • C range. They found a linear dependency of magnetite diameter with time and determined an activation energy of around 30 kJ/mole.…”

Formation of gold/silver composite nanoparticles by pulsed laser ablation of gold–silver layered films in liquid

“…in the production process. The main drawbacks of chemical methods are the presence of impurities, the use of hazardous chemicals [25,26] and the complexity of the synthetic processes [27,28]. NPs can also be produced using a biological approach.…”