Study of intracluster atomic mobility in ultrafine clusters of γ-ferric oxide by Mossbauer spectroscopy and thermodynamical analysis

Abstract

Abstract. The atomic dynamics of ultrafine clusters of y-ferric oxide with diameters of 1-3 nm, obtained by thermal decomposition of ferric oxalate, has been studied by gamma-resonance (Mossbauer) spectroscopy and by thermodynamic analysis. The intracluster atomic mobility has been shown to increase by the action of surfactants. Thermodynamical and phenomenological cluster models describing the dynamic state of clusters have been developed and are compared with the experimental data. The conditions for formation of a specific solid-liquid state of clusters are discussed.

Hydrazine-Assisted, Low-Temperature Aerosol Pyrolysis Method to Synthesize γ-Fe2O3

“…The two-step decomposition of FeC 2 O 4 ·2H 2 O is due to the dehydration and oxidative decomposition of the anhydrous oxalate, which ends up in the formation of Fe 3 O 4 in nitrogen. However, in air, the Fe 3 O 4 further reacts with oxygen to form thermodynamically stable α-Fe 2 O 3 as the final product, preceded by metastable γ-Fe 2 O 3 intermediate, as proposed in the literature ,– Fe C 2 O 4 ·2 H 2 O → − 2 H 2 O Fe C 2 O 4 → − CO 2 − CO FeO → − normalH 2 − normalH 2 normalO Fe 3 O 4 → + O 2 γ-Fe 2 O 3 → Δ α-Fe 2 O 3 The hydrazinated ferrous oxalate decomposes in a single sharp step at 150 °C producing γ-Fe 2 O 3 particles in air (Test 11) with a weight loss of 61.2% as observed by TGA analysis (Figure …”

“…The two-step decomposition of FeC 2 O 4 • 2H 2 O is due to the dehydration and oxidative decomposition of the anhydrous oxalate, which ends up in the formation of Fe 3 O 4 in nitrogen. However, in air, the Fe 3 O 4 further reacts with oxygen to form thermodynamically stable R-Fe 2 O 3 as the final product, preceded by metastable γ-Fe 2 O 3 intermediate, as proposed in the literature 40,[48][49][50][51][52] FeC…”

Critical sizes and characteristics of nanoclusters and nanostructures

“…The increase of mean square displacements for surface atoms of cluster leads to the increase of heat capacity and the decrease of melting point. Thermodynamic formalism permits to predict cluster melting and to bind it with the values of mean square displacement [11][12][13][14][15]. The difference between the free energies of the cluster in liquid and solid states may be expressed by…”

Nanoclusters and nanocluster systems. Assembling, interactions and properties

“…In several publications, melting of iron oxide nanoclusters has been studied. 135,190,191 It was noted that melting of these clusters is accompanied by an increase in the mean square displacements of atoms. Figures 12 and 18 present the MoÈ ssbauer spectroscopy data for iron hydroxide clusters formed in polysorbs with pore diameters of 7.5 to 0.75 nm and for the nanosystem formed from the iron oxide clusters prepared by thermal decomposition of iron oxalate.…”