Structural, magnetic and size transformations induced by isothermal treatment of ferrous oxalate dihydrate in static air conditions

Abstract

Thermal decomposition of the FeC 2 O 4 .2H 2 O powder has been studied isothermally in static air conditions at minimum decomposition temperature of 180 °C using 57 Fe Mössbauer spectroscopy, XRD, HRTEM, AFM and BET surface area measurements. Dehydration and liberation of carbon oxides from powdered sample is accompanied by direct oxidation of Fe(II) to nanocrystalline Fe 2 O 3 without any indications of the stabilization of the magnetite (Fe 3 O 4 ) phase. Decomposition process is completed after two hours and as-prepared nanopowder (3-5 nm), with a large surface area of about 250 m 2 /g, is comprised of ultrafine superparamagnetic particles of γ-Fe 2 O 3 (maghemite) and α-Fe 2 O 3 (hematite) as proved by low temperature Mössbauer spectroscopy, XRD and HRTEM analysis. The simultaneous formation of both polymorphs is probably related with the non-equivalent diffusion conditions on the surface and in the bulk of oxalate particles. With increasing time, the particle size induced phase transformation of maghemite to hematite has been observed by AFM and XRD. Mössbauer spectra demonstrate that maghemite particles are formed only in superparamagnetic state (doublet), while magnetic components (sextet) in room temperature spectra can be assigned exclusively to hematite particles with size distribution produced by gradual crystallization of primary superparamagnetic nanoparticles of the same structure as well as by the phase transition of maghemite phase.

Thermal Decomposition of Ferric Oxalate Tetrahydrate in Oxidative and Inert Atmospheres: The Role of Ferrous Oxalate as an Intermediate

“…[37] Moreover, the decomposition in air does not proceed in differentiable stages (dehydration and consequent decarboxylation), but considerable oxalate breakdown takes place although some water still remains in the sample. [33] The present work resumes our recent investigations on the mechanism of FeC 2 O 4 ·2H 2 O decomposition, [28][29][30]32] which represents an intermediate phase in the thermal decomposition of ferric oxalate under inert conditions. As already mentioned, the literature data are quite inconsistent; various intermediates and products are mentioned, and the mechanism of the Fe III …”

Preparation of Magnetite by Thermally Induced Decomposition of Ferrous Oxalate Dihydrate in the Combined Atmosphere

“…The thermal decomposition of ferrous oxalate dihydrate in oxygen rich atmosphere (e.g., in air) has been reported in many studies. [16][17][18][19][20][21][22][23][24] If the FeC 2 O 4 • 2H 2 O is decomposed in air, the reaction is straight-forward and proceeds in two consecutive steps. It was shown that these two steps (endo + exothermal) partially overlap in differential thermal analysis (DTA) in the range up to 450 °C.…”

The Effect of Surface Area and Crystal Structure on the Catalytic Efficiency of Iron(III) Oxide Nanoparticles in Hydrogen Peroxide Decomposition

“…One of the most commonly used precursors is ferrous oxalate dihydrate (FeC 2 O 4 ·2H 2 O), which is a typical example of a readily decomposable substance. The course of ferrous oxalate thermolysis has been extensively studied in recent years, [52][53][54][55][56][57][58][59] although it is still difficult to reach an unambiguous conclusion from the published data. Differences in the published results arise due to the different experimental conditions applied, which substantially affect the final composition of the iron oxide product.…”