Thermal Decomposition Of Iron Research Articles

SYNTHESIS OF MAGNETITE NANOPARTICLES BY THERMAL DECOMPOSITION: TIME, TEMPERATURE, SURFACTANT AND SOLVENT EFFECTS

Monodispersed magnetite ( Fe 3 O 4) nanoparticles can be synthesized by thermal decomposition of iron(III) acetylacetonate, Fe ( acac )3. High saturation magnetization M S of the magnetite particles is extremely important to realize the full potential of magnetite materials in biomedical application. In this work, we have studied the different effects (time, temperature and surfactant) on structure and magnetic properties of Fe 3 O 4 nanoparticles. The M S of the particles are enhanced after the synthesis at a higher reaction temperature and/or a longer reaction time. However, the increase in reaction temperature and/or reaction time resulted in particle size increase and the broadening of the particle size distribution. In this work, high M S value of the magnetite particles has been achieved through adopting surfactant or modification of solvent to overcome the temperature and time effects, while the smaller size particles with an acceptable size distribution has been maintained. Size and morphology of the particles were studied by TEM while magnetic properties of the particles were measured using VSM. The saturation magnetization M S of the particles can be increased at higher reaction temperature and/or longer reaction time, while narrow size distribution of the particles can be maintained either by the selective adsorption of oleic acid to the particle surface or by synthesizing them using solvent free thermal decomposition reaction.

Nonaqueous Magnetic Nanoparticle Suspensions with Controlled Particle Size and Nuclear Magnetic Resonance Properties

We report the preparation of monodisperse maghemite (gamma-Fe2O3) nanoparticle suspensions in heptane, by thermal decomposition of iron(III) acetylacetonate in the presence of oleic acid and oleylamine surfactants. By varying the surfactant/Fe precursor mole ratio during synthesis, control was exerted both over the nanocrystal core size, in the range from 3 to 6 nm, and over the magnetic properties of the resulting nanoparticle dispersions. We report field-cycling 1H NMR relaxation analysis of the superparamagnetic relaxation rate enhancement of nonaqueous suspensions for the first time. This approach permits measurement of the relaxivity and provides information on the saturation magnetization and magnetic anisotropy energy of the suspended particles. The saturation magnetization was found to be in the expected range for maghemite particles of this size. The anisotropy energy was found to increase significantly with decreasing particle size, which we attribute to increased shape anisotropy. This study can be used as a guide for the synthesis of maghemite nanoparticles with selected magnetic properties for a given application.

Polymorphous Exhibitions of Iron(III) Oxide during Isothermal Oxidative Decompositions of Iron Salts: A Key Role of the Powder Layer Thickness

Thermal decomposition of iron(II) oxalate dihydrate, FeC2O4·2H2O, was studied under isothermal conditions in air by using of X-ray diffraction (XRD), transmission electron microscopy (TEM), magnetic measurements, and Mossbauer spectroscopy. Direct in situ monitoring of sample temperature was found to be a breaking point in understanding the decomposition mechanism resulting in different polymorphous product compositions which are simultaneously dependent on the powder layer thickness and reaction temperature. At a certain temperature, there exists a critical sample layer thickness (weight, mc), below which the optimal oxygen access into the whole powder volume is enabled and the reaction proceeds under truly isothermal conditions. In such a case hematite (α-Fe2O3) is the only crystalline decomposition product. Above mc, at worsened diffusion conditions, a dramatic time-limited increase in the sample temperature has been observed. The appearance of such an “exoeffect” is a consequence of the violent diffus...

External Magnetic Field-Induced Mesoscopic Organization of Fe3O4 Pyramids and Carbon Sheets

The current investigation is centered on the thermal decomposition of iron(II) acetyl acetonate, Fe(C5H7O2)2, in a closed cell at 700 degrees C, which is conducted under a magnetic field (MF) of 10 T. The product is compared with a similar reaction that was carried out without a MF. This article shows how the reaction without a MF produces spherical Fe3O4 particles coated with carbon. The same reaction in the presence of a 10 T MF causes the rejection of the carbon from the surface of pyramid-shaped Fe3O4 particles, increases the Fe3O4 particle diameter, forms separate carbon particles, and leads to the formation of an anisotropic (long cigarlike) orientation of Fe3O4 pyramids and C sheets. The macroscopic orientation of Fe3O4 pyramids+C sheets is stable even after the removal of an external MF. The suggested process can be used to fabricate large arrays of uniform wires comprised of some magnetic nanoparticles, and to improve the magnetic properties of nanoscale magnetic materials. The probable mechanism is developed for the growth and assembly behavior of magnetic Fe3O4 pyramids+C sheets under an external MF. The effect of an applied MF to synthesize morphologically different, but structurally the same, products with mesoscopic organization is the key theme of the present paper.

Thermal Decomposition of Iron(VI) Oxides, K2FeO4 and BaFeO4, in an Inert Atmosphere.

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A new nonhydrolytic synthesis of magnetite nanocrystallites in the presence of ω‐functionalized polystyrene matrix

AbstractThis article describes the synthesis of iron oxide nanocomposites from thermal decomposition of iron(III) acetylacetonate, in organic medium, in the presence of linear ω‐functionalized polystyrenes. The nature of the magnetic particles was identified as magnetite (Fe3O4), based on X‐ray powder diffraction and Raman spectroscopy, while the morphology and particle size of the so‐prepared materials were evaluated by TEM technique. The resultant magnetic composites, with average particle sizes below 10 nm, can be easily dissolved in organic solvents, producing stable organosols. Magnetization measurements revealed that the nanocomposites exhibit superparamagnetic behavior at room temperature. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 186–191, 2006

Effect of Organic Solvents on Iron Oxide Nanoparticles by the Solvothermal Method

γ-Iron oxide nanoparticles were produced by the solvothermal method at 250−300 °C. Phase identification, crystal size analysis, and morphology were performed using X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The influences of iron(III) acetylacetonate concentration and reaction time on nanoparticles suggested differences in the crystallization pathway of products prepared in 1,4-butanediol and in toluene. Iron oxides prepared in 1,4-butanediol have been proposed to crystallize and precipitate from glycoxide, while those prepared in toluene are obtained by thermal decomposition of iron(III) acetylacetonate. The calcinations of nanoparticles at 350 °C indicated that iron oxides prepared in 1,4-butanediol have a higher thermal stability than those prepared in toluene due to phase transformation from γ- to α-iron oxides in samples prepared in toluene.

Effect of α-Fe 2O 3 surface coating on reconstruction of platinum–rhodium catalysts during oxidation of ammonia

Surface coating of α-Fe 2O 3 has been shown to affect the reconstruction of platinum–rhodium catalysts during oxidation of ammonia at 900 °C and atmospheric pressure. Surfaces of wire-formed Pt–Rh specimens with 0–30 and 100 wt.% Rh were coated with thin layers of α-Fe 2O 3, deposited by thermal decomposition of iron(III) nitrate or by atomic layer chemical vapor deposition. Scanning electron microscopy, electron microprobe analysis, and powder X-ray diffraction were used to examine the catalyst wires before and after use in ammonia oxidation. The reconstruction on Pt–Pt/10 wt.% Rh and Rh catalysts with α-Fe 2O 3-coated surfaces involves “cauliflower”-like excrescences similar to those observed on corresponding materials without coatings. The reconstructions on α-Fe 2O 3-coated catalysts of Pt/20 wt.% Rh and Pt/30 wt.% Rh carry the same characteristics. However, for these alloys the reconstruction process becomes much faster and the resulting patterns more extensive than for corresponding materials without α-Fe 2O 3 coating. The boundary zones between the α-Fe 2O 3 cover and the liberated Pt–Rh surfaces appear to stand out as spots (hotspots in the thermal sense) with enhanced catalytic activity. A certain decrease in activity and selectivity with time is observed for all tested specimens. This is attributed to gradual degradation of α-Fe 2O 3 to more inactive Fe 3O 4. The progressing degradation of α-Fe 2O 3 to Fe 3O 4 shows that the temperature in the hotspots must exceed some 1400 °C or that reducing conditions prevail locally at the surface.

Oxidizer−Fuel Interactions in Aqueous Combustion Synthesis. 1. Iron(III) Nitrate−Model Fuels

Aqueous (solution) combustion synthesis of iron oxide is investigated using iron(III) nitrate nonahydrate and three model fuels, each containing one specific functional group. The investigated ligands, in order of experimentally determined reactivity, are −NH2 > −OH > −COOH, where only the amino group triggers a vigorous combustion reaction. On the basis of the experimental findings, a reaction mechanism for iron oxide synthesis is proposed. During the first step, nitric acid is released during thermal decomposition of iron(III) nitrate. Subsequently, two reactions occur: nitric acid reacts with the amino group in a fast exothermic redox reaction, and it also decomposes thermally to release oxygen. The latter may react with carbon available in the fuel and thus increase the overall process exothermicity.

Mössbauer effect studies and X-ray diffraction analysis of cobalt ferrite prepared in powder form by thermal decomposition method

Cobalt ferrite (CoxFe3−xO4) is prepared in powder form by thermal decomposition of iron and cobalt salts and is analysed by X-ray diffraction and Mössbauer spectroscopic techniques. The variation of Mössbauer parameters, lattice parameters and crystallite size of the products formed with variation in the composition of Fe and Co ratios are studied. The studies confirm the formation of nano-size cobalt ferrite particles with defect structure and it is found to be maximum for the Fe : Co = 60 : 40 ratio of the initial precursor oxides.

Iron(III) Oxide Nanoparticles in a Polyethylene Matrix

A method is proposed for the preparation of iron(III) oxide nanoparticles via thermal decomposition of iron(III) acetate in a high-temperature solution of polyethylene. The nanoparticles were characterized by EXAFS, EPR, and Mossbauer spectroscopy. The nearest neighbor environment of Fe in the nanoparticles was shown to be similar to that in the structure of γ-Fe2O3 . According to the Mossbauer results, the material contains iron(III) oxide in superparamagnetic and ferromagnetic states similar to γ-Fe2O3 . The particle size determined by high-resolution transmission electron microscopy is consistent with x-ray diffraction data. Experimental data are presented on the field-dependent magnetization of the material.

Thermal decomposition of iron(II) oxalate–magnesium oxalate mixtures

The thermal decomposition of iron(II) oxalate–magnesium oxalate mixture (2:1 mole ratio) was investigated using DTA-TG, XRD and Mössbauer effect measurements. The decomposition of the anhydrous oxalate mixture proceeds in two steps and kinetic analysis of the two steps were performed under non-isothermal conditions using different integral methods of analysis. Integral composite analysis of data showed that the decomposition reactions are best described by the three-phase boundary, R 3 model. Kinetic analysis of data were also carried out in accordance with the methods of Ozawa and Coats-Redfern and the results are discussed in comparison with the composite analysis of data. Mössbauer spectra of samples calcined at different temperatures are discussed and show that in the early stages of the decomposition at about 300 °C, part of the Fe(III) oxide is formed in superamagnetic doublet state. As the temperature is increased, supermagnetism disappears. The results of XRD analyses are in accordance with the results of the Mössbauer effect and show that magnesium ferrite forms in samples heated at higher temperatures.

Mössbauer effect studies on thermal decomposition of iron(III) hydroxy- and amino-benzoates

The thermal decomposition of iron(III) aminobenzoates (o-, m-, p-) and iron(III) hydroxybenzoates (p-, m-, p-) have been investigated from ambient temperature to 873 K in air using derivatography DTG-DTA-TG, Mössbauer, IR spectroscopy and XRD. The importance of Mössbauer spectra recorded at various stages of heating, without separating the product mixture, in studying the mode of decomposition is highlighted. The intermediates (e.g., Fe(II)-species) were confirmed. The nature of water of hydration and the order of stability (p->m->o-) have been investigated from decomposition temperatures. The kinetic model and parameters have been investigated for dehydration.

Thermal decomposition of iron(III) oxalate-magnesium oxalate mixtures

The differential thermal analysis-thermogravimetry (DTA-TG) behaviour of chemically coprecipitated iron(III) oxalate-magnesium oxalate (1:1 mole ratio) was investigated. X-ray diffractometry (XRD) of samples calcined at different temperatures showed that magnesium ferrite is formed in samples heated at higher temperatures. Integral composite analyses of dynamic TG data of the decomposition reactions in the coprecipitated mixture were carried out using various solid state reaction model equations, and the results showed that the decomposition reactions are best described by the two- and three-phase boundary, R 2 and R 3 models. Kinetic analyses of dynamic data were also carried out in accordance with the integral methods of Ozawa and Coats-Redfern and the results are discussed in comparison with the integral composite analysis of data.

Thermal decomposition of iron(III) complex of 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone

A pyrazolonate (PMBP) of iron(III) was prepared and its metal to ligand stoichiometry was shown to be 1∶3. The decomposition of the complex was studied by thermogravimetry and differential analyses under an air atmosphere. The complex undergos two endothermic reactions without loss in mass, at 160 and 218°C, followed by an exothermic reaction at 480°C involving decomposition of the ligands. Intermediates obtained by melting of the Fe-PMBP complex were characterized by X-ray diffraction analysis. The Fe-PMBP complex was confirmed by HPLC to be a mixture of two isomers.

Mössbauer and infrared study of the thermal decomposition of iron and nickel compounds impregnated in alumina

Abstract In this work, studies of Fe 3 (CO) 12 and a mixture of Fe 3 (CO) 12 and Ni (acac) 2 impregnated in Al 2 O 3 were undertaken using Mossbauer and i.r. spectroscopies. In freshly prepared samples, low oxidation species were shown to be present. After thermal decomposition, the data indicate the appearance of aluminum compounds of Fe II and Fe III plus superparamagnetic Fe III . No Fe° species were detected, even under H 2 atmosphere.

Thermal decomposition of iron(II) sulphate heptahydrate in air in the presence of calcium, strontium and barium carbonates

The thermal decomposition in air of iron(II) sulphate heptahydrate in the presence of calcium, strontium and barium carbonates has been carried out. The decomposition path varies from carbonate to carbonate. Also, these decompositions are different from those of basic beryllium carbonate and basic magnesium carbonate. The results obtained for the kinetics of thermal decomposition have also been presented.

Mössbauer spectroscopic and X-ray diffraction study of the thermal decomposition of Fe(CH3COO)2 and FeOH(CH3COO)2

Thermal decomposition of iron(II) acetate, Fe(CH3COO)2, and iron(III) acetate hydroxide, FeOH(CH3COO)2, has been studied using57Fe Mossbauer spectroscopy and X-ray diffraction. Samples were thermally treated in air atmosphere between 150°C and 1000°C. The formation of maghemite 'γ-Fe2O3, and hematite, α-Fe2O3, is discussed. Hematite appears as the final decomposition product.

Thermal decomposition of iron(II) sulphate heptahydrate in air in the presence of basic magnesium carbonate

Thermal decomposition of iron(II) sulphate heptahydrate in air in the presence of basic magnesium carbonate

The thermal decomposition of iron(III) formate

The thermal decomposition of iron(III) formate takes place through competitive formate anion decomposition (to yield CO+H 2O) and electron transfer from formate to Fe(III) (to yield Fe(II) formate(s) and CO, CO 2, H 2 and H 2O as gaseous products). The processes are overlapped by reactions that yield HCOH.