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Abstract  

From a model for isothermal oxidation kinetics in nanosized ferrite spinels based on a diffusion-induced stress effect, the authors present a modeling of the DTG curves for the oxidation of Fe2+ and Mo3+ cations on octahedral sites of a molybdenum ferrite. This has been made by considering that the chemical diffusion coefficient is given by the relation
\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $$\tilde D = D_o \exp \left( {\frac{{E'_{\text{a}} + pV_{\text{a}} }}{{RT}}} \right)$$ \end{document}
, when D o is a pre-exponential factor, E a an activation energy and V a an activation energy induced by the oxidation.
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Abstract  

Mössbauer effect technique has been used for the comparative study of Cu1−xZnxFe2O4 and Cu1−xCdxFe2O4 (x = 0.0−1.0) ferrites. Both Zn2+ and Cd2+ cations are divalent, non-magnetic ions with different ionic radii. With the substitution of these non-magnetic cations the average internal magnetic field decreases and paramagnetic behavior is dominated at x = 0.7 in both series. It is observed that the occupancy of Cu2+ ions for tetrahedral site is not constant for all compositions but fluctuate between 8–15%. It is also found that Cu2+ ions have more preference for tetrahedral site in Cu-Zn system as compared to the Cu-Cd system. Zn2+ and Cd2+ both ions occupy tetrahedral site completely and form normal spinels for x = 1.0.

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Abstract  

The transformation mechanism of Fe cations in natural olivine after thermal treatments in air has been studied using mainly57Fe Mössbauer spectroscopy. -Fe2O3 nanoparticles appear as the primary Fe3+ phase in Mössbauer spectra of olivine samples heated at 600-900 °C. These nanoparticles are thermally unstable and they are transformed to -Fe2O3 with the increase of heating time. Another transformation mechanism of iron related with the complete decomposition of olivine structure has been observed at temperatures of 1000 °C and higher. The mixed oxide MgFe2O4 with the spinel structure and enstatite MgSiO3 were identified as iron-bearing decomposition products.

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Abstract  

The thermal stability and thermal decomposition pathways for synthetic woodallite have been determined using thermogravimetry in conjunction with evolved gas mass spectrometry. Chemical analysis showed the formula of the synthesised woodallite to be Mg6.28Cr1.72Cl(OH)16(CO3)0.36⋅8.3H2O and X-ray diffraction confirms the layered LDH structure. Dehydration of the woodallite occurred at 65C. Dehydroxylation occurred at 302 and 338C. Both steps were associated with the loss of carbonate. Hydrogen chloride gas was evolved over a wide temperature range centred on 507C. The products of the thermal decomposition were MgO and a spinel MgCr2O4. Experimentally it was found to be difficult to eliminate CO2 from inclusion in the interlayer during the synthesis of the woodallite compound and in this way the synthesised woodallite resembled the natural mineral.

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Abstract  

The binary system Li2Se-In2Se3 was investigated in the range of 40 to 100 mol% In2Se3 by thermoanalytical and X-ray methods. The system is characterized by two eutectic points. Beside the two binary components and the known ternary compound LiInSe2 another ternary compound crystallizes in this binary system at 83.3 mol% In2Se3. This compound was identified as LiIn5Se8. In contrast to (Cu, Ag)IB5 IIIC8 VI compounds such as CuIn5S8 [1] it does not crystallize in the spinel structure. LiIn5Se8 shows a stratified structure. The melting point was determined to be at 810C. Starting from room temperature up to the melting point no phase transitions were observed.

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Abstract  

The thermal stability and thermal decomposition pathways for synthetic iowaite have been determined using thermogravimetry in conjunction with evolved gas mass spectrometry. Chemical analysis showed the formula of the synthesised iowaite to be Mg6.27Fe1.73(Cl)1.07(OH)16(CO3)0.336.1H2O and X-ray diffraction confirms the layered structure. Dehydration of the iowaite occurred at 35 and 79C. Dehydroxylation occurred at 254 and 291C. Both steps were associated with the loss of CO2. Hydrogen chloride gas was evolved in two steps at 368 and 434C. The products of the thermal decomposition were MgO and a spinel MgFe2O4. Experimentally it was found to be difficult to eliminate CO2 from inclusion in the interlayer during the synthesis of the iowaite compound and in this way the synthesised iowaite resembled the natural mineral.

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The physico-chemical characterization of magnesium-modified ZSM-5 zeolite catalysts has been performed by differential scanning calorimetry. Evidence has been found of the formation of magnesium oxide and the magnesium spinel phase in alumina-bonded ZSM-5 catalysts. DSC proved a suitable technique for characterization of these systems.

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Abstract  

A TG, DTG and DTA study of three polynuclear coordination compounds, containing Al(III)-Mg(II), namely (NH4)4[Al2Mg(C4O5H4)4(OH)4]⋅2H2O, (NH4)4[MgAl2(C4H4O6)4(OH)4]⋅3H2O and (NH4)2[Al2Mg(C6O7H11)5(OH)5]⋅3H2O, has been reported together with the associated thermal decomposition mechanism rationalized in terms of intermediate products. As decomposition end-product, magnesium-aluminum spinel is obtained. The values of MgAl2O4 mean crystallite size depend on the anionic ligand contained by the precursor compound, varying in the order: malate (143 Å) ligand contained by the precursor compound, varying in the order: malate (143 Å)

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Preparation and characterization of Co0.5Zn0.5Fe2(C4H2O4)3·6N2H4

A precursor to prepare Co0.5Zn0.5Fe2O4 nanoparticles

Journal of Thermal Analysis and Calorimetry
Authors: L. Gonsalves, V. Verenkar, and S. Mojumdar

Abstract  

A good precursor is foremost in the preparation of nanosized metal or mixed metal oxides. In the present study a novel precursor, cobalt zinc fumarato-hydrazinate Co0.5Zn0.5Fe2(C4H2O4)3·6N2H4 has been prepared which decompose at a much lower temperature to give nanosized mixed-metal oxides. X-ray investigations, confirms the formation of single spinel phase. The FTIR spectra show N-N stretching vibration at 965 cm−1 which confirms the bidentate bridging hydrazine. The thermal decomposition of the precursor has been studied by isothermal, thermogravimetric and differential scanning calorimetric analysis. The precursor shows two-step dehydrazination followed by decarboxylation to form Co0.5Zn0.5Fe2O4, the chemical analysis of the sample is corroborative of this.

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Abstract  

The homopolynuclear coordination compound [CoL · 2.5H2O]n with L=C2O4 2− was synthesized by a new unconventional method. It consist in the redox reaction between 1,2-ethanediol and cobalt nitrate in presence of nitric acid. The coordination compound was characterized by chemical analysis, electronic and vibrational spectra respectively, thermal analysis. In the coordination compound the Co(II) ion exists in a high spin octahedral configuration and oxalate anion acts as double-bridge ligand, tetradentate, similar as in CoC2O4 · 2H2O obtained by the classical method. Nonstoichiometric oxide, Co3O4+0.25 with deficit in cobalt and normal spinel Co3O4 where identified as thermal decomposition intermediates. As final product of decomposition, the oxide CoO was obtained.

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