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  • Author or Editor: B. Randhawa x
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Abstract  

Mössbauer spectra of alkali tris(maleato) ferrates(III), i.e., M3[Fe(C2H2C2O4)3nH2O [M=Li, Na, K, Cs] at 300 K display a doublet. The Mössbauer parameters indicate these complexes to be high spin with octahedral symmetry. The isomer shift shows a decreasing trend with the increase in electronegativity/polarizing power of the substituent cation (Li+, Na+, K+, Cs+). A linear correlation between isomer shift values and the (Fe−O) stretching frequencies has also been observed.

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Abstract  

Solid state reactivity between iron/II/oxalate dihydrate, i.e., FeC2O4.2H2O and para-chloro aniline hydrochloride, i.e., p-ClC6H4NH2.HCl has been studied at 373, 393 and 413 K. The reaction seems to follow the diffusion controlled mechanism. The product, [FeCl/oxH/.AN–Cl], has been characterized by elemental analysis, infrared and Mössbauer spectroscopic techniques, mass spectrometry and derivatographic methods /TG, DTA/.

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Abstract  

Magnesium and calcium ferrites have been prepared from the thermolysis of M3[Fe(C6H5O7)2]2·xH20 (M=Mg, Ca) precursors. Thermal decomposition of the precursors has been studied employing various physico-chemical techniques, i.e., TG-DSC, XRD, IR and Mössbauer spectroscopy. After dehydration the anhydrous precursors undergo an abrupt oxidative pyrolysis to yield α-Fe2O3 and a metastable acetone-dicarboxylate intermediate. A subsequent exothermic decomposition leads to the formation of MgO and CaCO3 from the respective intermediates. Finally ferrite is formed as a result of solid state reaction between MO/MCO3 and α-Fe2O3. Nanosized ferrites of the stoichiometry MgFe2O4 and Ca2Fe2O5 have been obtained from magnesium and calcium bis(citrato) ferrates(III). The temperature of ferrite formation is much lower than possible in conventional ceramic method. The results have been compared with the respective oxalate and maleate precursors.

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Abstract  

Thermal analysis of alkaline earth metal ferrisuccinate precursors, M3[Fe(C4H4O4)3]2xH2O (M=Mg, Ca) has been studied isothermally and non-isothermally employing simultaneous TG-DTG-DSC, XRD, IR and M�ssbauer spectroscopy to characterize the intermediates/end products. After dehydration, the anhydrous complexes decompose to yield an iron(II) oxalate intermediate, Fe(II)C2O4 in the temperature range 180–250�C. Decomposition of this iron(II) species leads to the formation of α-Fe2O3 and respective alkaline earth metal oxide/carbonate in the temperature range 250–300�C. Finally, ferrites of the stoichiometry, MgFe2O4 and Ca2Fe2O5 are formed as a result of solid-state reaction between α-Fe2O3 and MO/MCO3. A special feature of the precursor method, adopted by us, is that the formation of ferrites occurs at much lower temperature than that of conventional ceramic method.

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Abstract  

Thermal analysis of magnesium tris(maleato) ferrate(III) dodecahydrate has been studied from ambient to 700C in static air atmosphere employing TG, DTG, DTA, XRD, Mssbauer and infrared spectroscopic techniques. The precursor decomposes to iron(II) intermediate species along with magnesium maleate at 248C. The iron(II) species then undergo oxidative decomposition to give α-Fe2O3 at 400C. At higher temperatures magnesium maleate decomposes directly to magnesium oxide, MgO, which undergoes a solid state reaction with α-Fe2O3 to yield magnesium ferrite (MgFe2O4) at 600C, a temperature much lower than for ceramic method. The results have been compared with those of the oxalate precursor.

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Abstract  

Thermal analysis of zinc hexa(formato)ferrate(III) decahydrate, Zn3 [Fe(HCOO)6]2 10H2O has been investigated up to 800°C in static air atmosphere employing TG, DSC, XRD, IR, ESR and Mössbauer spectroscopic techniques. After dehydration at 160°C, the anhydrous complex decomposes into α-Fe2 O3 and zinc carbonate in successive stages. Subsequently the cations remix to yield fine particles of zinc ferrite, ZnFe2 O4 , as a result of solid state reaction between α-Fe2 O3 and zinc carbonate at a temperature (600°C) much lower than for ceramic method.

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Abstract  

Thermal decomposition of M(mal/fum)�xH2O (M=Mn, Co, Ni) has been studied in static air atmosphere from ambient to 500�C employing TG-DTG-DTA, XRD and IR spectroscopic techniques. After dehydration the anhydrous maleate salts decompose to metal oxalate in the temperature range of 320–360�C, which at higher temperature undergo an abrupt oxidative pyrolysis to oxides. The anhydrous fumarate salts have been found to decompose directly to oxide phase. A comparison of thermal analysis reveals that fumarates are thermally more stable than maleates.

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Abstract  

The thermal decomposition of alkali tris(maleato)ferrates(III), M3 [Fe(C2 H2 C2 O4 )3 ] (M =Li, Na, K) has been studied isothermally and non-isothermally employing simultaneous TG-DTG-DTA, XRD, Mssbauer and IR spectroscopic techniques. The anhydrous complexes decompose in the temperature range 215–300C to yield Fe(II)maleate as an intermediate followed by demixing of the cations forming α-Fe2 O3 and alkali metal maleate/oxalate in successive stages. In the final stage of remixing of the cations (430–550C) a solid state reaction occurs between α-Fe2 O3 and alkali metal carbonate leading to the formation of fine particles of respective ferrites. The thermal stabilities of the complexes have been compared with that of alkali tris(oxalato)ferrates(III).

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Abstract  

Thermal decomposition of transition metal malonates, MCH2C2O4xH2O and transition metal succinates, M(CH2)2C2O4xH2O (M=Mn, Fe, Co, Ni, Cu, Zn) has been studied employing TG, DTG, DTA, XRD, SEM, IR and Mssbauer spectroscopic techniques. After dehydration, the anhydrous metal malonates and succinates decompose directly to their respective metal oxides in the temperature ranges 310–400 and 400–525C, respectively. The oxides obtained have been found to be nanosized. The thermal stability of succinates have been found to be higher than that of the respective malonates.

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Summary  

The thermal analysis of strontium and barium hexa(formato)ferrates(III), M3[Fe(HCOO)6]2 . xH2O, has been carried out from ambient temperature to 800 °C. Various physico-chemical techniques, i.e., TG, DTG, DSC, XRD, IR, Mössbauer spectroscopy, etc., have been employed to characterize the intermediates/end products. After dehydration, the anhydrous complexes undergo decomposition to yielda-Fe2O3and metal oxalate in the temperature range of 275-290 °C. A subsequent oxidative decomposition of metal oxalate leads to the formation of respective alkaline earth metal carbonate in successive stages. Finally, nanosized ferrites of Sr2Fe2O5and BaFe2O4stoichiometry have been obtained as a result of a solid-state reaction betweena-Fe2O3and a fraction of MCO3. The temperature of ferrite formation is much lower than possible in the conventional ceramic method.

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