Thermal decomposition of managanese hexa(formato)ferrate(III)hexahydrate, i.e., Mn3[Fe(HCOO)6l2·6H2O has been studied upto 700°C in static air atmosphere employing TG, DSC, XRD, IR and Mössbauer spectroscopic techniques. The anhydrous complex decomposed directly into ferric oxide and manganese carbonate in successive stages without undergoing reduction to iron(II) intermediate. Finally a solid state reaction between Fe2O3 and manganese carbonate leads to the formatin of manganese ferrte (MnFe2O4) at a temperature (655°C) much lower than for ceramic method. A saturation magnetization value (4 Ms) of 2550 Gauss makes MnFe2O4 suitable for functioning at high frequencies.
Thermolysis of cesium bis (citrato) ferrate (III) trihydrate, Cs3[Fe(C6H5O7)2].3H2O, has been studied in the temperature range of 373–1073 K in static air atmosphere, using Mössbauer and infrared spectroscopy and thermogravimetric methods. The anhydrous complex decomposed into an iron (II) intermediate at 453 K and -Fe2O3 of varying particle sizes in successive stages. Finally a solid state reaction between -Fe2O3 and cesium carbonate/oxide gives fine particles of cesium ferrite (CsFeO2) at a temperature lower than that of conventional ceramic method.
Solid state photolysis of alkali tris(malonato)ferrates(III), i.e., M3[Fe(CH2C2O4)3]xH2O (M=Li, Na, K, NH4) has been studied employing Mössbauer, infrared and reflectance spectroscopic techniques. The complexes were irradiated for
300 hours using a medium pressure mercury vapour lamp of 250 W, Photodecomposition led to the formation of an iron(II) intermediate,
M2[FeII(CH2C2O4)2(H2O)2] (M=Li, Na, K) which on prolonged standing in air oxidized to M[FeIII(CH2C2O4)2(H2O)2]. However, in case of ammonium complex, FeIICH2C2O4·2H2O once formed remained stable. The extent of photoreduction showed the sequence: NH4, K>Li>Na. The results have been compared with those of alkali tris (oxalato) ferrates(III).
Thermal decomposition of alkali dihydroxo tetrapropionato ferrates(III), M3[Fe(C2H5COO)4(OH)2]xH2O (M=Li, Na, K) has been studied upto 973 K. The complexes were calcined isothermally at various temperatures i. e., 473, 573, 773 and 973 K. The intermediates/products have been characterized by Mössbauer, infrared spectroscopies and XRD powder diffraction. The anhydrous complexes directly decompose to give -Fe2O3 and alkali metal carbonate without undergoing reduction to iron(II) moiety. An increase in the particle size and internal magnetic field of -Fe2O3 has been observed with increasing decomposition temperature. At higher temperature (973 K) MFeO2 is formed as the final thermolysis product due to a solid state reaction between -Fe2O3 and alkali metal carbonate.
The thermal decomposition of cesium tris(oxalato) ferrate(III) dihydrate, Cs3 Fe(ox)3 2H2O has been studied at various temperatures in air, employing Mössbauer and infrared spectroscopies, and thermogravimetric methods. The complex undergoes reduction to an iron(II) intermediate at 473 K. The particle size of -Fe2O3 formed during thermolysis increases with increasing decomposition temperature. Finally, a solid state reaction between -Fe2O3 and cesium carbonate/oxide occurs, leading to the formation of fine particles of cesium ferrite (CsFeO2).
The thermolysis of strontium and barium tris(maleato)ferrates(III), M3 [Fe(C2 H2 C2 O4 )3 ]2 ·x H2 O has been investigated from ambient temperature to 800 °C using simultaneous TG-DTG-DTA, XRD, Mössbauer and IR spectroscopic techniques. After dehydration the anhydrous complexes undergo decomposition to yield an iron(II)maleate/oxalate intermediate in the temperature range of 240-280 °C. An oxidative decomposition of iron(II) species leads to the formation of -Fe2 O3 and respective alkaline earth metal carbonate in the successive stages. Finally at 540-590 °C, a solid state reaction occurs between -Fe2 O3 and strontium/barium carbonate resulting in the formation of SrFeO2.5 and BaFe2 O4 , respectively.
The thermolysis of zinc bis(citrato)ferrate(III)dodehydrate has been investigated from ambient temperature to 600 °C using various physico-chemical techniques, i.e., simultaneous TG-DTG-DTA, XRD, Mössbauer and I.R. spectroscopy. After dehydration at 200 °C, the anhydrous complex undergoes oxidative decomposition to yield -Fe2O3 and ZnO at 350 °C. Subsequently, the cations remix to yield fine particles of zinc ferrite, ZnFe2O4 as a result of solid state reaction between -Fe2O3 and ZnO at a temperature (450 °C) much lower than for ceramic method.
Thermal decomposition of sodium tris(maleato)ferrate(III) hexahydrate, Na3[Fe(C4H2O4)3]·6H2O and sodium tris(fumarato)ferrate(III) heptahydrate, Na3[Fe(C4H2O4)3]·7H2O has been studied upto 973 K in static air atmosphere employing TG, DTG, DSC, XRD, Mössbauer and infrared spectroscopic techniques.
Dehydration of the maleate complex is complete at 455 K and the anhydrous complex immediately undergoes decomposition till
α-Fe2O3 and sodium carbonate are formed at 618 K. In the final stage of remixing of cations, a solid state reaction between α-Fe2O3 and sodium carbonate leads to the formation of α-NaFeO2 at a temperature (773 K) much lower than for ceramic method. Almost similar mode of decomposition has been observed for the
fumarate complex. A comparison of the thermal stability shows that the fumarate precursor decomposes at a higher temperature
than the maleate complex due to the trans geometry of the former.
Thermal analysis of alkaline earth metal ferrisuccinate precursors, M3[Fe(C4H4O4)3]2�xH2O (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.
Thermal decomposition of ammonium tris (malonato) ferrate (III) tetrahydrate, i. e. (NH4)3[Fe(CH2C2O4)3]·4H2O has been studied up to 973 K in static air atmosphere employing Mössbauer and infrared spectroscopies, and non-isothermal techniques (TG, DTG, DTA). The anhydrous complex decomposes into an iron (II) intermediate at 453 K. The iron (II) species on further heating is reoxidized to -Fe2O3 as the final thermolysis product. An increase in particle size of -Fe2O3 with increasing decomposition temperature has been observed. The results are compared with the analogous oxalate complex.