Search Results

You are looking at 1 - 10 of 39 items for

  • Author or Editor: B. Randhawa x
  • Refine by Access: All Content x
Clear All Modify Search

Abstract  

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).

Restricted access

Abstract  

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.

Restricted access

Abstract  

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.

Restricted access

Abstract  

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).

Restricted access

Abstract  

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.

Restricted access

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.

Restricted access

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.

Restricted access

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.

Restricted access

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).

Restricted access

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.

Restricted access