B. S. Randhawa

Calcium ferrite formation from the thermolysis of calcium tris (maleato) ferrate(III)

For preparing calcium ferrite, calcium tris (dmaleato) ferrate(III) precursor was prepared by mixing aqueous solutions of iron(III) maleate, calcium maleate and maleic acid. Various physico-chemical techniques i.e. TG, DTG, DTA, Mössbauer, XRD, IR etc have been used to study the decomposition behaviour from ambient to 900°C and ferrite formation. Three consecutive decomposition steps leading to the formation of α-Fe2O3 and calcium carbonate have been observed at various stages of thermolysis. In the final stage the ferrite, bdCa2Fe2O5, is obtained as a result of solid state reaction between α-Fe2O3 and calcium carbonate at 788°C, a temperature much lower than for ceramic method. The results have been compared with those of the oxalate precursor.

Mössbauer effect studies on alkali tris (malonato) ferrates(III)

Mössbauer spectra of alkali tris(malonato) ferrates(III) i.e. M3[Fe(C3H2O4)3].4H2O(M=Li, Na, K, NH4) at 298±2K display a single broad absorption band due to spin lattice relaxation effect. The isomer shift values 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+, NH4+). A linear correlation between isomer shift values and the (Fe-O) stretching freguencies has also been observed.

Comparative study of the thermal analyses of some transition metal(II) maleates and fumarates

The thermal decompositions of maleates and fumarates of Cu(II) and Zn(II) have been studied by employing simultaneous non-isothermal techniques (DTG, DTA and TG). The end-products are the corresponding metal oxides, as characterized by chemical analysis and X-ray diffraction. Comparison of theTm values led to the stability sequences Cu(F)>Cu(M); Zn(F)>Zn(M) and Cu(M)≈ Cu(F); Zn(F)>Zn(M) for dehydration and decomposition, respectively.ZusammenfassungDie thermische Zersetzung von Maleaten und Fumaraten von Cu(II) und Zn(II) wurde mittels simultan angewandter nicht-isothermer Techniken (DTG, DTA und TG) untersucht. Die Endprodukte sind die entsprechenden Metalloxide, wie durch chemische Analyse und Röntgendiffraktometrie nachgewiesen wurde. Ein Vergleich der Tm-Werte ergab für die Stabilität in der Dehydratisierungs- bzw. Zersetzungsreaktion die Reihenfolgen Cu (F) > Cu (M); Zn (F) > Zn (M) bzw. Cu (M) ≈ Cu (F); Zn (F)>Zn (M).РезюмеСовмещенным неизоте рмическим методом ДТ Г, ДТА и ТГ изучено термичес кое разложение малеатов и фумаратов меди и цин ка. Конечными продуктам и реакции разложения являлись окиси соотв етствующих металлов, идентифицированных химическим анализом и рентгенофазовым ана лизом. Согласно значе ниямTm, устойчивость компле ксов располагается в ряд Cu (F)>Cu (M); Zn (F)>Zn (M) и Cu (M) ≈ Cu (F); Zn (F)>Zn (M), соотв етственно, для реакций дегидратаци и и разложения.

MOSSBAUER STUDY ON THERMAL DECOMPOSITION OF CESIUM TRIS(OXALATO)FERRATE(III) DIHYDRATE

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 α-Fe2O3 formed during thermolysis increases with increasing decomposition temperature. Finally, a solid state reaction between α-Fe2O3 and cesium carbonate/oxide occurs, leading to the formation of fine particles of cesium ferrite (CsFeO2).

THERMAL DECOMPOSITION OF MAGNESIUM MALONATE TRIHYDRATE

The decomposition of magnesium malonate trihydrate has been studied isothermally and non-isothermally using TG, DSC, scanning electron microscope etc. The activation energy and frequency factor for isothermal dehydration are 100±5 kJ mol−1 and 1010 s−1 respectively and the corresponding values for decomposition from DSC are 332.9±113 kJ mol and 1017 s−1 respectively. The participation of liquid phase during dehydration is suggeseed while further decomposition is a solid state process. Final decomposition product at 673 K is crystalline magnesium oxide.ZusammenfassungMittels TG, DSC, Scanningelektronenmikroskop usw. wurde die Zersetzung des Trihydrates von Magnesiummalonat isotherm und nicht isotherm untersucht. Die Aktivierungsenergie und der Frequenzfaktor für die isotherme Dehydratation betragen 100±5 kJ·mol−1 bzw. 1010 s−1. Die entsprechenden DSC Werte für die Zersetzung betragen 332.9±113 kJ·mol−1 bzw. 1017 s−1. Während der Dehydratation scheint auch eine flüssige Phase aufzutreten, die weitere Zersetzung ist jedoch eine Feststoffreaktion. Das Endprodukt der Zersetzung bei 673 K ist kristallines Magnesiumoxid.РезюмеИспользуя методы ТГ, Д СК и сканирующую электронную микроск опию, изучено изотермическое и неи зотермическое разло жение тригидрата малоната магния. Значения энер гии активации и частотно го множителя для реак ции изотермической деги дратации составляли, соответственно, 100±5 кдж ·моль−1и 1010 сек−1, тогда как данные, полученные ме тодом ДСК, равнялись, соответст венно 332±113 кдж·моль−1 и 1017 сек−1. Установлено уч астие жидкой фазы в процессе дегид ратации, тогда как дал ьнейшее разложение является твердотельным процессом. Конечным п родуктом разложения при 673 К является кристаллич еский оксид магния.

MOSSBAUER STUDY ON THERMAL DECOMPOSITION OF SOME HYDROXY IRON(III) CARBOXYLATES

Thermal decomposition of some hydroxy iron(III) carboxylates, i.e., iron(III) lactate, Fe(CH3CHOHCOO)3, iron(III) tartrate, Fe2(C4H4O6)3 and iron(III) citrate, Fe(C6H5O7) · 5H2O has been studied in static air atmosphere in the temperature range 298–773 K employing Mössbauer, infrared spectroscopies and themogravimetric methods. The compounds directly decompose to α-Fe2O3 without undergoing reduction to iron(II) intermediates. An increase in particle size of α-Fe2O3 has been observed with increasing decomposition temperature. The thermal stability follows the sequence: iron(III) tartrate > iron(III)citrate > iron(III)lactate.

Thermal Analysis of Magnesium Tris(maleato) Ferrate(III) Dodecahydrate. Physico-chemical studies

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

Thermal analysis of lithium tris (malonato) ferrate(III) tetrahydrate

Thermal decomposition of lithium tris (malonato) ferrate (III) tetrahydrate i.e. Li3[Fe(CH2C2O4)3].4H2O has been studied in the temperature range of 353–873 K in static air atmosphere using Mössbauer, infrared spectroscopy and nonisothermal techniques (TG-DTG-DTA). The anhydrous complex decomposed into ferric oxide of varying particle sizes and alkali metal malonates/carbonates in succesive stages. Fimally a solid state reaction between α-Fe2O3 and alkali metal carbonate gives fine particles of lithium ferrite (LiFeO2) at a temperature lower than for oxalate precursor and for ceramic method.

Preparation of magnesium and calcium ferrites from the thermolysis of M3[Fe(cit)2]2.xH2O precursors

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.

The thermolysis of zinc bis(citrato)ferrate(III) dodecahydrate

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 α-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 α-Fe2O3 and ZnO at a temperature (450 °C) much lower than for ceramic method.