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The modes of decomposition of a few rare earth metal formates and benzoates were studied by the use of DTA, DSC, TG and DTG techniques in air, nitrogen and vacuum. The volatile products and residues were identified. The activation energies of decompositions and the heat of reaction for transitions were calculated.

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The silver, lead and mercuric toluenedithiolates were synthesised and analysed by both conventional chemical methods and thermoanalytical methods. The thermal decomposition was studied by thermogravimetric analysis in air, nitrogen and vacuum. The formulae of the decomposition products were derived using the mole weights and i.r. absorption spectra. The activation energies for the first stage of decomposition were calculated. The volatile products contain mostly carbon and hydrogen while the residues contain the corresponding metals either free or combined with sulfur.

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Abstract  

General purpose poly(styrene) prepared by conventional radical techniques contains a head-to-head unit as a consequence of polymerization termination by radical coupling. As has been previously demonstrated, thermal stress promotes homolysis of the bond linking the head-to-head components. The macroradicals generated depolymerize rapidly to generate styrene monomer. This decomposition during processing can lead to finished articles containing objectionable levels of styrene monomer, particularly for food packaging applications in which even low levels of monomer can promote objectionable taste and aroma. Polymer containing no head-to-head units should not be prone to this facile decomposition. In this instance, poly(styrene) has been prepared by nitroxyl-mediated polymerization of styrene monomer followed by reductive removal of nitroxyl end groups. Polymer prepared in this manner contains no head-to-head units and displays thermal stability much greater than that observed for conventional poly(styrene). A direct comparison of the stability for the two polymers is readily available by thermogravimetric techniques. A quantitative reflection of the difference in stability is available from the rate constants for the respective decomposition.

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Thermal behaviour of M(OH)2(8-HQ)2 (M=Ni, Cu and Zn; 8-HQ=8-hydroxyquinoline) has been studied by dynamic TG and DTA methods in nitrogen atmosphere. The percent weights lost in different temperature range was calculated from TG curves. The mode of decomposition has been supported by endotherms observed in DTA curves of the respective compounds.

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The thermal decomposition of iron(III) aminobenzoates (o-, m-, p-) and iron(III) hydroxybenzoates (p-, m-, p-) have been investigated from ambient temperature to 873 K in air using derivatography DTG-DTA-TG, Mössbauer, IR spectroscopy and XRD. The importance of Mössbauer spectra recorded at various stages of heating, without separating the product mixture, in studying the mode of decomposition is highlighted. The intermediates (e.g., Fe(II)-species) were confirmed. The nature of water of hydration and the order of stability (p->m->o-) have been investigated from decomposition temperatures. The kinetic model and parameters have been investigated for dehydration.

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2,4'-Bipyridyl (2,4'-bipy or L) complexes of Mn(II) with the formulae MnL2X2·2H2O (X =Cl, Br, NCS, NO3), MnLSO4·5H2O and MnL4(ClO4)2·2H2O were synthesized and characterized via the IR spectra and magnetic, and conductivity measurements. The nature of the Mn(II)-ligand coordination is discussed. The thermal decompositions of these compounds were studied in air atmosphere. The mode of decomposition depends on the anion present, but the final product in all cases is Mn3O4. Some of the intermediates (MnL2Cl2, MnLCl2, MnL2Br2, MnL2(NCS)2 and MnLSO4) formed during the pyrolysis are isomeric with 2,2'-bipy and 4,4'-bipy complexes.

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Mass spectral and thermal studies by TG and DTG of some iron(III) binuclear complexes of the general type Fe2(R2dtc)2(tds∮)X2X/′ have been carried out to determine their modes of decomposition. Fragmentation patterns are given and possible mechanisms are discussed.

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Abstract  

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.

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The techniques of thermal analysis are used to determine the mode of decomposition of nickel carbonates doped by the method of coprecipitation. Nickel carbonate prepared by this method is basic in nature with the stoichiometryxNiCO3·yNi(OH)2·zH2O. Isothermal Thermogravimetry was applied to determine the mechanism of decomposition. Rising temperature Thermogravimetry (TG) and Differential Scanning Calorimetry (DSC) were used to study the effects of doping on the kinetics of the decomposition. Doping was found to strongly influence the kinetics of the decomposition. The kinetics of thermal decomposition of the doped carbonates were compared with conductivity studies. A compensation effect has been observed and is discussed, in the thermal decomposition of the doped nickel carbonates.

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