E. Ingier-Stocka

Monitoring of the Gas Phase Composition: A Prerequisite for Unravelling the Mechanism of Decomposition of Solids. Thermal decomposition of cobalt oxalate dihydrate

The complexity of the processes occurring during cobalt oxalate dihydrate (COD) decomposition indicates that an interpretation of the mechanism based only on the TG curve is of little value. Mass change alone does not allow deeper insight into all of the potential primary and secondary reactions that could occur. The observed mass changes (TG) and thermal effects (DTA/DSC) are a superposition of several phenomena and thus do not necessarily reflect COD decomposition alone. Investigation of the mechanism of decomposition requires the application of different simultaneous techniques that allow the qualitative and quantitative determination of the composition of the gaseous products.Composition of the solid and gaseous products of COD decomposition and heats of dehydration and oxalate decomposition were determined for inert, oxidizing and hydrogen-containing atmospheres. Contrary to previous suggestions about the mechanism of cobalt oxalate decomposition, the solid product formed during decomposition in helium contains not only metallic Comet, but also a substantial amount of CoO (ca 13 mol%). In all atmospheres, the composition of the primary solid and gaseous products changes as a result of secondary gas-solid and gas-gas reactions, catalyzed by freshly formed Comet.The course of the following reactions has been investigated under steady-state and transient conditions characteristic for COD decomposition: water gas shift, Fischer-Tropsch, CO disproportionation, CoO reduction by CO and H2, Comet oxidation under rich and lean oxygen conditions.

Thermal and conductometric studies of NdBr3 and NdBr3-LiBr binary system

The heat capacity of solid NdBr3 was measured by Differential Scanning Calorimetry in the temperature range from 300 K up to the melting temperature. The heat capacity of liquid NdBr3 was also determined. These results were least-squares fitted to a temperature polynome. The melting enthalpy of NdBr3 was measured separately. DSC was used also to study phase equilibrium in the NdBr3-LiBr system. The results obtained provided a basis for constructing the phase diagram of the system under investigation. It represents a typical example of simple eutectic system. The eutectic composition, x(NdBr3)=0.278, was obtained from the Tamman construction. This eutectic mixture melts at 678 K. The electrical conductivity of NdBr3-LiBr liquid mixtures and of pure components was measured down to temperatures below solidification. Reflectance spectra of the pure components and their solid mixtures (after homogenisation in the liquid state) with different composition were recorded in order to confirm the reliability of the constructed phase diagram.

Phase diagram and electrical conductivity of TbBr3-NaBr binary system

Several experimental techniques were used to characterise the physicochemical properties of the TbBr3-NaBr system. The phase diagram determined by DSC, exhibits an eutectic and a Na3TbBr6 stoichiometric compound that decomposes peritectically (759 K) shortly after a solid-solid phase transition (745 K). The eutectic composition, x(TbBr3)=39.5 mol%, was obtained from the Tamman method. This mixture melts at 699 K. With the corresponding enthalpy of about 16.1 kJ mol-1. Diffuse reflectance spectra of the pure components and their solid mixtures (after homogenisation in the liquid state) confirmed the existence of new phase exhibiting its own spectral characteristics, which may be possibly related to the formation of Na3TbBr6 in this system. Additionally, the electrical conductivity of TbBr3-NaBr liquid mixtures was measured down to temperatures below solidification over the whole composition range.

Thermal decomposition reactions of amminecobalt(III)complexes

Simultaneous TG-DTG-DTA studies under non-isothermal conditions on [Co(NH3)6]Cl3, [Co(NH3)5]Cl2 and [Co(NH3)]2(C2O4)3.4H2O complexes have been carried out in air and argon atmospheres in the temperature range 293–1273 K. All the dissociation processes occur in three main stages. The kinetics of thermal decomposition of the complexes have been evaluated from the dynamic weight loss data, to determine the most probably mechanisms of the stages on the basis of statistical analysis. The decomposition of the compounds was controlled by diffusion and phase boundary reactions except stage III of the oxalate complex in argon (random nucleation). The activation energiesEa of the particular stages of the thermal decomposition were calculated.ZusammenfassungSimultane TG-DTG-DTA-Untersuchungen an den Komplexverbindungen [Co(NH3)6]Cl3, [Co(NH3)5Cl]Cl2 und [Co(NH3)6]2(C2O4)3.4H2O unter nichtisothermen Bedingungen wurden in Luft und Argonatmosphäre bei 293–1273 K durchgeführt. Die Zersetzung läuft in jeweils drei Stufen ab. Für die kinetische Auswertung der thermischen Zersetzung der Komplexverbindungen aus den dynamischen Gewichtsabnahmekurven wurde der wahrscheinlichste Mechanismus der einzelnen Stufen mit Hilfe von statistischen Analysen ermittelt. Die Zersetzung der Komplexverbindungen wird meist durch Diffusions- und Phasengrenzreaktionen kontrolliert, nur bei der 3. Stufe des Oxalatkomplexes in Argon herrscht statistische Keimbildung. Die AktivierungsenergienEa der einzelnen Zersetzungsstufen werden berechnet.РезюмеВ атмосфере воздуха и аргона проведены в интервале температу р 293–1273 К неизотермические со вмещенные ТГ—ДТГ и ДТ А исследования компле ксов [Co(NH3)6]Cl3, [Co(NH3)5Cl]G2 и [Co(NH3)6]2(C2O4)3.4H2O. Все проц ессы диссоциации протека ют в три стадии. Исходя из данн ых динамической поте ри веса, проведена оценка кин етика термического разложения и на основ ании статистическог о анализа определен наиболее в озможный механизм реакционных стадий. Р азложение определяе тся диффузионным механи змом и механизмом поверхности раздела фаз, за исключением ст адии III реакции разложения о ксалатного комплекса в аргоне, по дчиняющейся механиз му произвольного образ ования центров крист аллизации. Вычислены энергии ак тивации Еa отдельных стадий разложения.

Thermal Analysis of Cobalt(II) Salts with some Carboxylic Acids

The thermal analysis of CoC2O4·2H2O, Co(HCOO)2·2H2O and Co(CH3COO)2·4H2O was carried out with simultaneous TG-DTG-DTA measurements under non-isothermal conditions in air and argon atmospheres. The intermediates and the end products of decomposition were characterised by X-ray diffraction and IR and UV-VIS spectroscopy. The decomposition of the studied compounds occur in several stages. The first stage of dissociation of each compound is dehydration both in air and argon. The next stages differ in air and argon. The final product of the decomposition of each compound in air is Co3O4. In argon it is a mixture of Co and CoO for cobalt(II) oxalate and cobalt(II) formate but CoO for cobalt(II) acetate.

Kinetics of thermal decomposition of [Co(NH3)6]Cl3

Abstract The thermal decomposition of [Co(NH3)6]Cl3 was studied under non-isothermal conditions in dynamic air and argon atmospheres and under isothermal conditions in flowing air. Dissociation of the above complex occurs in three stages. The kinetics of the particular stages of [Co(NH3)6]Cl3 thermal decomposition have been evaluated from both dynamic and isothermal weight loss data. The Rn models were selected as those best fitting the experimental TG curves. These models suggest that the kinetics and macromechanism of the [Co(NH3)6]Cl3 dissociation can be governed by phase boundary processes. The activation energies, Eα, of the particular stages of the thermal decomposition were calculated. The results have corroborated the view that combination of isothermal and non-isothermal measurements facilitates the selection of the models best fitting experimental TG curves.

Thermal decomposition of [Co(NH3)6]Cl3

The thermal decomposition reactions of [Co(NH3)6]Cl3 were determined in dynamic argon and air atmospheres. The investigations were carried out with simultaneous TG-DTG-DTA measurements under non-isothermal conditions, thermogravimetry under quasi-isothermal conditions, reflectance spectroscopy, absorption spectroscopy, X-ray diffraction and chemical analysis. The data show that the thermal decomposition of [Co(NH3)6]Cl3 occurs in three and four stages in argon and air atmospheres, respectively. The determined sequences are in agreement with that proposed by Simons and Wendlandt [2, 5].The changes in the morphology of the studied complex crystalline powder in the course of thermal decomposition in air were followed by scanning electron microscopy.ZusammenfassungIn bewegter Argon- und Luftatmosphäre wurden die Zersetzungsreaktionen für [Co(NH3)6]Cl3 bestimmt. Zu den Untersuchungen wurden folgende Methoden zu Hilfe gezogen: simultane TG-DTG-DTA-Messungen unter nichtisothermen Bedingungen, Thermogravimetrie unter quasi-isothermen Bedingungen, Remissionsspektroskopie, Absorptionsspektroskopie, Röntgendiffraktion und chemische Analyse. Die Ergebnisse zeigen, daß sich [Co(NH3)6]Cl3 in Argon in drei und in Luft in vier Schritten thermisch zersetzt. Die festgestellten Sequenzen stehen in Übereinstimmung mit den von Simon und Wendlandt [2, 5] vorgeschlagenen. Veränderungen in der Morphologie des untersuchten Komplexkristallpulvers wurden über die thermische Zersetzung in Luft mittels Scanning-Elektronen-Mikroskopie beobachtet.РезюмеВ динамической атмос фере аргона и воздуха определены реакции т ермического разложения комплекс а [Co(NH3)6]Cl3. Исследования бы ли проведены с помощью совмещенного ТГ, ДТГ и ДТА метода в неизотер мических условиях, метода терм огравиметрии в квази-изотермическ их условиях, спектрос копии отражения, абсорбцио нной спектроскопии, рентгеноструктурно го и химического анал иза. Полученные результа ты показали, что термическое разложе ние комплекса в атмос фере аргона и воздуха протекает, с оответственно, в три и четыре стадии, по следовательность ко торых согласуется с таково й, предложенной Симонсом и Вепдландо м, Используя сканирую щую электронную микроск опию прослежено морфологическое изм енение порошкообраз ного комплекса в ходе его т ермического разложе ния в атмосфере воздуха.

Kinetics of the thermal decomposition of [Co(NH3)6]2(C2O4)3·4H2O

The thermal decomposition of [Co(NH3)6]2(C2O4)3·4H2O was studied under isothermal conditions in flowing air and argon. Dissociation of the above complex occurs in three stages. The kinetics of the particular stages thermal decomposition have been evaluated. The RN and/or AM models were selected as those best fitting the experimental TG curves. The activation energies,E, and lnA were calculated with a conventional procedure and by a new method suggested by Kogaet al. [10, 11]. Comparison of the results have showed that the Arrhenius parameters values estimated by the use of both methods are very close. The calculated activation energies were in air: 96 kJ mol−1 (R1.575, stage I); 101 kJ mol−1 (Ain1.725 stage II); 185 kJ mol−1 (A2.9, stage III) and in argon: 66 kJ mol−1 (A1.25, stage I); 87 kJ mol−1 (A1.825, stage II); 133 kJ mol−1 (A2.525, stage III).

Electrical conductivity of molten binary NdBr3 - alkali bromide mixtures

Electrical conductivity of liquid binary NdBr3 - alkali metal bromide mixtures was measured as a function of temperature over the whole composition range. Prior to these measurements, NdBr3 and alkali bromides were reinvestigated: a new assessment of literature data was made because of the discrepancy with reference values on NdBr3, LiBr and CsBr. The classical Arrhenius equation describes well our electrical conductivity data for mixtures. These results are discussed in terms of complex formation in the melts.

Thermochemistry of the Decomposition of Some Cobalt Compounds

Differential scanning calorimetry (DSC) was used to determine the molar enthalpies of dehydration and decomposition of CoC2O4·2H2O, Co(HCOO)2·2H2O and [Co(NH3)6]2(C2O4)3·4H2O. The first stage of dissociation of each compound is a single-step dehydration both in air and argon atmospheres. The next stages are decomposition processes influenced by experimental parameters. The enthalpies of dehydration and decomposition vary from compound to compound in each atmosphere. The obtained data have been related to the macromechanisms proposed for the thermal decomposition and the parallel-consecutive decomposition-oxidation processes.