Thermal decomposition processes of lanthanide trifluoroacetates trihydrates

The thermal decomposition of several lanthanide salts Ln(CF₃COO)₃·3H₂O (Ln=La, Gd, Tb) was studied under quasi-equilibrium conditions and under linear heating. According to mass spectral data, H₂O is the single product of thermal decomposition up to 120-140°C. Thermogravimetric data were processed with 'Netzsch Thermokinetics' computer program. Kinetics parameters of the first decomposition step (as the simple dehydration process, not complicated by the water hydrolysis with the liberation or the decomposition of the organic ligand) were calculated. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal treatment and analysis

Heating and/or cooling of substances is one of the oldest and basic methods for preparing materials with defined properties. This always leaves a definitive fingerprint of the thermal history. Beside knowing the structure we need to specify such materials by their thermodynamic behaviour, i.e., stability/metastability, phase relations and transitions, particularly establishing corresponding characteristic points. All this can be based on ordinary thermodynamics but its validity must be approved for non-equilibrium conditions of temperature changes where equilibrium and kinetic effects overlap. The slower the phase transition proceeds the greater is the deviation of the system state (kinetic curve) from its equilibrium state (equilibrium background). This makes possible to locate the actual phase boundary between two states investigated, resulting in the so-called kinetic phase diagrams. Most of modern technologies are intentionally based on non-equilibrium phenomena in order to create metastable/nonstable phases of specific properties. In this sense thermal analysis is understand as the method for determining the sample state on the basis of the sample interactions with the surroundings whose intensive parameters are controlled. Temperature is here considered as a basic parameter that connects all thermophysical measurements and thermal treatments. ICTA-TA Award lecture     

Thermal decomposition kinetics of some aromatic azomonoethers

Thermal analysis of three azomonoether dyes, exhibiting liquid-crystalline properties, was performed in dynamic air atmosphere. Thermal stability studies and the evaluation of the kinetic parameters of each physical or chemical transformations are essential for a full characterization, before attempting accurate thin films’ depositions of such materials used in non-linear optical applications. New synthesized dyes with general formula: where R is a nematogenic group: CN, CF₃ or a highly polarizable group: NO₂ were investigated using TG, DTG, DTA and DSC techniques, under non-isothermal regime. The evolved gases were analyzed by FTIR spectroscopy. The activation energies of the first decomposition step were evaluated for each compound, the obtained results revealing complex mechanisms.     

The basic processes of depolymerization and its real kinetic analysis

The method of computer-experiments can be applied successfully on the radical depolymerization under inclusion of initiation, depropagation and termination. The comfortable PC-program TA-kin for the non-linear estimation of parameters for TG- or DSC-experiments was applied to the determination of activation parameters of depropagation and termination. Therefore the overall-evaluation of three or more data sets is a prerequisite. The determination of kinetic parameters runs satisfactory if the measured curves are strongly different, e.g. by varying the heating rate, including acceptable experimental errors. Several recommendations for laboratory experts are given. A great support for a very sufficient estimation is the inclusion of simultaneous analysis of the radical concentration.     

The basic processes of polymerization and its real kinetic analysis

The method of computer experiments can be successfully applied to radical polymerization with the inclusion of initiation, propagation and termination. The convenient PC-program TAkin for non-linear estimation of the parameters of calorimetric and thermoanalytical experiments was applied for determination of the activation parameters of chain propagation and termination. The overall evaluation of three or more data sets was preferred. The determination of the kinetic parameters proceeds satisfactorily of the measured curves are strongly different, e.g. with a changed start temperature of modified application of batch and semi-batch technique, including acceptable experimental errors. Eight recommendations for laboratory experts are given.The autors thank Prof. H. A. Schneider (UniversitÄt Freiburg, FMF, Meierstr. 21, D79104 Freiburg) for helpful discussions concerning the rational application of modern kinetic methods.     

Thermal decomposition,kinetic study and evolved gas analysis of 1,3,5-triazine-2,4,6-triamine

The thermo-physical properties for four rock types (granite, granodiorite, gabbro, and garnet amphibolite) from room temperature to 1,173 K were investigated. Thermal diffusivity and specific heat capacity were measured using the laser-flash technique and heat flux differential scanning calorimetry, respectively. Combined with the density data, rock thermal conductivities were calculated. Rock thermal diffusivity and conductivity decrease as the temperature increases and approach a constant value at high temperatures. At room temperature, the measured thermal conductivity is consistently near or lower than the calculated conductivity using the mineral series model, which suggests that real thermal conduction is more complicated than is depicted in the model. Therefore, in situ measurement remains the best method for accurately obtaining thermal conductivity for rocks.     

Thermal and kinetic study of dehydration and decomposition processes for copper intercalated γ-zirconium and γ-titanium phosphates

Thermal dehydration and decomposition processes of some intercalation compounds were studied by simultaneous TG/DSC and evolved gas analysis (EGA). γ-Zirconium and γ-titanium phosphates were intercalated with 1,10-phenanthroline and subsequently reacted with copper ions to form the complex in situ. Reaction mechanisms for thermal decomposition of all the materials were investigated and proposed according to the mass losses recorded by TG and confirmed by EGA (TG-FTIR). The Ozawa-Flynn-Wall isoconversional method provided dependencies of activation energy on the degree of conversion. A “single point” model-free method was also applied using Kissinger equation and the derived results were compared to those of the former method.     

Thermal behaviour and non-isothermal decomposition kinetics of some Nd(III) coordination compounds

The authors present the results concerning the thermal behaviour of three polynuclear coordination compounds of Nd(III) and Co(II) or Fe(III) with triptophan. For the dehydration steps the values of the non-isothermal kinetic parameters have been determined.     

Theoretical prediction of enthalpies and temperatures of sublimation of organochlorine compounds including pesticides

Crystal lattice energies of several organochlorine compounds—including pesticides, of known crystal structures were calculated on the basis of a model which takes into account electrostatic, dispersive and repulsive interactions—using three different sets of empirical parameters. These characteristics compare reasonably with experimental heats of volatilization, and it was subsequently shown how statistical and classical thermodynamics can be employed to evaluate dependencies of function of states of gaseous and solid compounds on temperature and how enthalpies and temperatures of sublimation at standard pressure, as well as vapour pressurevs. temperature dependencies can be predicted.     

Thermal dehydration of some food products and kinetic parameters of this process

Metal poly(vinyl acetates) polymers were obtained by radical polymerization with azodiisobutyronitrile. The thermal stabilities of the metal polymers (M-PVAC) have been studied by thermogravimetry (TG) between 25 and 550°C under nitrogen flow. The decomposition temperature was obtained from the maximum of the first derivative from TG curve. The kinetic parameters of the thermal decomposition were determined by the Arrhenius equation. All these polymers degrade mainly in a single step with a very small second step, probably via a complex reaction. The kinetic data thus obtained show that the thermostabilities decrease in the order: Sb-PVA_c～Ge-PVA_c>Bi-PVA_c～Cd-PCA_c>Ag-PVA_c～PVA_c>Zn-PVA_c> Au-PVA_c>In-PVA_c>Sn-PVA_c>Ga-PVA_c>Pd-PVA_c. Again, the thermal stability is dependent upon the metal incorporated in the backbone polymer. They loose weight after 320°C. The order of reaction from the thermal decomposition of these metal polymers was found to be ?0.5 for the first step and 0 for the second. The pre-exponential factor, the reaction order and the activation energy of the decomposition for metal (PVA_c) have been determined in most of them.     

Thermal characterization and isothermal kinetic analysis of commercial Creosote decomposition process

Isothermal decomposition process of commercial Creosote was analyzed by thermogravimetric technique in a nitrogen atmosphere, at four different operating temperatures (T = 230, 250, 270, and 290 °C). It was found that the two-parameter autocatalytic ?esták–Berggren kinetic model best describes the investigated process. It was established that the applied logistic function can successfully perform a given kinetic predictions of investigated process, at all operating temperatures. The experimental density distribution function of the apparent activation energy values was evaluated. Based of the characteristic shape of distribution curve, it was concluded that the isothermal pyrolysis of commercial Creosote represent a complex process, which probably includes primary and secondary (autocatalytic) pyrolysis reactions, together with various decomposition reactions and radicals recombination pathways.     

Rapid thermal analysis of processes of thermal decomposition of mineral salts

Kinetic curves of thermal decomposition and synthesis of mineral salts are obtained in the conditions of rapid heating approaching the heating conditions in a low-temperature plasma flow. The kinetic characteristics are used in calculations of transformations in the path of a chemical plasma reactor.

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Zusammenfassung Für thermische Zersetzung und Synthese von Mineralsalzen wurden die kinetischen Kurven unter den Bedingungen schnellen Aufheizens in Annäherung der Aufheizbedingungen in einem Niedertemperatur-Plasmastrom ermittelt. Die kinetischen Eigenschaften wurden zur Berechnung der Umwandlungen bei einem chemischen Plasmareaktor verwendet.

     

A study of the thermodynamic properties and dehydration reaction kinetics of some salt-hydrates

Correlations were determined between heat capacity and temperature and phase change enthalpy of Ba(OH)₂·8H₂O. The phase diagram and DSC curve of the binary system Na₂CO₃·10H₂O?Na₂HPO₄·12H₂O were determined The kinetics of the dehydrating reaction of Ba(OH)₂·8H₂O, Na₂CO₃·10H₂O and Na₂HPO₄·12H₂O were measured and theoretically analyzed by TG.     

Synthesis and kinetic analysis of isothermal and non-isothermal decomposition of ammonium dinitramide prills

Ammonium dinitramide (ADN) prills were prepared by emulsion crystallization and characterized by optical microscopic, thermogravimetric (TG) and differential scanning calorimetric (DSC) techniques. The isothermal and non-isothermal decomposition kinetics of ADN prills were studied by TG. The differential isoconversional method of Friedman (FR) and integral isoconversional method of Vyazovkin were used to investigate the dependence of activation energy (E _a) with conversion (α) and the results were compared with literature data. The dependence of activation energy was also derived from isothermal data. A strong dependence of E _a with α is observed for the ADN prills. All the methods showed an initial increase in E _a up to α=∼0.2 and later decreases over the rest of conversion. The apparent E _a values of FR method are higher than that of Vyazovkin method up to α=∼0.45. The calculated mean E _a values by FR, Vyazovkin and standard isoconversional method for α between 0.05 and 0.95 were 211.0, 203.9 and 156.9 kJ mol⁻¹, respectively.     

Thermal decomposition of some hexaborates

Thermal decomposition of iron(II) and cobalt(II) hexaborates has been investigated. The methods applied to investigate the process were differential thermal analysis, derivatography, crystallooptics and x-ray study. The following iron(II) hexaborate hydrates, FeO · 3B₂O₃ · 7.5H₂O, FeO · 3B₂O₃ · 5H₂O, FeO · 3B₂O₃ · 0.5H₂O; iron(III) borates, Fe₂O₃ · 6B₂O₃ and 2Fe₂O₃ · B₂O₃; cobalt(II)hexaborate hydrates CoO · 3B₂O₃ · 7.5H₂O, CoO · 3B₂O₃ · 5H₂O, CoO · 3B₂O₃ · 0.5H₂O, CoO · 3B₂O₃ and the decomposition product 2CoO · 3B₂O₃ have been isolated. Hepta- and semihydrates of cobalt(II) and iron(II) hexaborates have been proved to be isomorphous. It has been established that in the case of cobalt and iron hexaborates the exothermic maximum refers to a decomposition reaction and to the formation of a borate containing a smaller proportion of boron and boric anhydride.     

Thermodynamic and kinetic properties of hydrogen adsorption on thin iron layers

Thermodynamic properties of hydrogen adsorption on iron layers evaporated under UHV conditions have been determined from calorimetric and volumetric measurements over the temperature range from 298 K to 363 K. Kinetic properties have been determined with the help of deconvolution of calorimetric curves and compared with the literature data on the sticking coefficient.

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Zusammenfassung Mittels kalorimetrischer und volumetrischer Messungen im Temperaturbereich von 298 bis 363 K wurden die thermodynamischen Eigenschaften der Wasserstoffadsorption an Eisenschichten untersucht. Die kinetischen Eigenschaften wurden mit Hilfe der Dekonvulotion kalorimetrischer Thermogramme ermittelt und mit Literaturangaben zum Haftkoeffizienten verglichen.

     

Thermal decomposition of bismuth stearates

Two bismuth salts, Bi₆O₄(OH)₄(C₁₇H₃₅COO)₆ and Bi₆O₄(OH)₄(C₁₇H₃₅COO)₆·nC₁₇H₃₅COOH, were synthesized. The thermogravimetry under quasi-isothermal conditions denotes the multi-step character of decomposition processes for both compounds. The thermogravimetry under linear heating was used for kinetic studies. Thermogravimetric data (obtained at different rates of linear heating) were processed with 'Netzsch Thermokinetics' computer program. Kinetic parameters were calculated only for the first decomposition step for both salts, the process is described by different nucleation equations (with and without autocatalysis). This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal decomposition processes and their nucleation characteristics

Die Bildung und das Wachstum von Keimen während thermischer Zersetzungsreaktionen wurde mit Hilfe der Thermomikroskopie untersucht. Diese Methode erlaubt eine kontinuierliche Beobachtung der verschiedenen Vorgänge und Effekte, welche für die Kinetik der Zersetzungsreaktionen maßgebend sind. Von besonderer Bedeutung sind die Geschwindigkeit der Keimbildung und die des Wachstums in Abhängigkeit von den kristallographischen Richtungen und in bezug auf die Oberflächendefekte. Weitere wichtige Faktoren für die Probe sind die umgebende Atmosphäre, die Bildung von Sprüngen und Rissen, welche auf die Diffusion der gasförmigen Zersetzungsprodukte und das Ausmaß des strukturellen Umbaus zurückzuführen sind.Keimbildungserscheinungen von: Gips, CuSO₄ · 5 H₂O, NiSO₄ · 6 H₂O, Hydrozinkit und Diamant werden diskutiert. Die Ergebnisse der thermooptischen Untersuchungen werden u. a. zu TG-Messungen und Röntgenuntersuchungen in Beziehung gesetzt. Die Aktivierungsenergie der Keimbildung von Selenit (Marienglas) wurde zu 16±3 kcal/Mol gefunden.Summary The formation and growth of nuclei during thermal decomposition processes was investigated by thermomicroscopy. This method permits the continuous observation of the various effects which determine the kinetics of the decomposition reaction. Of special importance are the rate of nuclei formation and growth in relation to the different crystallographic directions and to the surface defects. Other important factors are the surrounding atmosphere, the formation of fissures and cracks due to diffusion of the gaseous decomposition products, and the structural rearrangement. Nucleation characteristics of CaSO₄ · 2 H₂O, CuSO₄ · 5 H₂O, NiSO₄ · 6 H₂O, hydrozincite and diamond are also discussed. The thermooptical data are correlated to the TG, X-ray and other measurements for several of the systems studied. The activation energy for the nucleation of selenite was found to be 16±3 kcal/mole.

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Keimbildungsvorgänge bei thermischen Zersetzungsreaktionen

Some of the results were presented at the Fourth International Conference on Thermal Analysis, 8–13 July, 1974 Budapest, Hungary.