Isoconversional kinetic analysis of thermal decomposition of 1-butyl-3-methylimidazolium hexafluorophosphate under inert nitrogen and oxidative air atmospheres

Journal of Thermal Analysis and Calorimetry - Non-isothermal decomposition of 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim]PF6) in inert nitrogen and air atmospheres was investigated by...     

Isoconversional kinetic study of alachlor and metolachlor vaporization by thermal analysis

The vaporization kinetics of two acetamide pesticides, namely alachlor and metolachlor, was studied by thermogravimetric analysis under nonisothermal conditions (using heating rates between 1.0 and 10 K min^?1). A model‐free isoconversional method of kinetic analysis was proposed, and activation energy dependences on the extent of conversion α for nonisothermal experiments were given. An increase in activation energy is shown for alachlor from 50 to 60 kJ mol^?1, while E values do not significantly vary in the range α > 0.1: 63 kJ mol^?1 for metolachlor while 60 kJ mol^?1 for alachlor. At the end of vaporization (0.9 < α < 1.0), the activation energies are in close agreement with the enthalpies of vaporization calculated from DSC measurements. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 37: 74–80, 2005     

Thermogravimetric and differential thermal analyses of fluorescein dye in inert and static air atmosphere

Journal of Thermal Analysis and Calorimetry - Fluorescein dye was prepared and characterized on the basis of microanalytical methods, FTIR, NMR and UV–visible spectroscopy in order to ensure...     

Some observations on the thermal behaviour of curcumin under air and argon atmospheres

The TG, DTG and DTA curves of curcumin(I) have been recorded in static air and inert dynamic argon atmosphere over the range between ambient temperature and 600°–700°C using a Netzsch thermal analyser STA 429. Careful examination of these curves reveals appreciable differences in the behaviour of I under either atmospheres, which are easily recognized by comparing the profiles of their thermal curves, particularly in the melting point, thermalL stability of intermediates, percent weight loss and exothermicity of the chemical processes. Gaschromatographic analysis of volatile pyrolysates trapped during thermal analysis indicates the formation of (CH₃)₂CO, CH₃COH and C₆H₅OCH₂COOH (phenyl oxyacetic acid). However, in static air CO₂ and H₂O were identified as well. X-ray diffractometry reveals the formation of amorphous carbon as a final product in argon and a mixture of amorphous carbon and graphite in air. It seems that the relatively high mass of argon plays an important role in the reactions and stability of intermediates. In either atmospheres curcumin is thermally stable up to 249°C withm.p. of 176.4°–177.5°C. The unique shape of the DTA curve of I could be used forits identification.     

Isoconversional analysis of solid-state transformations

A key issue in kinetic analysis is the "prediction" of the evolution of a solid state transformation for a particular temperature program. Many methods have been proposed to calculate this evolution from kinetic parameters determined from non-isothermal isoconversional methods. In this study, we will review and compare the most accurate methods. We will then introduce a new method that provides an accurate prediction for an arbitrary temperature program.     

Comparative study on thermal degradation of some new diazoaminoderivatives under air and nitrogen atmospheres

The article is devoted to a comparative study on the thermal degradation of some new diazoaminoderivatives under both air and nitrogen atmosphere by TG-FTIR analysis. The TG–DTG–DTA curves show the thermal degradation in air to present two temperature domains: an endothermic one identical to the case of the degradation under nitrogen and an exothermic one which is not to be found under nitrogen atmosphere. The identification of the gaseous species released by degradation in air within the endothermic domain made evident the presence of the same components of the degradation in nitrogen atmosphere. In the exothermic domain of the sample degradation in air, the CO₂, H₂O, SO₂ species result by the burning of the molecular residues of the first domain. The obtained results afforded a degradation mechanism to be advanced that coincide for the endothermic domain with that of degradation under nitrogen atmosphere. Due to the importance of these compounds as possible reaction initiators and also as potentially bioactive substances (herbicides, acaricides, fungicides), the study on their thermal degradation could give useful information on the environmental impact of the degradation products resulting by the thermal processing of the plants which could possible retain these compounds, when the initial degradation temperature is exceeded.     

Non-isothermal degradation of a thermoset powder coating in inert and oxidant atmospheres

This paper studies the thermal stability of an epoxy powder coating. The study was carried out in a thermobalance at various heating rates and in different atmospheres: nitrogen, air and oxygen. Degradation in air and oxygen leads to a kinetic process which is clearly different from degradation in an inert atmosphere. To characterise each process, the DTG signal peaks were separated and kinetic parameters were associated to each by means of the isoconversional method and other standard methods. The results obtained were compared with the experimental results. This revised version was published online in July 2006 with corrections to the Cover Date.     

Cure kinetics of a cobalt catalysed dicyanate ester monomer in air and argon atmospheres from DSC data

A kinetic analysis of the cyclotrimerisation reaction of a dicyanate ester monomer catalysed by cobalt(II) acetylacetonate and nonylphenol in air and argon atmospheres has been carried out by differential scanning calorimetry (DSC). Dynamic and isothermal DSC scans as well as the glass transition temperature are the experimental data obtained. From isothermal scans a higher cyanate conversion in air than in argon was obtained. The cyanate conversions are satisfactorily described with a second-order kinetic equation in the kinetically controlled region, and by m-order (m<1) equation after vitrification is reached. Activation energies determined by different procedures agree among them, showing slightly higher values in argon than in air.     

Isoconversional analysis of solid state transformations

There are many mathematical methods to determine the activation energy from non-isothermal experiments. However, controversies arise over the different values obtained by these methods. We will show that the origin of these discrepancies is either inaccurate approximations of the so-called temperature integral or the occurrence of complex transformations. We will review and compare the most commonly used methods. For those methods that lack accuracy, we will introduce simple numerical modifications to make them exact. In addition, we will introduce a new method that allows easy and accurate determination of the activation energy.     

Isoconversional analysis of solid state transformations

We will analyze the discrepancies between isoconversional methods when applied to complex transformations. The practical analysis of particular transformations leads us to conclude that (a) conventional integral methods based on integrated equations are essentially incorrect when dealing with variable activation energy; and (b) experimental inaccuracies and noise tend to give an apparent evolution of the energy variation, so that, non-constancy of the activation energy does not necessarily mean deviations from single-step transformations with constant activation energy.     

Reaction kinetics by thermal analysis

The application of thermal analysis in the study of reaction kinetics and reaction mechanisms in combination with presently available powerful analytical tools, in the sphere of materials with particular reference to high energy materials is presented and discussed. Also an attempt has been made to correlate the kinetic data obtained by TA with the performance characteristics, for some important materials.

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Zusammenfassung Es wird die Anwendung der Thermoanalyse bei der Untersuchung der Reaktionskinetik und des Reaktionsmechanismus in Zusammenwirkung mit den gegenwärtig zur Verfügung stehenden leistungsfähigen analytischen Werkzeugen auf dem Gebiet von Materialien mit speziellem Bezug auf energiereiche Stoffe dargestellt Und besprochen. Es wurde auch versucht, die durch TA erhaltenen kinetischen Daten einiger wichtiger Stoffe mit deren Leistungskenndaten in Beziehung zu stellen.

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Refined analysis of the thermal dissociation of formaldehyde

New experimental results for the thermal dissociation of formaldehyde to radical and molecular products (Proc. Combust. Inst. 2007, 31, in press) form the basis of the present analysis of the respective low-pressure rate coefficients k(Rad,0) and k(Mol,0) of the reaction. The article supersedes an earlier analysis (J. Phys. Chem. A 2005, 109, 8320) which used less accurate and more preliminary input information. In addition, refined rotational factors F(rot) are determined and specific energy and angular momentum dependent branching ratios from a more detailed analysis of photolysis quantum yields (J. Phys. Chem. A 2007, 111, 3868) are employed as well. It is emphasized again that pyrolysis and photolysis are intimately related and should be analyzed in an internally consistent manner. The combination of the new with earlier experimental results for pyrolysis rates allows one to fit the height of the energy barrier for the molecular elimination channel with improved precision. A value of E0,1 = 81.7(+/-0.5) kcal mol(-1) is obtained. In addition, employing anharmonicity factors F(anh) from the earlier work, a total average energy transferred per collision of -DeltaE/hc = 100(+/-20) cm(-1) is fitted from the experiments in the bath gas Ar. This value is consistent with the value -DeltaE/hc = 80(+/-40) cm(-1) for the bath gas N(2) such as fitted from photolysis quenching experiments (using the same molecular parameters as for the pyrolysis). Rate coefficients for the temperature range 1200-3500 K are represented in the form k(Mol,0)/[Ar] = 7.3 x 10(14) T -6.1 exp(-47300 K/T) cm(3) molecule(-1) s(-1) and k(Rad,0)/[Ar] = 2.1 x 10(12) T -5.5 exp(-47300 K/T) cm(3) molecule(-1) s(-1) (accuracy +/-25%) and recommended for use in combustion chemistry.     

Isoconversional kinetic analysis of stoichiometric and off-stoichiometric epoxy-amine cures

The curing reaction of stoichiometric and off-stoichiometric diglycidyl ether of bisphenol A (DGEBA) and 1,3-phenylene diamine (m-PDA) mixtures was studied by differential scanning calorimetry, thermogravimetric analysis and rheological measurements. In order to highlight the side reactions such as etherification and homopolymerization, the neat DGEBA and DGEBA/DMBA (N,N-dimethylbenzylamine) mixture were examined. The classical model-fitting and the advanced isoconversional methods were used to determine the activation energy of the different reactions. The advanced isoconversional method leads to a good agreement between isothermal, nonisothermal and rheological results. The effective activation energies of primary amine epoxy reaction, etherification and homopolymerization were estimated to about 55-60, 104 and 170 kJ mol⁻¹, respectively.     

Thermogravimetric analysis and kinetics modeling of isothermal carbonization of olive wood in inert atmosphere

The kinetics of olive wood carbonization is investigated by means of isothermal thermogravimetric analysis method. Measurements were carried out in a thermobalance for different fixed temperatures between 498 and 648 K. A two-stage semi-global kinetic model consisting of four sequential steps was proposed to derive kinetic parameters. The olive wood is classified in three pseudo-components. For the first two, similar thermal degradation mechanisms take place in a single reaction step. For the third, the thermal degradation takes place in two consecutive steps. The isothermal conditions allow the kinetic constants (activation energy and pre-exponential factors) to be estimated by means of the analytical solution of the mass conservation equations. An overall good agreement was obtained with activation energy values available in the literature.     

On some errors committed in the studies of kinetics of thermal dissociation of solids

The methods of preparing the samples for kinetic studies are critically discussed with particular consideration to the effect of granulometric characteristics and structure of the material, conditions of performing the measurements, and choice of proper kinetic equation on the reliability of the results obtained.     

Isoconversional method to explore the mechanism and kinetics of multi-step epoxy cures

Epoxy-anhydride cure has been studied by differential scanning calorimetry under nonisothermal conditions. The isoconversional method of kinetic analysis yields a dependence of the effective activation energy on the extent of conversion (α) that increases from ≈ 20 to 70 kJ·mol^–1 with increasing α. The occurrence of the dependence suggests a mechanism of competing reactions that are found to be the processes of initiation and propagation of the polymer chain.     

The influence of sample cells for differential thermal analysis in controlled atmospheres

DTA curves for the thermal decomposition of uranyl oxalate trihydrate and ammonium vanadyl oxalate dihydrate, using different DTA instruments, are compared. It is shown that widely differing and misleading results can be obtained by an incorrect choice of sample cell. The anomalous effects are discussed in terms of the geometry of the sample holders and the consequent ease of removal of product gases and accessibility of the reactant gas.It is recommended that uranyl oxalate trihydrate could be used to assess the conditions of flow-rate, sample size, etc., necessary to achieve correct atmosphere control with a given DTA cell.     

The heat stabilities of trivalent metal 8-quinolinol chelates in inert atmospheres

The thermal stabilities of Al, Ga, In, Cr and Fe oxinates have been studied by thermogravimetry, differential thermal analysis, thermomanometric analysis and by a sealed tube extraction technique. The order of decreasing heat stability for the anhydrous chelates is Al>Cr~Ga>In>Fe. The compounds decompose with the evolution of hydrogen and the formation of large amounts of carbonaceous residue. The Al, Cr, Ga, and In oxinates can be melted without major decomposition when heated rapidly.     

Simultaneous use of isothermal,nonisothermal, and constant rate thermal analysis (CRTA) for discerning the kinetics of the thermal dissociation of smithsonite

The mechanism of the thermal decomposition of smithsonite has been determined from a comparison of the results obtained from isothermal, linear heating rate (TG), and Constant Rate Thermal Analysis (CRTA) experiments. Two important precautions have been taken in this work. Firstly, the chemical composition of the sample has been checked in order to be sure that pure anhydrous zinc carbonate has been used. Secondly, the experimental conditions have been selected in such a way to avoid the influence of heat and mass transfer phenomena on the forward reaction. It has been shown that the mechanism for the thermal decomposition of smithsonite depends upon temperature. Thus, at temperatures lower than 650 K, approximately, an A_0.5 kinetic model describes the reaction, whereas, at temperatures roughly higher than 690 K the above reaction obeys a F₁ kinetic law. An interpretation of this behavior is given. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 647–655, 1998