Thermal characterization of dental composites by TG/DTG and DSC

Dental composites can be improved by heat treatment, as a possible way to increase mechanical properties due to additional cure (post-cure). Direct dental composites are essentially similar to the indirect ones, supposing they have the same indication. Therefore, to establish a heat treatment protocol for direct composites, using as indirect (photoactivated by continuous and pulse-delay techniques), a characterization (TG/DTG and DSC) is necessary to determine parameters, such as mass loss by thermal decomposition, heat of reaction and glass transition temperature (T _g). By the results of this study, a heat treatment could be carried out above 160 °C (above T _g, and even higher than the endset exothermic event) and under 180 °C (temperature of significant initial mass loss).     

Thermal decomposition kinetics of some transition metal coordination polymers of fumaroyl bis (paramethoxyphenylcarbamide) using DTG/DTA techniques

In the present work, thermal degradation behaviors of the Zn (II), Cd(II), and Hg(II) coordination polymers of fumaroyl bis (paramethoxyphenylcarbamide) (fbpmpc) have been investigated by using thermogravimetric (TG) analysis, differential thermal analysis (DTA) and derivative thermogravimetry (DTG) analysis under non-isothermal conditions in nitrogen atmosphere at multiple heating rates. TG–DTA study noteworthy inferred the presence of lattice water in outer sphere of all the polymers. The decomposition was carried out in three-four well-separated stages where involved the loss of water molecules in the first step followed by organic ligand. Furthermore, the kinetics and thermodynamic stabilities of multi-steps thermal degradation were evaluated. The activation energy (E_a), order of reaction (n), Arrhenius factor (A), enthalpy change (ΔH), entropy change (ΔS) and free energy change (ΔG) of coordination polymers were obtained by using the Coats–Redfern (CR) method. Ultimately, based on initial, half and final decomposition temperature, and kinetics parameters values the orders of thermal stability were estimated.     

Thermal Decomposition of Hydrated Lanthanide Picrates by TG/DTG and DSC Analyses

Hydrated lanthanide picrates with a composition of: Ln(pic)₃⋅xH₂O (Ln=La–Lu, Y) were synthesized and characterized. Thermal decomposition of the picrates by TG/DTG and DSC techniques are reported. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal behavior of cashew gum by simultaneous TG/DTG/DSC-FT-IR and EDXRF

Cashew gum, an exudate polysaccharide from Anacardium occidentale L., was purified by alcohol precipitation. Thermal behavior of this polysaccharide was investigated by simultaneous TG/DTG/DSC-FT-IR analysis performed under nitrogen and air atmospheres and heating rate of 10 K min^?1. TG/DTG curves under oxidative atmosphere were similar to the curves under N₂ atmosphere until 340 °C, however, it was observed a profile difference due to the presence of two DTG peaks at 430 and 460 °C. DSC results showed endothermic and exothermic events corroborating with TG/DTG curves. The Simultaneous TG/DSC-FTIR analysis revealed that evolved gases from the decomposition of cashew gum sample were CO₂, CO, and groups: O–H, C–H, C=O, C–C, and C–O, in nitrogen and air atmospheres. Energy dispersive X-ray fluorescence analysis from the ash showed that the elements in larger amounts are CaO, MgO, and K₂O.     

Thermal characterization of asphalt mixtures by TG/DTG, DTA and FTIR

The quality of a road relies on the good use of the on road surface and its maintenance along the years. The technology used and the corrections contributes to the prevention of early road destructions. Pavement with polmyer and others additives exhibits greater resistance to rutting, thermal cracking, and decreased fatigue damage, stripping and temperature susceptibility. Samples of CAP 40, SBS 440/02, L 1861/04, L 784/05 and L 2000/04 were analyzed by thermogravimetry (TG), derivative thermogravimetry (DTG), differential thermal analysis (DTA) and FTIR. Thermal characterizations showed that the main decomposition stage refers to asphaltenes and samples with additives exhibited a slight increase in thermal stability. The kinetic study, by Kissinger, showed that the sample with the highest stability was the SBS 440/02. Fourier transform infrared spectroscopy (FTIR) analysis suggested that these asphalt samples were originated from light oil.     

TG/DTG/DTA for the oxidation behavior characterization of vegetable and animal fats

TG/DTG/DTA curves can be used to estimate alimentary fats quality and antioxidants insertion efficiency. Sunflower oil obtained from Carnia hybrid and pork lard were used as matrices for the non-isothermal measurements. The first stage of non-isothermal decomposition is mostly important for the characterization of the fats thermal stability. The corresponding onset temperature is a good value for the comparison of different fats thermal stability or for the effectiveness evaluation in case of antioxidant insertion. In this study, it can be seen a considerable improvement of the fats thermal stability by adding small amounts from a natural antioxidant liquid mixture (obtained by alcoholic maceration of equal amounts of seven plants, namely: milfoil, rosemary, marjoram, thyme, lovage, oregano, and basil). Chlorophylls removal from the plant extract using two different adsorbents was accompanied by a four time decrease of the antiradical activity (measured by the DPPH method) with Sephadex LH20 and seventeen times decrease when activated carbon was used.     

Soot oxidation kinetics from TG experiments

Thermogravimetric analysis (TG) has been used extensively for soot oxidation studies. Its known experimental and computational difficulties, however, have led to extended criticism concerning the reliability of the extracted kinetics and their potential for reliable reaction modelling. This study explores if TG kinetics could lead to successful simulation results notwithstanding the related disputes. For this, TG and mini-scale soot oxidation experiments with oxygen (O₂) were conducted. The TG kinetics reliability was controlled through comparison with the corresponding mini-scale results and by the satisfactory simulation of the mini-scale experiments.     

Characterization by TG/DTG/DSC and FTIR of frying and fish oil residues to obtain biodiesel

Biodiesel is a fuel derived from vegetable oils or wastes. It has a lot of advantages such as less offensive exhaust, more complete combustion, reducing emissions of carbon dioxide and sulfur in addition to generating employment and wealth. This biofuel can be produced through the transesterification reaction of an alcohol with a triglyceride, with the aid of a catalyst, resulting on a biodiesel as main product, glycerol, and other byproducts. The objective of this study is to determine the optimal reaction conditions for transesterification of waste frying oil and fish, varying the reaction time, the amount of catalyst and temperature, to determine which of these variables exert a greater influence on the reaction yield, and characterize biofuels obtained. For a more accurate assessment of the influence of a given variable on the reaction yield, it was performed a statistical experimental design, the full factorial of two levels with three parameters (2³) and three central points, implemented in Statistica 7.0. Regarding the transesterification of waste of the fish oil, the amount of catalyst was the variable that most influenced the reaction yield, the parameters time and temperature had negligible impact on income. Biofuels were also characterized using thermal analysis techniques and FTIR. Most reactions obtained thermogravimetric yield above 90%, a promising result.     

程序升温热重法研究扎赉诺尔煤的气化动力学

用程序升温热重法对扎赉诺尔煤（ＺＬ）的８００℃半焦进行ＣＯ２气化研究，考察了升温速率对ＴＧ／ＤＴＧ谱图的影响，分析讨论了ＤＴＧ参数（Ｔｍ和Ｒｍ）的变化；用单一升温速率法和多个升温速率组合法分别作了动力学计算，并对结果进行了分析讨论。结果表明：Ｔｍ和Ｒｍ均随升温速率的增高而增大，两种计算方法得到的动力学参数是不同的，单一升温速率法计算出的表观活化能Ｅ和指前因子Ａ遵循关系式：ｌｏｇＡ＝０．１０Ｅ－８．     

Evaluation of combustion characteristics of different size elbistan lignite by using TG/DTG and DTA

In this research, the relationship between particle size and combustion kinetics and combustion properties of lignite samples was examined by utilizing the thermogravimetric (TG/DTG) and differential thermal analysis (DTA) techniques. The lignite samples separated into different size fractions were subjected to non-isothermal thermogravimetric analysis between ambient and 900°C in the presence of 50 mL min⁻¹ air flow rate. Activation energy (E) and Arrhenius constant (A _r) of combustion reaction of each size was evaluated by applying Arrhenius kinetic model to the resulting data. Combustion properties of the samples were interpreted by careful examination of the curves. The apparent activation energies in major combustion region were calculated as 41.03 and 53.11 kJ mol⁻¹ for the largest size (−2360+2000 μm) and the finest size (−38 μm), respectively.     

Critical study on the identification of reaction mechanism by the shape of TG/DTG curves

It was proposed that the reaction mechanism of solid state reactions can be identified based on the asymmetry or shape of TG (Thermogravimetry) and DTG (Differential Thermogravimetry) curves in non-isothermal kinetics in the literature. A flow chart was also designed for the identification of the reaction mechanism by some authors. This paper has revisited this method and revised the flow chart with more reliable values of conversion at the maximum rate and the half width range of the DTG curves. The revised chart is proven to be more reasonable by an example application to identify the reaction mechanism of calcium carbonate decomposition and is recommended to replace the original one.     

Thermal degradation behaviour of some metal chelate polymer compounds with bis(bidentate) ligand by TG/DTG/DTA

Seven novel divalent transitional metal chelate polymers compounds (commonly known as chelate compounds or metal coordination complexes or polymer complexes) have been characterized by thermogravimetry (TG), differential thermal gravimetry (DTG) and differential thermal analysis (DTA) methods. Thermal decomposition behaviour of Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II) polymers with terphthaoyl-bis(p-methoxyphenylcarbamide) has been investigated by thermogravimetric analysis (TGA) at heating rate 10 °C min^?1 under nitrogen atmosphere. TG/DTA of chelate compounds were shown to be a stable compound against thermal decomposition which was measured on the basis of final decomposing temperature, but it is observed in some curves that decomposition takes place at low temperature due to the lattice water, which is always placed at outer coordination sphere of the central metal ion. The presence of both lattice and coordinated water were noteworthy investigated in Co(II), Ni(II) and Cu(II) chelate polymer compounds, whereas lattice water found in Zn(II), Cd(II) and Hg(II). However, Mn(II) showed only coordinated water. Thermal stabilities for release of lattice water, coordinated water and organic moiety that occur in sequential decomposition of chelate compounds are explained on the basis of ionic size effect and electronegativity. The processes of thermal degradation taking place in seven chelate polymers were studied comparatively by TG/DTG/DTA curves which indicating the difference in the thermal decomposition. Coats–Redfern integral method is used to determine the kinetic parameters for the successive steps in the decomposition sequence of TG curves. Scanning electron microscope images of some chelate polymers were shown in previous publication revealed that particle sizes of chelate polymers were found to be of nanomaterial level therefore, resulting chelate compounds might be called as nanomaterial.     

Kinetics of the oxidation of magnetite using simultaneous TG/DSC

Kinetics of the oxidation of magnetite (Fe₃O₄) to hematite (a-Fe₂O₃) are studied in air using simultaneous TG/DSC. The mechanism is complex and the differences between the kinetic conclusions and Arrhenius parameters based on either TG or DSC are discussed. As in our previous work on CaCO₃ [1], the determination of a satisfactory baseline for the DSC results adds considerable uncertainty to those kinetic results. Consequently the calculations based on the TG data are considered superior. Solid state reactivity varies from one source of material to another and the results are compared for two different commercial samples of magnetite, both presumably prepared by wet chemical methods. These materials are much more reactive than the material studied previously [2], which had been coarsened and refined at high temperatures. In that earlier study, the metastable spinel, g-Fe₂O₃, was formed as an intermediate in the oxidation to the final stable form, a-Fe₂O₃. The exothermic reaction of the gamma to alpha form of the product during the oxidation process destroys the direct comparison between the TG and DSC results, since the former only detects the change in mass of the sample and not the crystallographic transformation. The TG results, however, represent the true oxidation process without superposition of the structural aspects. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal decomposition of tetraamineplatinum(II) chloride by simultaneous TG/DTG/DTA/MS and direct insertion probe mass spectrometry

Simultaneous thermogravimetry (TG), derivative thermogravimetry (DTG), differential thermal analysis (DTA), and evolved gas analysis (EGA) by mass spectrometry (MS) have been used to determine the decomposition path for tetraamineplatinum(II) chloride and cis- and trans-diamineplatinum(II) chloride. Unequivocal identification of the evolved gases was done by direct insertion probe mass spectrometry.The thermal decomposition of (NH₃)₄PtCl₂ occurred in two steps. The first was endothermic loss of two moles of ammonia producing a mixture of cis- and trans-diaamineplatinum(II) chloride. The second step was decomposition of the diamine complex to metallic Pt and N₂, HCl, and NH₄Cl. Reduction of Pt(II) to metallic Pt was coupled with oxidation of ammonia to molecular nitrogen and protons.

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Zusammenfassung Simultane Thermogravimetrie (TG), derivative Thermogravimetrie (DTG), Differentialthermoanalyse (DTA) und Analyse der entwickelten Gase (EGA) durch Massenspektrometrie (MS) wurden zur Bestimmung des Reaktionsverlaufs bei Zersetzung von Tetraminplatin(II)-chlorid sowie cis- und trans-Diaminplatin(II)-chlorid herangezogen. Die eindeutige Identifizierung der entwickelten Gase erfolgte durch Massenspektrometrie mit direkter Probeneinführung. Die thermische Zersetzung von (NH₃)₄PtCl₂ erfolgt in zwei Schritten. Der erste ist die endotherme Abspaltung von zwei Mol Ammoniak unter Bildung eines Gemisches von cis- und trans-Diamin-platin(II)-chlorid. Der zweite Schritt ist die Zersetzung des Diaminkomplexes zu metallischem Pt, H₂, HCl und NH₄Cl. Die Reduktion von Pt(II) zu metallischem Pt ist mit der Oxydation von Ammoniak zu molekularem Stickstoff und Protonen gekoppelt.

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-, -, -, - - (II) - (II) . (II). -. (NH₃)₄PtCl₂ . - -(NHN₃)₂PtCl₂. , , . .

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The technical assistance of G. J. Dechert is gratefully acknowledged.     

Study on thermal decomposition and oxidation kinetics of cation exchange resins using non-isothermal TG analysis

Kinetics of two successive thermal decomposition reaction steps of cationic ion exchange resins and oxidation of the first thermal decomposition residue were investigated using a non-isothermal thermogravimetric analysis. Reaction mechanisms and kinetic parameters for three different reaction steps, which were identified from a FTIR gas analysis, were established from an analysis of TG analysis data using an isoconversional method and a master-plot method. Primary thermal dissociation of SO₃H⁺ from divinylbenzene copolymer was well described by an Avrami–Erofeev type reaction (n = 2, g(α) = [?ln(1 ? α)]^1/2]), and its activation energy was determined to be 46.8 ± 2.8 kJ mol^?1. Thermal decomposition of remaining polymeric materials at temperatures above 400 °C was described by one-dimensional diffusion (g(α) = α ²), and its activation energy was determined to be 49.1 ± 3.1 kJ mol^?1. The oxidation of remaining polymeric materials after thermal dissociation of SO₃H⁺ was described by a phase boundary reaction (contracting volume, g(α) = 1?(1 ? α)^1/3). The activation energy and the order of oxygen power dependency were determined to be 101.3 ± 13.4 and 1.05 ± 0.17 kJ mol^?1, respectively.     

A TG/DTA/MS study of the oxidation of nickel sulphide

The oxidative behaviour of synthetic millerite (Ni_0.994S) has been studied by TG and DTA in a dynamic oxygen atmosphere (0.2 l min^–1) over the temperature range 20–1000° (heating rate 10° min^–1). EGA was carried out by a coupled mass spectrometer. The reaction products at various intermediate temperatures were characterized by X-ray powder diffractometry. A reaction sequence has been deduced, in which in the temperature range 550–700° complete oxidation of Ni_0.994S had occurred with the formation of NiSO₄, Ni₃S₂, NiO and possibly-Ni₇S₆. Between 700–800°, NiSO₄ continued to be formed, whilst Ni₃S₂ and-Ni₇S₆ were oxidised. Above 800°, NiSO₄ decomposed to NiO, the latter being the only species evident above 800°.

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Zusammenfassung Das oxidative Verhalten von synthetischem Millerit (Ni_0.994S) wurde mittels TG und DTA in einer dynamischen Sauerstoffatmosphäre (0.2 l min^–1) im Temperaturbereich von 20 bis 1000° (Aufheizgeschwindigkeit 10° min^–1) untersucht. EGA wurde mit einem gekoppelten Massenspektrometer durchgeführt. Die Reaktionsprodukte bei verschiedenen Zwischentemperaturen wurden mittels Röntgen-Pulver-Diffraktometrie charakterisiert. Eine Reaktionssequenz wurde abgeleitet, nach welcher im Temperaturbereich von 550 bis 700° die vollständige Oxidierung von Ni_0.994S unter Bildung von NiSO₄, Ni₃S₂, NiO und wahrscheinlich-Ni₇S₆ vor sich geht. Zwischen 700 und 800° wird NiSO₄ auch weiterhin gebildet, während Ni₇S₂ und-Ni₇S₆ oxidiert wurden. Oberhalb von 800° wurde NiSO₄ zu NiO zersetzt, das einzig nachweisbare Produkt oberhalb von 800°.

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Résumé On a étudié l'oxydation de la millérite synthétique (Ni_0.994S) par TG et ATD en atmosphère dynamique d'oxygène (0,2 1· min^–1) et dans l'intervalle de températures allant de 20 à 1000° (vitesse de chauffage 10°· min^–1). L'analyse des gaz émis s'est effectuée avec un spectromètre de masse couplé. Les produits de réaction ont été caractérisés à diverses températures intermédiaires par diffractométrie de poudre aux rayons X. On a déduit une séquence de réactions, selon laquelle, dans l'intervalle compris entre 550 et 700°, l'oxydation complète de Ni_0.994S a lieu avec formation de NiSO₄, Ni₃S₂, NiO et probablement-Ni₇S₆. Entre 700 et 800°, la formation de NiSO₄ se poursuit tandis que Ni₃S₂ et-Ni₇S₆ sont oxydés. Au-dessus de 800°, NiSO₄ se décompose en NiO qui constitue l'unique composé qui puisse être décelé au-dessus de 800°.

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(Ni_0.994S) (0,2 . ^–1) 20–1000° 10° ^–1. - . . 550–700° Ni_0.994S NiSO₄, Ni₃S₂, NiO -Ni₇S₆. 700–800° , Ni₃S₂ -Ni₇S₆ . 800° NiO, 800°.

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We wish to thank Dr. T. Kennedy for useful discussions and Messrs. B. Sturman, I. Twaddle, K. Oliver and W. Thomas for technical assistance.     

Thermal properties and kinetics study of charged LiCoO2 by TG and C80 methods

The thermal stability of lithium-ion battery cathode could substantially affect the safety of lithium-ion battery. In order to disclose the decomposition kinetics of charged LiCoO₂ used in lithium ion batteries, thermogravimetric analyzer (TG) and C80 microcalorimeter were employed in this study. Four stages of mass losses were detected by TG and one main exothermic process was detected by C80 microcalorimeter for the charged LiCoO₂. The chemical reaction kinetics is supposed to fit by an Arrhenius law, and then the activation energy is calculated as E _a=148.87 and 88.87 kJ mol⁻¹ based on TG and C80 data, respectively.     

Characterization of Polyurethanes from Vegetable Oils by TG/DTG,DMA and FT-IR

Summary: Given the demand for renewable resources by industries and the promising potential of vegetable oils for this purpose, the current study aims to evaluate the properties of polyurethanes (PUs) obtained from linseed (Linum usitatissimun L.) oil (PULO) and passion fruit (Passiflora edulis Sims f. flavicarpa Degener) oil (PUPFO), by thermogravimetry (TG), derivative thermogravimetry (DTG), dynamic mechanical analysis (DMA) and Fourier transform infrared (FT-IR). The results showed that PULO is more thermally stable than PUPFO, suggesting that the first presents more urethane linkages. The DMA analysis showed that both prepared PUs have uneven porosity, causing the loss of the elastic plateau. It was found as well that PUPFO exhibits a higher value of glass transition temperature (T_g), signifying that it seems to be more crosslinked than PULO. The analysis by FT-IR showed that the curing reaction of PUs was successful.     

A TG/MS and DTA study of the oxidation of pentlandite

The oxidative behaviour of natural pentlandite (FeNi)₉S₈ has been studied by thermogravimetry (TG) and differential thermal analysis (DTA) in a dynamic oxygen atmosphere (0.21 min^–1) over the temperature range 20–1000°. Gaseous products were analysed by a coupled quadrupole mass spectrometer. The reaction products at various intermediate temperatures were characterised by X-ray diffractometry and chemical analysis. A reaction sequence has been deduced, in which in the temperature range 460–700° pentlandite breaks down with the formation of Fe₂O₃, NiSO₄, NiO, NiS and NiFe₂O₄; FeSO₄ was also formed but decomposed above 640°. Beyond 700° NiS was completely oxidised, and NiSO₄ decomposed slowly. Another sulphide phase, possibly Ni_3±xS₂, was formed at 740° and completely oxidised at 790°, and above 800° NiSO₄ decomposed completely leaving only Fe₂O₃, NiO and NiFe₂O₄ as stable products.

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Zusammenfassung Das oxidative Verhalten von natürlichem Pentlandit (FeNi)₉S₈ wurde durch Thermogravimetrie (TG) und Differentialthermoanalyse (DTA) in einer dynamischen Sauerstoffatmosphäre (0.21 min^–1) im Temperaturbereich 20–1000° untersucht. Die gasförmigen Produkte wurden durch ein gekoppeltes vierpoliges Massenspektrometer analysiert. Die Reaktionsprodukte bei verschiedenen Zwischentemperaturen wurden durch Röntgen-diffraktometrie und chemische Analyse charakterisiert. Es wurde eine Reaktionssequenz abgeleitet, bei welcher Pentlandit im Temperaturbereich von 450 bis 700° unter Bildung von Fe₂O₃, NiSO₄, NiO, NiS und NiFe₂O₄ zersetzt wird; FeSO₄ wurde auch gebildet, wurde aber bei Temperaturen über 640° zersetzt. Über 700° wurde NiS vollständig oxidiert und NiSO₄ langsam zersetzt. Eine weitere Sulfidphase, möglicherweise Ni_3±xS₂ wurde bei 740° gebildet und bei 790° vollständig oxidiert. Über 800° wurde NiSO₄ vollständig zersetzt, wobei nur Fe₂O₃, NiO und NiFe₂O₄ als stabile Produkte zurückblieben.

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Résumé On a étudié, par thermogravimétrie (TG) et par analyse thermique différentielle (ATD), en atmosphère dynamique d'oxygène (0.21 min^–1) et dans l'intervalle de températures allant de 20 à 1000°, le comportement de la pentlandite (FeNi)₉S₈ vis-à-vis de l'oxydation. On a analysé les produits gazeux formés avec un spectromètre de masse quadrupole couplé. On a caractérisé les produits de réaction à diverses températures intermédiaires par diffractométrie des rayons X et par analyse chimique. On en a déduit une séquence de réaction, dans laquelle la pentlandite se décompose dans l'intervalle 450–700° avec formation de Fe₂O₃, NiSO₄, NiO, NiS et NiFe₂O₄; FeSO₄ se forme également, mais se décompose au-dessus de 640°. Au-dessus de 700° NiS est complètement oxydé, et NiSO₄ se décompose lentement. Une autre phase sulfurée, probablement Ni_3±xS₂ se forme à 740° et est oxydée complètement à 790°. Au-dessus de 800°, NiSO₄ se décompose completèment ne laissant que Fe₂O₃, NiO et NiFe₂O₄ comme produits stables.

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(FeNi)₉S₈ (0.2 1 ^–1) 20–1000°. -. . . 450–700° Fe₂O₃, NiSO₄ NiO, NiS NiFe₂O₄. FeSO₄, 640°. NiS 700° , NiSO₄ — . , Ni_3±xS₂, 740° 790°. 800° NiSO₄ Fe₂O₃, NiO NiFe₂O₄.

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We wish to thank Dr. W. Barker (CSIRO) for the sample of pentlandite and valuable information, Dr. B. O'Conner (Physics) for XRD work, and Messrs. K. Oliver, B. Sturman and I. Twaddle (Chemistry) for technical assistance.     

Computer kinetic analysis of simultaneously obtained TG and DTG curves

The computer kinetic analysis of simultaneously obtained TG and DTG curves of CaCO₃ decomposition has been carried out. Ten different kinetic equations have been tested to decide the mechanism which drives the reaction. Either a two-thirds kinetic equation (phase boundary process) or a Jander equation (diffusion process) satisfactorily describe the kinetic data of both decomposition curves. From these results we conclude there is no chance of differentiating between these two mechanisms by only the kinetic analysis of TG and DTG curves separately.A better approach to the problem is possible if the kinetic analysis is performed on simultaneous TG and DTG curves, together with an isothermal one. This procedure might be a valid way to establish the mechanisms of thermal decomposition reactions by means of kinetic methods without additional information.

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Zusammenfassung Es wurde die kinetische Analyse simultan erhaltener TG- und DTG-Kurven der Zersetzung von CaCO₃ mittels Computer durchgeführt. Zehn verschiedene kinetische Gleichungen wurden zur Ermittlung des reaktionssteuernden Mechanismus erprobt. Die kinetischen Daten beider Zersetzungskurven können entweder durch eine Zwei-Drittel kinetische Gleichung (Phasen-Grenzflächenprozess) oder eine Jander-Gleichung (Diffusionsprozess) befriedigend beschrieben werden. Aus diesen Ergebnissen wird gefolgert, dass keine Möglichkeit besteht diese beiden Mechanismen ausschliesslich durch die kinetische Analyse der TG- und DTG-Kurven von einander zu unterscheiden. Eine bessere Annäherung an das Problem ist durch die kinetische Analyse simultaner TG- und DTG-Kurven gemeinsam mit einer isothermen Kurve möglich. Dieser Vorgang erscheint als ein möglicher Weg zur Unterscheidung der Mechanismen thermischer Zetsetzungsreaktionen an Hand kinetischer Methoden ohne Zusatzliche Information.

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Résumé L'analyse cinétique des courbes TG et TGD obtenues simultanément lors de la décomposition de CaCO₃ a été effectuée à l'aide d'un ordinateur. Dix équations cinétiques différentes ont été examinées pour établir le mécanisme moteur de la réaction. L'équation cinétique de type 2/3 (processus d'interface) ou l'équation de Jander (processus de diffusion) décrivent toutes deux de maniÊre satisfaisante les données cinétiques déduites des courbes TG et TGD. De ces résultats on conclut qu'il n'est pas possible de distinguer ces deux mécanismes en s'appuyant exclusivement sur l'analyse cinétique des courbes TG et TGD.Une meilleure approche du problÊme est possible si l'on effectue l'analyse cinétique des courbes TG et TGD simultanées en mÊme temps que celle d'une courbe isotherme. Ce procédé peut Être un bon moyen pour élucider le mécanisme des réactions de décomposition thermique à l'aide de méthodes cinétiques, sans informations supplémentaires.

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The authors' thanks are due to Dr. Delia Balbontin for her assistence with the computer, and Dr. I. Carrizosa for his helpful discussions.