Kinetic parameters obtained from TG and DTG curves of acrylamide-maleic anhydride copolymers

The thermal behaviour of acrylamide-maleic anhydride copolymers was studied by thermogravimetric (TG and DTG) analysis. The obtained data permitted the calculation of activation energies and reaction orders of the decomposition steps by the Coats-Redfern and Freeman-Carroll methods.Thermal analysis shows four distinct peaks in the case of polyacrylamide and AAMA (71) copolymer and only three for AAMA (11) copolymer.In AA:MA (11) copolymers intermolecular imidization occurs only and thermal degradation is influenced more by the anhydride groups which are equal in number with the amide ones.

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Zusammenfassung Das thermische Verhalten von Acrylamid-Maleinsäureanhydrid-Kopolymeren wurde durch thermogravimetrische Analyse (TG und DTG) untersucht. Aus den erhaltenen Daten wurden die Aktivierungsenergien und Reaktionsordnungen der Zersetzungsschritte nach den Methoden von Coats-Redfern und Freeman-Carroll berechnet. Durch thermische Analyse können im Falle von Polyacrylamid und AAMA (71 (-Kopolymeren 4 Peaks und bei AA:MA (11) -Kopolymeren nur 3 Peaks unterschieden werden. Bei AAMA (1 1)-Kopolymeren verläuft nur eine intermolekulare Imidisierung und der thermische Abbau wird mehr durch die in gleicher Zahl wie die Amidgruppen vorliegenden Anhydridgruppen beeinflußt.

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T () — (). , - -, . : ( 71) , : 11 — . : 11 , , .

     

Quantitative interpretation of TG and DTG curves obtained for some ferromagnetic substances in low intensity A.C. generated magnetic field

Earlier studies on the possibility of magnetochemical analysis, employing a simultaneous TG-DTG-DTA method, have been extended. Several magnetic samples of different chemical compositions, e.g. spinels, garnets and hexagonal ferrites, were examined. Investigations involved both soft (NiFe₂O₄, MnMg ferrite, Y₃Fe₅O₁₂) and hard magnetic materials such as BaFe₁₂O₁₉, SrFe₁₂O₁₉. The capability of the method, referred to in the following as DTMG, for the qualitative and the quantitative analysis of a wide variety of magnetic materials is proposed. The results are discussed in terms of the basic magnetic parameters such as a magnetocrystalline anisotropy, magnetic moment and ferromagnetic Curie point temperature, T_c. The relationship between DTMG line intensities and concentrations of the respective magnetic substances was found. The results are interpreted on the basis of the Curie point measurements by means of DTMG curves in the temperature range between 20 and 1200°C. It is a proposal to call the TG and DTG curves taken simultaneously in the presence of an alternating magnetic field as the TMG and DTMG curves, respectively. The term DTMG stands for Derivative Thermo-Magneto-Gravimetry. The idea of the method has been developed in this laboratory.The DTMG method is capable of good precision within resonable time. The method can be applied to polycrystalline as well as to single crystals of the magnetic materials and the sample can be in the solid or powder state.     

The effect of procedural variables on TG,DTG and DTA curves of calcium carbonate

The effect of procedural variables, including sample mass, heating rate, particle size and partial pressure of carbon dioxide, on TG, DTG and DTA curves for the decomposition of A. R. calcium carbonate and limestone has been studied. Such variables have a marked effect, similar in magnitude for both DTG and DTA. The effect of sample mass, or depth of undiluted sample, is shown to be due to an increase in the partial pressure of carbon dioxide within the reacting powder and has been called the bed-depth effect. This effect is most pronounced in nitrogen but is much reduced in carbon dioxide. Inert diluents have little effect on the TG curves but changing the composition of the inert carrier gas causes variations which are correlated with the thermal conductivity of the gas. Water vapour causes a lowering of the DTG and DTA peak temperatures.

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Zusammenfassung Bei der Zersetzung von A.R. Calciumcarbonat bzw. Kalkstein wurde der Einflu\ der Versuchsparameter, einschlie\lich Probenmasse, Aufheizgeschwindigkeit, Partikelgrö\e und Partialdruck von CO₂ auf den Verlauf der TG-, DTG- und DTA-Kurven untersucht. Diese Parameter haben einen deutlichen Einflu\ auf DTG und DTA, der sich in beiden FÄllen im gleichen Ausma\ bemerkbar macht. Der Einflu\ der Masse bzw. Tiefe einer unverdünnten Probe Äu\ert sich in einem Ansteigen des Partialdruckes von Kohlendioxid innerhalb des reagierenden Pulvers und wird als Bett-Tiefen-Effekt bezeichnet. Dieser Effekt kommt in Stickstoff besonders zur Geltung und tritt in Kohlendioxid in den Hintergrund. Inerte Verdünnungsmittel haben einen nur geringen Effekt auf die TG-Kurve aber eine Änderung der Zusammensetzung des inerten TrÄgergases verursacht VerÄnderungen, die auf der WÄrmeleitfÄhigkeit des Gases begründet sind. Wasserdampf verursacht, da\ DTG- und DTA-Signale bei niedrigeren Temperaturen auftreten.

     

The effect of procedural variables on TG,DTG and DTA curves of magnesite and dolomite

TG, DTG and DTA curves of magnesite are dependent on procedural variables, especially sample mass, heating rate and partial pressure of carbon dioxide, in a similar manner to those of calcite [1], although the magnitude of the effect is less for magnesite. The first stage of the decomposition of dolomite varies with increasing partial pressure of carbon dioxide in an anomalous manner and hence the effects of these procedural variables (except heating rate) are not similar to those observed for magnesite and calcite. The second stage of the decomposition of dolomite is, however, strongly dependent on these procedural variables and behaves in a manner that would be predicted for a sample of calcite diluted with magnesia. A 11 molar mixture of magnesite and calcite also behaves as would be predicted from the behaviour of the single carbonates but differently from that of dolomite.

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Zusammenfassung TG-, DTG- und DTA-Kurven von Magnesit sind Ähnlich wie bei Kalzit [1] abhÄngig von den Versuchsparametern, besonders von Probenmasse, Aufheizgeschwindigkeit und Partialdruck von Kohlendioxid, obwohl das Ausma\ dieses Einflusses bei Magnesit geringer ist. Der erste Schritt der Zersetzung von Dolomit Ändert sich in einer ungewöhnlichen Weise durch Erhöhung des Partialdruckes von Kohlendioxid und deshalb unterscheidet sich der Einflu\ dieser Versuchsparameter (mit Ausnahme der Probenmasse) von dem, der bei Magnesit und Kalzit beobachtet wurde. Der zweite Schritt bei der Zersetzung von Dolomit ist stark von diesen Versuchsparametern abhÄngig und verlÄuft so, wie man es für eine mit Magnesia verdünnte Kalzitprobe voraussagen würde. Eine Gemisch aus Magnesit und Kalzit im VerhÄltnis 11 verhÄlt sich ebenso, wie man es auf Grund des Verhaltens der einfachen Karbonate voraussagen würde, unterscheidet sich jedoch von dem des Dolomits.

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We wish to thank Pilkington Brothers plc for granting leave of absence to RMM.     

Computer-determined kinetic parameters from TG curves. Part IX

By applying the restriction that α (conversion) = constant to non-isothermal TG (NITG), isothermal TG (ITG) and a combination of both (NITG/ITG), various corresponding expressions have been derived for the evaluation of the activation energy, E. By means of a computer, all the expressions developed were tested against data which was generated from theoretical equations. Also, changes were made in the number of significant figures (s.f.) of data in order to ascertain their effects on values of E. Data were generated and tested for the three theoretical mechanisms, A₂, F₁ and R₂.     

Determination of kinetic parameters from TG curves by non-linear optimization

The results obtained so far by kinetic analysis of non-isothermal experiments indicate that the kinetic parameters found by the conventional methods, in general, do not describe the experimental curve in an optimum manner. This is due to the fact that the initial differential equation is transformed into the logarithmic and, consequently, linear form and that the initial and final weights of the conversion curve cannot be determined exactly, which may falsify the slope of the curve.Investigations have shown that the determination of the kinetic parameters by non-linear optimization (simplex method) results in a better fit of the theoretical conversion curve to the experimental one. But this procedure gives optimum results only when the initial and final weights of the reaction can be determined exactly. If this is impossible, exact parameters can be obtained only by the use of the non-standardized TG curve.Examples are cited to prove that it is possible to evaluate overlapping reactions by the formation of intervals. However, the evaluation of conversion curves merely by the use of mathematical methods can easily result in an erroneous interpretation of the reaction course investigated. Therefore, it is necessary to check the mathematical results as to their physical and chemical meaning.     

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.     

Characterization of monumental carbonate stones by thermal analysis (TG, DTG and DSC)

Thermogravimetry (TG), derivative thermogravimetry (DTG) and differential scanning calorimetry (DSC), were found to be suitable instrumental techniques for the study of monumental rocks because they need small amounts of sample and provide extensive qualitative and quantitative information. From DTG curves, the calcite/dolomite ratio in the samples as well as the differences between limestones and dolomites can be quantitatively determined. DSC curves are adequate for the identification of the degradation products in the monumental stones since they are usually salts (sometimes hydrates) which present first-order processes under 600°C. This technique makes it possible to carry out quantitative and semiquantitative analysis of the degradation of monumental rocks since it provides data about its mineralogic composition.     

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).     

Non-isothermal DSC and TG/DTG analysis of the combustion of Si̇lopi̇ asphaltites

In this research, non-isothermal combustion and kinetics of Silopi (Turkey) asphaltite samples were investigated by differential scanning calorimetry (DSC) and thermogravimetry (TG/DTG). A sample size of 10 mg, heating rates of 5, 10, 15 and 20°C min⁻¹ were used in the temperature range of 20–600°C, under air atmosphere. Two reaction regions were observed in DSC curves. The first region is due to the evaporation of moisture in asphaltite sample whereas, release of volatile matter and burning of carbon is called the second region. A general computer program was developed and the results of four different kinetic models (Arrhenius, Coats-Redfern, Ingraham-Marrier and Horowitz-Metzger) are compared and discussed with regards to their accuracy and the ease of interpretation of the kinetics of thermal decomposition. In general similar activation energy values were obtained when the kinetic models are compared with each other. It was also observed that there was no general trend in the activation energy values from the point of heating rates.     

Errors of kinetic data obtained from thermogravimetric curves at increasing temperature

Errors of kinetic data obtained from thermogravimetric curves at increasing temperature are discussed.     

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 kinetics study of light oil oxidation using TG/DTG techniques

In this study, the oxidation behavior of crude oils in the presence and absence of rock cuttings was investigated by thermogravimetry/derivative thermogravimetry (TG/DTG) techniques. Prior to these tests, the composition of cuttings and properties of crude oils were analyzed. Three obvious reaction regions were observed from the TG/DTG curves which are recognized as low-temperature oxidation (LTO), fuel deposition (FD), and high-temperature oxidation. The effects of light components (C_7–15), heavy fractions (asphaltene, paraffin, resin), and cutting on oil oxidation behavior were analyzed. Kinetic analysis of crude oils and oil + cutting mixtures was performed by Arrhenius method, and the data were analyzed at last. Results show that high content C_7–15 hydrocarbons can provide negative effect on the LTO behavior of crude oil. On the contrary, the high content unsaturated heavy hydrocarbons including asphaltene, paraffin, and resin are benefit for the oxidation performance. In addition, a shortened FD stage and higher peak temperature in LTO region are observed by addition of cutting. Cutting especially clay in it plays an active role of catalyzing in oil oxidation reaction.