DTG Peaks Research Articles

Systematic Effects of Coal Rank and Type on the Kinetics of Coal Pyrolysis

In this work, the global pyrolysis kinetics of a broad range of coals was studied by means of thermogravimetric experiments (heating rate = 25 °C/min). An Arrhenius-based deconvolution model was applied to the experimental DTG curves in order to obtain reliable kinetic parameters for the different DTG peaks. The model assumes that the weight loss rate ascribed to volatile release during primary and secondary pyrolysis is a result of the parallel occurrence of three pseudo-unimolecular nth-order reactions (peaks 1, 2, and 3). The kinetic results were expressed as a function of coal rank (0.43 ≤ R r ≤ 1.14%) and maceral composition in order to obtain reliable kinetic trends. By error minimization, an average apparent reaction order of 1.67 was found. The mass fractions corresponding to peaks 1, 2, and 3 were found to follow definite trends with rank and maceral composition. The temperature of maximum reactivity for peak 1 was almost coincident with that of the maximum overall reactivity and followed clear trends with coal rank and type. The activation energies of peaks 2 and 3 were found to be independent of coal type and clearly related to coal rank. The kinetic parameters (activation energy and preexponential factor) of the three peaks exhibited clear isokinetic effects. It is thought that the deviations of the obtained activation energies from those calculated by the isokinetic effect trends are a consequence of a narrow distribution of activation energies within each peak.

Kinetics of perlite glasses degassing. TG and DSC analysis

Kinetics of dehydration is one of the important characteristics of natural water-bearing glasses. This study deals with the simultaneous TGA/DSC of perlites. The dehydration profiling of natural perlite samples from Eastern Rhodopes (Bulgaria) and a pitchstone from the Eastern Transbaikal region (Russia) has been obtained by the use of a thermal balance. Initial water content in samples varied between 4.0 to 6.5 wt% H 2 O. In pitchstone TG and DTG signals indicate two degassing maxima at temperatures of 220 and 290°C. The peaks in the DTG signal mimic those in DSC signal. Perlitic water is driven out smoothly under heating over a wide range of temperatures from 140 to 700°C up to the glass transition temperature (T g ). The glass transition temperature has been determined independently from viscosity measurement using a micropenetration method. In slowly cooled perlites DTG and DSC signals have one distinct peak which extends from 140 up to 800 to 850°C. In fast cooled perlites DTG and DSC signals often exhibit two distinct peaks at around 200 to 450 and 600 to 700°C. The temperature range of DTG and DSC peaks is wider than in slowly cooled perlites. The enthalpy effect of perlite glass dehydration at 200 to 300°C has the enthalpy value of 55 to 75 kJ/mol, which is much larger than the enthalpy value (30 to 25 kJ/mol) of water evaporation at these temperatures. The additional thermal effect of perlite dehydration may be associated with the water desorption reaction and water vapour expansion in microcracks.

A Kinetic Study of the Dehydration of VOPO4.2H2O by Thermal Methods

The dehydration of VOPO4.2H2O hasbeen studied by thermogravimetric analysis (TGA),differential thermal analysis (DTA) and differentialscanning calorimetry (DSC). From the shift of the DTA,DTG, and DSC peaks, activation energies of thedehydration processes have been calculated based onKissinger's method. The most suitable kinetic modelsfor two-step dehydration have been found.

Kinetic studies of thermal degradation of natural cellulosic materials

The thermal degradation behaviors of various wood species have been studied from 200° to 650°C by TG and DTG in an atmosphere of nitrogen. The data show a complex pattern of overlapping DTG peaks. This is in contrast to α-cellulose thermal degradations. It is demonstrated that computer simulations can describe all the patterns of behavior on the basis of two overlapping mechanisms, differing in their reaction order and Arrhenius parameters. It is emphasized that, although such simulations can be drawn up on a computer, there are an infinite number of solutions to two overlapping peaks.

Critical comments concerning extension of the published kinetic results of some thermal decomposition measurements

The trial and error method was used for a kinetic evaluation of the first DTG peaks of the alanine complexes of four lanthanide isothiocyanates (La, Ce, Pr and Nd) after well-organised preparation, sample control and TG measurements [ 1 ]. According to the authors, from 19 alternative possibilities, the reaction follows Eq. 18, with second-order kinetics. They also conclude that the decomposition processes of the four complexes are identical, as the corresponding parameters of the kinetic compensation effects (CE) are approximately the same. The correlation coefficient of the CE, however, is greater than 0.99 in each case (Table 10 [ 1 ]), so it is arbitrary to choose the second-order mechanism from the 19 examined alternative possibilities as the rate-determining one [2]. Similar arbitrary conclusions are frequently observed in the literature. In strict connection with the dimensionless evaluation, the following equation is suitable for characterisation of the thermal processes [3]:

97/02533 Quantitative evaluation and comparison of the thermal properties of coals by dimensionless analysis

The I; = E;/ RT; dimensionless evaluation is suitable for describing TG measurements according to the E;/ RT; = InA+n[ln(1-a);]-ln(da/dt); equation. It is applicable for the examination of coals without any preconception like the so-called kinetic constants from the usual formal kinetic calculations. The I; function makes the quantitative comparison of different TG measurements possible, even in case of more DTG peaks. The dimensionless analysis opens a new way for further theoretical and practical studies of the thermal properties of coals, because it characterises quantitatively the details of the processes. Strict correlations exist also in the case of coals between the I; functions and the constants of the compensation effect (CE). The constants of the CE (InA = aE ± b, as slope (Tan a) and intercect) can be calculated directly from the measured data of the 1; functions for the general characterisation of the process structure.

Thermal analysis of some fly ashes

The self-hardening activity of fly ashes was investigated looking for the possibility of their chemical reactions with water without additives. A method had to be developed for separation of the structural water from the adsorbed or free one. The decomposition of the chemically bound water was measured by thermogravimetry. The‘I’ dimensionless number proved to be applicable for the quantitative characterisation of the measured data with more DTG peaks. The examined reaction depends on the chemical composition and the physical structure of the fly ashes and the time of interaction with water. The SO3 content seems important, but the characteristics of the formed compounds differ deeply from the CaSO4·2H2O. The observed and examined reaction is an important factor of the self-hardening process of fly ash deposits.

New correlations of the thermogravimetric analysis data of some commercial explosives

Stability of thirteen commercial explosives is specified by means of isothermal and non-isothermal thermogravimetric analysis (TGA). There is a linear dependence between the positions of TGA onsets, or characteristic DTG peaks, and amounts of explosive samples used. Analysis of the dependence for TGA onsets gave results which are correlated with explosion temperatures. A relationship is also found with temperatures of explosive points (i.e. autoignition temperatures) for the explosives studied. In connection with the former correlation, a value of explosion temperature of 3360°C is assessed for Composition B. In the case of isothermally TGA of explosives which contain liquid nitroesters, evaporation of these liquid parts is confirmed as the dominant process in the resulting mass losses.

The thermoanalytical study of some aminoderivatives of 1,3,5-trinitrobenzene

A thermoanalytical study of the aminoderivatives 1-amino-2,4,6-trinitrobenzene (PAM), 1,3-diamino-2,4,6-trinitrobenzene (DATB), 1,3,5-triammo-2,4,6-trinitrobenzene (TATB), 2,2',4,4',6,6'-hexanitrodiphenylamine (DPA), 2,2',4,4',6,6'-hexanitrooxanilide (HNO) and 2,4,6-tris(2,4,6-trinitrophenylamino)-1,3,5-triazine (TPM) has been carried out. In the case of TATB, an endothermic change was found in the temperature region 321–326°C by means of DSC. By comparing the melting points of 1,3,5-trinitrobenzene, PAM and DATB, and of the endothermic change of TATB, with the melting points of the derivatives 1,3,5-triazine derivatives, which are structural analogues, it can be deduced that this temperature region corresponds to the melting point range of TATB. The stability of all the compounds being studied was specified by means non-isothermal thermogravimetry (TGA). Linear dependences were found between the positions of the DTG peaks, or of the TGA onsets, and the weights of the samples. Analysis of the dependences gave results which were correlated with the rate constants of the isothermal thermolysis of the compounds and with their temperatures of explosion. From this analysis the Arrhenius parameters E = 153.3 kJ mol −1 and log A = 11 were determined for the DPA thermolysis in the temperature region 200–300°C.

Correlation between the shape of a TG/DTG curve and the form of the kinetic mechanism which is applying

A method of identifying the reaction mechanism in non-isothermal kinetics is presented based on the symmetry, width and height of the DTG curve. Using a computer program, which allows the calculation of a thermogravimetric curve from selected Arrhenius parameters, heating rate and reaction mechanism, it has been possible to study how these variables alter the shape of the DTG curves. It is shown that the value of α (fraction decomposed) at which the maximum rate is obtained is characteristic for any specific mechanism, and is altered only slightly by the magnitude of the Arrhenius parameters and the heating rate. As such, with complementary information based on the width of the DTG peaks, it is usually possible to identify the mathematical expression which describes the reaction.

A kinetic study of the thermal degradation of poly(dihexyl itaconate)

The kinetics of thermal degradation of poly(dihexyl itaconate) (PDHI), in the absence of oxygen, were determined on the basis of non-isothermal and isothermal TG data. Two PDHI samples of different weight average molar masses were used in the study. Two distinct DTG peaks were registered in the investigated range of 30°–600° C. Uniform values of the thermal degradation activation energy, E a, (118 kJ mol ) were obtained from non-isothermal data using the Flynn-Wall method for both samples up to mass losses of 60–70 %. The E a's at higher mass losses averaged about 150 kJ mol . Corresponding E a values were obtained from isothermal TG data analysed by classical kinetics. There seemed to be no influence of sample molar mass on the value of E a.

Thermogravimetric/mass spectrometric characterization of the thermal decomposition of (4‐O‐methyl‐D‐glucurono)‐D‐xylan

AbstractA thermogravimetric/mass spectrometric (TG/MS) system was used to characterize the thermolysis reactions of (4‐O‐methyl‐D‐glucurono)‐D‐xylan. The mass spectrometric peaks, measured as function of time, were attributed to water, methanol, carbon monoxide, carbon dioxide, formaldehyde, formic acid, acetic acid, acetone, acrolein, 2‐furaldehyde, and 3‐hydroxy‐2‐penteno‐1,5‐lactone. The time derivative of the thermogravimetric curve (DTG) consisted of two partially overlapping peaks, indicating a multistep mechanism. The mass spectrometric intensities of the peaks assigned to methanol and 2‐furaldehyde coincided with the first DTG peak, suggesting that the first DTG peak represents both dehydration and fragmentation pathways. Methanol, water, formyl group, and carbon dioxide contributed to both of the DTG peaks. This indicates that the dehydration, decarboxylation, and decarbonylation took place in two steps. The compounds observed only in the second DTG peak and later (acetone, formic acid, formaldehyde, acrolein, acetic acid, and 3‐hydroxy‐2‐penteno‐1,5‐lactone) are probably products of reactions which occur after the collapse of the original polysaccharide structure.

Thermal decomposition of ammonium copper chromate: effect of the addition of barium

The influence of the addition of barium (as barium chromate) to ammonium copper chromate on its thermal decomposition has been investigated by TG, DTG and DTA in the temperature range 303–1273 K. The solid products formed in the decomposition at different temperatures were characterised by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and also by measuring their specific surface area. The addition of BaCrO 4 at different concentrations (0–19.8%) was found not to change the general trend in the decomposition of ammonium copper chromate (which occurs in four distinct steps), except small changes in the temperature corresponding to DTG and DTA peaks. However, the sintering (or crystal growth) of the solid product is largely reduced by the presence of BaCrO 4.

Oxidative profiles of some australian oil shales by thermal analysis and infrared spectroscopy

Thermogravimetric and derivative thermogravimetric oxidative profiles were obtained for a number of Australian oil shales and kerogen concentrates heated in a dynamic air atmosphere. Evolved gas analysis curves and the associated first derivative curves were obtained for these materials by following the increase in optical absorption of the principal IR bands of gaseous species evolved during linear heating. Thermochemical changes in kerogens were also studied by means of solid-state IR transmission spectroscopy. Combustion of kerogen occurs in two stages, indicated by two sharply defined DTG peaks. The first stage involves complete or almost complete combustion of aliphatic components to give a char containing aromatic moieties. Evolved gas analysis and derivative evolved gas analysis curves for sulfur dioxide evolution, used in association with TG—DTG data, provide a means of characterising oil shale in terms of sulfur distribution.

Simultaneous DTA and DTG measurements on aluminium oxide monohydroxides

Simultaneous DTA and DTG curves (Mettler TA-2) have been measured for one diaspore and four different boehmites at temperatures up to 750° in a flow of dried argon. The crystallographic structures of the materials were assessed by X-ray diffraction and the degree of clustering of the elementary particles by scanning electron microscopy. To get straight base-lines a calibration curve was used to correct the DTA curves. The usefulness of the correction was established by comparison with DTA curves obtained with a Mettler TA-2000. The diaspore contained occluded water. Expulsion of the water at 300–350° brought about fragmentation of the crystals. The DTA and DTG peaks that correspond to the dehydration to alumina both lie at 560°. There is a noticeable spread in the DTA and DTG peaks for the different boehmites in the temperature range 455–530°. All the DTA peaks lie close to the corresponding DTG peaks. One of the boehmites displayed a double peak (470° and 502°). To trace the origin of the variation in peak temperature, the porous structure of the boehmite having its peak at 530° was varied by ball-milling and by dispersion into water, neither of which markedly affected the crystallographic structure and the crystallite size. Whereas ball-milling did not change the peak temperature much, dispersion into water brought about a transition from a single peak at 530° to a double peak at 450° and 490°. Prolonged storage in air led to a shift of the peaks to 480° and 520°. It is concluded that the porous structure of boehmites can profoundly affect the appearance and the temperature of their dehydration peaks.

Experimental results on the correlation between the areas of DTG and DTA peaks and the sample weight

Experimental results on the correlation between the areas of DTG and DTA peaks and the sample weight

Thermooxidative degradation of polyacrolein

Thermooxidative degradation of polyacrolein has been investigated with a derivatograph. It was found that up to 80° a physical process occurs — the evaporation of traces of water and monomer acrolein trapped by the polymer. Exothermic process of dehydration of hydrated aldehyde groups of polyacrolein takes place from 80 to 130°. A very pronounced exothermic process from 130 to 180° with a sharp weight loss is caused by the degradation of ring structures withn 3 in the polymer shifts the DTA and DTG peaks by 20° to lower temperatures. At temperatures of about 250° and higher side carbonyl groups are thermally oxidized and decarboxylated with a considerable weight loss. All these suggestions were confirmed by infrared spectroscopy.

Identification of Elastomers in Tire Sections by Total Thermal Analysis. III. White Sidewall Compounds of Neoprene Rubber Blends

Abstract DSC curves of sulfur-cured CR differ from peroxide-cured vulcanizates in the shape of the exotherm and the peak temperatures. The exothermic reaction, attributed to dehydrochlorination and subsequent crosslinking, is accelerated by sulfur. TG and DTG curves support this contention. In blends with NR, BR, or SBR, the second polymer intervenes in the crosslinking reaction, resulting in a lower residual weight for the CR network. White sidewall compounds of NR/CR or NR/CR/CSM can be identified by their DSC peaks in nitrogen, glass transition temperature, and DTG peaks. DSC and thermogravimetric curves supplement each other in the identification of these elastomers.

Thermogravimetric analysis of the salts and metal complexes of a soil fulvic acid

Salts and complexes of sixteen different mono-, di- and trivalent metal ions with a Podzol fulvic acid, a water-soluble soil humic compound, were prepared. Each salt and complex was characterized by chemical and i.r. methods and, in more detail, by thermogravimetry. The DTG curve of untreated fulvic acid exhibited a major peak with a maximum at 420°C which shifted to considerably higher temperatures when the fulvic acid had reacted with monovalent cations, but to lower temperatures when fulvic acid had complexed with di- and trivalent metal ions. The Na-, K- and Li-salts of fulvic acid appeared to be converted to inorganic carbonates at temperatures >700°C, whereas the NH 4-salt of fulvic acid formed the carbonate at >550°C. The stabilities of the metal—fulvic acid complexes, as measured by an ion-exchange equilibrium method, appeared in general to be inversely related to their thermal stabilities as indicated by major DTG peaks.