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Abstract  

In order to obtain a better understanding of the pyrolysis mechanism of urazole, molecular orbital (MO) calculations and evolved gas analysis were carried out. The MO calculations were performed using the density functional method (B3LYP) at the 6-311++G(d,p) levels by Gaussian 03. The geometrical structure of urazole and its tautomers were examined theoretically. Identification and real-time analysis of the gases evolved from urazole were carried out with thermogravimetry-infrared spectroscopy (TG-IR) and thermogravimetry-mass spectrometry (TG-MS). The evolved gases were identified as HNCO, N2, NH3, CO2, and N2O at 400 °C, but were different at other temperatures.

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Investigation of polymers by a novel analytical approach for evolved gas analysis in thermogravimetry

Gas chromatography comprehensively coupled to single photon ionization mass spectrometry

Journal of Thermal Analysis and Calorimetry
Authors: Mohammad R. Saraji-Bozorgzad, Thorsten Streibel, Markus Eschner, Thomas M. Groeger, Robert Geissler, Erwin Kaisersberger, Thomas Denner, and Ralf Zimmermann

thermophysical parameters as well as to observe chemical reactions. For more thorough and detailed investigations of the sample composition, a chemical investigation of the evolved gases, i.e., evolved gas analysis (EGA), is indispensable [ 1 ]. Depending on the

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Journal of Thermal Analysis and Calorimetry
Authors: A. J. Parsons, S. D. J. Inglethorpe, D. J. Morgan, and A. C. Dunham

Using a system based on non-dispersive infrared (NDIR) detectors, evolved gas analysis (EGA) was able to identify and quantify the principal volatiles produced by heating powdered samples of UK brick clays. From these results, atmospheric emissions likely to result from brick production can be predicted. In addition, EGA results for extruded brick clay test pieces are significantly different from those of powdered samples. Within an extruded brick clay body, evolved gases are contained within a pore system and evolved gas-solid phase reactions also occur. This EGA study provides further evidence on the nature of firing reactions within brick clay bodies. The qualitative and quantitative influence of heating rate — a key process condition in brick manufacture — on gas release is also outlined.

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Abstract  

In order to obtain a better understanding of thermal substituent effects in 1,2,4-triazole-3-one (TO), the thermal behavior of 1,2,4-triazole, TO, as well as urazole and the decomposition mechanism of TO were investigated. Thermal substituent effects were considered using thermogravimetry/differential thermal analysis, sealed cell differential scanning calorimetry, and molecular orbital calculations. The onset temperature of 1,2,4-triazole was higher than that of TO and urazole. Analyses of evolved decomposition gases were carried out using thermogravimetry–infrared spectroscopy and thermogravimetry–mass spectrometry. The gases evolved from TO were determined as HNCO, HCN, N2, NH3, CO2, and N2O.

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Abstract  

Thermal analysis combined with evolved gas analysis has been used for some time. Thermogravimetry (TG) coupled with Fourier transform infrared (FTIR) spectroscopy(TG/FTIR), Thermogravimetry (TG) coupled with mass spectrometry (TG/MS), and Thermogravimetry (TG) coupled with GC/MS offers structural identification of compounds evolving during thermal processes. These evolved gas analysis (EGA) techniques allow to evaluate the chemical pathway of the degradation reaction by determining the decomposition products. In this paper the TG/FTIR, TG/MS, and Pyrolysis/GC-MS systems will be described and their applications in the study of several materials will be discussed, including the analysis of the degradation mechanisms of organically modified clays, polymers, and coal blends.

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Abstract  

For complex decomposition reactions, traditional methods, such as TG and DSC cannot fully resolve all of the steps in the reaction. Evolved gas analysis (EGA) offers another tool to provide more information about the decomposition mechanism. The decomposition of sodium bicarbonate was studied by TG, DSC and EGA using a simultaneous thermal analysis unit coupled to a FTIR. The decomposition of sodium bicarbonate involves two reaction products H2O and CO2, which are not evident from either TG or DSC measurements alone. A comparison of the reaction kinetics from TG, DTG and EGA data were compared.

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Abstract  

Micro-thermal analysis employs a scanning probe microscope fitted with a miniature resistive heater/thermometer to obtain images of the surface of materials and then perform localised thermo analytical measurements. We have demonstrated that it is possible to use the same configuration to pyrolyse selected areas of the specimen by rapidly heating the probe to 600–800°C. This generates a plume of evolved gases which can be trapped using a sampling tube containing a suitable sorbent placed close to the heated tip. Thermal desorption-gas chromatogaphy/mass spectrometry can then be used to separate and identify the evolved gases. This capability extends the normal visualisation and characterisation by micro-thermal analysis to include the possibility of localised chemical analysis of the sample (or a domain, feature or contaminant). The isolation and identification of natural products from a plant leaf are given as an example to illustrate this approach. Preliminary results from direct sampling of pyrolysis products by mass spectrometry are also presented.

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Abstract  

Two enantiomeric forms of xylose were identified as α-D-xylopyranose and α-L-xylopyranose by powder diffraction. Their melting behaviour was studied with conventional DSC and StepScan DSC method, the decomposition was studied with TG and evolved gases were analyzed with combined TG-FTIR technique. The measurements were performed at different heating rates. The decomposition of xylose samples took place in four steps and the main evolved gases were H2O, CO2 and furans. The initial temperature of TG measurements and the onset and peak temperatures of DSC measurements were moved to higher temperatures as heating rates were increased. The decomposition of L-xylose started at slightly higher temperatures than that of D-xylose and L-xylose melted at higher temperatures than D-xylose. The differences were more obvious at low heating rates. There were also differences in the melting temperatures among different samples of the same sugar. The StepScan measurements showed that the kinetic part of melting was considerable. The melting of xylose was anomalous because, besides the melting, also partial thermal decomposition and mutarotation occurred. The melting points are affected by both the method of determination and the origin and quality of samples. Melting point analysis with a standardized method appears to be a good measure of the quality of crystalline xylose. However, the melting point alone cannot be used for the identification of xylose samples in all cases.

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Abstract  

FTIR spectrometry combined with TG provides information regarding mass changes in a sample and permits qualitative identification of the gases evolved during thermal degradation. Various fuels were studied: coal, peat, wood chips, bark, reed canary grass and municipal solid waste. The gases evolved in a TG analyser were transferred to the FTIR via a heated teflon line. The spectra and thermoanalytical curves indicated that the major gases evolved were carbon dioxide and water, while there were many minor gases, e.g. carbon monoxide, methane, ethane, methanol, ethanol, formic acid, acetic acid and formaldehyde. Separate evolved gas spectra also revealed the release of ammonia from biomasses and peat. Sulphur dioxide and nitric oxide were found in some cases. The evolution of the minor gases and water parallelled the first step in the TG curve. Solid fuels dried at 100C mainly lost water and a little ammonia.

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The enthalpies of formation and evolved gas detection

H4SiW12O40·6H2O and its DMF and DMSO adducts

Journal of Thermal Analysis and Calorimetry
Authors: Meiling Huang, Xian'e Cai, Daichun Du, Youming Jin, Jing Zhu, and Zemin Lin

Abstract  

The standard molar enthalpies of formation of H4SiW12O40·6H2O (I), H4SiW12O40·6DMF·H2O (II), H4SiW12O40·8DMSO·H2O (III) have been determined. Thermodynamic cycles were designed, and the heat of reactions in the thermodynamic cycles were measured calorimetrically. The infrared spectra were compared with those of the heteropoly anion α-H4SiW12O40 [1] and of the ligands DMF and DMSO. The evolved gas from the adducts was monitored by a quadrupole mass spectrometer at a heating rate of 16 deg·min−1.

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