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.
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 evolvedgases, i.e., evolvedgas analysis (EGA), is indispensable [ 1 ]. Depending on the
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.
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.
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.
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.
Authors:D. Price, M. Reading, R. Smith, H. Pollock, and A. Hammiche
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.
Authors:M. Lappalainen, I. Pitkänen, H. Heikkilä, and J. Nurmi
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.
Authors:I. Pitkänen, J. Huttunen, H. Halttunen, and R. Vesterinen
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.
Authors:Meiling Huang, Xian'e Cai, Daichun Du, Youming Jin, Jing Zhu, and Zemin Lin
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  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.