Thermal analysis/evolved gas analysis using single photon ionization

A simultaneous thermogravimetry/differential scanning calorimetry device (STA) was coupled to single photon ionization time of flight mass spectrometry (SPI-TOFMS) for evolved gas analysis (EGA). Thermal resolution with thermogravimetric signals (TG/DTG) is delivered by STA. On-line coupled EGA with SPI-TOFMS retains the thermal information from the STA and substantiates these with correlating mass spectra. The application of vacuum ultraviolet (VUV)-photons (8–12 eV) for soft ionization, allows almost fragment-free ionization. Thus, it becomes possible to interpret mass spectra of complex matrices, like natural products evolving simultaneously several molecules, without an additional separation step. The STA–SPI-TOFMS on-line coupling offers the possibility to track subset mass traces during one STA run. Focusing on material-depended mass traces, differentiation of organic matrices is obvious. In this work two types of research cigarettes, 3R4F and CM6 were used. While the 3R4F cigarette is composed of a blend of different tobacco sorts and different curing methods, the CM6 research cigarette consists of pure flue cured tobacco. The advantages of coupling on-line chemical analysis methods to thermal analysis (TA) are in the context of the achieved thermo-molecular signatures.     

Study of pyrolysis and incineration of disposable plastics using combined TG/FT-IR technique

Thermogravimetric analysis (TG) provides information regarding mass changes in the sample resulting from heat treatment under controlled environment. However, it does not provide any chemical information regarding the gases evolved during the thermal degradation. Using FT-IR spectrometry in combination with TG, it is often possible to identify the evolved gases, and also monitor their evolution profiles during thermal degradation. In this study, we present the TG/FT-IR combined analysis of incineration and pyrolysis of some common plastics such as high density polyethylene (HDPE), polyvinyl chloride (PVC), polyethylene terephthalate (PET), and polystyrene (PS). This study demonstrates the utility of such combined analysis in providing useful information regarding the use of thermal treatment for recycling or incineration.     

Comparative evolved gas analyses on thermal degradation of thiourea by coupled TG-FTIR and TG/DTA-MS instruments

Identification and monitoring of gaseous species released during thermal decomposition of pure thiourea, (NH₂)₂C=S in argon, helium and air atmosphere have been carried out by both online coupled TG-FTIR and simultaneous TG/DTA-MS apparatuses manufactured by TA Instruments (USA). In both inert atmospheres and air between 182 and 240°C the main gaseous products of thiourea are ammonia (NH₃) and carbon disulfide (CS₂), whilst in flowing air sulphur dioxide (SO₂) and carbonyl sulphide (COS) as gas phase oxidation products of CS₂, and in addition hydrogen cyanide (HCN) also occur, which are detected by both FTIR spectroscopic and mass spectrometric EGA methods. Some evolution of isothiocyanic acid (HNCS) and cyanamide (NH₂CN) vapours have also observed mainly by EGA-FTIR, and largely depending on the experimental conditions. HNCS is hardly identified by mass spectrometry. Any evolution of H₂S has not been detected at any stage of thiourea degradation by either of the two methods. The exothermic heat effect of gas phase oxidation process of CS₂ partially compensates the endothermicity of the corresponding degradation step producing CS₂.     

Thermal degradation of polyesters by simultaneous TG-DTA/FT-IR analysis

A combination system of thermogravimetric/differential thermal analysis (TG-DTA) and Fourier-transform infrared absorption spectroscopy (FT-IR) was described. This simultaneous TG-DTA/FT-IR technique gave spectroscopic and weight loss information about the thermal degradation process of engineering polyesters; poly(ethylene terephthalate)(PET) and poly(butylene terephthalate)(PBT). The evolved gases from PET were benzoic acid, carbon dioxide and carbon monoxide, while those from PBT were terephthalic acid esters and benzoic acid esters.

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Zusammenfassung Es wird ein kombiniertes System aus TG-DTA und FT-IR beschrieben. Mit dieser simultanen TG-DTA/FT-IR-Technik wurden spektroskopische und Massenverlustangaben über die thermische Zersetzung technisch wichtiger Polyester, namentlich von Poly(ethylenterephthalat) (PET) und Poly(Butylenterephthalat) (PBT) ermittelt. Die aus PET freigesetzten Gase waren Benzoesäure, Kohlendioxid und Kohlenmonoxid, die aus PBT freigesetzten Gase hingegen Terephthalsäureester und Benzoesäureester.

     

Thermal degradation and evolved gas analysis of thiourea-formaldehyde resin (TFR) during pyrolysis and combustion

Thiourea formaldehyde resin (TFR) has been synthesized by condensation of thiourea and formaldehyde in acidic medium and its thermal degradation has been investigated using TG-FTIR-MS technique during pyrolysis and combustion. The results revealed that the thermal decomposition of TFR occurs in three steps assigned to drying of the sample, fast thermal decomposition of polymers, and further cracking. The similar TG and DTG characteristics were found for the first two stages during pyrolysis and combustion. The combustion process was almost finished at 680?°C, while during pyrolysis a total mass loss of 93 wt% is found at 950?°C. The release of volatile products during pyrolysis are NH₃, CS₂, CO, HCN, HNCS, and NH₂CN. The main products in the second stage are NH₃ CO₂, CS₂, SO₂, and H₂O during combustion. In the next stage, the combustion products mentioned above keep on increasing, but some new volatiles such as HCN, COS etc., are identified. Among the above volatiles, CO₂ is the dominant gaseous product in the whole combustion process. It is found that the thermal degradation during pyrolysis of TFR produced more hazardous gases like HCN, NH₃, and CO when compared with combustion in similar conditions.     

Thermal behavior,decomposition mechanism by TG/MS/FTIR technique and theoretical study of some symmetric and asymmetric bent-core liquid crystals based on 2,7-dihydroxynaphthalene

Journal of Thermal Analysis and Calorimetry - The thermal stability of some symmetric and asymmetric bent-core liquid crystals derived from 2,7-dihydroxynaphthalene as well as the degradation...     

Study of crystal transformations by an evolved gas analysis technique

Small organic molecules can be entrapped within inorganic crystalline materials during precipitation. The material has no apparent influence on solid-solid transition temperatures, but some of it is released during the transition.Detection of the escape is reproducible within 1°C and may be used for temperature calibration. More generally, the escape of the organic during chemical reactions could be used for many of the applications of emanation thermal analysis.In coupled systems such as DTA or TG with mass spectrometry, or other systems involving gas transport, the time delay of the system can be measured accurately.

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Zusammenfassung Kleine organische Moleküle können während der Fällung in anorganische kristalline Substanzen eingeschlossen werden. Die Substanz hat keine scheinbare Wirkung auf Fest-Fest-Übergangstemperaturen, doch wird ein Teil derselben während des Überganges freigesetzt. Der Nachweis der freigesetzten Substanz ist innerhalb von 1°C reproduzierbar und kann zur Temperatureichung eingesetzt werden. Verallgemeinert könnte das Entfliehen organischer Substanzen im Laufe chemischer Reaktionen bei vielen Anwendungen der Emanations-Thermalanalyse eingesetzt werden. In gekoppelten Systemen, wie z.B. DTA oder TG mit Massenspektrometrie, oder andere Systeme mit Gastransport, kann die Verzögerung des Systems genau gemessen werden.

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Résumé De petites molécules organiques peuvent se trouver incluses dans des substances inorganiques cristallines, au moment de la précipitation. Les températures de transition solidesolide ne s'en trouvent apparemment pas affectées mais une partie de ces molécules incluses peut être éliminée pendant la transition. La détection du matériau qui s'échappe est reproductible à 1°C près et se prête à l'étalonnage de la température. En termes plus généraux, le départ de la substance organique au cours des réactions chimiques peut être utilisé pour de nombreuses applications de l'analyse thermique d'émanation. Dans le cas de techniques associées, comme l'ATD ou la TG avec la spectrométrie de masse, ou encore d'autres techniques avec transport de gaz, on peut mesurer exactement le temps de réponse du système.

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The authors are grateful to the National Science Foundation for support of parts of this work through institutional and research grants and to the Goodyear Tire and Rubber Company for use of the Chromatograph and other facilities.     

Kinetic analysis of complex decomposition reactions using evolved gas analysis

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.     

Qualitative analysis of activated sludge using FT-IR technique

The ability to measure and control the composition of activated sludge is an important issue, aiming at evaluating the effectiveness of changes occurring in the sludge, what determines its usefulness to treat wastewater. In this research, diffuse reflectance infrared Fourier transform (FTIR–DRIFT) technique was used, which relies on measuring the reflectance of the powdered substance’s surface layer and capturing spectra in range of infrared wave. First, spectra correlation table of the substances mostly occurring in wastewater was developed to assess the main components of the tested samples of activated sludge. The simplest compounds containing functional groups characteristic for particular chemical classes were chosen: peptides (peptone and albumin), fats (glycerin and fatty acids), carbohydrates (glucose and sucrose), nitrogen compounds (NaNO₃ and NH₄SO₄), sulfur compounds (Na₂SO₄ and Na₂S₂O₃), silicate, etc. The spectra of those substances were captured and characteristic absorption bands for respective bonds in the function groups were assigned. Second, samples of activated sludge from lab-scale membrane bioreactors (MBRs), which purifies petroleum wastewater, were taken. Samples were properly prepared (lyophilization and homogenization) and their spectra were captured. During spectra analysis, previously developed correlation table was used. In obtained spectra of activated sludge, absorption bonds characteristic for amides, peptides, carbohydrates, fats, and aliphatic was identified. The spectra profile of the sludge sample from MBR feed with petroleum wastewater was slightly different from the control MBR sample’s spectra. Intensity of bands in the area characteristic for aliphatic compounds and phenols was clearly higher. This study proves the usefulness of FT-IR technique to observe changes in the chemical composition of activated sludge.     

Thermal analysis study of imidazolinium and some benzimid azolium salts by TG

The imidazolinium and benzimidazolium bromide salts with pentafluor substituents on N atom were synthesized. The structures of imidazolinium and benzimidazolium bromide salts obtained were conformed by ¹H and ¹³C NMR, ¹⁹F NMR and elemental analysis. It was found that pyrolytic decomposition occurs with melting in salts. The imidazolinium and benzimidazolium bromide salts were studied by TG-DTG and DTA from ambient temperature to 1000°C in nitrogen atmosphere. The decomposition occurred mainly in one stage and the values of activation energy E, frequency factor A, reaction order n, enthalpy change ΔH ^#, entropy change ΔS ^# and Gibbs free energy ΔG ^#, of the thermal decomposition were calculated by means of Coats-Redfern (CR), MacCallum-Tanner (MC) and van Krevelen (vK) methods. The activation energy value obtained by CR and MC methods were in good agreement with each other while those obtained by vK were found to be 10–12 kJ mol⁻¹ larger.     

Influences of evolved gases on the thermal decomposition of zinc carbonate hydroxide evaluated by controlled rate evolved gas analysis coupled With TG

The influences of atmospheric CO₂ and H₂O on the kinetics of the thermal decomposition of zinc carbonate hydroxide, Zn₅(CO₃)₂(OH)₆, were investigated by means of controlled rate evolved gas analysis (CREGA) coupled with TG. Although CO₂ and H₂O were evolved simultaneously in a single mass-loss step of the thermal decomposition, different effects of those evolved gases on the kinetic rate behavior were observed. No distinguished effect of atmospheric CO₂ was detected within the possible range of self-generated CO₂ concentration. On the other hand, apparent acceleration effect by the increase in the concentration of atmospheric H₂O was observed as the reduction of reaction temperature during the course of constant rate thermal decomposition. The catalytic effect was characterized by the decrease in the apparent activation energy for the established reaction with increasing the concentration of atmospheric H₂O, accompanied by the partially compensating decrease in the pre-exponential factor.     

Thermal degradation and evolved gas analysis of epoxy (DGEBA)/novolac resin blends (ENB) during pyrolysis and combustion

The thermal degradation of epoxy (DGEBA) and phenol formaldehyde (novolac) resins blend was investigated by using thermogravimetric analysis (TGA) coupled with Fourier transform infrared spectroscopy and mass spectroscopy. The results of TGA revealed that the thermal degradation process can be subdivided into four stages: drying the sample, fast and second thermal decomposition, and further cracking process of the polymer. The total mass loss of 89.32 mass% at 950 °C is found during pyrolysis, while the polymer during the combustion almost finished at this temperature. The emissions of carbon dioxide, aliphatic hydrocarbons, carbon monoxide, etc., while aromatic products, are emitted at higher temperature during combustion and pyrolysis. It was observed that the intensities of CO₂, CO, H₂O, etc., were very high when compared with their intensities during pyrolysis, attributed to the oxidation of decomposition product.     

Qualitative and quantitative analysis of the unsaponifiable fraction of vegetable oils by using comprehensive 2D GC with dual MS/FID detection

The present investigation is focused on the development of a comprehensive two-dimensional GC (GC?×?GC) method, with dual MS/FID detection, for the qualitative and quantitative analysis of the entire unsaponifiable fraction of vegetable oils. The unsaponifiable fraction forms a minor, highly specific part of a vegetable oil, and can be used as an indicator of genuineness. The column set used consisted of a low-polarity first dimension, and a medium-polarity secondary one, both characterized by a high thermal stability. The use of dual detection enabled the attainment of both mass spectral information and relative % FID data. The complexity of the fingerprint, generated by the unsaponifiable fraction, fully justified the employment of the two-dimensional GC technology. Furthermore, two other GC?×?GC benefits contributed greatly to the attainment of promising results, namely sensitivity enhancement and the formation of group-type patterns. The method herein proposed could potentially open a new opportunity for the more in-depth knowledge of the unsaponifiable fraction of vegetable oils.     

Thermal analysis study of some transition metal complexes by TG and DSC methods

The thermodynamic and thermal properties of [Cu(L)₂·Cl₂], [Ni(L)₂]·Cl₂, [Co(L)₂·Cl₂]; L=1,2-bis(o-aminophenoxy)ethane (BAFE), complexes have been investigated. The thermal decomposition of the complexes took place in two distinct steps in endothermic reaction up to 700°C. The activation energy E, the entropy change S ^#, enthalpy H change and Gibbs free energy change G ^# were calculated from the results of thermogravimetry analysis (TG) and heat capacity from the results of differential scanning calorimetry (DSC). It was found that the thermal stabilities and activation energies of the complexes follow the order Ni(II)>Cu(II)>Co(II) and E _Co<E _Ni<E _Cu, respectively.This revised version was published online in November 2005 with corrections to the Cover Date.     

Analysis of the thermal decomposition of commercial vegetable oils in air by simultaneous TG/DTA

This work presents a study of the thermal decomposition of commercial vegetable oils and of some of their thermal properties by termogravimetry (TG), derivative termogravimetry (DTG) and by differential thermal analysis (DTA). Canola, sunflower, corn, olive and soybean oils were studied. A simultaneous SDT 2960 TG/DTA from TA Instruments was used, with a heating rate of 10 K min^-1 from 30 to 700°C. A flow of 100 mL min^-1 of air as the purge gas was used in order to burnout the oils during analysis to estimate their heat of combustion. From the extrapolated decomposition onset temperatures obtained from TG curves, it can be seen that corn oil presents the highest thermal stability (306°C), followed by the sunflower one (304°C). Olive oil presents the lowest one (288°C). The heat of combustion of each oil was estimated from DTA curves, showing the highest value for the olive oil. Except for corn oil, which presents a significantly different thermal decomposition behavior than the other oils, a perfect linear correlation is observed, with negative slope, between the heat of combustion of an oil and its respective extrapolated onset temperature of decomposition in air. This revised version was published online in August 2006 with corrections to the Cover Date.     

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.     

Determination of azaarenes in oils using the LC‐APCI‐MS/MS technique: New environmental toxicant in food oils

A novel method to determine of azaarenes in refined and cold‐pressed vegetable oils and animal fats is reported. The method may be used to determine eight most important acridine derivatives (benz[a]acridine, dibenz[a,i]acridine, benz[c]acridine, dibenz[a,j]acridine, 7,9‐dimethylbenz[c]acridine, dibenz[a,h]acridine, dibenz[a,c]acridine, dibenz[c,h]acridine) at a high sensitivity (LOQ in the 2–25 ng kg^?1 range), high analyte recovery rates (70.7–98.7%), sufficient linearity within the studied concentration range (r > 0.97). The method is fast, simple, and needs no expensive clean‐up procedures to successfully determine the analytes. Azaarene concentration in the studied oil samples ranged from 2 to 250 ng kg^?1. Benz[a]acridine and dibenz[a,j]acridine were the compounds found most commonly and at the highest concentrations. The observed concentrations most probably reflected levels of environmental contamination of raw materials used to produce the analyzed oil/fat samples.     

Study on the thermal degradation of high performance fibers by TG/FTIR and Py-GC/MS

The thermal degradation behaviors of Kevlar 49, Kevlar 129 (Poly(p-phenylene terephthamide), Nomex (polyisophthaloyl metaphenylene diamine), and PBO(poly(p-phenylene benzobisoxazole)) fibers were measured by TG/FTIR and Py-GC/MS. The characteristic temperatures of the fibers in air were obtained by TG. It indicated that the initial degradation temperature of the PBO is the highest. The initial degradation temperature of Nomex fiber is the lowest, but the end decomposition temperature of Nomex is the highest. The gases released by the pyrolysis in air were mainly CO₂, CO, H₂O, NO, and HCN, also containing a small amount of NH₃, and the absorption peaks of CO₂ were the strongest. The results of Py-GC/MS showed that CO₂ and benzene were the most pyrolysis fragment. With the change of pyrolysis temperature, the chromatogram and mass spectra results take a large variety. The pyrolysates can help us to study the pyrolysis process of high performance fibers.     

TGA/FT-IR: Thermogravimetric analysis with fourier transform infrared detection of evolved gases

Thermogravimetric analysis (TGA) is a widely employed technique for measuring the change in weight of a sample as a function of temperature or time in a controlled atmosphere. FT-IR has been utilized with success in the identification of gases [1]. The combination of these two techniques permits a complete characterization of materials in terms of thermal stability and decomposition mechanisms [2]. A complete integrated system for TGA/FT-IR analysis is described.