Thermal Analysis Mass Spectrometry Research Articles

Thermal decomposition mechanism of ammonium phosphotungstate hydrate in air atmosphere

Production of W from scheelite mineral (CaWO4) by hydrometallurgical processes has grown up in the last decade. CaWO4 dissolves in HCl solutions containing H3PO4 as chelating agent and forms phosphotungstic acid (H3(PW12O40), PhTA). Ammonium phoshpotungstate hydrate ((NH4)3[PW12O40]xH2O, APhT) can be precipitated by addition of NH4Cl to solutions containing PhTA and WO3 can be produced by the thermal decomposition of APhT. W powder can be obtained by H2 reduction of WO3.In W production, the thermal decomposition of APhT is one of the process steps. In this work, Thermogravimetric Analysis–Differential Thermal Analysis–Mass Spectrometry (TGA–DTA–MS), X-ray Powder Diffraction (XRD), Fourier Transform-Infrared Spectrometry (FT-IR), Scanning Electron Microscopy (SEM) and Thermo-Gas-Titration (TGT) analytical techniques were used to investigate the mechanism of thermal decomposition of APhT and the characterisation of its decomposition products. White coloured APhT losses its crystal water in the first decomposition step and turns its colour to light grey to form anhydrous ammonium phosphotungstate ((NH4)3(PW12O40), anhydrous APhT). Anhydrous APhT is stable up to 640K temperature. Anhydrous APhT is transformed into tetragonal structured, light green coloured phosphotungstate (P2O524WO3, PhT) which is stable up to 1282K temperature. PhT is then decomposed gradually into green coloured WO3 and P2O518WO3 mixture. The mixture formed does not vaporise until 1343K temperature. After this temperature, sublimation takes place followed by melting at 1490K temperature and loss of weight is observed due to evaporation. Thermal analysis up to 1573K temperature showed that the samples are transformed into light yellow coloured, monoclinic structured WO3.

Characterization and pervaporation dehydration of heat-treatment PAN hollow fiber membranes

In this study, heat-treated polyacrylonitrile (PAN) hollow fiber membranes have been used to investigate the pervaporation performances of aqueous ethanol solution. The heat-treated PAN hollow fiber membranes were prepared by heat treating the as-spun PAN precursor hollow fiber membranes at 120, 160 and 210°C for 12h under air atmosphere, respectively. Scanning electron microscopy (SEM), Fourier transform infrared (FT-IR), simultaneous thermal analysis/mass spectrometry (TA/MS) and thermogravimetric analysis (TGA) are used to characterize the properties of hollow fiber membranes. The 90wt.% aqueous ethanol solution at 25°C has been used to investigate the pervaporation performances through hollow fiber membrane. Furthermore, in this investigation, we also use the positron annihilation spectroscopy (PAS) to identify the effect of heat-treatment on free volume variation of PAN hollow fiber membranes. To our knowledge, it is the pioneering work for PAS analysis technique used in hollow fiber membranes. The results have shown that the pervaporation performances of PAN hollow fiber membrane can be improved by heat-treatment. The permeation rate decreases while water content in permeate increases with increasing heat-treatment temperature. These phenomena might be due to that after heat-treating, the PAN hollow fiber membrane morphology becomes denser and the free volume of PAN polymer chain is reduced. Finally, heat-treated PAN/polyethylene glycol (PEG)10K blended hollow fiber membranes are also fabricated to investigate the pervaporation performance of aqueous ethanol solution. It has shown that the permeation rate as well as water content in permeate increases with increasing heat-treatment temperature. These phenomena can be interpreted that some of the PEG10K in hollow fiber membrane matrix has burnt away by heat-treating, and the occupied space of PEG10K would lead water molecules more easy to permeate. The long-term pervaporation stability of 210°C heat-treated PAN hollow fiber membranes was also investigated in this study. It has shown that the long-term pervaporation stability can last at least 250 days.

Pyrolysis of biomass by thermal analysis–mass spectrometry (TA–MS)

The kinetic parameters such as pre-exponential factor and activation energy of hemicellulose, cellulose, and lignin were well determined by the linear regressions of selected, sufficient thermogravimetric data, and close to literature values. The pyrolysis of biomass can be divided into four stages. There was only drying in the zeroth stage (<150°C). In the first stage (150-250°C), some light hydrocarbons were produced with the early pyrolysis of biomass. The biomass was mainly pyrolyzed in the second stage (250-500°C) with higher reaction rates than those of other stages. The productions of H(2) and CO(2) in the third stage (>500°C) may be able to be the evidence of self-gasification of char existing at higher temperatures.

Thermal decomposition properties of 1,2,4-triazole-3-one and guanidine nitrate mixtures

1,2,4-triazole-3-one (TO) and guanidine nitrate (GN) have the potential to be used as alternative gas-generating agents. To obtain a better understanding of thermal decomposition properties of TO/GN mixtures, sealed cell differential scanning calorimetry, thermogravimetry–differential thermal analysis–infrared spectroscopy (TG–DTA–IR), and thermogravimetry–differential thermal analysis–mass spectrometry (TG–DTA–MS) were carried out. The endothermic peak and onset temperatures of TO/GN mixtures were lower than those of individual TO and GN. TG–DTA–IR and TG–DTA–MS showed that the mass of TO/GN mixtures decreased with heat generation and N2 evolved as the major gas during thermal decomposition. The interaction between TO and nitric acid from the dissociation of GN is proposed for the thermal decomposition of TO/GN mixtures.

ChemInform Abstract: Thermal Analysis Using Mass Spectrometry: A Review

Abstract Thermal analysis combined with mass spectrometric analysis is a powerful tool for studying thermal degradation pathways of materials. Early work in catalysis developed much of the theory necessary to obtain kinetic information from the degradation reactions observed when samples are heated in a temperature-programmed fashion. Since mass spectrometry is a vacuum technique, many problems exist when efficient coupling of thermal systems to mass analyzers is sought. Trade-offs must be made between minimizing pyrolysate condensation and maximizing sample temperature/weight measurement accuracy. These compromises have led to a wide range of instrumental approaches and terminology. The underlying theory and information obtained remain similar, however, regardless of the instrumental approach. Techniques which yield chemical information during thermal degradation by intimately coupling a sample heating element or furnace to a mass spectrometer are reviewed and presented as fundamentally identical. Issues pertinent to all the methods are discussed, including theory, sources of error, and systems suitable for thermal analysis mass spectrometry.

Diphenylmethane diisocyanate self-polymerization: Thermal hazard evaluation and proof of runaway reaction in gram scale

Thermal analysis by differential scanning calorimetry and thermogravimetric/differential thermal analysis mass spectrometry, adiabatic calorimetry, a gram-scale heating test, and infrared spectroscopy were performed to evaluate the thermal hazards of diphenylmethane diisocyanate (MDI) and prove the occurrence of a runaway reaction. The self-polymerization of MDI was found to occur at about 340 °C under rapid heating conditions. Carbon dioxide was eliminated and heat was generated to allow polymerization. Under adiabatic and closed conditions, the runaway reaction of MDI can begin at least from 220 °C. Besides it is highly probable that the runaway reaction of MDI can begin from a lower temperature in an actual process scale. More heat was generated than in the previous case and the pressure rose rapidly. A closed 2-mm-thick glass vessel exploded because of the runaway reaction of MDI even if the temperature was lower than 300 °C. Therefore, MDI could cause fatal runaway reactions below 300 °C, where MDI had been assumed to self-polymerize by eliminating carbon dioxide previously.

Study on the dehydrogenation kinetics and thermodynamics of Ca(BH 4) 2

Ca(BH 4) 2 is a promising hydrogen storage material due to its high gravimetric hydrogen density of 11.5 wt%. In this work, the dehydrogenation kinetics and thermodynamics of Ca(BH 4) 2 were systematically investigated by differential thermal analysis (DTA), thermal analysis mass spectrometry (TA/MS), temperature-programmed desorption (TPD), X-ray diffraction (XRD) and pressure, composition, and temperature (PCT) measurements. DTA, TA/MS, TPD and XRD results indicate that the dehydrogenation process of Ca(BH 4) 2 is a two-step reaction. The dehydriding reaction of Ca(BH 4) 2 starts at approximately 320 °C, and about 9.6% of hydrogen is desorbed through the two-step reaction. The apparent activation energy ( E a) of about 225.37 and 280.51 kJ/mol for the first-step and second-step dehydrogenation, respectively, were determined by Kissinger's method. The activation energy for the first-step dehydrogenation was further confirmed by the Arrhenius equation. As a result of in-depth kinetic investigations, a geometrical contraction-controlled kinetic mechanism has been identified for the first-step dehydrogenation by analyzing isothermal hydrogen desorption curves with a linear plot method. Finally, the thermodynamic parameters for the dehydrogenation are estimated based on the results of the PCT measurements: enthalpy of reaction Δ H = 87 kJ/mol-H 2, and entropy of reaction Δ S = 158 J/K mol-H 2. The relatively high activation energy and change in enthalpy indicate that a kinetic and thermodynamic barrier needs to be overcome for Ca(BH 4) 2 to be suitable as a hydrogen storage material for mobile applications.

Operando study of iridium acetylacetonate decomposition on amorphous silica–alumina for bifunctional catalyst preparation

The decomposition of iridium acetylacetonate Ir(acac)(3) impregnated on amorphous silica-alumina (ASA) has been investigated by combined thermogravimetry-differential thermal analysis-mass spectrometry (TG-DTA-MS) and by in situ X-ray diffraction (XRD). The resulting Ir/ASA hydrotreating catalysts have also been characterized by transmission electron microscopy (TEM). The effects of heating treatments under oxidative, reductive or inert gas flows are compared with each other and with similar experiments on ASA-supported acetylacetone (acacH). It is shown that Ir(acac)(3) undergoes exothermic combustion during calcination in air, leading to agglomerated IrO(2) particles. Conversely, direct reduction involves hydrogenolysis of the acac followed by hydrogenation of the ligand residues to alkanes and water. These two processes are catalyzed by Ir clusters, the gradual growth of which is followed in situ by XRD. The resulting nanoparticles are highly and homogeneously dispersed.

Sodium-Ion-Assisted Hydrothermal Synthesis of γ-MnO2 and Its Electrochemical Performance

A nanomaterial was synthesized by hydrothermally treating an amorphous manganese oxide, which was obtained by the reaction between and at ambient conditions. It is only in a narrow range of adding an amount of NaOH (e.g., in our case) that can be obtained. The addition of NaOH may affect the radii of hydrated and, consequently, the formation of ; the related mechanism was discussed. was characterized by X-ray diffraction (XRD), scanning electron microscope, transmission electron microscope, and temperature-programmed XRD. was also characterized by the combined thermogravimetric/differential thermal analysis–mass spectrometry; accordingly, the annealed forms of were prepared and characterized electrochemically. The results show that the calcined at for showed excellent capacity with a good rate capability.

Evolved gas analysis (EGA) in TG and DSC with single photon ionisation mass spectrometry (SPI-MS): molecular organic signatures from pyrolysis of soft and hard wood, coal, crude oil and ABS polymer

A combined thermogravimetry/differential scanning calorimetry device (TG/DSC) was coupled to single photon ionisation mass spectrometry (SPI-MS) for evolved gas analysis (EGA). Single photon ionisation (SPI) was performed with a new type of VUV light source, the so called electron beam pumped rare gas excimer lamp (EBEL). SPI does not fragment molecules upon the ionisation process. Thus the molecular mass signature of the evolving gases from thermal composition of carbonaceous material can be directly on-line recorded. In this work the thermo-analytical data and the SPI-MS information on the released organics is presented and discussed for various samples. Namely biomass (soft and hard wood), fossil fuel (crude oil and coal) as well as a complex polymer (ABS) are investigated. The general potential of hyphenating thermal analysis and soft photo ionisation mass spectrometry (EBEL-SPI-MS) for fundamental and applied research and material analysis is discussed.

Characterization of Pyridine-Octanethiolated Gold Nanoparticles: Desorption Kinetics by Thermal Analysis Mass Spectrometry

We describe a synthetic pathway to the formation of stable pyridine-functionalized octanethiolate mixed monolayer-protected Au clusters (MPCs). The spectroscopic characterization data of MPCs using NMR, UV-Vis, TEM, XPS, and thermal-analysis-mass techniques are discussed. TEM analysis showed that spherical nanoclusters of 3-5 nm were produced. Furthermore, the particle sizes are uniform with a narrow size distribution. The pyridine-functionalized MPCs formed 2D superlattices with hexagonal packing covering on the carbon-coated copper grids during the toluene evaporation. For all samples, the S 2p(3/2) and 2p(1/2) components that appeared at approximately 162 and approximately 163 eV, respectively, in the XPS spectra compare very well with the typical value of chemisorbed S species. Thermal analysis mass spectrometer was used to analyze desorption behavior of octanethiolated MPCs or pyridine-functionalized mixed MPCs. The TA-mass spectra have revealed that MCPs exist monomer and dimer desorption behavior from monomeric thiolate adsorbed on the surface.

Thermal behavior of europium tris(hexafluoroacetylacetonate) Eu(hfa)3 and the mixed-ligand 4-cyanopyridine-N-oxide complex [Eu(hfa)3(cpo)

The thermal behavior and thermodynamic properties of europium tris(hexafluoroacetylacetonate) Eu(hfa)3 and the mixed-ligand 4-cyanopyridine-N-oxide complex [Eu(hfa)3(cpo)] were investigated by thermal analysis and Knudsen effusion mass spectrometry. The compounds sublime congruently. The composition of the gas phase over the compounds and the partial pressures of the components were determined. The enthalpies of sublimation, polymerization, and dissociation of these compounds were derived from experimental data.

Preparation and thermal decomposition study of pyridinedicarboxylate intercalated layered double hydroxides

Supramolecular 2,3- and 2,5-pyridinedicarboxylate (PDC) intercalated ZnAl-layered double hydroxides (2,3- and 2,5-PDC–ZnAl–LDHs) have been prepared by ion exchange method. The structure and composition of the intercalated materials have been studied by X-ray diffraction (XRD) and inductively coupled plasma emission spectroscopy (ICP). The study indicates that the 2,3-PDC and 2,5-PDC anions are accommodated as interdigitated bilayer and monolayer arrangement respectively between the sheets of LDHs. Furthermore, their thermal decomposition processes were studied by the use of in situ high temperature X-ray diffraction (HT-XRD), and the combined technique of thermogravimetry-differential thermal analysis-mass spectrometry (TG-DTA-MS) under N2 atmosphere. Based on the comparison study on the temperatures of both decarboxylation and complete decomposition of interlayer PDC, it can be concluded that 2,5-PDC–ZnAl–LDHs has higher thermal stability than that of 2,3-PDC–ZnAl–LDHs.

Prediction of thermal stability of fresh and aged parchment

The hyphenated thermal analysis-mass spectrometry technique (TA-MS) was applied for the investigation of the thermal behavior of reference and aged parchment samples. The kinetic parameters of the process were calculated independently from all recorded TA and MS signals. The kinetic analysis showed the distinct dependence of the activation energy on the reaction progress. Such behavior is characteristic for the multistage mechanism of the reaction.

Structural study of oriental lacquer films during the hardening process

Oriental lacquer is the natural resin obtained by tapping lac trees. It hardens into a tough and insoluble film. The extreme hardness and insolubility are some of the most important functions, which are required for industrial coating materials. In this study, two kinds of oriental lacquer films, traditionally named Kiurushi (raw urushi) and Kuromeurushi produced by two different pretreatments, were analyzed during hardening with Fourier transform infrared spectroscopy (FT-IR), thermogravimetry/differential thermal analysis–mass spectrometry (TG/DTA–MS) and pyrolysis–gas chromatography/mass spectrometry (Py–GC/MS) to investigate their functional expression process. Typical functional groups of the lacquer films were detected by FT-IR. The TG/DTA–MS curves clarified that the thermal degradation of the lacquer films gradually began at around 200 °C, and reached the fastest rate at 400–500 °C. Apparently, FT-IR and TG/DTA–MS could not reveal any difference between the films. On the other hand, Py–GC/MS revealed differences between the films in the peak area ratios of 3-pentadecenylcatechol to 3-pentadecylcatechol and 3-pentadecadienylcatechol to 3-pentadecylcatechol. The ratios of Kiurushi lacquer film were higher than those of Kuromeurushi lacquer film. Both ratios, furthermore, decreased during hardening due to polymerization of the alkenylcatechols into an urushiol polymer skeleton comprising nucleus–side chain and side chain–side chain cross-linkages with 3-pentadecylcatechol at the terminal. The present results suggest that the reaction rate of these cross-linkages in Kuromeurushi lacquer film is faster than that in Kiurushi lacquer film. A good correlation was found between the peak area ratios obtained by Py–GC/MS and hardness obtained by pencil hardening testing. Oriental lacquer expresses the functions – an extreme hardness and insolubility – accelerating the nucleus–side chain and side chain–side chain cross-linkages. Furthermore, it has become clear that the traditional treatments called Nayashi and Kurome effectively accelerate the hardening rate by activating the cross-linkages.

Surface and catalytic properties of acid metal–carbons prepared by the sol–gel method

The sol–gel method has been applied for the synthesis of a series of acid metal–carbon xerogels (with M = V, Cr, Mo and Ni) by polymerisation of resorcinol with formaldehyde in the presence of metallic precursors. A blank sample was also prepared without any metal addition. The xerogels were heated in nitrogen at 1000 °C to obtain the pyrolysed products. The samples were characterised by different techniques such as thermal-mass spectrometry analysis, gas physisorption, and mercury porosimetry. In addition, the acid character of the pyrolysed products was tested by the Claisen–Schmidt condensation between benzaldehyde and acetophenone for the formation of chalcones.

Thermal decomposition process of silver behenate

The thermal decomposition processes of silver behenate have been studied by infrared spectroscopy (IR), X-ray diffraction (XRD), combined thermogravimetry–differential thermal analysis–mass spectrometry (TG-DTA-MS), transmission electron microscopy (TEM) and UV–vis spectroscopy. The TG-DTA and the higher temperature IR and XRD measurements indicated that complicated structural changes took place while heating silver behenate, but there were two distinct thermal transitions. During the first transition at 138 °C, the alkyl chains of silver behenate were transformed from an ordered into a disordered state. During the second transition at about 231 °C, a structural change took place for silver behenate, which was the decomposition of silver behenate. The major products of the thermal decomposition of silver behenate were metallic silver and behenic acid. Upon heating up to 500 °C, the final product of the thermal decomposition was metallic silver. The combined TG-MS analysis showed that the gas products of the thermal decomposition of silver behenate were carbon dioxide, water, hydrogen, acetylene and some small molecule alkenes. TEM and UV–vis spectroscopy were used to investigate the process of the formation and growth of metallic silver nanoparticles.

Application of simultaneous thermal analysis mass spectrometry and stable carbon isotope analysis in a carbon sequestration study

The simultaneous analysis of evolved gases and the determination of stable isotope composition (delta13C) as part of a thermal analysis experiment have been used to (a) distinguish bulk chemical hosts for carbon (C) and nitrogen (N) within a soil and (b) track labelled C within a soil sequestration experiment. C3 and C4 dung was applied to a pasture soil, and soil samples taken for analysis. The results of thermogravimetry-differential scanning calorimetry-quadrupole mass spectrometry-isotope ratio mass spectrometry (TG-DSC-QMS-IRMS) show that the proportion of more refractory C (lignin-like) is greater for the dungs than for the soil organic matter (SOM), and that this increases with time within the soil. Analysis of evolved gases shows that nitrogen is associated with the decomposition of more refractory C, and is not so strongly associated with the labile C component. IRMS analysis distinguished C3 and C4 dung, and allowed the amount of C from these sources to be estimated for the soil samples. Most dung C enters the refractory SOM fraction. This paper demonstrates the potential of TG-DSC-QMS-IRMS in the investigation of SOM.

Thermal properties of starch succinates

Starch succinates are starch derivatives used as binders and thickening agents in foods, tablet disintegrants in pharmaceuticals, surface sizing agents and coating binders in paper. A series of starch esters with different degrees of substitution (DS = 0.008–0.639) prepared by reactive extrusion were studied. Potato, wheat and corn starch were investigated. Thermooxidative behaviour of starch succinates was studied by simultaneous thermal analysis–mass spectrometry (STA–MS) method. The thermal stability of starch esters depends on the degree of substitution (DS). With an increase in DS, thermal stability increases. The major differential thermogravimetric (DTG) peaks are observed below 300 °C. The most abundant ions found are H 2O + and CO 2 +.

Combustion synthesis of lanthanum chromite starting from water solutions: Investigation of process mechanism by DTA–TGA–MS

The mechanism of combustion synthesis of lanthanum chromite was investigated by carrying out simultaneous differential thermal analysis (DTA), thermal-gravimetric analysis (TGA) and quadrupole mass spectrometry measurements (MS). The whole process was found to involve several phenomena: urea and nitrates thermal decomposition, exothermal reactions occurring directly between nitrates and urea as well as between their decomposition products, final reaction between solid oxides. In order to better understand the complex calorimetric, thermal-gravimetric and mass spectrometric curves, the behaviour on heating of each single reagent as well as that of binary mixtures, made by combining urea with each single nitrate, were also studied. Combustion synthesis was performed either under an oxidizing atmosphere or under an inert one. Chemical reactions possibly occurring during this combustion synthesis have been proposed on the basis of MS analysis of gaseous reaction products. The effect of using an excess of sacrificial fuel jointly with the addition of ammonium nitrate was also investigated.