Showing papers on "Thermogravimetric analysis published in 1992"
TL;DR: In this article, the glass transition temperature (Tg) of polyaniline films in emeraldine base form was determined and characterized for the first time to be in the range of ∼ 105-220°C for the films containing ∼ 16-0% of 1-methyl-2-pyrrolidinone (NMP) residual solvent, respectively.
207 citations
TL;DR: In this article, the Weisz modulus is used to distinguish between active and less active nano-silicalite-1 samples using X-ray diffraction, IR, 29Si magic angle spinning nuclear magnetic resonance (MAS NMR), diffuse reflectance electron absorption spectrometry (DREAS), thermogravimetric analysis (TGA), pore volume and particle size measurements are used to characterize these samples.
Abstract: Titanium silicalite-1 samples of different particle size are synthesized. X-ray diffraction (XRD), infrared (IR),29Si magic angle spinning nuclear magnetic resonance (MAS NMR), diffuse reflectance electron absorption spectrometry (DREAS), thermogravimetric analysis (TGA), pore volume and particle size measurements are used to characterize these samples. In the hydroxylation of phenol with hydrogen peroxide large differences in activity are found between different TS-1 samples. Using XRD, IR,29Si MAS NMR, and DREAS measurements it is impossible to differentiate between active and less active samples. Particle size determination (directly by scanning electron microscopy (SEM), Coulter Counter, and Malvern and indirectly by TGA and adsorption measurements) however can explain these differences. Smaller particles are more active than larger particles. From calculations of the Weisz modulus it can be concluded that large zeolite particle are not fully utilized because of pore diffusion limitations. The product distribution is also influenced by particle size.
179 citations
TL;DR: In this paper, the effects of sodium alginate on the physical properties of fibroin membranes, such as rupture elongation, rupture strength, water absorption, and thermal properties, were investigated.
Abstract: The effects of sodium alginate on the physical properties of fibroin membranes, such as rupture elongation, rupture strength, water absorption, and thermal properties, were investigated. The experimental results showed the β-form crystal and β-form molecular conformation increased due to the increase of intermolecular hydrogen bonds, such as CO---HN and CO---HO. The kind of intermolecular interaction and β-form molecular conformation of polymer blends were clarified by 13C–NMR and infrared spectroscopy. The increase in β-form crystal was examined by X-ray analysis. Further, membranes were characterized by thermogravimetric analysis (TGA) and by determining their water contents and tensile properties.
151 citations
TL;DR: In this article, the authors studied the heterogeneous reduction of NO by carbon in a thermogravimetric analysis system, employing both pseudosteady and transient reaction methods, at temperatures from near ambient up to 1073 K, and at NO partial pressures in the range 1.01-10.1 kPa.
Abstract: The heterogeneous reduction od NO by carbon was studied in a thermogravimetric analysis system, employing both pseudosteady and transient reaction methods. The reaction was studied at temperatures from near ambient up to 1073 K, and at NO partial pressures in the range 1.01-10.1 kPa. A relatively pure carbon derived from phenolic resin was studied. gaseous products of rection were measured. The gasification of carbon by NO involves two parallel processes: (1) somewhat slow desorption of relatively stable surface complexes; (2) processes involving NO attack on active unoccupied sites that results in essentially immediate desorption of gaseous products. The first process controls the overall gasification rate at lower temperatures and is governed by a distribution of desorption activation energies, involving mainly surface oxides that yield CO upon desorption
141 citations
ENEA1
TL;DR: In this paper, spherical powders of hydroxyapatite with particle diameters below 100 μm were prepared using the water extraction variant of the sol-gel process using a freshly prepared solution of calcium acetate and phosphoric acid (molar ratio Ca/P = 1.67) was emulsified in dehydrated 2ethyl-1-hexanol.
Abstract: Spherical powders of hydroxyapatite with particle diameters below 100 μm were prepared using the water extraction variant of the sol-gel process. A freshly prepared solution of calcium acetate and phosphoric acid (molar ratio Ca/P = 1.67) was emulsified in dehydrated 2-ethyl-1-hexanol. Drops of the emulsion were solidified by extraction of water with this solvent. The process was carried out continuously. The separated gel particles were calcined to hydroxyapatite particles with preservation of the spherical shape. This process was studied using differential thermal analysis, thermal gravimetric analysis, X-ray diffraction analysis and infrared spectroscopy. During thermal treatment, the formation of calcium carbonates is observed first. Above 400°C, the formation of hydroxyapatite starts and then at 580°C formation of carbonate hydroxyapatite starts. The last step, decomposition to hydroxyapatite, proceeds above 750°C.
95 citations
TL;DR: In this paper, structural and surface features of powder iron-doped titania photocatalysts have been investigated by applying a variety of complementary techniques: temperature programmed desorption-mass spectrometry analysis, non-isothermal thermogravimetric analysis, differential thermoanalysis, infrared spectroscopy, scanning electron microscopy and X-ray diffraction analysis.
Abstract: Some additional contributions to structural and surface features of powder iron-doped titania photocatalysts have been investigated by applying a variety of complementary techniques: temperature programmed desorption-mass spectrometry analysis, non-isothermal thermogravimetric analysis, differential thermoanalysis, infrared spectroscopy, scanning electron microscopy and X-ray diffraction analysis. The effects of iron concentration and pretreatment temperature, over the polymorphic transformation anatase-rutile, were analysed. The results obtained were used in an attempt to correlate structural and surface aspects of catalysts, with their reported activity versus inactivity to photoreduce dinitrogen to ammonia.
94 citations
TL;DR: In this paper, the mechanism of the thermal decomposition of tetraethylammonium (TEA) in zeolite was investigated under air and argon atmosphere using a combined technique of thermogravimetric analysis and mass spectrometry.
Abstract: The mechanism of the thermal decomposition of tetraethylammonium (TEA) in zeolite {beta} has been investigated under air and argon atmosphere using a combined technique of thermogravimetric analysis and mass spectrometry. The nature of the volatile products and the characterization of the solid after each thermal phenomenon shows that all TEA species, occluded ion pairs and counteranions, decompose into triethylamine and ethylene in a single step, in the temperature range 200-350{degrees}C. The amine readsorbs on the acidic sites of the zeolite and, as the temperature is increased, decomposes into lighter amines by sequential Hofmann elimination reactions. Part of the ethylene also reacts with the acid sites yielding aliphatic and aromatic hyrocarbons. Complete desorption of the organic species form the structure requires a temperature higher than 500 {degrees}C. 14 refs., 5 figs., 8 tabs.
93 citations
TL;DR: In this article, nitrogen-containing carbons were prepared by carbonization of sucrose with additions of urea, glucosamine hydrochloride, uracil, hydroxymethyl pyridine, or picolylamine.
75 citations
TL;DR: In this article, a polymeric steric stabilizer based on a polyvinylpyrrolidone copolymer was used for the synthesis of polyaniline colloids.
67 citations
TL;DR: In this article, a hydroxoperoxo compound of Zr and Ti (HXPZT) was prepared as a reactive powder by a sol-gel method, and X-ray diffraction and SEM studies showed it was formed from small (ca. 10-15 μm) amorphous particles.
Abstract: A hydroxoperoxo compound of Zr and Ti (HXPZT) was prepared as a reactive powder by a sol-gel method. X-ray diffraction and SEM studies showed it to be formed from small (ca. 10–15 μm) amorphous particles. The effects of progressive thermal treatment were determined by differential thermal analysis, thermogravimetric analysis, temperature programmed desorption, X-ray diffraction, energy-dispersive spectrometry and SEM. The features observed have been attributed to the removal of physically and chemically bonded water and of some nitrogen-containing compound. Crystallization of zirconium titanate occurs at low temperature (650 °C), giving rise to spherical (ca. 2 μm dia.) regular particles.
67 citations
TL;DR: Thermal expansion changes and exothermic reactions with temperature indicate secondary cure during postcure heating, and thermally-induced decomposition occurs in multiple stages indicating presence of different structural species in the resin matrix.
Abstract: Summary
Selected commercial and experimental composites and resin systems have been evaluated by thermal analysis techniques of Differential Scanning Calorimetry, Thermogravimetric Analysis and Thermomechanical Analysis. Important thermal data such as heat of cure, coefficient of thermal expansion, dimensional changes over selected temperature ranges, filler weight percent, onset temperature of decomposition, temperature of peak decomposition rate, temperature of the end of decomposition, etc. have been determined. Heat of cure, thermal expansion coefficient and dimensional changes appear to follow an inverse linear regression fit with filler fraction in the composite. Thermal expansion changes and exothermic reactions with temperature indicate secondary cure during postcure heating. The thermally-induced decomposition occurs in multiple stages indicating presence of different structural species in the resin matrix.
TL;DR: In this article, the thermal decomposition of manganese(II) acetate tetrahydrate was studied using isothermal and dynamic thermogravimetric techniques, and it was shown that the reactions are best described by the phase boundary and random nucleation models.
TL;DR: In this paper, the adsorption and reaction of isopropylamine has been studied using temperature-programmed desorption (TPD) and thermogravimetric analysis (TGA) on a series of silica-alumina catalysts as a function of alumina content, and the results have been correlated with cracking activities for n -hexane.
TL;DR: In this article, the transition-metal dichalcogenide solid solution is isolated by simply washing away the byproduct salt, and powder X-ray diffraction and thermogravimetric analyses of the solid solutions are performed.
Abstract: Solid-solution transition-metal dichalcogenides, traditionally synthesized from the elements at elevated temperatures over long periods of time, can now be prepared from rapid self-propagating reactions between transition-metal halides and alkali-metal mixed chalcogenides such as Na 2 (S,Se). The transition-metal dichalcogenide solid solution is isolated by simply washing away the byproduct salt. Powder X-ray diffraction and thermogravimetric analyses of the solid solutions
TL;DR: The thermal decomposition of 5-aminotetrazole (5-AT) has been studied by thermogravimetry, thermal volumetric, DSC, DTA and EGA as mentioned in this paper.
TL;DR: In this article, a superabsorbent polymers based on guargum have been prepared through a graft-copolymerization reaction using acrylonitrile as the monomer by a gamma ray-induced irradiation technique.
Abstract: Superabsorbent polymers based on guargum have been prepared through a graft-copolymerization reaction using acrylonitrile as the monomer by a gamma ray-induced irradiation technique. Various grafting parameters have been studied. The grafted products have been characterized using infrared spectroscopy, thermogravimetric, and differential thermal analysis. The thermograms reveal the superior thermal stability of the grafted product over the control at all stages of its degradative cycle. The maximum absorbency obtained of the superabsorbent product was around 300 g/g.
TL;DR: The new phosphate ca 2 V(PO 4 )(HPO 4 ) 2.H 2 O and the dehydrated compound Ca 2 V (PO4 )(P 2 O 7 ) have been synthesized hydrothermally at 230 and 450 o C, respectively, and characterized by single-crystal X-ray diffraction and thermogravimetric analysis.
Abstract: The new phosphate ca 2 V(PO 4 )(HPO 4 ) 2 .H 2 O and the dehydrated compound Ca 2 V(PO 4 )(P 2 O 7 ) have been synthesized hydrothermally at 230 and 450 o C, respectively, and characterized by single-crystal X-ray diffraction and thermogravimetric analysis
TL;DR: In this article, a combination of meltblending and hot-drawing was used to combine a wholly aromatic copolyester KU-9211 (also called K161 from Bayer A.G.) and an aliphatic containing LCP (liquid crystalline polymer) PET/PHB60 (from Kodak Tennessee Eastman).
Abstract: Thermotropic LCP/LCP fiber blends were prepared by a combination of meltblending and hot-drawing, using a wholly aromatic copolyester KU-9211 (also called K161 from Bayer A.G.) and an aliphatic containing LCP (liquid crystalline polymer) PET/PHB60 (from Kodak Tennessee Eastman). Morphological evidence, including scanning electron (SEM) and transmission electron microscopy (TEM), showed that the dispersed phase consisted primarily of highly oriented, 0.5 to 2 μm diameter rigid-rods of aromatic fibers imbedded in a matrix of predominantly aliphatic LCP fibrils with diameters in the range of 20 to 50 nm. An interphase of approximately 50 nm strongly bonded the two phases together. The fiber blends were characterized using dynamic mechanical thermal analysis (DMTA), thermogravimetric analysis (TGA), gas chromotography/mass spectroscopy (GC/MS), and rheological measurements. It appears that the processing conditions employed for melt blending had caused PET/PHB60 to undergo chain scission, thereby creating chemical interactions between the two LCP components during the melt blending process. Differential scanning calorimetry (DSC) thermograms as well as nuclear magnetic resonance (NMR) spectra of the extracted fraction from the mixture of 30 wt% K161/70 wt% PET(PHB60) confirmed the chemical interaction between the two thermotropic liquid crystalline polymers.
TL;DR: In this paper, the pyrolysis under argon of three polysiloxane gels, MeSiO1.5, PhSiO 1.5 and crosslinked oligovinylsiloxanes, was investigated by 29Si solid-state NMR and thermogravimetric analysis coupled to mass spectrometry.
Abstract: The pyrolysis under argon of three polysiloxane gels, MeSiO1.5, PhSiO1.5 and crosslinked oligovinylsiloxane, was investigated by 29Si solid-state NMR and thermogravimetric analysis coupled to mass spectrometry. Above 500–600°C, redistribution reactions involving the exchange of Si-C and Si-O bonds take place, which lead to a random environment of the silicon atom at 1200°C. The use of oligovinylsiloxanes crosslinked by hydrosilation leads to high yields of silicon oxycarbide glasses with an O/Si ratio close to 1.
TL;DR: In this article, thermogravimetric analysis of poly(dimethylsiloxane) elastomers that had been filled with in situ precipitated silica was performed under nitrogen and in air.
Abstract: Poly(dimethylsiloxane) elastomers that had been filled with in situ precipitated silica were studied by thermogravimetric analysis, under nitrogen and in air. Both types of measurements indicated that the filler raises the temperature of thermooxidative degradation of the polymer, possibly by inactivating the terminal OH groups on the chains. Commercial fume silica was found to cause more severe degradation problems than did the in situ precipitated silica. In all cases, the degradation was more pronounced in air than in the inert atmosphere provided by nitrogen. © 1992 John Wiley & Sons, Inc.
TL;DR: In this article, conducting polypyrrole films with p-toluenesulphonate, perchlorate and tetrafluoroborate dopants were aged at elevated temperatures in oxidizing and inert environments.
TL;DR: In this article, the mechanism of oxidation resistance in SiC-coated carbon-carbon composites containing boron-based inhibitors has been investigated using thermodynamic calculations, thermogravimetric analysis, and electron microscopy.
Abstract: The mechanism of oxidation resistance in SiC-coated carbon-carbon composites containing boron-based inhibitors has been investigated using thermodynamic calculations, thermogravimetric analysis, and electron microscopy. A model is developed based on the formation of a volatile B2O2 sub-oxide in the interior of the composite which condenses to B2O3 upon encountering a locally high oxygen partial pressure in coating cracks. The active-to-passive transition for the oxidation of elemental boron has been determined.
TL;DR: In this paper, the catalytic behavior of the copper on alumina sorbent-catalyst in NO reduction with NH 3 /O 2 during the simultaneous oxidation-adsorption of SO 2 was studied in a series of consecutive cycles of reaction-regeneration and as a function of the surface coverage with sulfate species.
Abstract: The catalytic behavior of the copper on alumina sorbent-catalyst in NO reduction with NH 3 /O 2 during the simultaneous oxidation-adsorption of SO 2 was studied in a series of consecutive cycles of reaction-regeneration and as a function of the surface coverage with sulfate species. The behavior of a CuO/SiO 2 system with simultaneous DeSO x /DeNO x reaction is also reported. Tests of thermal desorption for the analysis of residual adsorbed species after reaction and thermogravimetric tests of ammonia adsorption also were carried out
TL;DR: In this paper, anionic ring opening polymerization of 1-methyl-1-silacyclobutane, 1-phenyl- 1-silaclobutanes and 1-silia-clobutsane co-catalyzed by n-butyllithium and hexamethylphosphoramide (HMPA) in THF at-78°C yields poly(1-methyl, 1 -silabutane), poly(phenyl, 1 −silacclobuttane) and poly( 1 −sia-cl
Abstract: Anionic ring opening polymerization of 1-methyl-1-silacyclobutane, 1-phenyl-1-silacyclobutane and 1-silacyclobutane co-catalyzed by n-butyllithium and hexamethylphosphoramide (HMPA) in THF at-78°C yields poly(1-methyl-1-silabutane), poly(1-phenyl-1-silabutane) and poly(1-silabutane) respectively. These saturated carbosilane polymers possess reactive Si-H bonds. They have been characterized by 1H, 13C and 29Si NMR as well as FT-IR and UV spectroscopy. Their molecular weight distributions have been determined by gel permeation chromatography (GPC), thermal stabilities by thermogravimetric analysis (TGA) and glass transition temperatures (Tg) by differential scanning calorimetry (DSC).
TL;DR: In this paper, the surface morphology of single-phase microemulsions was examined using scanning electron microscopy (SEM) and the pore size distribution (PSD) was obtained using a high-resolution low-temperature DSC technique.
TL;DR: In this paper, the kinetic parameters of dehydrochlorination (DHCL) process of PVC and PVC mixed with different amount of ZnCl2 have been determined by using thermogravimetric analysis.
Abstract: The kinetic parameters of dehydrochlorination (DHCL) process of PVC and PVC mixed with different amount of ZnCl2 have been determined by using thermogravimetric analysis. These values have been compared with those obtained by using UV-visible spectroscopic analysis of PVC film containing ZnCh degraded at different temperatures. The values of apparent activation energy (Ea) decreases with the increase of the amount of ZnCl2 and the values obtained in the present work are in reasonable comparison with previous works. The catalytic effect of ZnCl2 on PVC DHCL process is explained here.
TL;DR: In this paper, the synthesis of polyaniline colloids using a new polymeric steric stabiliser of narrow molecular weight distribution based on poly(ethylene oxide) is reported.
Abstract: The synthesis of polyaniline colloids using a new polymeric steric stabiliser of narrow molecular weight distribution based on poly(ethylene oxide) is reported. This model stabiliser contains one tertiary amine group per polymer chain which is believed to participate in the in situ aniline polymerisation, leading to the chemical grafting of the stabiliser onto the surface of the polyaniline particles.These polyaniline colloids were characterised by a wide range of techniques including electron microscopy, FTIR and visible absorption spectroscopy, microanalysis, d. c. conductivity and thermogravimetric analysis. The colloids possess a polydisperse non-spherical morphology and remarkably high solid-state electrical conductivity (0.1–1.0 S cm–1), despite the presence of the electrically insulating grafted stabiliser. The mass ratio of grafted stabiliser : polyaniline was determined indirectly by 1H NMR spectroscopy analysis of the post-reaction supernatant solutions. In addition, flocculation experiments were carried out to assess the aggregation stability of these dispersions in the presence of added electrolyte.
TL;DR: In this article, the thermal decomposition of four aryl-alicyclic polyimides was studied by thermogravimetry/mass spectrometry and pyrolysis-gas chromatography/mass analyzer.