Showing papers on "Thermogravimetric analysis published in 1983"

Thermal degradation of poly(ethylene terephthalate): A kinetic analysis of thermogravimetric data

Abstract: The thermal decomposition of poly(ethylene terephthalate) has been studied using a conventional dynamic thermogravimetric technique in a flowing air atmosphere at several heating rates between 0.1°C and 100°C/min. The dynamic thermogravimetric analysis curve and its derivative have been analyzed using a variety of analytical methods reported in the literature to obtain information on the kinetic parameters. The degradation was found to be a complex process composed of at least three overlapping stages for which kinetic values can be calculated. The best approaches to solving the kinetics of the decomposition were found to be the multiple heating rate techniques of Friedman and Ozawa. The Friedman technique gave apparent activation energies (kJ/mol) for the three main decomposition stages of 122.2 ± 12.9, 201.0 ± 8.5, and 141.9 ± 12.7, with a value of 85.5 ± 10.2 for the prestage at low conversion. The Ozawa method, meanwhile, gave values of 101.6 ± 2.6, 182.6 ± 7.4, 142.5 ± 3.8, and 158.4 ± 26.1 for the prestage.

Addition polyimides. I

Abstract: Crosslinking of 4,4′(bismaleimido)diphenyl ether (BM) was investigated in presence of bis(m-aminophenyl)methylphosphine oxide (BAP), tris(m-aminophenyl)phosphine oxide (TAP), diaminodiphenyl ether (E) and 3,3-bis(p-aminophenyl)phthalide (AP). These crosslinked resins were examined for thermal stability by thermogravimetric analysis. A slight decrease in initial decomposition temperature, the temperature of maximum rate of weight loss, was observed, though the char yield in nitrogen atmosphere at 800°C did not change appreciably. Glass-cloth-reinforced laminates were fabricated from BM and amine mixtures. An improvement in mechanical properties was observed in the presence of phosphorus-containing di- and triamines.

Study of the clay effect on crude oil combustion by thermogravimetry and differential scanning calorimetry

Abstract: Thermogravimetry (TG) and differential scanning calorimetry (DSC) were used to study the effect of sand, silica and kaolinite on crude oil combustion. Three distinct regions, namely distillation and two combustion/cracking regions were observed on all TG curves. Thermogravimetric curves were analyzed using an Arrhenius-type kinetic model and a ratio method to obtain kinetic parameters. Activation energy and reaction order were obtained from this analysis. The reaction order seemed to be insensitive to the presence of granular materials. However, a significant reduction of activation energy was caused by addition of kaolinite to the crude oil, indicating that the kaolinite had a catalytic and surface area effect on crude oil combustion/cracking reactions.

Spin coated amorphous chalcogenide films: Thermal properties

Abstract: The annealing behavior of spin coated thin films prepared from solutions of As2S3 dissolved in n‐propylamine and n‐butylamine has been investigated using IR, mass spectrometry, thermogravimetric analysis, and scanning calorimetry. As prepared films containing arsenic sulfide glass domains with surfaces reacted as alkyl ammonium salt undergo loss of amine and hydrogen sulfide during heating. H2S removal is believed to be accompanied by cross linking of glass domains resulting in a network glass containing only arsenic and sulfur.

Thermogravimetric examination of the dehydration of calcium nitrate tetrahydrate under quasiisothermal and quasi-isobaric conditions

Abstract: The progressive nature of the process of dehydration of Ca(NO3)2·4 H2O has been shown not to be due to consecutive decomposition reactions, as believed so far, but is the result of various physical processes, such as the incongruent melting of the material, the boiling and evaporation of the unsaturated or saturated solution formed, as well as the crust formation and drying of the surface of the solidifying residue. The quasi-isothermal-quasiisobaric thermogravimetric technique and the phase diagram of the Ca(NO3)2-H2O system were used to evaluate the results.

A study of the kinetics of high-temperature carbon-silica reactions in an ablative polymer composite

Abstract: The kinetics of high-temperature carbon-silica reactions for a widely used glass-filled phenolic resin have been studied. Weight-loss and rate-of-weight-loss data were obtained at four heating rates ranging from 5 to 50°C per minute using standard thermogravimetric techniques. Experimental data were obtained at temperatures between 30 and approximately 1700°C. The kinetic parameters were calculated from these data using a multiple heating rate technique. Close agreement was obtained between the fractional weight loss calculated using the kinetic parameters and the measured values.

Synthesis, characterization, and study of thermal properties of methyl-substituted arylene sulfone ether polyimides, polyamides, and poly(amide–imides)†

Abstract: A number of methyl-substituted bis[(phenyleneoxy) sulfone] dianilines were synthesized and reacted with pyromellitic dianhydride (PMDA), benzophenone tetracarboxylic acid dianhydride (BTDA), terephthaloyl chloride (TPC), isophthaloyl chloride (IPC), and trimellitic anhydride acid chloride (TMAC) to prepare a series of polyimides, polyamides, and poly(amide–imides), respectively. Low temperature solution and interfacial polymerization techniques were utilized to prepare the above polymers. Most of the polymers prepared formed tough, transparent flexible films. The prepared polymers were characterized by solution viscosity, thermal gravimetric analysis (dynamic and isothermal), and differential scanning calorimetry. The effect of the number and the ring substitution of methyl groups on polymer properties is discussed.

Thermal stability of grafted fibers

Abstract: Presented the experimental results on the study of thermal stability of grafted fibers, i.e., polypropylene-, polyester-, and rayon-grafted fibers. These fibers were obtained by radiation grafting processes using hydrophylic monomers such as 1-vinyl 2-pyrolidone, acrylic acid, N-methylol acrylamide, and acrylonitrile. The thermal stability of the fibers was studied using a Shimadzu Thermal Analyzer DT-30. The thermal stability of the fibers, which can be indicated by the value of the activation energy for thermal degradation, was not improved by radiation grafting. The degree of improvement depends on the thermal stability of the monomers used for grafting. The thermal stability of a polypropylene fiber, either a grafted or an ungrafted one, was found to be inferior compared to the polyester of a rayon fiber, which may be due to the lack of C=O and C=C bonds in the polypropylene molecules. The thermal stability of a fiber grafted with acrylonitrile monomer was found to be better than that of an ungrafted one. However, no improvement was detected in the fibers grafted with 1-vinyl 2-pyrrolidone monomer, which may be due to the lower thermal stability of poly(1-vinyl-2-pyrrolidone), compared to the polypropylene or polyester fibers. 17 figures, 3 tables.

Effects of preparation procedure on the surface properties of rhodium supported on γ-alumina

Abstract: The decomposition of rhodium(III) nitrate, chloropentamminerhodium(III) chloride and rhodium(III) sulphite in atmospheres of hydrogen, nitrogen and nitrogen (80%)+ oxygen (20%) have been investigated by thermogravimetric analysis with the salts either pure or impregnated onto a γ-alumina support. The decomposition of rhodium(III) sulphite failed to give dispersions of rhodium metal on alumina but the reduction of the other salts to Rh0 was complete in nitrogen or hydrogen at temperatures between 400 and 690 K.Hydrogen and CO uptake data have shown that rhodium(III) nitrate led to a more finely divided dispersion of metal than did chloropentamminerhodium(III) chloride. Infrared spectra of CO absorbed on the Rh/Al2O3 dispersions were consistent with this conclusion. The effects of sintering and oxygen adsorption on the infrared spectra are reported. Linear and bridge-bonded CO were formed on exposed metal planes or two-dimensional rafts at Rh0 sites which were also active for the chemisorption of oxygen. Gem-dicarbonyl species were formed at monatomically dispersed rhodium sites or edge sites in rafts, both of which had cationic character through interaction with the alumina support. These sites were not active for the adsorption of oxygen.

Microstructure and stability of iron chloride graphites

Abstract: Two methods have been used to prepare iron chloride intercalates of natural graphite. Ferric chloride intercalates are demonstrated to be both extremely air sensitive and also to undergo gradual physical and chemical changes upon storage, solvent treatment, heating and washing. Gradual interconversion to higher staging or direct de-intercalation are the two observed reaction pathways.The ferrous chloride intercalates (obtained by H2 reduction) are found to be even more air sensitive than their ferric precursors, decomposing to yield disordered graphite and crystalline iron chloride hydrates and oxyhydrates. The Mossbauer spectrum of FeCl3 graphite was found to consist of two singlets (δ1= 0.47 mm s–1 and δ2= 0.61 mm s–1), giving rise to two different quadrupole doublets in the FeCl2 intercalate. High-resolution transmission electron microscopy confirms earlier results and regular first-stage intercalate is imaged for the first time. The discussion of the results is based on an island-structured intercalate and a stabilising influence of chemisorbed Cl2 and/or HCl.The limitations of different techniques to the study of graphite intercalates (including Mossbauer spectroscopy, X-ray powder diffraction, thermogravimetric analysis, weight-uptake measurements and electron microscopy) are discussed.

High‐temperature resins based on aromatic amine‐terminated bisaspartimides

Abstract: Various 4,4′-bis{N2-[4-(4-aminophenoxy)phenyl]aspartimido}diphenylmethane (APADM)-type precursors were synthesized by Michael-type reaction of an aromatic bismaleimide (1mol) with an aromatic diamine (2 mol) in an aprotic solvent. The structures of these materials were characterized by using Fourier-transform infrared (FT-IR), 1H nuclear magnetic resonance (NMR) and 13C-NMR; their curing behaviors and thermal stabilities were evaluated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The thermal polymerization of APADM by heating it above its melting temperature produced a tough polymer. From these preimidized precursors, graphite-fiber laminates were prepared and their mechanical properties evaluated. To elucidate the thermal curing mechanism and the structure of the polymer, a model compound, N-[4-(4′-aminobenzyl) phenyl] aspartimidobenzene was synthesized. The gas-chromatographic mass spectra of these compounds has suggested a mechanism for their decomposition. The structure of the polymer also was studied by using FT-IR and 1H-NMR.

Bis‐, tris‐, and tetrakis‐maleimidophenoxy‐triphenoxycyclotriphosphazene resins for fire‐ and heat‐resistant applications

Abstract: Novel fire- and heat-resistant polymers was obtained by the thermal polymerization of various maleimidophenoxy-triphenoxycyclotriphosphazenes. These polymers, in which the cyclic triphosphazene structure is preserved, have thermal stability to 350°C and char yields of 82–78% at 800°C in nitrogen and 78–71% at 700°C in air. Two groups of monomers were synthesized by reacting tris(4-aminophenoxy)-tris(phenoxy)cyclotriphosphazene with maleic anhydride alone or in combination with benzophenonetetracarboxylic or pyromellitic dianhydride. The structures of cyclic phosphazene-trimeric precursors and the polymers were characterized by Fourier-transform infrared, proton nuclear magnetic resonance, and elemental analysis. The thermal stabilities of the polymers were evaluated by thermogravimetric analysis.

A new solid‐phase polymerization—metal phthalocyanine sheet polymers

Abstract: The thermal reactions of pure metal(11) 4,4′,4″,4′″-phthalocyanine-tetracarboxylic acids of copper, cobalt, and nickel at 350–400°C in vacuum have been studied using Fourier transform infrared spectrometry, gas chromatography, and mass spectrometry. Based on these observations, novel in situ reactions for the synthesis of heat-resistant phthalocyanine “sheet” polymers are described. The poly(metal phthalocyanine) polymers of copper, cobalt, and nickel so synthesized have been characterized by elemental analysis, infrared spectroscopy, and dynamic thermogravimetric analysis. The most noteworthy property of these polymers is their extreme resistance to heat in an anaerobic atmosphere and their high char yields (89–93%) at 800°C in a nitrogen atmosphere.

Oxygen Potential of U0.85Zr0.15O2+x Solid Solutions at 15000°C

Abstract: Oxygen potentials for U0.85Zr0.15O2+x solid solutions with the fluorite structure (prepared at 1500°C) were measured at 1500°C by a thermogravimetric technique. The oxygen potentials were 12 to 20 kJ/mol lower than those of pure UO2+x at a given oxygen-to-metal ratio; they cannot be represented as a function of mean uranium valence.