Showing papers on "Thermogravimetric analysis published in 1986"

Solventless polyimide films by vapor deposition

Abstract: Vapor deposition polymerization (VDP) has been employed for the preparation of polyamic acid/imide films using a conventional thin film evaporator with a novel source design. The process utilizes the coevaporation of the dianhydride and diamine precursors. Control of source effusion rates permit film stoichiometry to be held to better than 1 mol %. Infrared, electron spectroscopy for chemical analysis (ESCA), and thermogravimetric analysis (TGA) results are consistent with the interpretation that the VDP films produced are polyamic acid curable to polyimide. The weight average molecular weight of the polyimide as determined by low angle light scattering (LALS) technique is 13 000, in agreement with the value estimated from the measured percent elongation at break point. Lift‐off tests showed that vapor deposited polyimide is more resistant to hydrolitic attack at the silicon interface than spin coated Dupont RC5878. Dielectric constant (e=2.91) and dissipation factor (tan δ=0.008) are lower than those rep...

Molten bisphenol‐A polycarbonate‐poly(ethylene terephthalate) blends. I. Identification of the reactions

Abstract: This paper is devoted to the study of the reactions taking place in molten bisphenol-A polycarbonate-poly(ethylene terephthalate) mixtures. The analysis of the reaction products by infrared, proton and nuclear magnetic resonance spectroscopy, and by thermogravimetric analysis shows that the main reaction is an exchange reaction identical to that occurring in bisphenol-A polycarbonate-poly(butylene terephthalate) mixtures. However, some other reactions consecutive to this exchange reaction also take place, probably resulting from the instability of the ethylene carbonates produced by transesterification.

Synthesis of Ultrafine Silicon Carbide Powders in Thermal Arc Plasmas

Abstract: Ultrafine s-SiC powders are synthesized in thermal plasmas by a reaction between methane and silicon monoxide. The reaction is carried out in an unconfined plasma jet (22.5 kW) operating at atmospheric Ar pressure. High temperatures (> 10 000 K) combined with ultrarapid quench rates (? 106 K/s) of the plasma lead to a high degree of supersaturation of the chemical vapor, resulting in homogeneous nucleation of ultrafine particles. Product characterizations are pursued with X-ray diffraction analysis, X-ray photoelectron spectroscopy (XPS), scanning, and transmission electron microscopy. The maximum SiC yield determined by thermogravimetric analysis (TGA) is 97.3 percent. Particle size analyses show a bimodal distribution with the majority of the particles falling in a size range from 2 to 40 nm. Triangular and hexagonal SiC particles are observed throughout this work and the nucleation and growth of these particles are discussed.

Evaluation of Gravimetric Methods for Dissoluble Matter in Extracts of Environmental Samples

Abstract: A number of gravimetric methods were evaluated for the determination of dissolved matter in solvent extracts of combustion samples. The methods described included thermogravimetric analysis, weighing after evaporation under nitrogen, and a microscale evaporation method developed in this study. A well characterized combustion sample, known to consist primarily of alkylated bicyclic and tricyclic aromatic compounds, served as a reference material. Results for the three methods are presented and compared. Although the thermogravimetric analyzer was found to be accurate and versatile, a good compromise between cost, time and accuracy was provided by the microscale evaporation method.

Wholly aromatic polyamide‐hydrazides. IV. Structure–property relationships for polymers containing p‐phenylene and m‐phenylene units

Abstract: A series of wholly aromatic polyamide-hydrazides was investigated in order to acquire clear understanding of the influence exerted by controlled structural variations in these polymers upon some of important properties, such as chain flexibility, membrane permselectivity, and thermal as well as thermo-oxidative stability. For that reason, the content of para and meta phenylene units was varied within this series so that the changes in the latter were 12.5 mol % from polymer to polymer, starting from an overall content of 0–50 mol %. The polymers were prepared by a low-temperature solution polycondensation reactin of p-aminobenzhydrazide (ABH) and terephthaloyl chloride (TCI), isophthaloyl chloride (ICI), and their appropriate combinations in N,N-dimethylacetamide (DMA) as solvent and all of these preparations were monitored viscometrically in order to prepare the products with as similar as possible average molecular weights. Polymer structures were characterized by elemental analysis, infrared spectrometry, and 13C NMR spectroscopy, while their molecular weights were determined by light scattering and dilute-solution viscometry. Polymer properties were evaluated by solution viscometry, reverse osmosis tests, and thermal gravimetric analysis. The results obtained during the preparation of these materials, their subsequent structural characterization, and their property evaluations are discussed. They clearly indicate that substitution of m-phenylene units for p-phenylene ones within this polymer series led to an increase in polymer chain flexibility (from what is usually referred to as semiflexible or semirigid to typically flexible macromolecules), disrupted selectivity of the asymmetric thin membranes under reverse osmosis conditions and decreased stability at elevated temperatures in inert as well as in oxidative atmospheres.

The Role of Thermal Analysis Techniques in the In-Situ Combustion Process

Abstract: Thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) studies were conducted on two Lloydminster heavy oil cores, extracted oil and mineral matter. The order of reaction was adjusted to best fit the data in nonisothermal kinetic analysis. The values of the order of reaction used and estimated activation energies, preexponential factors and rate constants for overall reactions occurring in appropriate temperature regimes are listed. A general schematic of the thermal processes, such as evaporation, distillation, thermolysis, low temperature oxidation, thermal cracking, combustion, coking, polymerization and thermal alteration of mineral matter, is depicted. The fuel contents in the core samples were determined from the TGA weight loss curves. The data generated by DSC and TGA experiments were used to calculate enthalpy values and ignition temperatures. Data suggests that heat generated by LTO reactions is significant during in situ combustion. Thermal alteration of the mineral matter at 600/sup 0/ and 900/sup 0/C was significant. The percentage of fine particles, <2..mu.., doubled at 600/sup 0/ and 900/sup 0/C compared to the mineral extracted at 100/sup 0/C. Although kaolinite constituted 65% of the fine particles in the extracted sand, it was not detected when the sand was heated at 600/sup 0/ or 900/supmore » 0/C. These results indicate potential production problems resulting from the migration of fine particles. The data obtained from the two reservoirs studied suggest that swelling of clays during wet combustion may not be sufficient to have a deleterious effect on air/water injectivity. It is apparent that the results generated by TGA/DSC experiments are complementary to those obtained by combustion tube tests and provide the kinetic, thermal and mineralogical data required for numerical simulation, planning and design of an in situ combustion project.« less

Block copolymers of poly(ethylene terephthalate–polybutylene terephthalate). I. Preparation and crystallization behavior

Abstract: Block copolymers of two crystallizable compounds, poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT), were developed with PET as the major component and the amount of PBT varying from 1.0 to 20.0 wt %. These block copolymers were prepared by end-group coupling of preformed oligomers. All polymers prepared were of equivalent molecular weight as determined by the intrinsic viscosity method. Thermal properties were determined by differential thermal analysis (DTA), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). With increasing PBT content, the block copolymers showed a general decrease in the values of glass transition temperature, melting temperature, initial decomposition temperature, and maximum decomposition temperature. The heat of fusion and heat of crystallization first increased and then decreased slightly. Rates of crystallization were determined by measuring density as a function of time of isothermal crystallization carried out at 95°C. It was found that small amounts of PBT increased the crystallization rate considerably over that of PET. Random copolymers did not show this phenomenon and behaved more like pure PET. The crystallization behavior of block copolymers was analyzed by the Avrami equation and Avrami exponents were determined. Results were explained on the basis that the faster-crystallizing PBT blocks crystallized first and provided built-in nucleation sites for the subsequent crystallization of PET, thus resulting in a relatively fast-crystallizing copolyester.

Characterization and thermal behaviour of gel grown mixed rare-earth (Didymium) tartrate crystals

Abstract: Sherulites, crystal aggregates and platelets of Di2 (C4H4O6)3 · 5H2O mixed crystals were grown in gel using the single tube diffusion method. The material was characterized by using different techniques such as chemical analysis, EDAX, X-ray and electron diffraction, infrared and mass spectroscopy. The thermal behaviour of the material was studied using differential thermal analysis, DTG, thermogravimetric analysis and differential scanning calorimetry. The material is thermally unstable and starts decomposing at 50‡ C. Thermal analysis results indicate the application of the contracting cylindrical kinetic model for the solid state reactions involved in the decomposition process. The values of kinetic parameters, e.g. order of reaction, activation energy and frequency factor are worked out. The implications are discussed.

High pressure synthesis and characterization of molybdenum disulphide

Abstract: Polycrystalline molybdenum disulphide has been grown by high pressure (about 54.88 × 106 N m−2) reduction of molybdenum trisulphide and characterized by various physicochemical methods. The chemical analysis of the compound established a sulphur to molybdenum ratio of 2, which was also confirmed by thermogravimetric analysis in air. The X-ray data was found to be consistent with 2H-MoS2, n-type conductivity (S = −275 μV °C−1) and diamagnetic behaviour ( χ m = −0.049 × 10 −6 c.g.s. e.m.u.). It is a semiconducting material with a room temperature conductivity of of 1.2 × 10 −4 Ω −1 cm −1 and an activation energy of 0.124 eV in the temperature range 150–300 K. A band gap of 0.95 ± 0.02 eV was found from optical absorption studies on a thin MoS2 film. Thermal studies of MoS2 in an argon atmosphere has shown its stability up to 1200 °C and thereafter it decomposes to Mo2S3. A model has been proposed which describes the thermal behaviour of MoS2 when heated at various temperatures up to 1200 °C and is based on the appearance of lines in X-ray powder diffractogram of the product resulting from the crystallization of MoS2. Scanning electron microscope studies have also been made.

Thermal properties, thermochemistry and kinetics of the thermal dissociation of hydrochlorides of some mononitrogen aromatic bases

Abstract: Thermal properties of the hydrochlorides of several nitrogen aromatic bases have been elucidated via thermoanalytical investigations. All the compounds studied undergo decomposition upon heating, leading to their total volatilization. The dissociation process proceeds in two stages having different kinetics. The existence of these stages is explained on the basis of the Jacobs and Russell-Jones model of the kinetics of dissociative sublimation processes. The enthalpies of thermal dissociation of the salts have been evaluated from the non-isothermal thermogravimetric curves, and these values, together with thermochemical data available in the literature, have been used to evaluate the enthalpies of formation and the crystal lattice energies of the compounds. The ‘thermochemical’ radii for appropriate cations have been determined from the Kapustinskii–Yatsimirskii equation. The influence of the structure of the nitrogen bases on the thermal behaviour of their hydrochlorides is also discussed.

The curing of epoxy resins with aminophenoxycyclotriphosphazenes

Abstract: Aminophenoxycyclotriphosphazenes have been used as curing agents for epoxy resins. The thermal curing was performed in stages at 120–125 and 175–180°C followed by postcuring at 225°C to give tough brown polymers. The thermal curing reaction was monitored using FTIR and differential scanning calorimetry. Thermogravimetric analysis of the cured resins has shown thermal stability up to 350–340°C. The char yield obtained in nitrogen at 800°C was about 55–42% and in air at 700°C was about 40–32%. Graphite cloth laminates were prepared. The mechanical properties evaluated were found superior to those of commonly used epoxy resin systems. These resins are useful for making fire- and heat-resistant composites, laminates, molded parts, and adhesives.

Surface reduction in low-temperature formation of nickel oxide from different nickel salts. Thermal analysis, surface area, electron microscopy and infrared studies

Abstract: The influence of source material, decomposition and annealing temperatures on the reactivity of nickel oxide surfaces has been studied. The process of thermal decomposition in air of four nickel salts (acetate, oxalate, carbonate and hydroxide) was followed using thermogravimetric and differential thermal analysis, differential scanning calorimetry, B.E.T. surface area determination and infrared spectroscopy. Nickel acetate and oxalate gave products consisting of nickel metal and nickel oxide. The reduction mechanisms are described. The carbonate and hydroxide gave only nickel oxide, but the martensitic decomposition of the carbonate (ΔHt= 28.8 kJ mol–1) is considerably more energetic than that of the hydroxide (ΔHt= 2.8 kJ mol–1). The loss of surface area in the decomposition is correspondingly larger for the carbonate. Infrared studies of the degassing process from 25–500 °C in vacuo produced evidence for reduction on the ex-carbonate NiO surface which correlated with reactivity in dissolution kinetics studies. An absorption at 2193 cm–1 was observed, with maximum intensity after 300 °C decomposition, assigned to an Ni⋯(O—C—O)– species resulting from CO interaction with surface O–ions. Other carbonate and hydroxyl surface groups were characterised for each oxide at different decomposition temperatures.

Thermal analyses of flame-retardant twills containing cotton, polyester and wool

Abstract: Medium weight twill fabrics constructed from cotton and cotton blended with polyester and/or wool were analyzed under nitrogen by three thermoanalytical techniques. Fabrics were tested both before and after treatment with [tetrakis(hydroxymethyl)phosphonium] sulfate (THPS), urea, and trimethylolmelamine. The presence of all fibers was distinguishable in differential scanning calorimetric analysis (DSC) of untreated fabrics; the relative positions of the endothermic, decomposition peak temperatures were only slightly changed. After flame-retardant (FR) treatment, the blended cotton and wool fibers were altered. Both fibers decomposed as exotherms during DSC analysis. These data supported earlier microscopical, X-ray evidence that wool fibers were actually reacting with the FR treatment. The two DSC peaks for polyester polymer melting and decomposing remained unaffected by either blending with other fibers or the presence of the FR finish on the fabric. There was excellent agreement between DSC peak temperatures and the temperature of maximum rate of weight loss obtained from thermogravimetric analysis (TGA). Blending cotton with either of these fibers increased the residue measured after TGA. The increased residue correlated with increased flame resistance as measured by the 45° angle, edge-ignition burning rate test.

Synthesis and preliminary processing of the sol-gel derived β-quartz lithium aluminum silicates

Abstract: Lithium aluminum silicate (LAS) glass-ceramic compositions with and without phosphorus have been synthesized using the sol-gel technique. Resulting LAS-type powders are herein designated as NZ and NZP. X-ray analysis, thermogravimetric analysis (TGA), particle size and thermal dilatometric measurements have been performed on these samples. The NZ and NZP powders in calcined form, as well as a commercially-available LAS glass-ceramic, produce an X-ray diffraction pattern very similar to the pattern of virgilite Li x A1 x Si 3− x O 6 ( x = 0.5–1.0). There is very little difference between the powders with and without phosphorus in the diffuse reflectance spectra (DRS). Preliminary results show that the material can be easily processed.