Showing papers on "Thermogravimetry published in 1987"

Thermal degradation of polyacrylamide and poly(acrylamide‐co‐acrylate)

Abstract: The thermal degradation behavior of polyacrylamide and poly(acrylamide-co-acrylate) was studied by differential scanning calorimetry, thermogravimetric analysis, gas chromatography/mass spectrometry, and carbon-13 solid state nuclear magnetic resonance. The degradation products over the temperature range of 115–450°C were characterized. Mechanisms are proposed for the degradation processes involved.

The electrical properties of poly(5,6-dihydroxy-2-cyclohexen-1,4-ylene) derivatives

Abstract: Synthese de diesters de cis-dihydroxy-5,6 cyclohexadiene-1,3 et polymerisation radicalaire des derives cis et trans

Preparation of Some Lanthanoid Picrates and the Behavior of Their Water of Hydration

Abstract: Lanthanoid(III) picrates (Ln=La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, and Yb) were prepared from picric acid and the corresponding lanthanoid carbonates in good yields. Combustion analyses, ICP emission ana...

Synthesis of aromatic poly(ether ketones)

Abstract: Preparation par polycondensation directe d'acides dicarboxyliques contenant des structures phenyle ether, avec le diphenoxybenzene ou par autopolycondensation d'acide phenoxybenzoique

Poly(di-n-pentylsilane). The spectral consequences of a helical conformation in the solid state

Abstract: Etude de la structure a l'etat solide par spectrometrie UV, RAMAN, RMN CPMAS du Si et diffraction RX (WAXD)

Thermal stability of isocyanate-based polymers. 2. Kinetics of the thermal dissociation of model urethane, oxazolidone, and isocyanurate block copolymers

Abstract: Determination des «groupes faibles» ou se produit la degradation par rupture de chaine, par analyse dynamique et thermogravimetrique isotherme. La stabilite augmente dans l'ordre urethanne

Kinetic analysis of thermal dehydration and hydrolysis of MgCl2·6H2O by DTA and TG

Abstract: The thermal decomposition of MgCl2·6H2O (non-dried and partly dried) and the kinetics of the process were studied by DTA, TG, DTG, IR, X-ray diffraction and chemical analysis of Mg and Cl. The reactions which occurred in the course of the thermal analysis were identified as dehydration (in steps), thermal hydrolysis of MgCl2·H2O and dehydrochloridization of magnesium hydroxy chlorides. Melting of the phases MgCl2·6H2O, MgCl2·4H2O and MgCl2 was also identified in the thermal curves. Thermal weight loss continued up to 800 °C in flowing air or nitrogen, but only up to 700 °C in static air. MgO was the end-product of thermal treatment in both cases.

Influence of silicon on the oxidation of titanium between 550 and 700°C

Abstract: The oxidation behavior of Ti-Si alloys (0.25, 0.5, and 1 Wt. % Si) was investigated between 550 and 700°C; in oxygen by continuous thermogravimetry for a maximum duration of about 500 hr and, in air by daily weighing for durations from a few hundred to several thousand hours. The kinetics results revealed that the presence of silicon leads to a decrease in oxidation rate which is more evident when the temperature is raised and the silicon content is increased. Morphological and structural examinations revealed that silicon modifies the internal architecture of oxide layers when compared with unalloyed titanium; in particular, reduced porosity in the layers is observed. Analysis showed that silicon is uniformly distributed in the oxide layer. However, while part of the silicon is in solid solution in the rutile, some is also precipitated as small crystals (φ <1 μm at 850°C) of SiO2, of cristobalite structure. The adherence of oxide layers to the metal substrate was measured after cooling of samples; the addition of silicon has been observed to modify, in a manner dependent on its content, the adherence of oxide layers.

The Microstructure of Selective Palladium Hydrogenation Catalysts Supported on Calcium Carbonate and Modified by Lead (Lindlar Catalysts), Studied by Photoelectron Spectroscopy, Thermogravimetry, X‐Ray Diffraction, and Electron Microscopy

Abstract: A detailed analysis of the system Pd + Pb on CaCO3 is presented. This system known as Lindlar catalyst is used for selective hydrogenations of CC bonds to CC bonds. It was found to consist of seven distinct chemical phases. Essential ingredients are solid solutions of hydrogen and oxygen in Pd. The latter phase enables the metal particles to be attached to the support via an orientational relationship calcite (113)∥Pd + O (111). The addition of Pb neither changes the micromorphology of the disk-shaped Pd particles nor does it modify the electronic structure of Pd as studied by chemisorption experiments. The addition of Pb seems to block certain active sites and, thus, to enhance the selectivity. The support was found to be a multi-domain mixture of calcite and aragonite with domain sites of several hundred A. The free surface of the pore-free solid is covered by a calcium-hydroxide carbonate. This phase as well as several other Pb phases seem to represent only spectator materials. Verification of this as well as finding the correlation between structure and function of the various components requires a kinetic analysis which is outside the scope of this paper. It is demonstrated that a variety of analytical techniques is required to unravel the complex nature of such a ‘simple' catalyst’ as it is Pd on CaCO3.

Thermolytic Formation of Noble Metals and Their Oxides from Chloride Precursors A Thermal Analysis Study

Abstract: The thermolysis of two compound series, namely, and was studied by differential scanning calorimetry, differential thermal analysis, and thermogravimetry. Product identification and confirmation of thermolysis pathways were accomplished by x‐ray powder diffraction analyses, moisture evolution analyses, and IR spectroscopy. The thermolysis was carried out both in reactive (air) as well as in inert (argon) atmospheres. In the case of , oxide was obtained as the major thermolysis product in air. In argon, metal was the major thermolysis product—the degree of oxide formation being a sensitive function of the partial pressure (or argon flow rate). The thermal stability of the oxide as well as the parent chloride precursor showed significant differences in the series. New data are presented for and . In both cases, intermediate formation of the trichloride was accompanied by oxide and metal formation depending on the gaseous ambient. Unlike the case of the Ir compound, no evidence for was found for the thermolysis of . Similarities and differences in data trends are discussed with the aid of thermochemical calculations. The results of this study may have implications in the synthesis of noble metals and their oxides for catalytic and electronic device applications.

New simultaneous thermogravimetry and modulated molecular beam mass spectrometry apparatus for quantitative thermal decomposition studies

Abstract: A new type of instrument has been designed and constructed to measure quantitatively the gas phase species evolving during thermal decompositions. These measurements can be used for understanding the kinetics of thermal decomposition, determining the heats of formation and vaporization of high‐temperature materials, and analyzing sample contaminants. The new design allows measurements to be made on the same time scale as the rates of the reactions being studied, provides a universal detection technique to study a wide range of compounds, gives quantitative measurements of decomposition products, and minimizes interference from the instrument on the measurements. The instrument design is based on a unique combination of thermogravimetric analysis (TGA), differential thermal analysis (DTA), and modulated beam mass spectroscopy (MBMS) which are brought together into a symbiotic relationship through the use of differentially pumped vacuum systems, modulated molecular beam techniques, and computer control and ...

Fourier transform infrared spectrometry and thermogravimetry of partially converted lignocellulosic materials

Abstract: Analyse des residus solides de l'extraction par le methanol supercritique de bois de Populus tremuloides

Preparation of positive photoreactive polyimides and their characterization

Abstract: Polyimide precursors were synthesized from a diamine and a diacid chloride that was derived from the reactant with promellitic dianhydride and o-nitrobenzyl alcohol. Their thermal properties were studied in nitrogen using dynamic thermogravimetry, and the photoreaction mechanism was investigated by ultraviolet and infrared spectrophotometry. The polyimide precursors were spin-coated onto silicon wafers, prebaked, and then exposed to UV light from a high pressure Hg–Xe lamp. When the films were dipped into 2% aqueous KOH after irradiation, the exposed area dissolved forming high resolution patterns. Relative sensitivities of the polymers were determined.

A study on the states of ethyl benzoate and TiCl4 in MgCl2-supported high-yield catalysts

Abstract: The states of ethyl benzoate (EB) and TiCl4 in the primary types of MgCl2-supported catalysts were studied by thermogravimetry/differential thermal analysis (TG-DTA) in combination with other methods. The results obtained by all experiments indicate that TiCl4 and EB in the MgCl2-supported high-yield catalysts interact only with MgCl2, leaving no vacant sites on TiCl4.

Thermal degradation of some polyimides

Abstract: Four different polyimides have been studied by thermogravimetry to ascertain their relative thermal stabilities in both inert and oxidising atmospheres. Experiments have been carried out at a rate of temperature rise of 2°C min −1 and isothermally at a number of temperatures in order to calculate overall activation energies for breakdown. The polymers have also been examined by pyrolysis-gas chromatography-mass spectrometry using two different procedures. In the first, fresh samples were pyrolysed at a number of increasing temperatures, whereas in the second, the same sample was subjected to successive pyrolyses at the same temperature intervals. The results are compared with those of other workers derived using different techniques.

Thermal decomposition of aluminium hydroxides

Abstract: The thermal decompositions of the crystalline aluminium hydroxides hydrargillite, bayerite and nordstrandite were investigated by thermogravimetry, differential thermal analysis, X-ray diffraction and infrared spectrophotometry. It was found that these aluminium hydroxides undergo thermal decomposition in the following sequences: hydrargillite-1

Fluoropolymers of very low surface energies

Abstract: Mesure de l'energie de surface d'une serie de poly(meth)acrylates ayant des groupes lateraux fluoroalkyl

Structure and pyrolysis of poly(methyl methacrylate peroxide): a thermochemical approach

Abstract: The structure of poly(methy1 methacrylate peroxide) (PMMAP) has been confirmed by using IR and NMR. The degradation of PMMAP has been studied by using differential scanning calorimetry, thermogravimetry, and pyrolysis gas chromatography. The degradation products were identified as methyl pyruvate and formaldehyde, accounting for more than 95% of the total degradation products. The measured heat of degradation of PMMAP was found to be -44 * 2 kcal mol-'. The mechanism of the primary exothermic degradation leading to the above products has been substantiated by thermochemical calculations.