Showing papers on "Thermogravimetry published in 1973"

Critical examination of several problems typically found in the kinetic study of thermal decomposition under vacuum

Abstract: After considering several problems peculiar to the kinetics of thermal decompol sition under vacuum (formalism, separation of successive steps, influence of residuapressure and of heat or mass transfers) the author suggests, as a possible answer, the use of constant decomposition rate thermal analysis, in association or not with thermogravimetry or calorimetry. The interest of the method is shown for the following measurements: apparent orders of reaction, energies of activation, differential enthalpies of dissociation. It appears to be specially suited to the study of thermal decomposition under high vacuum.

Poly α-ester degradation studies. V. Thermal degradation of polyglycollide

Abstract: The thermal degradation of polyglycollide [poly(methylene carboxylate)] has been studied over the temperature range 250–400°C by using the combined kinetic and analytical technique previously described. The results obtained from thermogravimetry and product analysis were in many ways similar to those from previous work involving higher poly-α-esters. Thus the reaction was predominantly first-order and the major degradation product was glycollide monomer. This confirms the observations of Carothers and is best interpreted in terms of an intramolecular ester interchange process. Kinetic studies have shown that the first-order rate constant k is related to temperature T by the expression: The results from gas evolution analysis showed consistent and marked deviation from first-order behavior. This is interpreted in terms of the greater sensitivity of this technique to traces of acidic degradation products. Solution viscometry was used to demonstrate the effect of degradation conditions on molecular weight change in both thermogravimetric and gas evolution techniques.

Thermally-induced structural and electrical effects in GeTe-based amorphous alloys

Abstract: The thermal, structural electrical properties of bulk glasses based on GeTe compositions near the binary eutectic, Ge15Te85, are studied Information regarding the non-crystalline state and the transformation from the non-crystalline to the crystalline state is reported The particular alloys studied represent binary (Ge17Te83), ternary (Ge15Te80As5) and quaternary (Ge15Te81Sb2S2) compositions Structural information is obtained using X-ray diffraction techniques and density measurements Thermal data are reported from differential scanning calorimetry (DSC), thermogravimetry (TGA) and mass spectrometry results The electrical conductivity is measured as a function of temperature and, on the ‘as-prepared’ glasses, shows semi-conducting behavior with activation energies, E, of 043–048 eV DSC, TGA and X-ray powder diffraction patterns indicate the samples crystallize as Te and GeTe in a two-step process, and melt at the binary eutectic temperature The binary vaporizes as Te and GeTe in a two-step process GeTeAs and GeTeSbS vaporize by essentially the same mechanism, with As evaporating ( ⋍125−133° C ; crystallization temperature ⋍206−228° C as determined by DSC) DSC, TGA and mass spectrometry results have been correlated to electrical and structural changes Results show that crystalline Te nucleates at the surface and forms a conductive surface layer The conductivity of this surface layer is nearly temperature independent with E ≈ 10−2 eV for all three alloys Crystallization and the associated electrically conductive regions extend into the bulk material with further annealing In these disordered alloys the additives As and Sb + S apparently do not act as electrical dopants in the sense of affecting the conductivity activation energy The additives Sb + S however do retard crystallization of GeTe The secondary crystallization product, GeTe, apparently changes the conduction mechanism to either a metallic or degenerate semiconductor type behavior

Graft copolymerization of nylon 6 with methylmethacrylate and methylacrylate, I. Optimum conditions of grafting and thermal behaviour of the copolymers

Abstract: Nylon 6, 20 denier, monofilaments were grafted with methylmethacrylate and methylacrylate using ceric ion/sulphuric acid as initiator. Grafted nylon samples with different % graft-on were prepared by varying the reaction conditions. The thermal stabilities of these grafted samples were compared with parent nylon using dynamic thermogravimetry in air at a heating rate of 6 °C/min up to a temperature of 550 °C. The initial decomposition temperature (IDT) integral procedureal decomposition temperature (IPDT) and activation energy (E) values indicated that thermal stability decreased as a result of grafting. Nylon-6 wurde mit Methylmethacrylat und Methylacrylat unter Verwendung von Cer-Ionen/Schwefelsaure als Initiator gepfropft. Proben mit verschiedenem Pfropfungsgrad wurden durch Variation der Reaktionsbedingungen hergestellt. Die thermische stabilitat dieser gepfropften Produkte wurde im Vergleich zum Ausgangsnylon durch dynamische Thermogravimetry untersucht; danach nimmt die thermische Stabilitat als Folge der Pfropfung ab.

Characterization of differently bound water by means of the constants of thermal decomposition kinetics

Abstract: Compounds containing differently strong bound water molecules were investigated by thermogravimetry and derivative thermogravimetry. The following models were used: inorganic adsorbents, salts containing water of crystallization and a compound with structural water. The temperature interval, the stoichiometry of the water release were determined and kinetic parameters of the processes were calculated. These results could be brought into connection with the nature of the adsorption and crystallization water.

Poly‐α‐ester degradation studies. II. Thermal degradation of poly(isopropylidene carboxylate)

Abstract: The thermal degradation of poly(3-pentylidene carboxylate) has been studied kinetically over the temperature range 200–300°C using thermogravimetry, gas evolution analysis, and rheogoniometry together with isolation and analysis of the reaction products. The observed behavior is completely different from that previously reported for poly(isopropylidene carboxylate) and poly(methylene carboxylate). Whereas in the latter cases the decomposition occurs by a first-order intramolecular ester interchange process characterized by an activation energy in the region of 27 kcal mole−1, poly(3-pentylidene carboxylate) decomposition occurs by random chain scission superimposed on a first-order hydrogen abstraction process. The activation energy associated with this decomposition reaction is in the region of 47 kcal mole−1, and the major degradation products are cis- and trans-2-ethyl crotonic acid.

Thermal analysis and synthesis of pentazinc hexahydroxide dicarbonate: Investigations by thermogravimetry, thermo molecular beam analysis and x-ray measurements

Abstract: A combination of thermobalance and X-ray camera is described which allows simultaneous thermogravimetric (TG) and X-ray measurements under high vacuum. During these measurements the sample is positioned in the sample holder of the camera in the usual fashion and is X-raved while the temperature is varied. The molecular beam of the gaseous decomposition products flows through a connecting tube which acts as a molecular beam former between camera and thermobalance. The molecular beam is directed towards the empty balance pan. The orifice through which the beam exits as well as the pan have special shapes that allow transfer of the angular momentum of the decomposition beam to the balance. The exerted force is a function of time and corresponds to the first derivative of the TG curve. i.e. to the DTG curve. The integrated curve is directly proportional to the change in mass of the probe. A quantitative evaluation is possible if the molecular composition of the beam is known. The calibration of the molecular beam and the evaluation of the measurements will be discussed. The results show that simultaneous detection of X-ray scattering and indirect TG curves allows a better interpretation of decomposition reactions. An additional investigation shows that thermal synthesis of chemical com- pounds can also be studied by thermogravimetry. Based on the same compound as described in the analysis. the pyrosynthesis is demonstrated. The special instrumentation and the test conditions are discussed.

Thermal Dehydroxylation and Phase Transformation of Bayer's Alumina

Abstract: Thermal dehydroxylation of Bayer's alumina has been studied by DTA, thermogravimetry, microscopy and X-ray. Giving due consideration to the mechanisms suggested by previous workers and based on the experimental observations made in this study, it is suggested that aluminium tri-hydrate (gibbsite) breaks up in the first instance to mono and dihydrates which subsequently transform to α-alumina through a series of intermediate phases.

Effect of Additives on Thermal Decomposition of Basic Magnesium Carbonate

Abstract: The effect of eleven halides on the thermal decomposition of basic magnesium carbonate (4MgCO3·Mg(OH)2·4H2O) has been studied by means of thermogravimetry (TG), differential thermal analysis (DTA) and gas chromatography. The size of crystallite of magnesium oxide prepared by heating the carbonate containing halide was determined by X-ray diffractometry, the oxides being studied by transmission electron microscopy. The thermal decomposition of basic magnesium carbonate was influenced by the addition of beryllium chloride tetrahydrate, magnesium chloride hexahydrate, calcium chloride hexahydrate and magnesium bromide hexahydrate. The DTA curve was changed with the amount of additive, i.e., three endothermic peaks (at about 300, 430, and 530 °C) and an exothermic peak (at 490 °C) turned to only two endo-thermic peaks in the case where the molar ratio of an additive to the carbonate exceeded 0.005, the peak at higher temperature becoming sharp with shift toward lower temperature. The results of TG of basic ma...

Deaquation-anation reaction of aquopentaammineruthenium(iii) complexes

Abstract: The deaquation-anation reaction of [Ru(H2O)(NH3)5]X3 type complexes in solid state, as shown by the equation, [Ru(H2O)(NH5)3]X5 (s) → [RuX(NH3)5]X2 (s) + H2O (g), where X=NO3 and Br was investigated by means of the differential thermal analysis (DTA) and of the thermogravimetry (TG) The activation energies in the deaquation-anation processes of the nitrate and bromide were calculated as 175 and 230 kcal/mol by the isothermal rate study, and as 190 and 268 kcal/mol by the Freeman–Carroll analysis

Thermal decomposition reaction of halogenopentaammineruthenium(iii) complexes

Abstract: The thermal decomposition reaction of halogenopentaammineruthenium(III) complexes was studied by the techniques of thermogravimetry, differential thermal analysis and evolved gas analysis. The complexes were dissociated by two different mechanisms:(a) those in which the Ru(III) was reduced by halide ion; and (b) those in which the Ru(III) was reduced by ammonia molecule. Which mechanism is preferably selected for a thermal decomposition reaction, it seems to be determined by the composition of ligands in the complexes.

Effect of additives on thermal decomposition of basic magnesium carbonate

Abstract: The effect of eleven halides on the thermal decomposition of basic magnesium carbonate (4MgCO3·Mg(OH)2·4H2O) has been studied by means of thermogravimetry (TG), differential thermal analysis (DTA) and gas chromatography. The size of crystallite of magnesium oxide prepared by heating the carbonate containing halide was determined by X-ray diffractometry, the oxides being studied by transmission electron microscopy. The thermal decomposition of basic magnesium carbonate was influenced by the addition of beryllium chloride tetrahydrate, magnesium chloride hexahydrate, calcium chloride hexahydrate and magnesium bromide hexahydrate. The DTA curve was changed with the amount of additive, i.e., three endothermic peaks (at about 300, 430, and 530 °C) and an exothermic peak (at 490 °C) turned to only two endo-thermic peaks in the case where the molar ratio of an additive to the carbonate exceeded 0.005, the peak at higher temperature becoming sharp with shift toward lower temperature. The results of TG of basic ma...

Mass transfer in fuel cells

Abstract: Results of experiments on electron microscopy of fuel cell components, thermal decomposition of Teflon by thermogravimetry, surface area and pore size distribution measurements, water transport in fuel cells, and surface tension of KOH solutions are described.