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Abstract  

Differential scanning calorimetry was used to study the isothermal kinetics of three-dimensional ordering formation from the mesophase of the thermotropic polyester poly(ethylethylene-4,4-diphenoxyterephthalate). An Avrami exponent of 4 was found and the measured rates of transformation were related with the efficiency of packing. A nucleation and growth process was assumed in the determination of the temperature coefficient, and the interfacial free energies are discussed in terms of the chain flexibility.

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Abstract  

Insertion of lattice-valued functions in a monotone manner is investigated. For L a ⊲-separable completely distributive lattice (i.e. L admits a countable base which is free of supercompact elements), a monotone version of the Katětov-Tong insertion theorem for L-valued functions is established. We also provide a monotone lattice-valued version of Urysohn’s lemma. Both results yield new characterizations of monotonically normal spaces. Moreover, extension of lattice-valued functions under additional assumptions is shown to characterize also monotone normality.

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Summary The SCTA methods for the kinetic analysis of solid-state reactions have been reviewed. It has been shown that these methods present two important advantages with regards to the more conventional rising temperature experiments. Firstly, they have a higher resolution power for discriminating among the reaction kinetic models and, secondly, SCTA is a powerful tool for minimizing the influence of the experimental conditions on the forward reaction.

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Abstract  

Radioisotope X-ray fluorescence spectrometry, RIXRF, was used for the determination of vanadium in Venezuelan petroleum coke samples using a simple standardless method and fundamental parameter approach. The values obtained by this method were in agreement with values measured by graphite furnace atomic absorption spectrometry, GFAAS.

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Abstract  

The curing kinetics of lignin-novolac and methylolated lignin-novolac resins were studied using non-isothermal methods employing differential scanning calorimetry (DSC) at different heating rates. The Belichmeier, Ozawa and Kissinger methods were applied, which give the kinetic parameters of the curing process studied. In addition, the model-fitting Coats-Redfern method was used to analyze the experimental data. The kinetic study evaluated the effect of the lignin (softwood ammonium lignosulfonate), methylolated or not, on the resin curing process. Results for lignin-novolac and modified lignin-novolac resins were compared with a commercial novolac resin as a reference. When lignosulfonate is modified by methylolation and is incorporated in the novolac resin, there is an important reduction in activation energy. The lignin-novolac showed slightly higher values of activation energy than methylolated-lignin resins, but lower values than commercial resins. This behavior has been attributed to the extra methyol groups introduced by lignosulfonate.

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Journal of Thermal Analysis and Calorimetry
Authors: M. Jiménez de Haro, L. Pérez Maqueda, E. Stepkowska, J. Ma Martínez and J. Pérez-Rodríguez

Abstract  

Grinding and contact with water or salt solution increased the specific surface (ssa) but lowered the first dehydration effect (escaping up to 150C) and increased the second dehydration effect (150 to 500C). The dehydroxylation was moved to lower temperatures and was only ΔM(500-1100C)=3.70.3 % as compared to 5.5% in the parent vermiculite (V). Except ΔM(20-150C), the mass losses measured at the remaining T ranges, were consistent in the ground samples, thus the grinding for 2 min caused the homogenization of the crystal structure of vermiculite [ΔM(150-500C)=7.60.7%]. DTA curves after grinding and cation exchange indicate an important exothermal peak at 795-870C, its temperature depending on exchangeable cation. It indicates the formation of high temperature phases (enstatite, forsterite, spinel). The lowest temperature of the peak (795C) was observed in V-gr-Li, here lithium silicate was formed. The highest peak temperature (870C) was found in V-gr-K, where almost only forsterite developed. These exothermal peaks were very weak in unground V with various exchangeable cations.

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Journal of Thermal Analysis and Calorimetry
Authors: J. Poyato, L. Perez-Maqueda, M. Jimenez de Haro, J. Perez-Rodriguez, J. Šubrt and V. Balek

Abstract  

Emanation thermal analysis (ETA), DTA, SEM, and XRD were applied for the characterization of the effect of Na+ and NH 4 + ions used for saturation of natural Mg-vermiculite on the microstructure during heating. The microstructure changes were characterized by ETA under in situ conditions of samples heating in air in the temperature range 20–1300°C. It was found that Na+ and NH 4 + ions have a significant effect on the microstructure changes during heat treatment of the natural Mg-vermiculite sample saturated with these ions. For Mg-vermiculite and Na+ saturated vermiculite thet emperatures of the onset of the collapse of interlaminar space were determined by ETA. Differences in thermal stability of the microstructure of dehydrated vermiculite samples were observed by ETA: the microstructure of dehydrated Mg-vermiculite, and Na-vermiculite was found stable until 650 and 350°C, respectively. For dehydrated NH4-vermiculite the annealing of the microstructure started at 730°C. The onset temperatures of the formation of new crystalline phases were indicated by ETA as the increase of the radon release rate. The onset temperatures of the ordering of the vermiculite structure or sintering under presence of the glassy stage (for Na-vermiculite), respectively, were determined from the decrease of the radon release rate. The ETA results were confirmed by DTA, XRD and SEM.

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