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Abstract  

The effect of the dyeing on the melting behavior of poly(lactic acid) fabrics was investigated by differential scanning calorimeter. The DSC melting peaks at 10C min-1 of the untreated poly(lactic acid) fabric were observed at a temperature higher than those of the dyed fabrics. The restricting force from the extended tie molecules along the fiber axis seems to decrease in the dyeing process. When the sample was rapidly heated, the crystallites melted at lower temperatures since recrystallization was restricted. It was estimated, based on the heating-rate dependency of melting behavior, that the original crystallites of the untreated sample melted at 146.1C and those of the dyed samples melted at higher temperatures, suggesting that their crystallites are grown to be more perfect in the dyeing process.

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Abstract  

The studies were devoted to determination of the effect of gas atmosphere and its pressure on the second step of decomposition of hydrated titanium dioxide (HTD) promoted by sulfate groups. It has been found that thermal decomposition of HTD at temperatures above 300C consists of a number of processes such as dehydroxylation, desulfuration, recrystallization and sintering of solid grains, photochemical processes (if the decomposition proceeds in the presence of light) and adsorption of gas phase components (in the presence of air or SO2). Kinetic parameters characterizing this step of decomposition have been determined for processes carried out in vacuum and in argon or air atmospheres (at a pressure of 13.33hPa). The kinetic curves of decomposition carried out in the presence of gases capable of being adsorbed on the surface of partly dehydrated HTD are featured by local extrema due to simultaneous processes of decomposition and adsorption of gas components.

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Abstract  

Carrier-free strontium and cesium isotopes were used to study the heterogeneous exchange of the systems strontium/strontium carbonate and cesium/cesium tetraphenylborate. The elements under consideration are among the long-lived isotopes most desired to be removed from waste solutions and consequently the use of heterogeneous exchange as an applied phenomenon for selective fixation is possible. The results obtained show that the above two systems are unstable ones (i. e., undergoing either formation or dissolution of the precipitated solid phase). New modified equations were proposed for quantitative calculation of the fraction of exchange, using only radiometric data and avoiding the use of microanalytical data. The equations are useful for all unstable systems, especially if no precise microquentitative method of analysis is known for the element under consideration. Recrystallization and self-diffusion were proposed to explain the two parts characterizing the exchange curves.

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Summary  

The differences on the thermal behaviour (DTG-DTA) of antigorite sample measured before and after sonication have been studied. Sonication treatment produces negligible changes in the structure of the material but substantial textural modifications. These modifications produce changes in the thermal behaviour of antigorite sample. Thus, it has been observed a decrease in the dehydroxylation temperature as measured by DTG and DTA effects. For sonication treatments longer than 20 h, two new effects of dehydroxylation are observed, the intensity of these two new effects increases with the sonication time showing a modification in the release of structural OH. It has been also observed that the formation of forsterite takes place simultaneously with the dehydroxylation of the antigorite. The high temperature exothermic effect is due to the recrystallization of forsterite and not to the formation of forsterite as traditionally assumed. Modifications in the thermal dehydroxylation of antigorite observed in this study are related to the pronounced decrease in particle size obtained by sonication.

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Abstract  

Equal channel angular pressing (ECAP) was carried out on solution annealed samples of Al–Mg–Si–Zr and Al–Mg–Si–Zr–Sc alloys to achieve a substantial grain refinement of the materials. Post ECAP aging was then investigated on the ultrafine grained alloys by DSC and TEM analyses. DSC scans were carried out with heating rates ranging from 5 to 30°C min–1. Peak identification was performed by the support of literature information and TEM analyses. Precipitation kinetics revealed to be similar for both alloys but the Sc-free alloy showed a recrystallization peak at temperatures ranging from 310 to 340°C, depending on the strain accumulated during ECAP. On the contrary, the Sc-containing alloy showed a greater grain stability. Analyses of peak positions and of activation energies as a function of ECAP passes experienced by the samples revealed large modifications of precipitation kinetics in the ultrafine-grained alloys with respect to the coarse-grained materials.

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Journal of Thermal Analysis and Calorimetry
Authors: Gabriel de Araujo, Dalva de Faria, Márcio Zaim, Flávio de Souza Carvalho, Fabio de Andrade, and Jivaldo Matos

Abstract  

Tibolone polymorphic forms I (monoclinic) and II (triclinic) have been prepared by recrystallization from acetone and toluene, respectively, and characterized by different techniques sensitive to changes in solid state, such as polarized light microscopy, X-ray powder diffractometry, thermal analysis (TG/DTG/DSC), and vibrational spectroscopy (FTIR and Raman microscopy). The nonisothermal decomposition kinetics of the obtained polymorphs were studied using thermogravimetry. The activation energies were calculated through the Ozawa’s method for the first step of decomposition, the triclinic form showed a lower E a (91 kJ mol−1) than the monoclinic one (95 kJ mol−1). Furthermore, Raman microscopy and DSC at low heating rates were used to identify and follow the thermal decomposition of the triclinic form, showing the existence of three thermal events before the first mass loss.

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Abstract  

DA-5018 is a new capsaicin derivative and has analgesic effect. The objective of this work was to investigate the existence of polymorphs and pseudopolymorphs of DA-5018 and the transformation of crystal forms. Eight crystal forms of DA-5018 have been isolated by recrystallization and characterized by powder X-ray diffractometry (PXRD), differential scanning calorimetry (DSC), and thermogravimetric analysis (TG). The PXRD and DSC patterns of the eight crystal forms were different respectively. In the dissolution studies in simulated intestinal fluid at 37±0.5°C, the solubility of Form 2 was the highest. And the solubility in water decreased in rank order: Form 2>Form 3>Form 1>Form 5>Form 7>Form 4>Form 6>Form 8. Eight crystal forms were shown to have a good physical stability at room temperature for 60 days.

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Abstract  

Methods for kinetic description of induction periods, based on the single-step kinetics approximation and various expressions of the temperature functions, are presented. The formulas for evaluation of both isothermal and non-isothermal lengths of induction periods are derived. Use of the formulas is demonstrated on the thermooxidative degradation of polyolefines. The kinetic parameters obtained from isothermal and non-isothermal experiments are compared and possible reasons of inconsistencies are analyzed. Applications of the determination of induction periods for thermooxidation of various systems are reviewed. The theory outlined in this paper can be applied not only for thermooxidation in condensed phase, but also for other processes exhibiting the induction period, such as the curing of rubber compounds, recrystallization of nickel sulfide and crystallization of silicate and metal glasses.

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The pressing of equal channel angular pressing - parallel channel process has an effect on microstructure and mechanical properties of the composite materials. Finite element has been used for conducting pressure effect through parallel channel for knowing distribution effect pressing. The materials AA1070 and AA6061 powder matrix composite with Al2O3 nano fiber were used as reinforcement. Mechanical properties and scanning electron microscope were observed in room temperature pressure and in case where the temperatures were higher than recrystallization value. Both results were compared to determine the effectiveness of pressure on each process. The characterization of aluminum composites on the aspects and phenomena of the distribution of pressing effect on hot and cold conditions treasured by finite elements will be explained in this paper.

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Abstract  

High hydrostatic pressure (HHP) has been investigated as an alternative to thermal processing for food preservation. HHP has been known to affect high molecular weight polymers causing phase change. Starch is gelatinized at a pressure on the order of 600–700 MPa, at 25 °C. Gelatinized starch recrystallizes during storage affecting the texture and shelf life of food products. The effect of HHP processing on the crystallization of starches from different botanical origins during storage at 4 and 23 °C was investigated. Crystallization kinetics of HHP treated wheat and corn starch gels were compared using DSC. The effect of crystallization on structure was evaluated in terms of storage modulus. The rate of retrogradation depended on the storage temperature (23 °C and 4 °C) and the botanical origin of the starch. The least crystallization was observed in HHP treated wheat starch stored at 23 °C. The storage modulus increased with crystallization of starch.

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