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Incorporation of graphene‐based fillers such as graphene oxide (GO) and reduced graphene oxide (rGO) into polyvinylidene fluoride (PVDF) followed by uniaxial stretching can significantly improve their electroactive phase content as well as the dielectric properties. In this study, the nonisothermal crystallization kinetics of unstretched and uniaxially stretched PVDF‐GO and PVDF‐rGO composite films are investigated through differential scanning calorimetry (DSC) at different cooling rates. Avrami‐modified Jeziorney's model is used to understand their crystallization behavior which leads to the nucleation of electroactive crystalline phases in PVDF. Avrami's exponent "n" values in the range of 2–4 are obtained for nonisothermal crystallization of PVDF in different samples which reveal both two‐ and three‐dimensional growth of spherulites in the crystalline region. Kissinger's method is used to calculate the activation energy of crystallization and the results reveal accelerated crystallization of PVDF after addition of GO and rGO fillers followed by uniaxial stretching. [ABSTRACT FROM AUTHOR]

A new Ti-based amorphous alloy without any harmful additions of elements and supplementary Ag content was developed for applications in orthopedics and dentistry. Since complete elimination of toxic elements is reducing the glass-forming ability and direct casting of massive components is no longer possible, the new alloy was produced by melt spinning as thin ribbons, which could be subsequently processed by powder metallurgy. Investigations of X-ray diffraction and high-resolution transmission electron microscopy evidenced the fully amorphous structure of the new alloy. Differential scanning calorimetry was used to determine the crystallization point and the heating behavior at rates between 5 and 30 K min−1 in order to estimate by Kissinger’s method the activation energy for crystallization. Investigations evidence that the new Ti30Zr32Ag7Pd24Sn7 crystallizes at around 500 °C and the value of activation energy is relatively low in comparison with similar Ti-based alloys that were successfully processed by powder metallurgy; therefore, thermomechanical processing should be performed exclusively below 500 °C during short fabrication cycles, in order to preserve the amorphous structure. [ABSTRACT FROM AUTHOR]

Crystallization kinetics parameters of a stoichiometric glass with the composition Li1.5Al0.5Ge1.5(PO4)3 were investigated by subjecting parallelepipedonal samples (3 × 3 × 1.5 mm) to heat treatment in a differential scanning calorimeter at different heating rates (3, 5, 8 and 10 °C/min). The data were analyzed using Ligero's and Kissinger's methods to determine the activation energy (E) of crystallization, which yielded, respectively, E = 415 ± 37 kJ/mol and 378 ± 19 kJ/mol. Ligero's method was also employed to calculate the Avrami coefficient (n), which was found to be n = 3.0. A second set of samples were heat-treated in a tubular furnace at temperatures above the glass transition temperature, Tg, to induce crystallization. The X-ray diffraction analysis of these samples indicated the presence of LiGe2(PO4)3 which displays a NASICON-type structure. An analysis by optical microscopy revealed the presence of spheric crystals located primarily in the volume, in agreement with the crystallization mechanism predicted by the Avrami coefficient.

Neste trabalho são apresentados resultados de análise térmica para poliacrilonitrila (PAN) plastificada com glicerina. Foram observados os efeitos da glicerina de alta pureza (glicerol) e demais aditivos à base de glicóis na fusão e degradação térmica da PAN pela técnica de DSC sob alta taxa de aquecimento (90 °C/min) e atmosfera inerte. Foi constatado que o glicerol reduziu a temperatura de fusão da PAN de 290 °C para 217 °C. Em uma etapa preliminar foi empregado o método de Kissinger para verificar o efeito da composição química da PAN sob sua degradação térmica. A energia de ativação aparente para o copolímero de PAN foi calculada em 149 kJ.mol-1. Sugeriu-se que a presença do comonômero acetato de vinila (AV) na composição química da PAN proporcionou menor entalpia de degradação (353 J.g-1) em comparação com outros comonômeros constituintes de uma PAN precursora de fibras de carbono (988 J.g-1).This paper presents results from thermal analysis of polyacrylonitrile (PAN) plasticized with glycerin, where effects from the high purity glycerin (glycerol) and other additives to glycol were studied. Using differential scanning calorimetry (DSC) at high heating rate (90 °C/min) and inert atmosphere, we observed a decrease in the melting temperature of PAN (from 290 °C to 217 °C) owing to the presence of glycerol. The Kissinger's method was used to investigate the kinetics of thermal degradation for acrylonitrile (AN) with vinyl acetate (AV). The apparent activation energy for the copolymer AN/AV was calculated as 149 kJ.mol-1. The AV comonomer resulted in a lower degradation enthalpy for the copolymer AN/AV (353 J.g-1) compared with the comonomers comprising a precursor PAN for carbon fibers (988 J.g-1).

Ti-based amorphous alloys produced by ultra-rapid melt cooling represent an excellent option as biomaterials because of their mechanical properties and corrosion resistance. However, complete elimination of toxic elements is affecting the glass-forming ability and amorphous structure could be obtained only for thin ribbons or powders that are subsequently processed by powder metallurgy. Amorphous ribbons of special TiZrTaSi alloy, which is completely free of any toxic element, were produced by melt spinning, and the thermostability of resulting material was investigated in order to estimate its ability for further heat processing. Isochronal differential scanning calorimetry (DSC) was used to determine transformation points such as glass transition temperature T or crystallization temperature T . The activation energy for crystallization of amorphous phase was calculated based on Kissinger method, using heating rates ranging between 5 and 20 °C min. Amorphous structure of resulting ribbon was evidenced by means of X-rays diffraction (XRD) and high-resolution transmission electron microscopy (HR-TEM). It was determined that amorphous TiZrTaSi alloy has a high activation energy for crystallization, similar to other Ti-based amorphous alloys, which provides good thermal stability for subsequent processing, especially by means of powder metallurgy techniques. [ABSTRACT FROM AUTHOR]

A new powder metallurgy technique was developed in order to increase the reinforcement proportion of aluminum with two different fractions of AlO. Aluminum powders were mixed with 20 % vol of alumina particles as primarily reinforcement, and additional alumina was produced in situ as a result of reaction between Al and additional 7.5 % vol of FeO powder. The three grades of powders were milled and hot-pressed into small preforms, and differential scanning analysis (DSC) was performed to determine the kinetics of microstructural transformations produced on heating. DSC curves were mathematically processed to separate the superposing effects of thermal reactions. Transformation points on resulting theoretical curves evidenced two distinct exothermal reaction peaks close to the melting point of aluminum that were correlated with formation of Fe-Al compounds and oxidation of aluminum. Microstructural investigations by means of SEM-EDX and XRD suggested that these exothermal reactions produced complete decomposition of iron (III) oxide and formation of Fe-Al compounds during sintering at 700 °C, and therefore, heating at higher temperatures would not be necessary. These results, along with calculation of activation energies, based on Kissinger's method, could be used to optimize the fabrication of Al-AlO composites by means of reactive sintering at moderate temperatures. [ABSTRACT FROM AUTHOR]

Poly( l-lactide-co-propylene carbonate) was synthesized via the terpolymerization of l-lactide, CO and propylene oxide using zinc carboxylates as catalyst. The nonisothermal crystallization behavior and kinetics of the samples with and without catalyst residual were investigated using differential scanning calorimetry. Both the peak of melt crystallization temperature ( T) and the enthalpy of the cold crystallization process (∆ H) decrease with increasing PC content. Avrami-Jeziorny model, Owaza model and Mo model were used to describe the crystallization process. Avrami-Jeziorny analysis presents the crystallization kinetics, while neither the Ozawa nor the Mo model could successfully describe them. Kissinger's method was finally employed to calculate the activation energy for the transport of the macromolecular segments to the growing crystal surface. The results show that the existence of catalyst within polymer sample and increased PC content lead to an increase of energy barrier. [ABSTRACT FROM AUTHOR]