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  • Author or Editor: J. Suñol x
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Abstract  

Transformation diagrams are one of the most reliable ways to predict the thermal behavior of the materials. In this work, the crystallization process of several metallic glasses and polymer materials was analyzed and two isoconversional methods are applied to perform kinetic analysis of non-isothermal heating/cooling and isothermal processes. Moreover, the diagrams were constructed from modeling experimental data without the knowledge of the kinetic model. There was a good agreement between experimental data and the calculated curves, which verifies the reliability of the method and the validity of the rate constant model description.

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Abstract  

HDPE based composites were produced with 10-20-30 and 40% composite mass of wood fiber. The coupling agents were epolene and silane. The thermal behavior of composite samples was analyzed as a function of the coupling agent content, the exposure time and the wood fibers content by means of differential scanning calorimetry. Calorimetric curves of all samples of first and second heating shows a similar behavior. Some significant relation has been observed between the exposure time and the degree of crystallinity for the same percentage of fiber samples. A linear relation between the melting enthalpy average vs. content in cellulosic fibers is detected. Nevertheless, the fibers non-pretreated with coupling agent show a lower loss of crystallinity of the HDPE matrix at low wood fiber content (10%). A slight diminution of the melting peak temperature is detected as increasing the exposure time.

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Abstract  

In this study, the temperature-heating rate diagram of the main crystallization process of two metallic glasses, Fe74Ni3.5Mo3B16Si3.5 and Fe41Ni38Mo3B18, was obtained from one experimental differential scanning calorimetry (DSC) scan and the knowledge of their activation energy as determined by an isoconversional method. A good concordance was observed between the diagram curves obtained by calculation (isoconversional approach) and the experimental data, which verifies the reliability of the method and the validity of the kinetic approach in these alloys.

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Abstract  

The alloys, Fe60Ni14Zr6B20 and Fe85Nb9B6, were produced by mechanical alloying. The formation of the nanocrystallites (about 40 nm) was detected by X-ray diffraction. Furthermore, a slight oxygen presence (<3 at.%) was found by induced-coupled plasma and EDX microanalysis. After milling, calorimetry scans show low temperature recovery process and several crystallization processes related with the crystal growth and reordering of the crystalline phases. The apparent activation energies, 360 and 290 kJ mol-1, were determined by the Kissinger method. A mass increase (about 1 mass%) was detected by thermogravimetry.

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Abstract  

The crystallization kinetics of a melt spun Fe-Ni based alloy has been investigated, with both isothermal and continuous heating experiments, by means of differential scanning calorimetry. The alloy presents two separated crystallization processes. In order to perform the kinetic analysis of a melt spun metallic glass and to decide which kinetic model agrees better with the experimental crystallization data as the crystallized fraction x. We compare the experimental dependence of ln(k0f(x)) vs. (1-x) and that predicted, assuming different model equations for f(x). Both crystallization processes follow the JMAE equation and the master curve is the same for isothermal and non-isothermal data.

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Abstract  

A modified isoconversional method is applied to perform the kinetic analysis of non-isothermal processes. The solidification process of a polyethylene glycol with a mean molecular of 4000 (PEG 4000) was here analyzed. It was stated that the Avrami model provides a good description of the solidification process. Temperature-cooling rate-transformation diagrams were constructed and there was a good agreement between experimental data and the calculated T-CR-T curves. Moreover, morphological qualitative analysis has been performed by means of scanning electron microscopy.

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Abstract  

In this work three alloys, Fe74Nb6B20, Fe64Ni10Nb6B20 and Fe54Ni20Nb6B20, were obtained by mechanical alloying to analyze the influence of Ni content on Fe–Nb–B alloy formation. Structural analysis by X-ray diffraction (XRD) confirms that partial substitution of Fe by Ni favours the formation during milling of a more disordered structure. Furthermore, thermal stability study was performed by differential scanning calorimetry (DSC) because thermally induced structural changes can affect soft magnetic behaviour. After 40 h of milling time, all DSC curves show several exothermic effects on heating associated to structural relaxation and crystallization. All alloys present a crystallization process with associated activation energy values ranged between 238 and 265 kJ mol–1 related to the crystalline growth of the bcc-Fe rich phase. In alloys with Ni, a second crystallization process appears at temperatures over 500°C with activation energies 397 (10% Ni alloy) and 385 kJ mol–1 (20% Ni alloy) probably associated to the nucleation and crystalline growth of a new phase.

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