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Abstract  

The crystallization behaviour and Curie temperatures of Fe−(Nb,Cu)−Si−B metallic glasses were studied by means of differential scanning calorimetry (DSC), thermomagnetic gravimetry (TMG) and X-ray diffraction. The agreement between the DSC and TMG results was complete. For all Fe−Si−B amorphous alloys, two-peak crystallization was observed with the primary crystallization of α-Fe(Si) followed by eutectic crystallisation. The effects of Cu and Nb additions on the crystallization behaviour and on the activation energies for each stage of the crystallization process of Fe−Si−B glass were investigated.

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Journal of Thermal Analysis and Calorimetry
Authors: K. Chrissafis, K. Efthimiadis, E. Polychroniadis, and S. Chadjivasiliou

Abstract  

In this work we study the influence of Mo admixtures on the crystallization process of amorphous Fe78-xMoxSi9B13 (x=1, 2, 3 and 4) alloys by measurements of differential scanning calorimetry and on the soft ferromagnetic properties of the alloys by magnetic measurements. The addition of Mo by replacing Fe, results in magnetic hardening of materials. In DSC curves two peaks appear which are distinct when the concentration of Mo is 1 at.% and partly overlap when the Mo content is 2 at.%. Further increase in the Mo content leads to the appearance of just one peak. The activation energy was calculated both with Kissinger's and isoconversional Flynn, Wall and Ozawa methods.

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Abstract  

Secondary crystallization of PEA, occurring during DSC scan and performed after isothermal primary crystallization has been investigated. The high temperature exotherm peak has been attributed to the crystallization of amorphous fraction included between crystallites formed at the primary crystallization. The temperature position of the highest rate of the secondary crystallization depended on the temperature of the isothermal primary crystallization.

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Abstract  

Thermochemistry of crystal phase formation in vitrified municipal and hospital waste combustion ash and Ca, Fe pyroxene crystallization mechanism are presented. Pyroxene structure is capable of accumulate heavy metals and toxicants contained in ash. Due to this vitrification and crystallization is one of most effective method of immobilization dangerous contaminant of waste.

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The crystallization of poly(ethylene terephthalate) (PET) was studied in the presence of nucleating agents and promoters. The effect of both by themselves and in concert was investigated using differential scanning calorimetry. The aim of this work is to find conditions of fast crystallization of PET. Sodium benzoate(SB) and Surlyn® (S) substantially increase the crystallization rate of PET at higher temperature owing to a reduction in the energy barrier towards primary nucleation, but they accelerate crystallization even more at lower temperature with an additional improvement of the molecular mobility of PET chains. Chain scission of PET caused by the reaction with the nucleating agents was proven by determination of molecular weight. The addition of S alone led to a lower reduction in molecular weight. A series of N-alkyl-p-toluenesulfonamides (ATSAs) were shown to effectively promote molecular motion of the PET chains, leading to an increase in crsytallization rate at lower temperature. A remarkable acceleration of crystallization of PET was attained at lower temperature when S and ATSA were added together. When the content of ATSA is low, S has the dominant influence due to its dual effect of decreasing energy barrier towards nucleation and promoting molecular motion of PET chains. A further increase of crystallization rate of PET was found only after an addition of ATSA of above 5 wt.%.

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Abstract  

The work deals with crystallization of photodegraded polypropylene containing various amounts of β-nucleating agent based on N,N′-dicyclohexylnaphthalene-2,6-dicarboxamide. Compression-moulded samples were irradiated by UV-light, melted and subsequently non-isothermally crystallized. The results showed that the crystallization temperature decreased with increasing irradiation time. The irradiation caused the splitting of crystallization exotherms into two peaks indicating two crystallization mechanisms. The presence of β-nucleating agent in the material suppressed the peak splitting; the higher was the amount of nucleating agent in the sample, the later was the splitting observed.

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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  

The crystallization behavior of Co75-xFexGe15B10 (x=3.0, 4.6 and 6.0) amorphous alloys was monitored by differential thermal analysis and thermo-mechanical analysis. The crystallization process of the melt spun ribbons was interrupted at 450, 525, 650, 800 and 900C and their microstructures were investigated by X-ray diffractometry. It was observed that the crystallization occurs in a sequential mode attributed to the formation of different types of precipitates. It was shown that the crystallization products change as a function of Fe content. After full crystallization, GeFe, Co3B, FeGe2 and Co2Ge compounds were found as well as a Co rich solid solution.

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Abstract  

Fluoride glasses have been extensively studied due to their high transparency in the infrared wavelength. The crystallization kinetics of these systems has been studied using DTA and DSC techniques. Most of the experimental data is frequently investigated in terms of the Johnson-Mehl-Avrami (JMA) model in order to obtain kinetic parameters. In this work, DSC technique has been used to study the crystallization of fluorozirconate glass under non-isothermal conditions. It was found that JMA model was not fit to be applied directly to these systems, therefore, the method proposed by Mlek has been applied and the Šestk-Berggren (SB) model seems to be adequate to describe the crystallization process.

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Abstract  

The melting and crystallization of copolymers of tetrafluoroethylene with ethylene, synthesized in bulk and in suspension by semi-flow method, were studied by DSC. X-ray diffractions and infrared spectra of the copolymers were measured and new crystalline reflections different from those of the homopolymers were observed. The melting temperature of the copolymers synthesized in bulk depends strongly on the composition and exhibits several maxima. A certain small decrease in the melting temperature within the range of the alternating composition is observed. For alternating copolymers synthesized in suspension, the peaks are monomodal indicating a higher structural and chemical homogeneity of the copolymer. The nonisothermal crystallization kinetics in the temperature interval from 260 to 255°C of the alternating copolymer prepared in suspension can be described by a modified Avrami equation. The mechanism of nucleation and nuclei growth during the nonisothermal crystallization of the tetrafluoroethylene-ethylene copolymer is close to that of polyethylene.

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