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Abstract  

The crystallization of a hydrogen-charged melt-spun Mg76Ni19Y5 amorphous alloy was studied in order to understand the influence of hydrogen absorbed on the crystallization kinetics and mechanism. Hydrogenation does not affect the thermal stability, but decreases significantly the enthalpy of crystallization. The glass transition, which is well manifested in the hydrogen-free alloy, is not observed after hydrogen charging. The main crystalline phases in the H-free and H-charged alloys are the same after complete transformation, but with finer microstructure for the hydrogenated samples.Analysis of the crystallization kinetics reveals that during annealing of hydrogen charged Mg76Ni19Y5 growth of nanocrystals surrounded by amorphous phase takes place just in the beginning of the transformation, followed by grain growth in fully crystallized material, which is the main process.

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Abstract  

Structural relaxation for simple and more complex thermal histories is described by a phenomenological model based on a non-exponential relaxation function, the reduced-time concept and the nonlinear structural contribution to the relaxation time. The history, development of experimental techniques and data analysis is described. It is shown that the volume and enthalpy relaxation response can conveniently be compared on the basis of a fictive relaxation rate, R f. A simple equation relating R f and the parameters of the phenomenological model is given. The calculated data for moderate departures from equilibrium are in good agreement with our experiments and data previously reported in the literature.

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Abstract  

Crystallization behaviour of the amorphous Bi0.96Pb0.24SrCaCu1.6O5+x (0<x<1), obtained by rapidly quenching the melt, has been investigated by the differential thermal analysis (DTA) method under different atmosphere e.g. Ar, air, O2 and vacuum. Crystallization temperatures, activation energies and heat of crystallization are found to be 708–728 K, 2.25–2.32 eV and 0.16–1.81 kJ/g-atom, respectively, depending upon the atmosphere used during DTA. This material undergoes a number of structural and thermochemical transformations on continuously heating during DTA upto the melting temperature, which depends critically upon the atmosphere used.

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processes. In these cases, the amorphous regions in crystals can constitute reactive centres that can lead to product instability followed by changed bioavailability. Because of that, the ability to detect and quantify the amount of amorphous material within

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Abstract  

In this paper we present an electrical model of simulation. This model is used to simulate Thermally Stimulated Depolarization Current measurements. The time constant of the model shows the same temperature behaviour as that observed for amorphous materials. The computations by means of SPICE software give results which are very close to be behaviour laws used in the theory of relaxation in amorphous materials.

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Abstract  

The relaxation strength at the glass transition for semi-crystalline polymers observed by different experimental methods shows significant deviations from a simple two-phase model. Introduction of a rigid amorphous fraction, which is non-crystalline but does not participate in the glass transition, allows a description of the relaxation behavior of such systems. The question arises when does this amorphous material vitrify. Our measurements on PET identify no separate glass transition and no devitrification over a broad temperature range. Measurements on a low molecular weight compound which partly crystallizes supports the idea that vitrification of the rigid amorphous material occurs during formation of crystallites. The reason for vitrification is the immobilization of co-operative motions due to the fixation of parts of the molecules in the crystallites. Local movements (Β-relaxation) are only slightly influenced by the crystallites and occur in the whole non-crystalline fraction.

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Thermal behaviour of mechanically amorphized colemanite

II. Internal structure reconstitution processes of ground colemanite

Journal of Thermal Analysis and Calorimetry
Author: I. Waclawska

The effect of mechanical treatment on phase transitions of calcium borate-colemanite was studied. The decrease in the particle size of the original material and the increase in its internal structural disorder affect the thermal stability, characteristic temperatures and thermodynamic parameters of phase transitions such as structural relaxation and crystallization, occurring during the heating of this amorphous material. With increasing degree of amorphization of colemanite a change is observed in the structural mechanism of its crystallization.

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Synthetic inorganic ion-exchange materials

XXVIII. The ion-exchange properties of Na+ and K+ ions on crystalline and amorphous antimonic(V) acids treated thermally at elevated temperatures

Journal of Radioanalytical and Nuclear Chemistry
Authors: M. Abe and M. Tsuji

Abstract  

The change in selectivities by thermal treatment was studied on crystalline (C-SbA) and amorphous (A-SbA) antimonic(V) acids. The equilibrium distribution coefficients (Kd) of Na+ and K+ ions in HNO3 solution showed a maximum on the C-SbA heated at 330 °C. An inverse relationship was noticed between the changes in Kd values and in the lattice constants for the heated C-SbA. A-SbA heated at 20–500°C showed two steps of time dependence of adsorption for Na+, while a maximum for K+. This behavior can be explained in terms of the transformation from amorphous material to C-SbA.

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