A study on isothermal kinetics of glassy Sb9.1Te20.1Se70.8 alloy (original) (raw)
Related papers
Thermochimica Acta, 2007
In this work, the activation energies of crystallization of amorphous Sb 9.1 Te 20.1 Se 70.8 have been studied under non-isothermal conditions using a differential scanning calorimetric (DSC) technique. The analysis focuses on the effect of temperature (413 ≤ T ≤ 437 K) on the DSC results. The three isoconversional methods of Friedman, Kissinger-Akahira-Sunose (KAS) and Vyazovkin were used to determine the variation of the activation energy for crystallization with temperature, E α (T). The KAS and Vyazovkin methods gave identical values, and the range of E α (T) was found to vary from 128.7 down to 77.8 kJ mol −1 , while the Friedman method gave lower values with E α (T) from 84.1 to 31.2 kJ mol −1. The effects of annealing were revealed by studying the morphology of the samples using scanning electron microscopy.
Materials Chemistry and Physics, 1998
Crystallization kinetics of the glassy alloy Sb 0.12 As 0.36 Se 0.52 was studied by made using a method in which the kinetic parameters are deduced bearing in mind the dependence of the reaction rate constant on time, through temperature. The method was applied to the experimental data obtained by differential scanning calorimetry, using continuous-heating techniques. In addition, two approaches are used to analyze the dependence of glass transition temperature, T g , on the heating rate, . One is empirical linear relationship between T g and . The other approach is the use of straight line lnT 2 g a vs. 1/T g for evaluation of the activation energy for glass transition. The kinetic parameters determined have made it possible to ®nd a bulk nucleation mechanism with decreasing nucleation rate and diffusion controlled growth for the crystallization process. The phases at which the alloy crystallizes after the thermal process have been identi®ed by X-ray diffraction. The diffractogram of the transformed material suggests the presence of microcrystallites of Sb 2 Se 3 and AsSe, in the residual amorphous matrix. # 1998 Elsevier Science S.A. All rights reserved.
Journal of Physics and Chemistry of Solids, 2007
A procedure has been developed to determine the reliable form of the glass-crystal transformation function, and to deduce the kinetic parameters by using differential scanning calorimetry data, obtained from experiments performed under non-isothermal conditions. It is an integral method, which is based on a transformation rate independent of the thermal history and expressed as the product of two separable functions of absolute temperature and the fraction transformed. Considering the same temperatures for the different heating rates, one obtains a constant value for temperature integral, and, therefore, a plot of a function of the volume fraction transformed versus the reciprocal of the heating rate leads to a straight line with an intercept of zero, if the reaction mechanism is correctly chosen. Besides, by using the first mean value theorem to approach the temperature integral, one obtains a relationship between a function of the temperature and other function of the volume fraction transformed. The logarithmic form of the quoted relationship leads to a straight line, whose slope and intercept allow to obtain the activation energy and the frequency factor. The method developed has been applied to the crystallization kinetics of the Sb 0.12 As 0.36 Se 0.52 glassy alloy and it has been found that the kinetic model of normal grain growth is the most suitable to describe the crystallization of the quoted alloy. The mean values obtained for the activation energy and the frequency factor have been 27.36 kcal mol À1 and 1.5 Â 10 9 s À1 , respectively.
Journal of Alloys and Compounds, 1999
A procedure has been developed for analyzing the evolution with time of the volume fraction crystallized and for calculating the kinetic parameters at non-isothermal reactions in materials involving formation and growth of nuclei. By means of this method, and considering the assumptions of extended volume and random nucleation, a general expression of the fraction crystallized has been obtained, as a function of the temperature in bulk crystallization. The kinetics parameters have been deduced, assuming that the crystal growth rate has an Arrhenius-type temperature dependence, and the nucleation frequency is either constant or negligible. The theoretical method described has been applied to the crystallization kinetics of glassy alloy Sb As Se with and without previous reheating. According to the 0.12 0.40 0.48 study carried out, it is possible to state that the reheating did not cause the appearance of nuclei, but that the as-quenched material already contains a sufficient number of them. The phases at which the alloy crystallizes after the thermal process have been identified by X-ray diffraction. The diffractogram of the transformed material suggests the presence of microcrystallites of Sb Se and AsSe, remaining in a 2 3 residual amorphous matrix.
Physica B-condensed Matter, 2007
The kinetics of crystallization in a-Se 73.2 Te 21.1 Sb 5.7 were determined at different heating rates (2-99 K/min) using differential scanning calorimetric (DSC) technique. It is evident from this study that the effective activation energy associated with crystallization, E c in a-Se 73.2 Te 21.1 Sb 5.7 is not constant but heating rate dependent. Attempt is made to explain this variation in terms of recent theoretical models based on the concept of variable effective activation energy. Using isoconversional method, the temperature dependence of E c was determined. It is shown here that the apparent variation of E c with the heating rate is a result of this temperature dependence. It is also shown that the JMA-based models (Kissinger model etc.) which assume constant effective activation energy show clear deviation from linearity giving at least two values of effective activation energy. r
Crystallization kinetics of bulk amorphous Se 80−x Sb x Te 20
Journal of Materials Science, 1991
Crystallization kinetics of the Se80−x Sbx Te20 (0⩽x⩽9) alloys have been studied using differential scanning calorimetry. The activation energies for the glass transition and that for crystallization have been determined from the heating rate dependence of the glass transition temperature and the peak crystallization temperature. The results have been analysed using the modified Kissinger's and Matusita's equations for the non-isothermal crystallization of materials. The variation of glass transition temperature with composition suggests that a small amount of Sb (⩽ 4 at %) leads to an increase in the chain length of Se-Te, whereas further increase in Sb atomic per cent increases the number of Se-Te chains in the alloys.
Glass transition and crystallization kinetics of Sb 14.5 As 29.5 Se 53.5 Te 2.5 amorphous solid
physica status solidi (a), 2006
The results of differential scanning calorimetry (DSC) under non-isothermal conditions of the chalcogenide In x (Se 0.75 Te 0.25 ) 100−x (where 0 ≤ x ≤ 10 at.%) glasses are reported and discussed. The dependence of the characteristic temperatures "glass transition temperature (T g ), the crystallization onset temperature (T c ) and the crystallization peak temperature (T p ) on the heating rate (˛) utilized in the determination of the activation energy for the glass transition (E g ), the activation energy for crystallization (E c ) and the Avrami's exponent (n). The composition dependence of the T g , E g , and E c were discussed in terms of the chemical bond approach, the average heats of atomization (H s ) and the cohesive energy (CE). The diffractogram of the transformed material shows the presence of some crystallites of Se-Te and In-Se in the residual amorphous matrix.
Kinetics of crystallization in amorphous Se73 2Te21 1Sb5 7
The kinetics of crystallization in a-Se 73.2 Te 21.1 Sb 5.7 were determined at different heating rates (2-99 K/min) using differential scanning calorimetric (DSC) technique. It is evident from this study that the effective activation energy associated with crystallization, E c in a-Se 73.2 Te 21.1 Sb 5.7 is not constant but heating rate dependent. Attempt is made to explain this variation in terms of recent theoretical models based on the concept of variable effective activation energy. Using isoconversional method, the temperature dependence of E c was determined. It is shown here that the apparent variation of E c with the heating rate is a result of this temperature dependence. It is also shown that the JMA-based models (Kissinger model etc.) which assume constant effective activation energy show clear deviation from linearity giving at least two values of effective activation energy. r
Evaluation of the activation energy of crystallization in Se79 1Te20Sb0 9
Differential scanning calorimetry (DSC) technique was used to study the kinetics of amorphous to crystalline transformation in Se 79.1 Te 20 Sb 0.9 chalcogenide glass. Non-isothermal measurements were performed at different heating rates (2-20 K/min). The activation energy of crystallization was determined by analyzing the data using the isoconversional methods of Friedman, Kissinger-Akahira-Sunose (KAS) and Vyazovkin. The present work shows that the activation energy of crystallization is not constant but varies with the degree of conversion and hence with temperature. The different values of the activation energy obtained from Friedman method as compared with KAS and Vyazovkin methods were attributed to possible errors involved in the Friedman method.
Journal of Physics and Chemistry of Solids, 2005
The glass-forming ability and devitrification of alloys in the Sb-As-Se system have been studied by differential scanning calorimetry (DSC). A comparison of various simple quantitative methods to assess the level of stability of glassy materials in the above-mentioned system is presented. All these methods are based on the characteristic temperatures, obtained by heating of the samples in non-isothermal regime, such as the glass transition temperature, T g , the temperature at which crystallization begins, T in , the temperature corresponding to the maximum crystallization rate, T p , or the melting temperature, T m. In this work, a kinetic parameter K r (T) is added to the stability criteria. The thermal stability of some ternary compounds of Sb x As 0.60K(2xCy) Se 0.40CxCy-type has been evaluated experimentally and correlated with the activation energies of crystallization by this kinetic criterion and compared with those evaluated by other criteria.