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1.
The crystallization process affects solid properties through the crystal structure and morphology established during the transition process. An important aspect of the crystallization process is its kinetics, both from the fundamental point of view of amorphous material as well as the modeling and phase transition. In the present research work, non-isothermal crystallization data in the form of heat flow vs. temperature curves has been studied by using some well known models for amorphous Ga10Se87Pb3 and Ga10Se84Pb6 chalcogenide glasses, prepared by the melt quenching technique. The glass transition phenomena and crystallization of these glasses have been studied by using non-isothermal differential scanning calorimetery (DSC) measurements at constant heating rates of 5, 10, 15, 20, 25 and 30 K/min. The glass transition temperature (Tg), crystallization temperature (Tc), and melting temperature (Tm) were determined from DSC thermograms. The dependence of Tg and Tc on the heating rate was used to determine different crystallization parameters such as the order parameter (n), the glass transition energy (ΔEg) and the crystallization activation energy (ΔEc). The results of crystallization were discussed on the basis of different models such as Kissinger's approach and the modification for non-isothermal crystallization in addition to Johnson, Mehl, Ozawa and Avrami. 相似文献
2.
E.A. Marseglia 《Journal of Non》1980,41(1):31-36
Careful analysis of the Avrami equation [x = 1 ?exp(?Atn)] shows that an activation energy for crystallization (Ec) for amorphous materials can be defined over a selected range of temperatures. This activation energy can be determined experimentally using non-isothermal differential scanning calorimetry (DSC) by determining the crystallization temperature (Tc) as a function of heating rate (φ). A plot of (ln(φ/Tc) has a slope equal to Ec/n. The activation energy for the crystallization of amorphous arsenic obtained by this non-isothermal method is found to be in fair agreement with that obtained from an isothermal DSC experiment. 相似文献
3.
《Journal of Non》2007,353(24-25):2346-2349
Metallic glasses are kinetically metastable materials. These amorphous materials can be transformed into a crystalline state by both isothermal and isochronal methods. The study of this transformation, and hence the thermal stability of metallic glasses, are important from an application view-point. In the present work, the non-isothermal crystallization kinetics of two titanium-based amorphous alloys namely, Cu50Ti50 and Ti50Ni30Cu20, are reported. The activation energies for crystallization, Ec for both the systems have been evaluated using different non-isothermal methods viz. derived through Kissinger, Augis and Bennet and Ozawa. The values of Ec obtained using these methods are consistent for both the metallic glasses and it is found that Ec for the ternary metallic glass is considerably higher than the binary metallic glass. The increase in the activation energy on the substitution of Ni in the Cu–Ti metallic glass suggests the increase in the thermal stability. 相似文献
4.
A.A. Joraid 《Journal of Non》2008,354(28):3380-3387
In this work, the activation energies of crystallization of amorphous Se were studied under non-isothermal conditions using a differential scanning calorimetric (DSC) technique. The Johnson-Mehl-Avrami and isoconversional models were used to describe the DSC crystallization data. The isoconversional methods of Friedman, Kissinger-Akahira-Sunose (KAS) and Vyazovkin were used to determine the variation of the activation energy for crystallization with temperature, Eα (T). The KAS and Vyazovkin methods gave identical values, and the range of Eα (T) was found to vary in the range 110.4-44.2 kJ mol−1, while the Friedman method gave lower values with Eα (T) in the range 100.5-28.3 kJ mol−1. The effects of annealing were revealed by studying the morphology of the samples with a scanning electron microscope. 相似文献
5.
Sang-Mun Kim Wen-Ming Chien Dhanesh Chandra Narendra K. Pal Anjali Talekar Joshua Lamb Michael D. Dolan Stephen N. Paglieri Ted B. Flanagan 《Journal of Non》2012,358(9):1165-1170
The glass transition and crystallization kinetics of melt-spun Ni60Nb20Zr20 amorphous alloy ribbons have been studied under non-isothermal and isothermal conditions using differential scanning calorimetry (DSC). The dependence of glass transition and crystallization temperatures on heating rates was analyzed by Lasocka's relationship. The activation energies of crystallization, Ex, were determined to be 499.5 kJ/mol and 488.6 kJ/mol using the Kissinger and Ozawa equations, respectively. The Johnson–Mehl–Avrami equation has also been applied to the isothermal kinetics and the Avrami exponents are in the range of 1.92–2.47 indicating a diffusion-controlled three-dimensional growth mechanism. The activation energy obtained from the Arrhenius equation in the isothermal process was calculated to be Ex = 419.5 kJ/mol. The corresponding three dimensional (3D) time–temperature–transformation (TTT) diagram of crystallization for the alloy has been drawn which provides the information about transformation at a particular temperature. In addition, the intermetallic phases and morphology after thermal treatment have been identified by X-ray diffraction (XRD) and scanning electron microscope (SEM). 相似文献
6.
I. Avramov 《Journal of Non》2009,355(1):23-2633
Kinetics of structural relaxation and crystallization of NaPO3 glassforming melt is studied by means of thermal analyses. It is demonstrated that activation energy depends strongly on fictive temperature Tf. The dependence of the onset temperature To of the glass transition interval on the heating rate q+ is investigated for samples that were previously cooled down at a rate q− of about 850 K/min. The dimensionless fragility F is a measure of the dependence of the activation energy for spatial rearrangement on the changes of structure. According to the present results F is large for NaPO3 (i.e. phosphates are ‘fragile’ substances). 相似文献
7.
Bulk glasses of the system Ga20SbxS80−x (x = 5 and 40) were prepared for the first time by the known melt quenching technique. Non-isothermal differential scanning calorimetric (DSC) measurements of as-quenched Ga20SbxS80−x (x = 5 and 40) chalcogenide glasses reveal that the characteristic temperatures e.g. the glass transition temperature (Tg), the temperature corresponding to the maximum crystallization rate (Tp) recorded in the temperature range 400-650 K for x = 5 and 480-660 K for x = 40 are strongly dependent on heating rate and Sb content. Upon heating, these glasses show a single glass transition temperature (Tg) and double crystallization temperatures (Tp1 and Tp2) for x = 5 which overlapped and appear as a single crystallization peak (Tp) for x = 40. The activation energies of crystallization Ec were evaluated by three different methods. The crystallization data were examined in terms of recent analysis developed for non-isothermal conditions. The crystalline phases resulting from (DSC) have been identified using X-ray diffraction. 相似文献
8.
Adam A. Bahishti M.A. Majeed Khan B.S. Patel F.S. Al-Hazmi M. Zulfequar 《Journal of Non》2009,355(45-47):2314-2317
The crystallization parameters such as glass transition temperature (Tg), onset crystallization temperature (Tc), peak crystallization temperature (Tp) and enthalpy released (ΔHC) of the bulk Se–Te chalcogenide glass has been studied by using Differential Scanning Calorimeter (DSC), under non-isothermal condition at a heating rate of 20 K/min. The values of Tg, Tc, Tp and ΔHC with and without laser irradiation for different exposure time have been studied. The optical absorption of pristine and laser irradiated thermally evaporated Se–Te films has been measured. The films shows indirect allowed interband transition that is influenced by the laser irradiation. The optical energy gap has been found to decrease from 1.61 to 1.38 eV with increasing irradiation time from 5 to 20 min. The results have been analyzed on the basis of laser irradiation-induced defects in the film. 相似文献
9.
The internal friction Q?1 and the oscillation frequency f of Zr–Ti–Cu–Ni–Be metallic glass specimens were measured using an inverted torsion pendulum with the free decay method. A single-roller melt-spinning apparatus was used for preparing the specimens. Isothermal annealing near the glass transition temperature Tg was performed to investigate the stabilization of the specimens. Q?1 decreased with annealing time t due to the stabilization. Q?1-vs-t was measured at various annealing temperatures Ta, and the values of relaxation time τ for the stabilization process were determined. The dependence of τ on Ta showed that the hydrodynamic behavior represented by the Vogel–Tammann–Fulcher form and the hopping behavior represented by the Arrhenius form were observed in high- and low-temperature regions, respectively. The crossover of the two behaviors was seen at a temperature near and somewhat higher than Tg. The result was discussed on the basis of the viscoelastic relaxation in glassy materials. 相似文献
10.
Alexander Karamanov Isak Avramov Lorenzo Arrizza Radost Pascova Ivan Gutzow 《Journal of Non》2012,358(12-13):1486-1490
The influence of grain size on the surface crystallization kinetics is investigated by non-isothermal Differential Thermal Analysis and Scanning Electron Microscopy. For this purpose, different powder fractions of a model glass forming diopside via surface crystallization and crystallization induced porosity, are used. The activation energy of crystallization, EC, is determined from Kissinger plot, and the Avrami parameter, m, is estimated by both Ozawa and of Augis–Bennett methods. The values of EC decrease from 530 to 300 kJ/mol when grain size increases. Simultaneously, the m value drops from 2.5 to 1.3. This result contradicts to the widespread fallacy that the reaction order should be equal to one in the case of surface crystallization. During the initial stage of surface crystallization three dimensional growth takes place, a fact confirmed by the SEM investigations. Later on, one dimensional growth inwards the grain is observed, leading to the reaction order changes from 3 to 1. 相似文献
11.
《Journal of Non》2007,353(41-43):3853-3861
The molecular dynamics of glass-forming poly(methyl phenyl siloxane) (PMPS) is studied by thermal (10−3–5 × 102 Hz), dielectric (10−3–109 Hz) and neutron (5 × 108–1012 Hz) spectroscopy. Because of the broad frequency range of 15 orders of magnitude the study provides a precise determination of glassy dynamics in a wide temperature range using different probes. The relaxation rates extracted from the different methods agree quantitatively in both their absolute values and in their temperature dependencies. A detailed analysis of the temperature dependence of the relaxation rate fp by a derivative technique shows that the α-relaxation of PMPS has to be characterized by a high and a low temperature branch separated by a crossover temperature TB = 250 K. In both temperature ranges the temperature dependence of fp has to be described by Vogel/Fulcher/Tammann laws with different Vogel temperatures. Also the analysis of the dielectric strength in its temperature dependence gives a crossover behavior from a low to a high temperature region with a similar value of TB. TB can be interpreted as onset of cooperative fluctuations and the formation of dynamical heterogeneities. The dependence of the relaxation rate on the scattering vector Q extracted from neutron scattering obeys a power law τ ∼ Q−Slope, where the power Slope varies between Slope = 2 and Slope = 3.5 with increasing temperature. This anomalous dependence of the relaxation time on the momentum transfer is discussed in terms of dynamic heterogeneities in the underlying motional processes even at temperatures above TB. Besides the segmental dynamics the fast Methyl group rotation is considered as well. The relaxation rates of this process have an activated temperature dependence with an activation energy of 8.3 kJ/mol. The data were discussed in the framework of the threefold jump model were the incoherent elastic scattering from ‘fixed’ atoms which are frozen on the time scale of the Methyl group rotation was taken into account. 相似文献
12.
《Journal of Non》2007,353(18-21):2014-2019
The work considers the kinetics of non-isothermal crystallization, especially from the point of view of the possibility of applying the Augis–Bennett method for the determination of activation energy. The necessity of introducing the usual approximation T ≫ T0 was analyzed. It was shown that the method can be applied not only in the cases when T ≫ T0, but also when T > T0 that is, when the two temperatures differ only by about 10%. We show also that the application of the Augis–Bennett formula in such cases is more accurate the higher the value of the Avrami index n is. The method was applied to study the crystallization kinetics of the glass Sb32As5S48I15. The results obtained by differential scanning calorimetry (DSC) under non-isothermal conditions were also analyzed using the Kissinger and Matusita method. In the process of glass heating, a single peak is observed for glass transformation and a double peak for glass crystallization. The activation energies of glass transition (Eg) and crystallization (Ec) were determined, as well as the value of the Avrami index n for the second crystallization process. The obtained values for n and m indicate that the crystallization phase involves three-dimensional nucleation and growth. On the other hand, in agreement with the obtained results of the theoretical analysis, such n value justifies the application of the Augis–Bennett method for the investigated glass for which T and T0 do not differ significantly. 相似文献
13.
《Journal of Non》2007,353(32-40):3332-3337
The viscosity of the model AgCu alloy is simulated by several methods using (i) correlation functions through the Green–Kubo formalism, (ii) a non-equilibrium molecular dynamics approach and (iii) creep tests under constant stress. Temperature dependences of the shear viscosity and the diffusion coefficient show the breakdown of the Stokes–Einstein relation well above the glass-transition temperature Tg. This observation is interpreted as a manifestation of the development of heterogeneities in the supercooled liquid approaching Tg. Based on a generalized Einstein formula for the viscosity of liquid, a temperature dependence of heterogeneity degree of supercooled liquid is estimated. Using the dependence of the deformation rate on external stress, the activation volume is evaluated to be four atomic volumes in liquid state. However, below the mode-coupling temperature Tc the activation volume increases by several times. 相似文献
14.
Mousa M.A ImranN.S Saxena Y.K VijayR Vijayvergiya N.B MaharjanM Husain 《Journal of Non》2002,298(1):53-59
Results of differential scanning calorimetry (DSC) under non-isothermal condition on Se96In4 semiconducting chalcogenide glass before and after slow neutron irradiation, for different exposure times, have been reported and discussed. Some of Sn atoms have been injected into the glass by nuclear transmutation processes and the binary glass is converted into a ternary. This is accompanied by an increase in the activation energy of crystallization, Ec, and in the glass transition temperature, Tg and a decrease in the glass transition activation energy, Et, in the onset crystallization temperature, Tc and in the peak temperature of crystallization Tp. Optical band gap measurements have also been carried out, before and after irradiation, on identical thin pellets of Se96In4 glass. The energy band gap, Eg, is found to decrease upon irradiation. These effects have been attributed to a structural change upon doping and to irradiation induced defects. 相似文献
15.
Through the use of differential scanning calorimetry, the heat capacity and crystallization parameters of amorphous As2Se3 have been studied. It is found that the heat capacity above the glass transition temperature (Tg) exceeds, by a factor of 1.6, the Dulong-Petit limiting value found below Tg. The crystallization process is found to obey first-order kinetics with an activation enthalpy of 1.24 eV and an enthalpy of crystallization of 0.36 eV · molecule?1. The effect of sample age on the rate constant is also reported. 相似文献
16.
We have studied the effects of thermal cycling and annealing on the Hall resistivity ?H and electrical resistivity ? of an amorphous magnetic material, Metglas 2826A. Thermal cycling up to 600 K has no significant effect on ? but changes ?H, especially at T > 300 K. Annealing at higher temperatures Ta affects ?H more strongly that it influences ?. For Ta = 650 K the Curie temperature jumps by ~300 K and this, combined with X-ray data, is regarded as being symptomatic of the onset of crystallization. It is demonstrated that, for a fixed T, the variation of the extraordinary Hall coefficient R1 is simply correlated with that of ? for both the amorphous material and the annealed (crystallized) specimens. Furthermore, for a given Ta, the variations of R1 and ? as functions of temperature exhibit the same formal relationship. The temperature dependence of ? in the annealed specimens is rendered plausible in terms of recent theories of disordered materials. Room-temperature studies of electron spin resonance and the field dependence of the magnetization are also reported. 相似文献
17.
The non-isothermal crystallization kinetics of La2CaB10O19 (LCB) from a La2O3-CaO-B2O3 glass was studied. Differential thermal analysis methods were performed on three glass powders to obtain the kinetic parameters of LCB crystallization mechanism. The activation energies for overall crystallization (E), obtained by the methods of Kissinger and Ozawa, were in the range of 479-569 kJ/mol. Multiple (five) analysis methods were used to estimate the Avrami exponent (n), which could consequently be reduced into the single value of n = 3.1 ± 0.3. The growth morphology index (m) of LCB was corroborated by microscopy (optical and electron) images, which revealed a three dimensional growth. Energy dispersive spectroscopy confirmed that LCB is the crystallizing phase from the glass by an interface controlled mechanism. The parameters of the Johnson-Mehl-Avrami kinetic model for the analysis of LCB crystallization from glass were found to be n = m = 3. 相似文献
18.
J.C. Qiao 《Journal of Non》2011,357(14):2590-2594
Crystallization transformation kinetics in isothermal and non-isothermal (continuous heating) modes were investigated in Cu46Zr45Al7Y2 bulk metallic glass by differential scanning calorimetry (DSC). In isochronal heating process, activation energy for crystallization at different crystallized volume fraction is analyzed by Kissinger method. Average value for crystallization in Cu46Zr45Al7Y2 bulk metallic glass is 361 kJ/mol in isochronal process. Isothermal transformation kinetics was described by the Johnson-Mehl-Avrami (JMA) model. Avrami exponent n ranges from 2.4 to 2.8. The average value, around 2.5, indicates that crystallization mechanism is mainly three-dimensional diffusion-controlled. Activation energy is 484 kJ/mol in isothermal transformation for Cu46Zr45Al7Y2 bulk metallic glass. These different results were discussed using kinetic models. In addition, average activation energy of Cu46Zr45Al7Y2 bulk metallic glass calculated using Arrhenius equation is larger than the value calculated by the Kissinger method in non-isothermal conditions. The reason lies in the nucleation determinant in the non-isothermal mode, since crystallization begins at low temperature. Moreover, both nucleation and growth are involved with the same significance during isothermal crystallization. Therefore, the energy barrier in isothermal annealing mode is higher than that of isochronal conditions. 相似文献
19.
K.T. Liu 《Journal of Non》2008,354(27):3159-3165
The crystallization kinetics in Ni45.6Ti49.3Al5.1 film were studied by differential scanning calorimetry through isothermal and non-isothermal approaches. The activation energy for crystallization was determined to be 374 and 280 kJ/mol by the Kissinger and the Augis & Bennett method, respectively, in non-isothermal methods. In the isothermal annealing study, the Avrami exponents were in the range of 2.78-3.80 between 793 and 823 K, suggesting that the isothermal annealing was governed by three dimensional diffusion-controlled growth for Ni45.6Ti49.3Al5.1 thin films, in which the activation energy of nucleation is higher than that of growth. In addition, the transformation rate curves of Ni45.6Ti49.3Al5.1 film were also constructed by isothermal methods. The crystallization kinetics of amorphous Ni45.6Ti49.3Al5.1 film can thus be appreciated and the transformation rate also can be employed to control the degree of crystallization. 相似文献
20.
M. Abu El-Oyoun 《Journal of Non》2011,357(7):1729-13419
Differential scanning calorimetry (DSC) technique was used to study the kinetics of amorphous to crystalline transformation in Ge12.5Te87.5 chalcogenide glass. The kinetic parameters of glassy Ge12.5Te87.5 under non-isothermal conditions are analyzed by the model-free and model-fitting approaches from a series of experiments at different constant heating rates (5-50 K/min). The effective activation energy of crystallization was determined by analyzing the data using the isoconversional methods of Kissinger-Akahira-Sunose (KAS), Tang, Starink, Flynn-Wall-Ozawa (FWO) and Vyazovkin. The analysis of the present data shows that the effective activation energy of crystallization is constant throughout the entire interval of conversions and hence with temperature. The transformation mechanism examined using the local Avrami exponents indicates that one mechanism (three-dimensional growth) is responsible for the transformation process for all heating rates used. The reaction model that may describe the transformation process of the Ge12.5Te87.5 chalcogenide glass is the Avrami-Erofeev model (g(α) = [− ln(1 − α)]1/n) with n = 3 for all heating range at the whole range of crystallized fraction (α = 0.05-0.95). A good agreement between the experimental and the reconstructed (α-T) curves has been achieved. The transformation from amorphous to crystalline phase in Ge12.5Te87.5 chalcogenide glass demonstrates a single-step mechanism. 相似文献