Search

In the present paper, the study of amorphous-crystalline transformation in (Se80Te20)94−x Ge6Bix (x = 0, 1, 2, 4, 6, 8, 10 and 12 at.%) chalcogenide alloys has been done using non-isothermal differential scanning calorimetry (DSC). Characteristic temperatures indicate that the samples with x = 1 at.% and x = 6 at.% can be considered as a critical configurations at which the system becomes a chemically ordered alloy. Kissinger and Moynihan approaches which utilized dependence of glass transition temperature (Tg) on heating rate (α) are used to deduce activation energy of glass transition (Eg). Crystallization process is characterized by various kinetic parameters such as activation energy and frequency factor deduced using different methods. Dietzel, Hruby, Saad and Poulin criteria are employed to assess glass forming ability and thermal stability of investigated alloys. The alloy with x = 12 at.% of Bi content has highest ∆T confirms maximum thermal stability, further validated from the values of Hruby parameter (Kgl) and thermal stability parameter (S). The fragility index infers that the composition studied in the present study is made from strong glass forming liquids. [ABSTRACT FROM AUTHOR]

The crystallization of the 3F5FPhF6 compound from the liquid crystalline antiferroelectric smectic CA* phase is investigated in various conditions using differential scanning calorimetry and polarizing optical microscopy. The kinetics of isothermal melt and cold crystallization is studied on the basis of the Avrami model. The kinetics of non-isothermal cold crystallization is analysed using the Ozawa model and the activation energy is determined by the Augis-Bennett, Friedman's differential isoconversional and Matusita methods. The border temperature between the diffusion-controlled crystallization and thermodynamically-controlled crystallization is estimated. The high fragility index of 105 is determined from the α-process in the smectic CA* phase by the broadband dielectric spectroscopy. The metastable, conformationally disordered crystal phase, forming only via cold crystallization, is reported. [ABSTRACT FROM AUTHOR]

A ZBLAN glass is a heavy metal fluoride (HMF) glass that possesses high thermal stability and excellent property as a transmitting material. The current study examines the thermal properties of ZBLAN glass utilizing Differential scanning calorimetry (DSC) at various heating rates. The temperature of glass transition, Tg, is observed to vary with heating rate, indicating its kinetic nature. Through the use of Kissinger's and Augis- Bennett's methodologies and the heating rate dependency of Tg, the activation energy (E) has been determined. These methodologies have also been used to obtain the fragility index (m), which can be used to evaluate the glass forming ability (GFA) of the system. The fragility index found is greater than 16, indicating that the ZBLAN glass is "fragile." [ABSTRACT FROM AUTHOR]

Present communication reports the crystallization and glass transition kinetics of xBi2O3–(50 − x)ZnO–50V2O5 glass system using the non-isothermal method of differential scanning calorimetry. The activation energies for crystallization (Ec) and glass transition (Eg) have been extracted from the fitting of various theoretical models with experimental data. The values of Ec and Eg for the studied glass samples lie in the range of 158.60–223.74 kJ mol−1 and 406.06–479.23 kJ mol−1, respectively. The activation energies of crystallization extracted from the fitting of experimental data with Avrami's equation and the Augis–Bennet model are in close agreement. The thermal stability of studied glass compositions has been analysed in the light of various parameters, viz. temperature difference (∆T), Hruby parameter (Hr), full width at half maximum of crystallization peak, frequency factor (ν), configurational constant (B), fraction of fluctuation free volume (fg) and thermal expansion coefficient (αf). It has been observed that volume nucleation occurs in the glass system under reference. The studied glass compositions are of low fragile nature, having a fragility index (m) ~ 40. [ABSTRACT FROM AUTHOR]

There has been increasing interest in the use of bioactive glasses for soft and hard tissue regeneration due to their excellent ability in supporting angiogenesis and osteogenesis. Silicate 45S5 glass, discovered by Hench in 1969, remains as the "Gold Standard" in this material family. However, the ability to form 45S5 into complex 3D shapes is challenging due to its tendency to crystallize upon sintering. Another silicate 13‐93 glass shows better processing characteristics through viscous flow sintering. Our work attempts to provide a comprehensive understanding of the viscosity and crystallization kinetics on these two glasses and two intermediates between them (designated as 48S1T and 50S2T). Viscosity analysis reveals a low liquidus viscosity and a high fragility index for all four compositions, making it necessary to use a traditional sintering process to produce structures of desired, complex shape. Nonisothermal crystallization kinetics study using differential scanning calorimetry indicates that the two intermediates show better thermal stability than the 45S5 glass and approach that of 13‐93 glass. A gradual change in physical properties, thermal stability, and phase assemblage was noticed with the composition transitioning from 45S5 to 13‐93. Results from this work suggest the promising attributes in both intermediates 48S1T and 50S2T compositions, making them attractive candidates for further studies for wide biomedical applications. [ABSTRACT FROM AUTHOR]

Ionic liquids (ILs) are neoteric solvents characterized by unique physicochemical properties and considerable structural variability. The thermal behavior of 24 ILs, belonging to two structurally related families with either bromide or Tf2N as counteranion, was analyzed. For bromide mono- and dicationic ionic liquids (DILs), thermal gravimetric analysis showed similar decomposition events, with only small gain in stability for a few members of the latter class. Conversely, all Tf2N DILs displayed higher stabilities (up to 34 K) than the corresponding monocations, thus highlighting the different role played by the two counteranions. Mono- and dicationic ILs bearing a reactive group on the imidazolium substituent resulted instead the least stable ILs studied. Differential scanning calorimetry analyses of most of the (D)ILs only showed glass transition temperatures, a behavior in agreement with the broad liquid range of ILs. The impact of the cationic structure and/or of the type of anion on the above-mentioned transition temperatures has been studied. The apparent activation energy (Ea) and the fragility index (m) for some (D)ILs have also been obtained. Finally, a few bromide (D)ILs presented peculiar thermal events. [ABSTRACT FROM AUTHOR]

This study of the thermal behaviour of two glass formers showed that rofecoxib has a good ability to vitrify while celecoxib displays a moderate glass forming ability. On the other hand, celecoxib forms an instable glass while rofecoxib displays moderate glass stability. The α-relaxation of the two amorphous drugs was studied by differential scanning calorimetry (DSC) and thermally stimulated depolarization currents (TSDC). The values of the dynamic fragility obtained by the two techniques are in good mutual agreement and suggest that both drugs are moderately fragile glass formers. These values are however considerably lower than those obtained by dielectric relaxation spectroscopy (DRS) and published in the literature. In the present work we will compare the values of the dynamic fragility obtained by TSDC and DRS for a set of ~30 glass-forming liquids, in order to evaluate their relative suitability for the determination of the m-index. The observed differences are discussed and interpreted. Finally, secondary mobility modes were detected by TSDC in both celecoxib and rofecoxib. The kinetic parameters are identical in both cases and similar to those found by DRS for the slow-b relaxation of celecoxib. These secondary relaxations, that are precursors of the main relaxation on its lower temperature side, are believed to be Johari-Goldstein relaxations. [ABSTRACT FROM AUTHOR]

The glass transition temperature dependence on a heating rate was investigated by differential scanning calorimetry for chalcogenide glasses from the Agx(As2(S0.5Se0.5)3)100−x system for x = 0, 0.5, 2 and 3 at.%. According to this dependence, apparent glass transition activation energies Eg were calculated for differently defined glass transition temperatures (onset Tg1, midpoint Tg2, endpoint Tg3 and endset Tg4). Also, Eg was analysed using isoconversional (model free) method. The results showed that the activation energy is not constant during the investigated process and vary with the extent of transformation from the glassy to the supercooled phase, pointing out that a complicated, multi-step process occurs. Eg decreases from about 340 to 200 kJ mol−1 in the composition with 2 at.% of silver. The values of the fragility index showed that these glasses do not exhibit large configuration changes during the glass transition process. Influence of silver content on investigated parameters was discussed. Apparent glass transition activation energy, variability parameter and fragility index showed a significant change in their values for the composition with 3 at.% of silver. Application of the isoconversion model for determination of apparent glass transition activation energy has showed that this parameter (at extent of conversion of 0.5) decreases from about 260 kJ mol−1 for x = 0, 0.5, 2 at.% to about 185 kJ mol−1 for x = 3 at.% of silver content. Likewise, fragility parameter drops from ~ 28.5 for x = 0, 0.5, 2 at.% to 21.5 x = 3 at.% of silver. [ABSTRACT FROM AUTHOR]

The nature of glass transitions in chalcogenides and modified oxides depends on the network mean coordination number $\langle r\rangle$. These display systematic trends when spanning across the three topological phases: flexible, intermediate, and stressed-rigid. Trends in the glass-transition temperature Tg($\langle r\rangle$) show a monotonic increase with $\langle r\rangle$, but the nonreversing enthalpy of relaxation at Tg, ΔHnr($\langle r\rangle$), shows a deep- and square-well-like minimum with the walls representing the rigidity and stress transitions with increasing $\langle r\rangle$, respectively. In the well, the ΔHnr($\langle r\rangle$) term remains minuscule (∼0) corresponding to the isostatically rigid intermediate phase (IP). The melt fragility index (m) shows rather low values, m($\langle r\rangle$) < 20 for IP compositions, but increases outside the IP. Glass compositions in the IP show absence of network stress, form compacted networks, possess thermally reversing glass transitions, and display high glass-forming tendency—functionalities that have attracted widespread interest in understanding the physics of glasses and applications of the new IP formed. [ABSTRACT FROM PUBLISHER]

The calorimetric parameters of glassy SeCdIn ( x = 0, 2, 6 and 10) alloys were investigated using differential scanning calorimetry (DSC) under non-isothermal conditions at different heating rates of 5, 10, 15 and 20 K min. The composition dependencies of activation energy of glass transitions ( E), crystallization activation energy ( E), fragility index ( F), Hruby number ( K) and rate constant ( K) were evaluated from DSC curves. Results indicate that kinetic parameter varies with In content in Cd-Se glassy matrix. It is observed that crystallization activation energy ( E) and K are minimum and K is maximum for SeCdIn glass. Therefore, SeCdIn glass is the most thermally stable glass and has highest glass-forming ability in this series. It can be explained by chemical bond theory of solids. [ABSTRACT FROM AUTHOR]

The slow molecular mobility of the active pharmaceutical drug fenofibrate is studied by differential scanning calorimetry (DSC) and thermally stimulated depolarization currents (TSDC). The general kinetic features of the secondary relaxations and of the main relaxation, in particular their distribution of relaxation times, were determined by TSDC. Different experimental procedures were used to determine the fragility index by DSC and the obtained results were discussed. The TSDC fragility is in very good agreement with the value obtained by dielectric relaxation spectroscopy (DRS), and all the DSC, TSDC and DRS values indicate that fenofibrate is a very fragile liquid. Given that this means a strong aging sensitivity, we profited from this property to evaluate the influence of physical aging on the fragility values determined by TSDC. From the results of experiments designed to achieve this goal we can conclude that this influence can be considered as negligible. [ABSTRACT FROM AUTHOR]

Glass-transition kinetics of $$\mathrm{Se}_{80}\mathrm{In}_{20-\mathrm{x}}\mathrm{Pb}_{\mathrm{x}}$$ ( $$x =$$ 0, 5, 10, and 15) chalcogenide glasses have been carried out at different heating rates by using differential scanning calorimeter (DSC) under the non-isothermal condition. The glass-transition temperature $$T_{\mathrm{g}}$$ and peak glass-transition temperature $$T_{\mathrm{pg}}$$ have been determined from DSC thermograms. The reduced glass temperature $$T_{\mathrm{rg}}$$ , total relaxation time $$\tau _{T_{g}}$$ thermal-stability parameters $$K^{l}$$ and $$S$$ , the activation energy of glass transition $$E_{\mathrm{g}}$$ , the fragility index $$F_{\mathrm{i}}$$ , and the average coordination number $$\langle Z\rangle $$ have been calculated on the basis of the experimental results. The temperature differences $$(T_{\mathrm{c}}-T_{\mathrm{g}}), K_{\mathrm{gl}}, K^{l}, S$$ , and $$E_{\mathrm{g}}$$ are found to be maxima for $$\mathrm{Se}_{80}\mathrm{In}_{10}\mathrm{Pb}_{10}$$ glass. This indicates that $$\mathrm{Se}_{80}\mathrm{In}_{10}\mathrm{Pb}_{10}$$ glass has the highest thermal stability and glass-forming ability in the investigated compositional range. These results could be explained on the basis of modification of the chemical bond formation due to incorporation of Pb in the Se-In glassy matrix. [ABSTRACT FROM AUTHOR]

Highlights: [•] The dynamics of the glass transition in Se76Te21Sb3 was investigated using DSC. [•] The activation energy of the glass transition was determined. [•] The fragility index of the glass was estimated from the activation energy. [Copyright &y& Elsevier]

Abstract: Differential scanning calorimetry (DSC) has been used to study the kinetics of structural relaxation in the glass transition region of Se80Sb12Sn8−y In y (y=0, 0.5, and 1) chalcogenide glasses, which were previously annealed at 394K below the glass transition temperature. Based on the Kovacs–Aklonis–Hutchinson–Ramos model, the dependence of the endothermic peak temperature (T p ) on heating rate has been used to evaluate the relaxation parameter. From the knowledge of this parameter the structural relaxation activation energy (Δh) has been obtained. The shift in T p with heating rate and annealing time (t a ) has been used to calculate the structural parameter, which controls the contribution of temperature and structure to the relaxation time. Results reveal that Δh decreases with In content due to the replacement of some SnSe4/2 structural units of strong bond energy by Se3In2 of weak bond energy. This reduces the cross-linking energy as well as the overall mean bond energy of the studied glasses as predicted by the chemical bond approach. The values of Δh were used to estimate the fragility index which is found to be in the range 29.7–31.7 indicating that the glasses under investigation were obtained from strong glass-forming liquids. The excess enthalpy (δ H ) has also been calculated, for different annealing times t a , from the knowledge of the excess specific heat. The values of δ H were plotted as a function of ln(t a ) and exhibit a linear behavior which indicates that the studied glasses were not completely relaxed. [Copyright &y& Elsevier]

In this study, the kinetics of glass transitions of TiCuNi and FeCoBSi metallic glasses are studied using thermal analysis technique, i.e., differential scanning calorimetry, by means of continuous heating of the sample at various heating rates. In the present study, based on the heating rate dependence of glass transition temperature ( T), the activation energy ( E) of the glass transition region is determined by two most frequently used approaches, i.e., Moynihan's method and Kissinger's equation. The fragility index, m, is also calculated using T, which is a measure of glass-forming ability of the given system. The result shows that the fragility index, m, of the given systems is <16. This indicates that the given systems are strong liquids with excellent glass-forming ability. [ABSTRACT FROM AUTHOR]