Thermal stability and crystallization kinetics of ternary Se–Te–Sb semiconducting glassy alloys

This paper presents the results of kinematical studies of glass transition and crystallization in glassy Se_85?x Te₁₅Sb _x (x = 2, 4, 6 and 8) using differential scanning calorimetry (DSC). From the dependence on heating rates of, the glass transition temperatures (T _g), and temperature of crystallization (T _p) the activation energy for glass transition (E _g) and the activation energy for crystallization (E _c) are calculated and their composition dependence can be discussed in term of the average coordination number and cohesive energy. The thermal stability of Se_85?x Te₁₅Sb _x was evaluated in terms of criterion ΔT = T _c ? T _g and kinetic criteria K(T _g) and K(T _p). By analyzing the crystallization results, the crystallization mechanism is characterized. Two (two- and three-dimensional growth) mechanisms are working simultaneously during the amorphous–crystalline transformation of the Se₈₃Te₁₅Sb₃ alloy while only one (three-dimensional growth) mechanism is responsible for the crystallization process of the chalcogenides Se_85?x Te₁₅Sb _x (x = 4, 6 and 8) glass. The phases at which the alloy crystallizes after the thermal process have been identified by X-ray diffraction.     

Crystallization kinetics of tellurium-rich Se–Te–Sn glassy alloys

The objective of this study was to explore an innovative type of form-stable phase-change materials (PCMs) with flexible cellulose acetate (CA) nano-fibrous felts (nano-felts) absorbed with capric–myristic–stearic acid ternary eutectic mixture for thermal energy storage/retrieval. Capric–myristic–stearic acid (CMS) ternary eutectic mixture as model PCM was firstly prepared. The developed CA nano-felts as supporting material was mechanically flexible and was made from CA/polyvinylpyrrolidone (PVP) precursor composite nanofibers followed by removal of PVP components. The effects of original mass ratio of CA/PVP on absorption capacities of CA nano-felts were studied. The modified CA nano-felts with groove/porous structure and rough surfaces were capable of absorbing a large amount of PCMs. The morphological structures, as well as the properties of thermal energy storage, thermal stability and reliability, and thermal insulation of composite PCMs were characterized by scanning electron microscopy, differential scanning calorimetry, and thermal performance measurement, respectively. The results showed that CMS eutectic was absorbed in and/or supported by modified CA nano-felts. The heat enthalpy values of composite PCMs have slightly decreased in comparison with the corresponding theoretical values. The composite PCMs demonstrated good thermal stability and reliability after thermal cycles. The composite PCMs had high thermal insulation capability for temperature regulation.     

Thermal analysis of cadmium addition on the glass transition and crystallization kinetics of Se–Te–Sn glassy network

Journal of Thermal Analysis and Calorimetry - Calorimetric measurements have been performed in quaternary glassy system Se78−xTe20Sn2Cdx (x = 0, 2, 4, and 6) to study the...     

Extended study of crystallization kinetics for Se–Te glasses

Crystallization kinetics of chosen compositions from Se–Te glassy system were studied under non-isothermal conditions depending on particle size using differential scanning calorimetry. The purpose of this article is to demonstrate the extent of information accessible by the modern kinetic analysis provided by the differential scanning calorimetry, and to suggest its importance and merit for the development of new, high-tech PCM materials. The crystallization kinetics was described in terms of the nucleation-growth Johnson–Mehl–Avrami model. Complexity of the crystallization process was in this case represented by very closely overlapping consecutive competing surface and bulk nucleation-growth mechanisms. Mutual interactions of both mechanisms as well as all other observed effects were explained in terms of thermal gradients, surface crystallization centers arising from the sample preparation treatments, and changing amount of volume nuclei originating from the combination of pre-nucleation period, and the very glass preparation phase. Accent was laid on the merits resulting from interpretations of characteristic kinetic functions. A new criterion for quick determination of the dominating crystallization mechanism—surface or bulk—was introduced.     

Thermal stability and crystallization kinetics in superionic glasses using electrical conductivity–temperature cycles

The present work demonstrates application of electrical conductivity (σ)–temperature (T) cycles to investigate thermal properties viz., crystallization and glass transition kinetics in AgI–Ag₂O–V₂O₅–MoO₃ superionic glasses. The σ–T cycles are carefully performed at various heating rates, viz., 0.5, 1, 3, 5, and 7 K/min. The conductivity in Ag⁺ ion conducting glasses exhibit anomalous deviation from Arrhenius behavior near glass transition temperature (T _g) followed by a drastic fall at crystallization (T _c). The temperature corresponding to maximum rate of crystallization (T _p) is obtained from the derivative of σ–1/T plots. With increasing heating rates, the characteristic temperatures (T _g, T _p) are found to be shifting monotonically toward higher temperatures. Thus, activation energy of structural relaxation E _s, crystallization E _c and other thermal stability parameters have been obtained from σ–T cycles using Kissinger equation and Moynihan formulation. For a comparative study, these kinetics parameters have also been calculated from differential scanning calorimetry plots. The parameters obtained from both the methods are found to be comparable within experimental error.     

Crystallization study of Sn additive Se–Te chalcogenide alloys

Calorimetric study of Se_85−x Te₁₅Sn _x (x = 0, 2, 4 and 6) glassy alloys have been performed using Differential Scanning Calorimetry (DSC) under non-isothermal conditions at four different heating rates (5, 10, 15 and 20 °C/min). The glass transition temperature and peak crystallization temperature are found to increase with increasing heating rate. It is remarkable to note that a second glass transition region is associated with second crystallization peak for Sn additive Se–Te investigated samples. Three approaches have been employed to study the glass transition region. The kinetic analysis for the first crystallization peak has been taken by three different methods. The glass transition activation energy, the activation energy of crystallization, and Avrami exponent (n) are found to be composition dependent. The crystallization ability is found to increase with increasing Sn content. From the experimental data, the temperature difference (T _p − T _g) is found to be maximum for Se₈₃Te₁₅Sn₂ alloy, which indicates that this alloy is thermally more stable in the composition range under investigation.     

Simultaneous measurements of X-ray diffraction–differential scanning calorimetry

Journal of Thermal Analysis and Calorimetry - Ganciclovir (GCV) is an antiviral drug for treating cytomegalovirus infections. This drug is reported to exist in four crystal forms in the solid...     

Effect of Ag addition on crystallization kinetics and thermal stability of As–Se chalcogenide glasses

Chalcogenide glasses of (As₅₀Se₅₀)_100?xAg_x (0 ≤ x ≤ 25) were prepared using the melt quenching technique under non-isothermal conditions. Differential scanning calorimetry curves measured at different heating rates (5 ≤ β ≤ 40 K min^?1) are used to characterize the as-quenched samples. The thermal stability was monitored through the calculation of the temperature difference T _c ? T _g, stability parameter S and crystallization rate factor K _p. The glass-forming ability (GFA) was investigated on the basis of Hurby parameter H _r which is a strong indicator of GFA. In addition, the activation energy of glass transition E _t, activation energy of crystallization E _c and Avrami exponent n of the studied compositions were determined. The mechanism of crystallization was found to be a combination of two- and three-dimensional crystal growth.     

Glass transition and crystallization kinetics analysis of Sb–Se–Ge chalcogenide glasses

Differential thermal analysis (DTA) has been employed to investigate the effect of Ge addition on the glass transition behavior and crystallization kinetics of Sb₁₀Se_90?xGe_x (x = 0, 19, 21, 23, 25, 27) alloys. The three characteristic temperatures viz. glass transition (T _g), crystallization (T _c), and melting (T _m) have been determined and found to vary with the heating rates and Ge content. Thermal stability and glass forming tendency have been evaluated in terms of ΔT (= T _c ? T _g) and reduced glass transition temperature. The activation energies for glass transition and crystallization have been used to analyze the nucleation and growth process. The activation energy analysis also determines the suitability of alloys to be used in switching applications. Results have been interpreted in terms of bond energies and structural transformations in the investigated alloys.     

Crystallization kinetics of Ag-doped Se–Bi–Te chalcogenide glasses

Effect of Ag doping on the crystallization kinetics of amorphous Se_80.5Bi_1.5Te_18?yAg_y (for y = 0, 1.0, 1.5, and 2.0 at.%) glassy alloys has been studied by differential scanning calorimetry (DSC). The DSC curves recorded at four different heating rates are analyzed to determine the transition temperature, activation energy, thermal stability, glass forming ability, and dimensionality of growth during phase transformation. Present study shows that the thermal stability and the glass-forming ability increase with an increase in the Ag content which is in agreement with the earlier studies. Our results show that Se_80.5Bi_1.5Te₁₆Ag₂ composition is thermally more stable and has a little tendency to crystallize in comparison to other compositions under study. The increase in thermal stability with increasing Ag concentration is attributed to an increase in the cohesive energy.     

Investigation of curing kinetics of epoxy resin/novel nanoclay–carbon nanotube hybrids by non-isothermal differential scanning calorimetry

Chemical hybrid of nanoclay (NC)/carbon nanotube (CNT) was synthesized via growth of CNTs by chemical vapor deposition. The cure kinetics of epoxy resin in the presence of novel chemical hybrid of NC/CNT (CNC) was studied by non-isothermal differential scanning calorimetry. The effect of the CNC on cure kinetics was compared with conventional nanofillers such as CNTs, NC, and physical mixture of them (PNC). The kinetic parameters of the cure reaction were determined by iso-conversional method. The accelerating effect of CNT, CNC, and PNC in initial stage of cure reaction was related to the high thermal conductivity of CNTs, while the decelerating effect of nanofillers as the cure proceeded can be attributed to the reduction of polymer molecules motion caused by enhanced viscosity. The apparent activation energy (E _α) as the function of conversion (α) was calculated by five methods categorized into two different types: (1) conversion-dependent methods: Kissinger–Akahira–Sunose (KAS), Ozawa–Flynn–Wall (OFW), and Friedman; (2) conversion-independent methods: Kissinger and Augis. The accelerating effect of CNT, PNC, and CNC was observable as the reduced E _α values in low conversion only with KAS and OFW methods. The reverse trend of E _α values was observed with the introduction of these nanofillers at high conversions. The uniqueness of the CNC was more marked in increasing E _α values of epoxy after initial stage due to its special 3D structure of CNC. Calculated data using KAS and OFW methods showed the best agreement with the obtained experimental data.     

Calorimetric study of Sb-modified Ge–Se–Te glassy alloys

The glassy compositions of Ge ₁₆ Se ₅₂ Te _32?x Sb _x system, obtained using rapid melt quenching technique, have been characterized by calorimetric study at different heating rates in this study. A systematic investigation of the crystallization kinetics is carried out for these compositions. Composition corresponding to atomic % 8 of Sb has good thermal stability. The material exhibits the unique thermal properties, which makes it suitable to use for electrical or memory switching devices. Various thermal parameters, activation energies of glass transition and crystallization are calculated using relevant approaches.     

Fast-scan vs conventional differential scanning calorimetry (DSC) techniques in detection of crystallization events of tolbutamide–polyethylene glycol composite

This study investigated the capacity of fast-scan (400 °C min^?1) against conventional (10 °C min^?1) differential scanning calorimetry (DSC) techniques to track crystallization phenomenon in tolbutamide–polyethylene glycol 3000 composites prepared by hot melt method (mass ratios 1:1, 1:5, and 1:9) and stored at 25 and 75 % relative humidities. Drug crystallization in composites was indicated by X-ray diffractometry (XRD) and scanning electron microscopy characterization over 40 days storage. With reference to XRD as gold measurement standard, fast-scan DSC could not map the crystallization events of composites (Pearson correlation: fast-scan DSC peak temperature and enthalpy versus XRD peak intensity and area, p > 0.05). Conventional DSC was able to indicate marked drug crystallization through an increase in endothermic enthalpy value of peaks at high temperature regimes between 250 and 360 °C due to formation of high melting point crystal form.     

The density and surface tension of In–Sn and Cu–In–Sn alloys

Abstract  

The density and surface tension of binary In–Sn and ternary Cu–In–Sn alloys have been measured by a sessile-drop method. Decrease of the density and of the surface tension was observed with rising temperature. With increased Sn content in the alloys, the density increased while the surface tension reduced slightly. Addition of Cu could significantly increase the density and surface tension in the Cu–In–Sn system. The surface tension of the Cu–In–Sn alloys was also calculated by means of Butler’s equation, and compared with experimental values, showing good agreement.     

Thermogravimetric and differential scanning calorimetric investigations of manganese–glycine interactions

Thermogravimetric (t.g.) and differential scanning calorimetric (d.s.c.) data have been used to study metal–amino acid interactions in adducts of general formula MnCl₂ · ngly (gly = glycine, n = 0.7, 2.0, 4.0 and 5.0). All the prepared adducts exhibit only a one step mass loss associated with the release of glycine molecules, except for the 0.7gly adduct, which exhibits two glycine mass loss steps. From d.s.c. data, the enthalpy values associated with the glycine mass loss can be calculated: MnCl₂ · 0.7gly = 409 and 399 kJ mol^–1, MnCl₂ · 2.0gly = 216 kJ mol^–1, MnCl₂ · 4.0gly = 326 kJ mol^–1 and MnCl₂ · 5.0gly = 423 kJ mol^–1, respectively. The enthalpy associated with the ligand loss, plotted as function of the number of ligands for the n = 2.0, 4.0 and 5.0 adducts, gave a linear correlation, fitting the equation: H (ligand loss)/kJ mol^–1 = 67 × (number of ligands, n) + 76. A similar result was achieved when the enthalpy associated with the ligand loss was plotted as a function of the _a(COO^–) bands associated with the coordination through the carboxylate group, 1571, 1575 and 1577 cm^–1, respectively, for the n = 2.0, 4.0 and 5.0 adducts, giving the equation H (ligand loss) /kJ mol^–1 = 33.5 × _a(COO^–) /cm^–1 – 52418.5. This simple equation provides evidence for the enthalpy associated with the ligand loss being very closely related to the electronic density associated with the metal–amino acid bonds.