Amorphous to crystalline phase transition in glassy Se65Te20Ag15 alloy

In the present work, the amorphous to crystalline phase transition of chalcogenide glass Se₆₅Te₂₀Ag₁₅ has been studied using differential scanning calorimetric (DSC) measurements. The heating rate dependence of crystallization peaks has been used for the determination of activation energies of glass transition (E _g) and crystallization (E _c). Different non-isothermal methods have been used for this purpose. Other useful kinetic parameters such as the order parameter (n), the numerical factor of crystallization mechanism (m) and the frequency factor (K _o) of the rate constant (K) have been also determined.     

Metal-induced effects on the glass transition kinetics of glassy Se70Te30 alloy

The calorimetric measurements have been made in glassy Se₇₀Te₃₀ and Se₇₀Te₂₈M₂ (M?=?Ag, Cd, and Zn) alloys using non-isothermal differential scanning calorimetry technique to see the effects of Ag, Cd, and Zn additives on the glass transition kinetics of binary Se₇₀Te₃₀. From the heating rate dependence of glass transition temperature, T _g, different kinetic parameters of glass transition have been evaluated. The composition dependence of glass transition temperature T _g and the related activation energy (E_t ) is also discussed.     

Role of Bi incorporation on glass transition kinetics in glassy Se78Te20Sn2 alloy

In this communication, we report the results of calorimetric measurements on the samples of recently synthesized multi-component glassy alloys of Se_78?xTe₂₀Sn₂Bi_x (0 ≤ x ≤ 6) system. For calorimetric study of glass transition kinetics, differential scanning calorimetry (DSC) technique has been used in non-isothermal mode. Peak glass transition temperature (T_g) is determined using the DSC scans. Kinetic parameters A and B of glass transition are determined using heating rate dependence of T_g. Activation energy of glass transition (E_g) has been calculated using Moynihan and Kissinger methods. Glass-forming ability and thermal stability are also determined using Hurby and Saad–Poulin relations, respectively.     

Crystallization kinetics and thermal stability in Se85-xTe15Sbx chalcogenide glasses

Crystallization process of Se_85-xTe₁₅Sb_x (x = 2.7, 7.5, 10 and 15 at %) chalcogenide glasses has been studied by using differential scanning calorimetry (DSC) with different heating rates. These glasses are found to have a double glasses transition and overlapped crystalline phases for Se₇₀Te₁₅Sb₁₅ glass while single glasses transition and single crystallization stage for other glasses. Glass transition temperature, T_g, onset crystallization temperature, T_c, and peak crystallization temperature, T_p, are found to be dependent on composition and heating rates. Values of various kinetic parameters such as activation energy of glass transition, E_g, activation energy of crystallization, E_c, Hurby number, H_r, thermal stability, S_p, rate constant, K_p, and Avrami exponent, n, are determined for the present systems. Results indicate that rate of crystallization is dependent on thermal stability and glass-forming ability. Crystallization mechanism occurs in two dimensions for studied compositions. Crystalline phases resulting from DSC and scanning electron microscopy have been identified by using X-ray diffraction.     

Kinetic study of non-isothermal crystallization of BixSe100−x chalcogenide glasses

Results of differential thermal analysis (DTA) under non-isothermal conditions on four glasses of Bi_xSe_100−x (x=5, 10, 15 and 25 at%) are reported and discussed. The glass transition temperatures (T_g), the onset crystallization temperatures (T_c) and the peak temperatures of crystallization (T_p) were found to be dependent on the compositions and the heating rates. From the dependence on the heating rates of (T_g) and (T_p), the activation energy for glass transition, E_g, and the activation energy for crystallization, E_c, are calculated and their composition dependence is discussed. The crystalline phases resulting from DTA and scanning electron microscopy (SEM) have been identified using X-ray diffraction. According to the Avrami exponent (n), the results show a one-dimensional growth for the composition Bi₅Se₉₅ and two-dimensional growth for the compositions Bi₁₀Se₉₀, Bi₁₅Se₈₅ and Bi₂₅Se₇₅. The kinetic parameters determined have made it possible to discuss the glass-forming ability.     

Thermo-kinetic behaviour of Ge20Te75I5 glass for infrared optics

The iodine-doped GeTe₄ infrared chalcogenide glass was studied by means of differential scanning calorimetry DSC, X-ray diffraction XRD, Raman spectroscopy and infrared microscopy. Extensive non-isothermal thermo-kinetic characterisation of the glass transition, crystallisation and melting phenomena was performed in dependence on the particle size. The Tool–Narayanaswamy–Moynihan model was applied to describe the enthalpy relaxation processes: the compositional evolution of the relaxation parameters was then explained in terms of the structural changes and movements of the characteristic structural units. Mathematic deconvolution was applied to treat the complex crystallization kinetics – two crystal growth sub-processes were identified and described in terms of the autocatalytic ?esták-Berggren model. Based on the XRD and microscopic analyses the following crystallization mechanisms were revealed: initial precipitation of tellurium (surface-located) followed by a combined surface- and bulk-located formation of GeTe and GeI₄ phases. Based on the DSC results obtained for fine powders, the presence of mechanically induced defects was found to accelerate the Te precipitation, the consequences of which are discussed with regard to the performance of nowadays glass stability criteria.     

Cold crystallization from chiral smectic phase

Cold crystallization of liquid crystalline (S)-4’-(1-methylheptyloxycarbonyl) biphenyl-4-yl 4-[7-(2,2,3,3,4,4,4-heptafluorobutoxy) heptyl-1-oxy]-2-fluorobenzoate (3F7HPhF) was studied in isothermal as well as non-isothermal conditions. For isothermal conditions at temperatures between 233 and 250?K X-ray diffraction and differential scanning calorimetry were used. The crystallization kinetics was described by the Avrami–Avramov model, and the values of Avrami exponent, characteristic time and activation energy were determined. The kinetics of the cold crystallization in non-isothermal conditions for chosen heating rates up to 0.5?K/s was studied by differential scanning calorimetry and analyzed using Ozawa, Mo and Augis–Bennett models. Cold crystallization was found to be three-dimensional and controlled by diffusion both in the isothermal and non-isothermal process, however the activation energy determined in the non-isothermal process is about two times smaller than in the isothermal one.     

Crystallization kinetics and thermal stability of Se98-x Zn2In x chalcogenide glasses

In this paper, we report on the non-isothermal crystallization kinetics of Se_{98 ?x} Zn₂In _x (0 ≤ x ≥ 10) chalcogenide glasses. The onset crystallization activation energy E _c, peak crystallization activation energy E _p and overall crystallization activation energy E have been determined by different approaches. The values of E _c, E _p and E have minima at a composition corresponding to 6 at% In. However the stability factor S and the crystallization rate constant stability factor K have a maximum and a minimum, respectively, at in the same composition. The nucleation and growth order parameter n, and the dimension order parameter m, are also determined and discussed for the present glasses.     

The effect of indium additive on crystallization kinetics and thermal stability of Se-Te-Sn chalcogenide glasses

The crystallization kinetics of bulk Se_90−xTe₅Sn₅In_x (x=0, 3, 6 and 9) multi-component chalcogenide glasses have been studied using differential scanning calorimetry (DSC) with heating rates 5, 10, 15 and 20 K/min under non-isothermal conditions. Values of various kinetic parameters of crystallization, such as onset crystallization temperature (T_c), peak crystallization temperature (T_p), activation energy of crystallization (E_c), rate constant (K_p), Hruby number (K_gl) and the order parameter (n) have been determined. It was found that activation energy of crystallization and rate constant (K_p) are minimum at 9 at% In. On the basis of the obtained experimental data the temperature difference (T_c−T_g) and K_gl increase with In concentration, which further indicates that 9 at% In glass is most thermally stable in the entire composition range of investigation.     

Structural and crystallization behavior of (Ba,Sr)TiO3 borosilicate glasses

Various glass samples were prepared by melt quench technique in the glass system [(Ba_{1? x} Sr _x ) TiO₃]–[2SiO₂–B₂O₃]–[K₂O] doped with 1?mole% of La₂O₃. Infrared spectra show the number of absorption peaks with different spliting in the wave number range from 450 to 4000?cm^?1. Absorption peaks occurs due to asymetric vibrational streching of borate by relaxation of the bond B–O of trigonal BO₃. Raman spectra show the Raman bands due to ring-type metaborate anions, symmetric breathing vibrations BO₃ triangles replaced by BO₄ tetrahedra, and symmetric breathing vibrations of six-member rings. The differential thermal analysis of a glass sample corresponding to composition x?=?0.0 shows crystallization temperature at 847°C and glass transition temperature at 688°C. X-ray diffraction (XRD) pattern of glass ceramic samples shows the major crystalline phase of BaTiO₃ whereas pyrochlore phases of barium titanium silicate. Scanning electron micrographs confirm the results of XRD as barium titanate is major crystalline phase along with pyrochlore phase of barium titanium silicate.     

压力对Zr46.75Ti8.25Cu7.5Ni10Be27.5大块非晶合金玻璃转变和晶化动力学的影响

利用X射线衍射和差示扫描量热分析研究了高温高压下Zr_46.75Ti_8.25Cu_7.5Ni₁₀Be_27.5大块非晶合金的玻璃转变和晶化行为，结果发现压力降低了该大块非晶合金中的自由体积、热焓和晶化激活能. 关键词： 大块非晶合金 高压 差示扫描量热分析 玻璃转变     

Effect of WO3 on the glass transition and crystallization kinetics of borotellurite glasses

Tellurite glasses of the system xWO₃–75TeO₂–(25 ? x)B₂O₃ (0 ≤ x ≤ 25 mol. %) were prepared and studied by differential thermal analysis to explore the effect of WO₃ on their glass transition and crystallization kinetics. The crystallization kinetics was studied under non-isothermal conditions using the formal theory of transformations for heterogeneous nucleation. The crystallization results were analyzed and both the activation energy of the crystallization process and the crystallization mechanism characterized. The phases into which the glass crystallizes were identified by X-ray diffraction. Diffractograms of the transformed material indicate the presence of microcrystallites of α-tellurite, Te_0.95W_0.05O_2.05, Te₂W and B₂O₃ in the amorphous matrix.     

Thermal and Structural Behaviors of Polypropylene Nanocomposites Reinforced with Single-Walled Carbon Nanotubes by Melt Processing Method

In this work, polypropylene (PP) matrix reinforced with several single-walled carbon nanotubes (SWNTs) concentrations were prepared by a melt-mixing method. The effect of SWNTs on the thermal degradation behavior of polypropylene was studied by thermal gravimetric analysis. The results revealed that adding the SWNTs into the PP can increase the decomposition temperature. The results obtained from differential scanning calorimetry showed that incorporating SWNTs reduced the crystallinity but increased the crystallization temperature of the PP. The mechanical measurements showed that the tensile modulus of the nanocomposite was greatly enhanced to 882 MPa, compared to 485 MPa for pristine PP. For wide-angle X-ray diffraction tests, two cooling methods were used. The addition of SWNTs to the polymer in slow-cooled samples resulted in partial crystallization in the γ -form, while SWNTs had no effect in water-cooled samples, the sample crystallizing in the α -form. Scanning electron microscopy observations on the fracture surface of the nanocomposites showed the dispersion of the SWNTs in the nanocomposites.     

In-situ and ex-situ study of crystallization behaviour of magnetron sputtered Ni63Zr37 amorphous thin film

ABSTRACT

The stages of crystallization of magnetron sputter-deposited Ni₆₃Zr₃₇ film with mostly amorphous structure have been investigated by differential scanning calorimetry (DSC) and in-situ annealing at 300°C by use of heating stage on a high-resolution transmission electron microscope (HRTEM). These results have been further confirmed by grazing incidence X-ray diffraction analyses of thin film specimens annealed ex-situ at 300°C for various durations. The temperature for crystallization found by DSC has been found to increase from 371°C to 434°C with an increase in heating rate from 3°C/min to 10°C/min, and the apparent activation energy for amorphous to crystalline transformation has been found as ～260.2?kJ/mol from the Kissinger plot. Studies on HRTEM using in-situ heating stage have shown the crystallization to occur on annealing at 300°C for ～10?min. Crystallization at a temperature lower than that found by DSC is attributed to structural relaxation with reduction of free volume due to thermal activation. It has been observed that Ni₃Zr forms first due to its large negative enthalpy of formation, and is followed by the formation of Ni-rich solid solution (Ni_ss) grains. HRTEM studies have shown grain rotation with the formation of partial dislocations at Ni₃Zr-Ni_ss interfaces as well as twinning followed by detwinning with dislocation formation in the Ni_ss matrix possibly to reduce the interfacial energy.     

Zr60Al15Ni25大块非晶合金晶化动力学研究

通过等温示差扫描量热法研究了Zr₆₀Al₁₅Ni₂₅大块非 晶合金的晶化动力学.实验结果表明，晶化过程的孕育期很短，即使在743 K这样低的温度下也不过0.52 min，而放热峰宽（反应整个晶化过程进行的时间）却随退火温度的降低明显增大，这说明了结晶过程是一个晶核长大控制的过程.Avrami指数表明在不同的退火温度，该合金的晶化机制发生了变化.晶化机制的变化是由于合金原子在不同温度下的扩散能力相差很大所致. 关键词： 晶化动力学 60Al₁₅Ni₂₅大块非晶合金')" href="#">Zr₆₀Al₁₅Ni₂₅大块非晶合金 示差扫 描量热法（DSC）     

Effect of Bi2O3 content on physical and optical properties of 15Li2O-15K2O-xBi2O3-(65−x) B2O3: 5V2O5 glass system

Multi-component bismuth borate glasses doped with vanadium ions 15Li₂O-15K₂O-xBi₂O₃-(65−x) B₂O₃: 5V₂O_5, (x=3, 5, 7, 10, 12 and 15) have been prepared using conventional melt quench technique. Characterization of the prepared glasses has been done using X-ray diffraction, differential scanning calorimetry and density measurements. The effect of Bi₂O₃ content on the optical properties of the present glass system is studied from the optical absorption spectra recorded in the wavelength range 200-800 nm. The fundamental absorption edge has been identified from the optical absorption spectra. The values of optical band gap for indirect allowed transitions have been determined using available theories. The origin of the Urbach energy is associated with the phonon-assisted indirect transitions. The density and molar volume studies indicate that Bi₂O₃ in these glasses is acting partly as network modifier and partly as network former. The variations in the optical band gap energies, density and molar volume with Bi₂O₃ content have been discussed in terms of changes in the glass structure. Values of the theoretical optical basicity, average crosslink density and the average electronic polarizability are also reported.     

Multiphase modelling of the growth kinetics of precipitates in Al-Cu alloys during artificial aging

ABSTRACT

In the aluminum industry, the needs of predictability of the kinetics of precipitation during the artificial aging processes increase as the targeted applications require the maximisation of properties at the lowest costs possible. In this regard, kinetics modelling can be helpful to design the heat treatment processes. Despite using many fitting parameters, available models show a lack of fitting with experimental data, especially for the apparent heat capacity measured at high temperatures by a differential scanning calorimeter (DSC). To address this issue, a mixed-mode model was recently developed for isothermal heat treatment, whereas non-isothermal heat treatment must be considered to compare the calculated results with those measured by isochronal heating in a DSC. In this contribution, the model is extended to non-isothermal heat treatments. To this end, the growth kinetics pathway and sequence of precipitation in a binary Al-Cu alloy have been simulated, optimising the pre-exponential factor and the activation energy of the interfacial mobility of the secondary phases. This calibration of the interfacial mobilities allowed a very good reproduction of the evolution of the apparent heat capacity with temperature. The model and calibrated interfacial mobilities were then used to compute the size evolution of θ′ precipitates in an Al-4?wt%Cu. The isothermal growth rates calculated at 4 temperatures were in good agreement with those measured and reported by independent researchers. The good predictability of the model indicates that the assumptions made were suitable and well funded, especially regarding the growth rates of embryos emerging from the subcritical growth regime.     

Physical properties of 8OS5 thioester studied by complementary methods

ABSTRACT

Properties of 4-n-pentylphenyl-4’-n-octyloxythiobenzoate (8OS5), belonging to the nOS5 homologous series, have been studied by complementary methods. The phase sequence, the phase transition temperatures, the thickness of molecular layers, the average distance between long axes of molecules and the correlation length were determined during cooling and heating. For the first time, simultaneous X-ray diffraction and differential scanning calorimetry measurements have been used to study mesomorphic properties. The results are compared with the ones obtained in standard measurements by means of differential scanning calorimetry, X-ray diffraction and polarizing optical microscopy. Meaning of experimental procedures applied in investigations of monotropic mesophases below a melting point is discussed.     

Design of high T g Zr-based metallic glasses using atomistic simulation and experiment

In this paper, we systematically investigate local atomic structures of Zr_100?x Al _x (0???x???72) alloys using molecular dynamics simulations. Radial distribution functions of Zr-Al configurations at 300 K indicate that Zr-Al metallic glasses form only when the Al atomic concentration is larger than 32%. Voronoi polyhedral analysis shows that Zr₄₀Al₆₀ has the highest fraction of ?0,0,12,0? icosahedra around Al atoms, which are characteristic of amorphous microstructures. Variations of thermal expansion coefficient and heat capacity of Zr_100?x Al _x (40???x???72) metallic glasses as a function of temperature from 1100 to 800?K reveal that Zr₄₀Al₆₀ has the highest transition temperature of 1008?K. To confirm the simulation results, Zr-Al metallic glasses were fabricated using co-sputtering deposition; differential scanning calorimetry testing suggests the highest crystallisation-onset temperature of above 920?K is within Zr_100?x Al _x where 43?<?x?<?61. The experimental finding is in a good agreement with the simulation predictions.     

Impingement effect on the glass-crystal transformation kinetics by using DSC under non-isothermal regime. Application to the crystallization of the several semiconducting alloys of the Sb-As-Se and Ge-Sb-Se glassy systems

A procedure has been developed for analyzing the evolution with time of the actual volume fraction transformed, for calculating the kinetic parameters and for analyzing the glass-crystal transformation mechanisms in solid systems involving formation and growth of nuclei. By defining an extended volume of transformed material and assuming spatially random transformed regions, a general expression of the extended volume fraction has been obtained as a function of the temperature. Considering the mutual interference of regions growing from separate nuclei (impingement effect) and from the above-mentioned expression, the actual volume fraction transformed has been deduced. The kinetic parameters have been obtained, assuming that the reaction rate constant is a time function through its Arrhenian temperature dependence. The theoretical method developed has been applied to the crystallization kinetics of a set semiconducting alloys, prepared in our laboratory, corresponding to the Sb-As-Se and Ge-Sb-Se glassy systems. The obtained values for the kinetic parameters agree satisfactorily with the calculated results by the Austin-Rickett kinetic equation, under non-isothermal regime. This fact allows to check the validity of the theoretical model developed.