Investigation DSC and XRD on the Crystallization Kinetics in the Phosphate Li2O−Li2WO4−TiO2−P2O5 Glassy Ionic System

This work aims to investigate the prepared glasses within the 20Li2O−(50−x)Li2WO4−xTiO2−30P2O5 system, with 0≤x≤15 mol%. The bonds constituting the framework of these glasses were studied by Raman spectroscopy. The data analysis of the chemical durability showed that the dissolution rates depend on the composition of each glass. Thermal analysis by DSC technique was used to determine the activation energy of crystallization, it found in the glass of composition (x= 5) that Ec= 184.482 kJ/mol. The determinate Avrami parameter is around 1.7 which allows suggesting the mechanism is surface crystallization. The crystallization process of the prepared glasses is carried out by heating samples at 550°c for 4 hours and 12 hours. The crystallized phases are identified by XRD. The results of X−ray diffraction analysis confirm that TiO2 acts mainly as network forming units. The crystalline phases Li2WO4 (JCPDS# 01−072−0086) and (JCPDS# 01−087−0409) are formed during the crystallization process. The formation of these crystalline phases into the glasses depends on the time of heating at fixed crystallization temperature. FTIR spectra of the glass–ceramics show nearly the same IR vibrational modes as their parent glasses.

Devitrification of Zr55Cu30Al15Ni5Bulk Metallic Glass under Heating and HPT Deformation

The nanocrystal formation in Zr55Cu30Al15Ni5 bulk metallic glass was studied under heat treatment and deformation. The activation energy of crystallization under heating is 278 kJ/mol. Different crystalline phases were found to be formed during crystallization under heating and deformation. At the first crystallization stage, the metastable phase with a hexagonal structure (lattice of space group P63/mmc with the parameters a = 8.66 Å, c = 14.99 Å) is formed under heat treatment. When the temperature rises, the metastable phase decays with the formation of stable crystalline phases. The crystalline Zr2Cu phase with the lattice of space group Fd3m is formed during crystallization under the action of deformation. It was determined that during deformation nanocrystals are formed primarily in the subsurface regions of the samples.

Comparative Investigation of Se–Te–M (M = Sb, Ge) Semiconducting Glassy Alloys: Thermal Characterization

Structural and thermal measurements have been performed in glassy Se78Te18M4 (M = Sb and Ge) alloys to study the effect of Sb and Ge additives on the kinetics of glass transition and crystallization. Kinetic parameters of glass transition and crystallization such as the activation energy of glass transition (Eg), the activation energy of crystallization (Ec) have been determined using different non-isothermal methods. It was found that Ge was more suitable dopant for phase change memory (PCM) devices due to its low activation energies as compared to Sb dopant.

Kinetic model of the crystallization process of Cu46Zr50Al4 metallic glass

Nanocomposite materials based on the Cu-Zr glass-forming system, which are an amorphous matrix with crystalline inclusions of the cubic B2 phase of the CuZr compound, are promising structural materials due to their unique mechanical properties. One of the methods for producing such materials is the heat treatment of amorphous samples. To develop optimal conditions for such processing, it is necessary to study the kinetics of crystallization of amorphous copper-zirconium. In this work, the crystallization processes, structure and thermal properties of the amorphous Cu46Zr50Al4 alloy, obtained by suction casting were studied for the first time in a wide temperature range from room temperature up to 600 °C. We reveal the complex character of the crystallization process of this alloy described by a three-step sequential reaction. Using a comprehensive approach, including calorimetric studies, X-ray phase analysis and kinetic modeling by multivariate nonlinear regression, we develop the kinetic model and estimate kinetic parameters of the crystallization processes in the alloy. We find that the best description of the experimental data is achieved when autocatalytic equations are used to model crystallization processes: a heterogeneous n-th order reaction with autocatalysis, as well as the Prout-Tompkins equation. The found activation energy of crystallization of the alloy is Ea = 387.59 kJ/mol. Based on the results obtained, we propose a procedure for fabricating the nanocomposite materials by heating an amorphous alloy up to temperatures of about 420-460 °C.

Effect of Bubbles on Crystallization Behavior of CaO–SiO2 Based Slags

Surface longitudinal cracks are a serious problem and particularly prevalent in the casting of peritectic steel (carbon content between 0.10%C and 0.18%C, non-alloyed). It is usually alleviated by controlling the horizontal heat transfer from the steel shell to the mold through increasing the crystallization performance of slags. In the actual continuous casting process, a large number of bubbles are formed in the molten slags, and the crystallization properties of the mold fluxes are affected by bubbles. Therefore, an investigation of the influence of bubbles on the crystallization performance of mold fluxes was carried out by applying the hot thermocouple technique and it is hoped that surface longitudinal cracks can be solved in this way in the peritectic steel casting process. The continuous cooling transformation (CCT) diagrams and time–temperature transformation (TTT) diagrams were constructed for an analysis of the crystallization kinetics. The results showed that the crystallization ability of mold fluxes was enhanced by adding bubbles through shortening the incubation time of crystallization, increasing the critical cooling rate, and decreasing the activation energy of crystallization. As a result, the crystalline fraction, slag film thickness, and surface roughness of the slag films were improved, but the crystalline phase was not affected by bubbles. With an increase of the bubble content remaining in the molten slag, the growth mechanism of the cuspidine crystal phase changed from a low dimension to a high dimension, and the content of the molten slag’s structure unit (Q1) needed for cuspidine in the molten slag was markedly increased.

Effect of Mg contents on the mechanical proprieties and precipitation kinetics in Al–3.3 wt.% Cu alloy

The effect of additional Mg on the microstructure, mechanical properties, and transformation kinetics during aging in Al–3.3 wt.% Cu alloy was studied. The compositions and microstructure were examined by X-ray diffraction, Differential scanning calorimetry (DSC) and scanning electron microscope (SEM) with energy dispersive X-ray spectroscopy (EDS). The results show that the Mg in the Al–Cu alloy mainly precipitated to the grain boundaries during the process of transformation and formed a ternary Al2CuMg metallic compound and the rate of discontinuous precipitation reaction decreases with increasing concentration of Mg. The activation energy of crystallization was evaluated by applying the Kissinger equation.

Non-Isothermal Crystallization Kinetics of Mg61Zn35Ca4 Glassy Alloy

The non-isothermal crystallization kinetics of Mg61Zn35Ca4 glassy alloy prepared via melt-spinning were studied by using isoconversion method. The crystalline characterization of Mg61Zn35Ca4 was examined by X-ray diffraction. Different scanning calorimeter was used to investigate the non-isothermal crystallization kinetics at different heating rates (3-60 K/min). The calculated value of Avrami exponent obtained by Matusita method indicated that the crystalline transformation for Mg61Zn35Ca4 is a complex process of nucleation and growth. The Kissinger-Akahira-Sunose method was used to investigate the activation energy. The activation energy of crystallization varies with the extent of crystallization and hence with temperature. The Sestak-Berggren model was used to describe the non-isothermal crystallization kinetics.

Effect of montmorillonite on the crystallization and thermal degradation of poly(propylene-co- ethylene-co-1-butene) nanocomposites

Polymeric nanocomposites based on poly(propylene- co-ethylene- co-1-butene) (PEBC) were elaborated by melt mixing using an organophilic montmorillonite (o-MMT) and maleated PEBC (PEBCg) as compatibilizer. The effect of clay concentration, PEBCg:o-MMT ratio, and grafting degree of the compatibilizer were studied. X-ray diffraction and scanning electron microscopy show formation of partially intercalated structures in all compatibilized composites with well-distributed small tactoids. According to the differential scanning calorimetry results, the anhydride groups of the compatibilizer have a marginal nucleating effect, while the o-MMT causes a slight decrease in the crystallization temperature of the polymer. PEBC presents the largest activation energy of crystallization ( Eα), while the composites show lower Eα than their matrices. It is also observed that the rate of degradation of PEBC is not affected by the presence of PEBCg. The nanoclay, on the other hand, retards the decomposition process of the polymeric matrix in about 40°C and augments its rate of degradation approximately four times.

Experimental and theoretical approaches on thermal and structural properties of Zn doped BSCCO glass ceramics

Thermal properties of Cu–Zn partially substituted Bi1.8Sr2Ca2Cu3.2-xZnxO10+δ (x = 0, 0.1 and 0.5) glass-ceramic systems have been investigated with the help of a differential thermal analyzer (DTA) by using Johnson-Mehl-Avrami-Kolmogorov (JMAK) approximation. Non-isothermal crystallization kinetics of the samples has been tested. The calculated values of activation energy of crystallization (E) and Avrami parameter (n) ranged between 306.1 and 338.3 kJ.mol-1 and 1.29 and 3.59, respectively. Crystallization kinetics was compared following the partial substitution, before and after Zn doping of the sample. In addition, by using a scanning electron microscope (SEM) and X-ray powder diffractometer (XRD), structural properties of Zn doped BSCCO glass-ceramic samples were determined. Surface morphology of the samples was studied by SEM measurements. Lattice parameters and volume of the samples were calculated from the XRD measurements.