Activation Energy Of Crystallization Process Research Articles

Structural development and kinetic analysis of PbTiO3 powders processed at low-temperature via new sol-gel approach

The synthesis of crystalline lead titanate powder by a generic low-temperature sol-gel approach is developed. Acetoin was added as ligand, instead of the commonly used alkanolamines, to ensure total dissolution of the precursor compounds. The feasibility of the acetoin-Ti isopropoxide complex as a new precursor of PbTiO3 perovskite particles via sol-gel method has been demonstrated. No excess lead has been introduced. Nanometric PbTiO3 crystallites have been formed at 400 °C under atmospheric pressure from titanium isopropoxide and lead acetate in alcoholic solution by remarkably low activation energy of crystallization process of 90 kJ mol−1. The powders show tetragonal lattice and dendritic morphology. In addition to the effect of heat-treatment temperature, time, and atmosphere, the sol chemistry particularly influenced the phase composition, particle size, and particle morphology. The use of different ligands significantly modified powder morphology. The extent of the crystallization was quantitatively evaluated by differential thermal analysis and analyzed by Johnson-Mehl-Avrami approach. The crystallization followed two rate regimes depending on the interval of the crystallized fraction.

Polyethylene Glycol–CaCl2 Coordination Compounds as a Novel Form‐Stable Phase Change Material with Excellent Thermophysical Properties

Polyethylene glycols (PEGs) have been extensively studied as phase change materials (PCMs). To overcome the problem of liquid leakage, the authors firstly report a novel form‐stable phase change material (FSPCM) using coordination compound. The structure, morphology, thermal property, and thermal stability of the self‐prepared samples are determined. The obtained results confirm the existence of coordination bonds between PEG and Ca2+ species, and no liquid leakage is observed for the synthesized PEG–CaCl2 composites at temperatures as high as 120 °C. The PEG8000–CaCl2 (1:2) FSPCM exhibits a relatively large latent heat of 147.7 J g−1, corresponding to 87.8% of that of pure PEG. From the dynamical viewpoint, the activation energy of crystallization process is increased by only 5.2% for the PEG8000–CaCl2 composite due to the formation of coordination bonds; however, the activation energy is reduced by 18.3% during melting process. After adding 3 wt% conductive carbon black, the heat storage performance of the PEG phase change material can be optimized. The PEG‐CaCl2 composite would be a promising material for thermal energy storage applications and can be used in various engineering fields.

Crystallization kinetics of PbTiO3 ferroelectric films: Comparison of microwave irradiation with conventional heating

Lead titanate (PTO) films were deposited onto Pt/Ti/SiO2/Si substrates by a sol-gel method and annealed by microwave irradiation and conventional heating. In contrast to conventional heating, microwave irradiation can crystallize the PTO films at a low temperature of 450°C or at 550°C for only 5min. The XRD and TEM studies reveal that microwave radiation can reduce the nucleation time, and increase the growth rate of perovskite grains in the crystallization process. Moreover, the results using the Avrami’s model show that the effective activation energy for crystallization process by microwave irradiation is 131kJ/mol, much lower than that for the PTO films by conventional heating (216kJ/mol). Therefore, microwave irradiation can reduce the effective activation energy for the nucleation and grain growth of the perovskite phase during the crystallization process, contributing to a low-temperature or a short-time preparation process of ferroelectric films.

Non-isothermal free-models kinetic analysis on crystallization of europium-doped phosphate glasses

A kinetic analysis under non-isothermal conditions has been performed on europium-doped phosphate glasses with molar composition 20.42 Li2O–10.25 Al2O3–58.49 P2O5–7.23 BaO–1.44 La2O3–2.16 Eu2O3 and particle size <30µm, >50µm. Differential scanning calorimetry measurements at four heating rates, from room temperature up to 900°C using synthetic air have revealed that no significant mass change occurs during the heat treatment, as normally expected for glass samples. The step changes in heat flow signals are associated with the presence of three important effects: the first one, that occurs as a slope corresponds to the glass transition effect (Tg) is followed by two exothermic peaks, first of them more pronounced, associated with the first crystallization process (Tp1), while, the second one, lower in intensity corresponds to the second crystallization (Tp2) process. As expected, all peaks (Tg, Tp1 and Tp2) increase with the increasing of the heating rate. Both the activation energy of crystallization process and the crystallization mechanism were comparatively analyzed by two free-model estimations and using the formal theory of transformations for heterogeneous nucleation.

Crystallization kinetic studies on Bi1.75Pb0.25Sr2Ca2Cu3-xSnxOδ glass-ceramic by using non-isothermal technique

The Sn substituted Bi1.75Pb0.25Sr2Ca2Cu3-xSnxOδ glass ceramic (where x=0, 0.1, 0.3, and 0.5) samples were prepared by the melt-quenching method. Crystallization kinetic studies of the samples were conducted using the differential thermal analysis (DTA). The oxidation behavior of the samples was also analyzed using the thermogravimetry analysis (TG). The DTA curves were registered with different heating rates (5, 10, 15, and 20Kmin−1) up to 1200±0.5K. The crystallization results were analyzed, and activation energy of crystallization process as well as the crystallization mechanisms and the effect of Sn substitution on powder glass ceramic were characterized. The glass transition temperature (Tg), the first crystallization peak temperature (Tx1) and the second crystallization peak temperature (Tx2) values were obtained as 713.0±0.5–746.6±0.5, 731.0±0.5–760.8±0.5 and 789.0±0.5–820.1±0.5K, respectively. The activation energy (Ea) of crystallization was estimated from DTA results to be about 332.8±0.1, 358.0±0.1, 353.1±0.1 and 348.9±0.1kJ/mol for x=0, 0.1, 0.3 and 0.5, respectively, by using the Kissinger method. The Avrami parameter (n) values calculated at different Sn ratio from DTA results were found to be between 1.70±0.01 and 2.57±0.01, results reflect the growth of small particle with a decreasing nucleation rate.

Thermal characteristics and crystallization kinetics of tellurite glass with small amount of additive As2O3

The crystallization kinetics of the TeO2/TiO2/As2O3 glassy system was studied under nonisothermal conditions. The method was applied to the experimental data obtained by differential thermal analysis (DTA), using continuous-heating techniques. In addition, two approaches were used to analyze the dependence of glass transition temperature (Tg) on the heating rate (β): One is the empirical linear relationship between (Tg) and (β); The other approach is the use of straight line from the plot of \( \ln \left( {T_{\text{g}}^{2} /\beta } \right)\,{\text{vs}} .\,1/T_{\text{g}} \) for evaluation of the activation energy for glass transition. The crystallization results are analyzed, and both the activation energy of crystallization process and the crystallization mechanism are characterized.

Crystallization kinetics of new compound of V 2O 5–PbO–Li 2O–Fe 2O 3 glass using differential thermal analysis

Different glasses with nominal compositions of (70 − x)V 2O 5– xPbO–20Li 2O–10Fe 2O 3 (0 ≤ x ≤ 12.5 mol.%) were successfully obtained by the melt quenching technique. Crystallization kinetics of these glasses was studied under non-isothermal conditions using the formal theory of transformations for heterogeneous nucleation. The procedure was applied to the experimental data obtained by differential thermal analysis, using several measurements at different heating rates. In addition, from the heating rate dependence of the glass transition temperature, the glass transition activation energy was derived. The crystallization results are analyzed and both the activation energy of crystallization process and the crystallization mechanism are characterized in terms of Gao–Wang method. The phases at which the glass crystallizes after the thermal process have been identified by X-ray diffraction. The diffractogram of the transformed material indicates the presence of microcrystallites of LiV 15O 35.5, Pb 3(VO 4) 2 and PbO 2 beside the remaining an additional amorphous matrix.

Non-isothermal crystallization kinetics of ZnO–BaO–B 2O 3–SiO 2 glass

Glass of composition 40SiO 2–30BaO–20ZnO–10B 2O 3 (mol%) was made by conventional melting and casting process. Crystallization kinetics of above glass has been investigated under non-isothermal conditions, using the formal theory of transformations for heterogeneous nucleation. The procedure is applied to the experimental data obtained by differential thermal analysis (DTA), using continuous-heating techniques. The crystallization results are analyzed, and both the activation energy of crystallization process as well as the crystallization mechanism is characterized. Dilatometric measurement of this glass was also done and data obtained was used to calculate the viscosity of the formed glass. Development of crystalline phases on thermal treatments of the glass at various temperatures has been analyzed by X-ray diffraction. Microstructure of the crystalline phases was investigated by scanning electron microscopy (SEM) and the development of various structural features with variation in heat treatment cycle was observed. The nucleation and growth of these phases in the matrix of glass has been described and discussed.

Influence of Alloying Additions on Enhancement of Soft Magnetic Properties Effect and Crystallization in FeXSiB (X=Cu, V, Co, Zr, Nb) Amorphous Alloys

The crystallization and optimization of magnetic properties effects in FeXSiB (X=Cu, V, Co, Zr, Nb) amorphous alloys were studied by applying X-ray diffraction methods, high resolution transmission electron microscopy (HRTEM), resistometric and magnetic measurements. The temperatures of the first and the second stage of crystallization, the 1h optimization annealing temperature and the Curie temperature were determined for different amorphous alloys. Activation energies of crystallization process were obtained by applying the Kissinger method. The influence of alloy additions on optimization effect and crystallization processes was carefully examined.

Non-isothermal crystallization kinetic studies on a ternary, Sb 0.14As 0.38Se 0.48 chalcogenide semi-conducting glass

Crystallization kinetics of ternary, Sb 0.14As 0.38Se 0.48, chalcogenide glassy alloy was studied under non-isothermal conditions, using the formal theory of transformations for heterogeneous nucleation. The procedure was applied to the experimental data obtained by differential scanning calorimetry (DSC), using continuous-heating techniques. In addition, from the heating-rate dependence of the glass transition temperature, the glass transition activation energy was derived. The crystallization results are analyzed, and both the activation energy of crystallization process and the crystallization mechanism are characterized. The phases at which the alloy crystallizes after the thermal process have been identifed by X-ray diffraction. The diffractogram of the transformed material indicates the presence of microcrystallites of Sb 2Se 3 and AsSe, remaining an additional amorphous matrix.

The effect of hydrogen on the crystallization behavior of amorphous PdSi alloys

Differential scanning calorimetry, X-ray diffractometry and Optical metallography were used to study the effect of hydrogen atmosphere and surface treatment on the crystallization process in PdSi metallic glasses. In Pd 80Si 20 metallic glasses, the surface treatment by mechanical polishing with 1200 SiC induces surface crystallization in which preferred nucleation at the surface occurs, while homogenous crystallization occurs in as-quenched samples without surface grinding. In amorphous Pd 85Si 15, the crystallization occurs simultaneously from the sample surface and in the bulk. Surface treatment by mechanical polishing does not change the crystallization morphology. These results were not affected by the atmosphere of argon or hydrogen. It is shown that the surface crystallization, which is dominant in the initial stages of the transformation, is revealed by the low temperature shoulder of the main peak of crystallization in a DSC trace. The process of crystallization of amorphous Pd 80Si 20 and Pd 85Si 15 is found to be impeded by absorbed hydrogen, this having been measured by the increase of both crystallization temperature and activation energy for crystallization process in a hydrogen environment. Such crystallization behavior can be explained by assuming that hydrogen reduces the free volume available for rearrangements of host atoms of the metallic glasses.

Dissolution kinetics of complexes of sulfamethoxazole and sulfamonomethoxine with 18-crown-6.

The dissolution profiles of the complexes of sulfamethoxazole (SMO) and sulfamonomethoxine (SMM) with 18-crown-6 (1, 4, 7, 10, 13, 16-hexaoxacyclooctadecane, 18-C-6) involving simultaneous decomplexation were investigated kinetically in detail by a dispersed amount method and a stationary disk method in comparison with those of intact SMO and SMM. The dissolution rates of the complex before and after the phase change, Rc and Ro, respectively, the saturated concentrations of complex and intact drug, Csc and Cso, respectively, the rate constant of crystallization process, kr, and the dissolution rate constant, kt, were calculated by the stationary disk method. Analyzing the values of kr and kt obtained at various temperatures, the activation energies of crystallization and dissolution process were determined. The activation energy of crystallization process seemed small compared with the past data reported on organic medicinals.