Study Of Non-isothermal Crystallization Kinetics Research Articles

Crystallization Kinetics and Melting Behaviour of the Novel Biodegradable Polyesters Poly(propylene azelate) and Poly(propylene sebacate)

AbstractNovel biodegradable poly(propylene sebacate) (PPSeb) and poly(propylene azelate) (PPAz) polyesters were synthesized and fully characterized using WAXD, standard DSC, high‐rate DSC, and modulated‐temperature DSC. Multiple‐melting behaviour, observed for samples isothermally crystallized from the melt, was attributed to sequential melting–recrystallization–remelting. Study of isothermal and nonisothermal crystallization kinetics revealed a higher crystallization rate for PPSeb compared to PPAz. The Avrami and the Lauritzen‐Hoffman models were successfully applied to DSC measurements, using also data obtained after self‐nucleation, in order to diminish the effect of primary nucleation. Finally, the effective activation energy was estimated using the differential isoconversional method of Friedman.magnified image

Effect of BaO on the crystallization kinetics of glasses along the Diopside–Ca-Tschermak join

We report on the effect of BaO on the crystallization kinetics of glasses in the diopside (CaMgSi2O6)–Ca-Tschermak (CaAl2SiO6) system. Partial substitution (i.e. 5%, 10% and 20%) of Ba2+ for Ca2+ was attempted in composition CaMg0.8Al0.4Si1.8O6, in three different glasses while partial substitution of B3+ for Al3+ was made in the fourth glass. Structural investigations on the glasses have been made by density measurements, molar volume and Infra-red spectroscopy (FTIR). Non-isothermal crystallization kinetic studies have been employed to study the mechanism of crystallization in all the four glasses. The Avrami parameter for the glass powders is ∼2, indicating the existence of intermediate mechanism of crystallization. Crystallization sequence in the glasses has been followed by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM) and FTIR. Augite crystallized out being the dominant phase in all the glass–ceramics, while different polymorphs of BaAl2Si2O8 were present as secondary or minor phases.

Study of Crystallization Kinetics in Glasses along the Diopside-Ca-Tschermak Join

We report on the thermal stability and crystallization kinetics of the glasses in the diopside (CaMgSi2O6)–Ca-Tschermak (CaAl2SiO6) system. Four glasses with compositions corresponding to different diopside/Ca-Tschermak ratio were studied. Structural investigations on the glasses have been made by employing Infrared spectroscopy (FTIR). Activation energies for structural relaxation and viscous flow have been calculated using the data obtained from differential thermal analysis. The existence of glass-in-glass phase separation was observed in all the glasses. Kinetic fragility of the glasses along with other thermal parameters have also been calculated. Nonisothermal crystallization kinetic studies have been employed to study the mechanism of crystallization in all the four glasses. The Avrami parameter for the glass powders is ∼2, indicating the existence of intermediate mechanism of crystallization. Crystallization sequence in the glasses has been followed by X-ray diffraction analysis, scanning electron microscopy, and FTIR.

A Study on Synthesis, Crystallization, and Magnetic Behavior of Nanocrystalline Fe-Based Metallic Glasses

In the present work, structure of the as-cast melt-spun ribbons, nonisothermal crystallization kinetics, and the effect of heat treatment on the magnetic properties have been studied. X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses have revealed the presence of amorphous and partly crystalline structures in the as-cast Fe67Co18Si1B14 and Fe57Co26Cr3B14C0.2 metallic-glass ribbons, respectively. The crystalline phase present in the as-cast Fe57Co26Cr3B14C0.2 metallic-glass was identified as α-Fe. Direct transformation from liquid to α-Fe has been analyzed from a thermodynamic and kinetics point of view. The differential scanning calorimetry (DSC) studies have shown two-stage crystallization behavior. The primary and secondary crystallization phases were identified as bcc-Fe(Co) and bct-(Fe,Co)3(Si,B), respectively. Kissinger and Gao et al. methods were employed for nonisothermal crystallization kinetic studies. The activation-energy values obtained by the two models were in good agreement. The nucleation and growth morphologies of crystalline phases have been explained on the basis of the Avrami exponent, which were found to be consistent with the observed microstructures. The magnetic properties of as-cast amorphous ribbons showed low coercivity, and this has been attributed to averaging of magnetocrystalline anisotropy over grains coupled within an exchange length, i.e., based on a random anisotropy model. The influence of microstructure on magnetic properties was studied by crystallizing the amorphous phase at 400 °C for 3 hours. The saturation magnetization and coercivity had increased after crystallization for both alloys.

Influence of NiO on the crystallization kinetics of near stoichiometric cordierite glasses nucleated withTiO2

This work presents the effect of NiO on the thermal behavior and the crystallizationkinetics of glasses lying near the stoichiometric cordierite composition nucleated withTiO2. Three glasses with NiO content varying between 1 and 5 mol% have been synthesized inPt crucibles. Activation energies for structural relaxation and viscous flow have been calculatedusing the data obtained from differential thermal analysis (DTA). Kinetic fragility of theglasses along with other thermal parameters has been calculated. Non-isothermalcrystallization kinetic studies have been employed to study the mechanism of crystallization inall three glasses. The crystallization sequence in the glasses has been followed by x-raydiffraction analysis of the heat treated glass samples in the temperature range of800–1200 °C. μ-cordierite has been observed to be the first crystalline phase in all the glass samples after heat treatmentat 850 °C, while NiO plays an important role in determining the crystallizationsequence at higher temperatures, leading to the formation ofα-cordierite.

Study of characteristic temperatures and nonisothermal crystallization kinetics in As [sbnd]Se [sbnd]Te glass system

Results of differential scanning calorimetry of high purity As 40Se 60− x Te x ( x = 0 – 40 ) chalcogenide glasses are reported. The characteristic temperatures were studied under nonisothermal conditions. The activation energy of the glass transition ( E g ), the activation energy of crystallization ( E c ), the Avrami exponent ( n), the frequency factor ( K o ) and the crystallization criteria of these glasses were determined. The present investigation indicates that the crystallization of high purity As 40Se 60− x Te x ( x = 0 – 40 ) depends from glass composition and impurity content and occurs in a single stage with one- or two-dimensional crystal growth. The glass having the minimal tendency to crystallization is As 40Se 40Te 20.

Non-isothermal Crystallization of UHMWPE

Processing of Ultra High Molecular Weight Polyethylene (UHMWPE) parts involves non-isothermal cooling leading to crystallinity variations, which cause variations in the mechanical properties. Study of non-isothermal crystallization kinetics of UHMWPE forms the basis for process modelling. The crystallization of UHMWPE was studied at seven different cooling rates. The crystallization onset and peak temperatures were linearly related to the cooling rate. The crystallization of UHMWPE was concluded to be a nucleation dominated process with small contribution from growth of nuclei. Differences in ultimate crystallinity (≈11%) were produced due to different cooling rates. A significant portion of the change in ultimate crystallinity occurred at lower cooling rates (<6°C min−1). At higher cooling rates (6–22°C min−1) the change in ultimate crystallinity was insignificant.