Isothermal Crystallization Kinetics and Melting Behavior of a Luminescent Conjugated Polymer,Poly(9,9-Dihexylfluorene-Alt-2,5-Didodecyloxybenzene)

A study of the isothermal crystallization behaviors of poly(9,9-dihexylfluorene-alt-2,5-didodecyloxybenzene) (PF6OC12) was carried out using differential scanning calorimetry (DSC). The crystallization kinetics under isothermal conditions could be described by the Avrami equation. The Avrami exponent n ranges from 3.43 to 3.71 for PF6OC12 at crystallization temperatures between 100.0°C and 90.0°C, indicating a three-dimensional spherical crystal growth with homogeneous nucleation in the primary crystallization stage for the isothermal melt crystallization process. In the DSC scan, after the isothermal crystallization, multiple melting behavior was found. The multiple endotherms could be attributed to melting of recrystallized materials produced originally during different crystallization processes. According to the Arrhenius equation, the activation energy was determined to be 211.29 kJmol^?1 for the isothermal melt crystallization of PF6OC12.     

Kinetics study of a-Se80Te20−xPbx using non-isothermal crystallization

The kinetics of crystallization in Se₈₀Te_20−xPb_x (x=0, 2, 6 and 10) glasses is studied by non-isothermal method using differential scanning calorimetry (DSC). DSC is performed at different heating rates of 5, 10, 15 and 20 K/min. The values of glass transition and crystallization temperatures are found to be composition and heating-rate dependent. From the heating-rate dependence of the glass transition and crystallization temperatures, the activation energy of crystallization (ΔE_c) and order parameter (n) are calculated.     

Heterogeneous crystallization of amorphous silicon expedited by external force fields: a molecular dynamics study

Applying a molecular dynamics simulation technique with the Tersoff potential, we investigate the isothermal crystallization processes of amorphous silicon (a-Si). To obtain a realistic amorphous structure, a rapid quenching process from liquid-phase at 3500 K to solid-phase at 500 K is simulated at a rate of 10¹² K/s and the Voronoi analysis is conducted to observe atomic structural changes during this cooling process. This amorphous structure is utilized to simulate the crystallization processes at various process temperatures with and without external force fields. While homogeneous crystallization of a-Si could not be achieved readily, it is shown that the heterogeneous crystallization can be significantly accelerated by external force fields. This enhancement is owing to increased molecular jumping frequencies associated with the molecular potential energies being increased by external excitations, rather than due to thermal mechanisms normally found in conventional solid-phase crystallization processes.     

Crystallization Kinetics of Nucleated Polypropylene with Organic Phosphates

The crystallization kinetics of isotactic polypropylene (iPP) and nucleated iPP with two organic phosphates, sodium salt (NA7) and triglyceride ester (NA8) of 2,2'-methylene-bis(4,6-di-tert-butylphenyl) phosphoric acid, were investigated by means of a differential scanning calorimeter under isothermal and nonisothermal conditions. During isothermal crystallization, a modified Avrami equation was used to describe the crystallization kinetics. Moreover, kinetics parameters, such as the Avrami exponent, n, the crystallization rate constant, k, and the half-time of crystallization, τ_1/2, are compared. The results showed that a dramatic decrease of the half-time of crystallization, as well as a significant increase of the overall crystallization rate, were observed in the presence of the organic phosphates. During nonisothermal crystallization, the primary crystallization was analyzed using the Ozawa model, leading to similar Avrami exponents for iPP and iPP/NA7, which means simultaneous nucleation with three-dimensional spherulitic growth. However, for iPP/NA8, the Avrami exponent in nonisothermal crystallization is evidently different from that in isothermal crystallization, which would indicate a different mechanism of crystal growth. Adding the nucleating agent to iPP makes the overall crystallization activation energy increase.     

Miscibility and Isothermal Crystallization Behavior of Poly (Butylene Succinate-co-Adipate) (PBSA)/Poly (Trimethylene Carbonate) (PTMC) Blends

Poly(butylene succinate-co-adipate) (PBSA)/poly (trimethylene carbonate) (PTMC) blend samples with different weight ratios were prepared by solution blending. The morphologies after isothermal crystallization and in the melt were observed by optical microscopy (OM). Differential scanning calorimetry (DSC) was used to characterize the isothermal crystallization kinetics and melting behaviors. According to the OM image before and after melting, it was found that the blends formed heterogenous morphologies. When the PTMC content was low (20%), PBSA formed the continuous phase, while when the PTMC contents was high (40%), PBSA formed the dispersed phase. The glass transition temperatures (T_g) of the blends were determined by DSC and the differences of the T_g values were smaller than the difference between those of pure PBSA and PTMC. In addition, the equilibrium melting points were depressed in the blends. According to these results, the PBSA/PTMC blends were determined as being partially miscible blends. The crystallization kinetics was investigated according to the Avrami equation. It was found that the incorporation of PTMC did not change the crystallization mechanism of PBSA. However, the crystallization rate decreased with the increase of PTMC contents. The change of crystallization kinetics is related with the existences of amorphous PTMC, the partial miscibility between PLLA and PTMC, and the changes of phase structures.     

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.     

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）     

同步扫描光谱方法研究聚合物结晶动力学过程

固体表面反射光与其折射指数之间存在余弦函数关系,而折射指数的均方起伏又和固体表面的密度和浓度起伏有关。因此从反射光的变化可以反映材料内部结构的一些变化。基于此理论指导,本文利用同步扫描光谱(SSS)方法,即荧光光谱仪的同步扫描模式进行反射光的检测,成功地监测了聚己内酯(PCL)薄膜在铜片上的熔融和非等温结晶过程。PCL薄膜的SSS谱图出现了两个明显的荧光光谱仪的光源峰(467和473 nm),利用这两个峰的信息可以表征聚合物的熔融和结晶过程中分子链结构的变化。采用SSS方法表征分析得到了PCL的热动力学和结晶动力学参数,其结晶Avrami exponent n为2.8～3.2,平均值为3.1,表明PCL的非等温结晶遵循异相成核、三维球晶生长机理。这些与差示扫描量热仪(DSC)得到的参数一致。研究结果表明SSS方法是一种简单、有效的原位测试聚合物熔融和结晶动态过程的方法。此外,SSS方法是一种基于荧光光谱仪的具有普适性的光谱方法,对发光和不发光固态聚合物均可以检测研究。     

Isothermal Crystallization Kinetics and Melting Behavior of Poly(ethylene terephthalate)/Attapulgite Nanocomposites Studied by Step-scan DSC

The crystallization kinetics of poly(ethylene terephthalate)/attapulgite (AT) nanocomposites and their melting behaviors after isothermal crystallization from the melt were investigated by DSC and analyzed using the Avrami method. The isothermal crystallization kinetics showed that the addition of AT increased both the crystallization rate and the isothermal Avrami exponent of PET. Step-scan differential scanning calorimetry was used to study the influence of AT on the crystallization and subsequent melting behavior in conjunction with conventional DSC. The results revealed that PET and PET/AT nanocomposites experience multiple melting and secondary crystallization processes during heating. The melting behaviors of PET and PET/AT nanocomposites varied in accordance with the crystallization temperature and shifted to higher temperature with the increase of AT content and isothermal crystallization temperature. The main effect of AT nanoparticles on the crystallization of PET was to improve the perfection of PET crystals and weaken its recrystallization behavior.     

Analysis of crystallization kinetics of sputtered SmCo based permanent magnetic films

Crystallization kinetics of the sputtered SmCo based permanent magnetic films was investigated by differential scanning calorimeter, x-ray diffraction, and atomic force microscope methods. The results show that the apparent activation energy for crystallization is observed as 173.7 kJ/mol, and the local activation energy for crystallization decreases with increasing crystal phase transformation fraction in non-isothermal crystallization. For isothermal crystallization, the apparent activation energy for crystallization is 159.8 kJ/mol. The local activation energy for crystallization exhibits non-monotonic dependence on the crystal phase transformation fraction. The crystallization mechanism is obtained from the investigation of Avrami exponent and microstructure.     

Isothermal Crystallization of Isotactic Polypropylene Nucleated with a Novel Aromatic Heterocyclic Phosphate Nucleating Agent

The incorporation of a nucleating agent into isotactic polypropylene (iPP) is one of the most important and widely used methods to improve performance in the polypropylene industry. Aromatic heterocyclic phosphate salt is a kind of highly effective nucleating agent for iPP and one of the typical products is a compound nucleating agent based on 2, 2-methylene-bis (4, 6-di-tert-butylphenyl) phosphate hydroxyl aluminum (commercial product name: ADK NA-21). In this paper the isothermal crystallization kinetics of iPP nucleated with the α-nucleating agent NA-21, investigated using differential scanning calorimetry (DSC), is described with the crystallization data being analyzed by using the classic Avrami method. During isothermal crystallization the addition of nucleating agent NA-21 dramatically shortened the crystallization half time (t_1/2) of iPP under the same conditions and the crystallization activation energy, ΔE, decreased from 422 kJ/mol for virgin iPP to 369 kJ/mol with the addition of NA-21. Thus, the addition of NA-21 significantly increased the crystallization rate of iPP.     

Direct Observation of Crystallization of Polybutene-1 Under Low Shear Rate Flow

The isothermal crystallization process of polybutene-1 melt under shear flow was investigated with an optical microscope and a device (shear flow direct observation system, SF-DOS) newly developed by our group. The nucleation rate and growth rate of polybutene-1 were studied under slow shear rates (0–0.1 s^?1) at high crystallization temperature (102–108°C) with the SF-DOS. The nucleation remains heterogeneous. The number of nuclei after long times increased and induction time decreased by increasing the shear rate. Anisotropic and distorted spherulites were observed under shear flow, while the spherulites in the static condition were isotropic. It was clearly observed that the spherulites were rotating under shear. The average growth rates were enhanced by increasing shear rates, which acts as the main factor affecting the overall crystallization kinetics. Finally, the crystallization kinetics were analyzed on the basis of the secondary nucleation theory of Hoffman and Lauritzen. Even under very low shear rates, the product of lateral‐surface free energy σ _s and fold-surface free energy σ _e was found to be reduced as shear rate increased.     

Crystallization kinetics of a-Ga5Se95−xSbx

The kinetics studies of a-Ga₅Se_95−xSb_x (x=0, 1, 5, 10) is analyzed by an isothermal and non-isothermal technique. By isothermal technique the analysis of crystallization kinetics is taken at temperatures between the glass transition and crystallization. The activation energy of crystallization (ΔE_c) and order parameter (n) are calculated by fitting the values of extent of crystallization (α) in the Avrami's equation. By non-isothermal technique crystallization kinetics of a-Ga₅Se_95−xSb_x (x=0, 1, 5, 10) with different heating rates of 5, 10, 15 and 20 K/min have been studied by using the Differential Scanning Calorimeter (D.S.C.). The glass transition temperature, crystallization temperature at different heating rates and structural change during glass transition has been determined from an empirical relation. From the heating rate, the dependence of the glass transition and crystallization temperatures, the activation energy for structural relation (Δe_t), the activation energy of crystallization (ΔE_c), and the order parameter (n) are calculated.     

The kinetics of precipitation in Al-2.4 wt% Cu alloy by Kissinger, Ozawa, Bosswel and Matusita methods

The isothermal and non-isothermal ageing of an Al-2.4 wt% Cu alloy have been studied using X-ray diffraction analysis and differential scanning calorimetry (DSC) at different heating rates. Quantitative metallography methods have been applied to measure the corresponding transformed volume fractions at various temperatures and times of precipitation. The variation of the heating rate using DSC technique has allowed us to calculate two kinetics parameters of precipitation which are the Avrami exponent and the activation energy of the process using Kissinger, Ozawa and Bosswell methods. These parameters are similar to those found for the precipitation reaction of θ′ and θ (Al₂Cu) phases.     

Study of crystallization kinetics of Se77.5Te15Sb7.5 glass using isoconversional models

The crystallization process of Se_77.5Te₁₅Sb_7.5 glass is studied by differential scanning calorimetry (DSC) technique under non-isothermal conditions at various heating rates. The crystallization parameters are deduced using different models. The validity of the Johnson–Mehl–Avrami (JMA) model to describe the crystallization process for the studied composition is investigated. Comparing experimental and calculated DSC curves indicate that the crystallization process of Se_77.5Te₁₅Sb_7.5 glass cannot satisfactorily be described by the JMA model. In general, simulation results indicate that the Sestak–Berggren model is more suitable to describe the crystallization kinetics. The crystalline phases are identified using the X-ray diffraction technique and scanning electron microscopy.     

An investigation of the crystallization kinetics of zeotype SAPO-34 crystals synthesized by hydrothermal and sonochemical methods

The kinetics study of SAPO-34 crystallization from a gel containing morpholine as a structure directing agent (SDA) was investigated by means of X-ray diffraction (XRD) patterns in order to determine the kinetics parameters, i.e. induction times, rate constants, frequency factors, and activation energies for the induction and growth stages. The kinetics data of growth period were determined by using the Avrami–Erofeev nucleation growth model. SAPO-34 molecular sieves were synthesized by using both sonochemical-assisted hydrothermal and conventional hydrothermal heating at temperatures of 180, 200, and 220 °C to elucidate the influence of crystallization method on the crystallization kinetics of SAPO-34. The activation energy values indicated that the crystal growth mechanism was enhanced for samples synthesized sonochemically, whereas the induction energy was not greatly affected by using sonication process. Also, the kinetic compensation effect (KCE) was considered in order to obtain the isokinetic temperature.     

Monitoring the evolution of crystallization processes by in-situ solid-state NMR spectroscopy

Crystallization processes play a crucial role in many aspects of biological and physical sciences. Progress in deepening our fundamental understanding of such processes relies, to a large extent, on the development and application of new experimental strategies that allow direct in-situ monitoring of the process. In this paper, we give an overview of an in-situ solid-state NMR strategy that we have developed in recent years for monitoring the time-evolution of different polymorphic forms (or other solid forms) that arise as the function of time during crystallization from solution. The background to the strategy is described and several examples of the application of the technique are highlighted, focusing on both the evolution of different polymorphs during crystallization and the discovery of new polymorphs.     

Crystallization Behavior of Rare‐earth Doped Luminous Pigment/Polyamide 6 Composites

The crystallization behavior of well‐dispersed rare‐earth doped luminous pigment/polyamide 6 (PA6) composites prepared through in situ polymerization was investigated by DSC. The rare‐earth doped luminous pigments could accelerate the forming of γ form crystals and also had a great effect on the crystallinity and crystallization rate of PA6 composites. The Ozawa, Jeziorny, and Mo methods were used to analyze the non‐isothermal crystallization kinetics. It was found that the Ozawa method was unsuitable for non‐isothermal crystallization of PA6 composites. The results of Jeziorny analysis showed that the crystallization rates of PA6 composites increased when the luminous pigment content was larger than 5 wt.%. Mo's analysis also showed that the presence of the pigment shortened the crystallization time and accelerated the crystallization rate. Polarized optical microscopy showed that the spherulites became smaller with increasing of the luminous pigment amount due to the heterogeneous nucleation.     

Model fitted and model free approaches for crystallization kinetics in Se85Te15-xBix glasses

In this research work, we have described the model-fitted and model free approaches for the study of crystallization kinetics in Se₈₅Te_15-xBi_x chalcogenide glasses. Se₈₅Te_15-xBi_x bulk alloys were synthesized by melt quenching technique. High Resolution X- Ray diffraction (HRXRD) was used to confirm the amorphous nature of prepared alloys. Non-isothermal Differential Scanning Calorimetry (DSC) measurements were done at heating rates of 5, 10, 15, 20 and 25 K/min for crystallization kinetics studies in Se₈₅Te_15-xBi_x glasses. The various characteristic temperatures, such as glass transition (T_g), on-set crystallization (T_c) temperature, peak crystallization temperature (T_p) and melting temperatures (T_m) have been obtained from various DSC thermograms. The activation energies of glass transition (ΔE_t) were calculated by using Kissinger and Moynihan approaches and found to be minimum for Se₈₅Te₁₂Bi₃ chalcogenide glass which indicates that this alloy has maximum probability to jump into a less configurational energy state and has larger stability. The model-free approaches; Kissinger–Akahira–Sunose (KAS), Flynn-Wall-Ozawa (FWO), Tang and Straink (TS) reveal that the activation energy of crystallization varies with crystallization degree and temperature both. This variation shows that amorphous to crystalline phase transformation in Se₈₅Te_15-xBi_x chalcogenide glasses is a complex process with various nucleation and growth mechanisms.     

Crystallization and grain growth characteristics of yttria-stabilized zirconia thin films grown by pulsed laser deposition

Knowledge about the crystallization and grain growth characteristics of metal oxide thin films is essential for effective microstructural engineering by thermal post-annealing and the integration to Si-based miniaturized electroceramic devices. Finite size and interface effects may cause fundamentally different behavior compared to three dimensional macroscopic systems. This work presents a comprehensive investigation of the crystallization kinetics and microstructural evolution upon thermal post-annealing of amorphous 200 nm and 1.2 μm thin films of 8 mol% yttria-stabilized zirconia grown by pulsed laser deposition (PLD) using ex- and in-situ X-ray diffraction, Raman spectroscopy, and electron microscopy techniques. The layers exhibit a remarkably low crystallization temperature of 200-250 °C while exposure to energetic electrons induces the formation of randomly dispersed ~ 20 nm sized crystallites already at ambient temperature. The isothermal amorphous to crystalline phase transformation kinetics can be described quantitatively by the Johnson-Mehl-Avrami-Kolmogorov model. They reveal characteristics of a three dimensional growth under cation bulk diffusion control with heterogeneous nucleation that changes from continuous to instantaneous initial seeding at temperatures above 300 °C. Large (> 100 nm) equiaxed grains are formed rapidly without a stabilization of transient nanocrystals during the thermally induced phase transformation. A stagnation of normal grain growth resulting in a logarithmic normal size distribution is observed once the average grain dimensions approach the film thickness. The results on the crystallization and grain growth of the PLD-grown YSZ films are evaluated with regards to the fabrication of YSZ solid electrolyte membranes for Si-supported micro solid oxide fuel cells and gas sensors.