Fast Crystallization Kinetics Research Articles

Ellipsometric Simulation and Preliminary Observation of Fast Crystallization Behavior of Ge2Sb2Te5 Amorphous Thin Films at Elevated Temperature

We examine the fast crystallization kinetics of the stoichiometric Ge–Sb–Te alloy film by using a modified Johnson–Mehl–Avrami (JMA) equation and additive reaction for nonisothermal transformation. It is expected that utilization of the fast crystallization kinetics of the recording medium occurring at the first stage of cascaded crystallization will significantly reduce the erase time at elevated temperatures. We also show an ellipsometric configuration which enables one to confirm the fast crystallization kinetics in nanosecond time resolution.

Energy equation and the crystallization kinetics of semi-crystalline polymers: regimes of coupling

The processing conditions play an important role in the development of the crystallinity of thermoplastic polymers and the energy equation describing the heat transfer problem can be strongly coupled to the material kinetics. In this paper, the importance and nature of the coupling is evaluated by comparing the temperature and crystallinity distributions obtained from a fully coupled zone model (considered as the most general approach) with two cases: Neumann's solution (sharp interface-moving boundary) and the one-domain diffusion equation with no heat generation (uncoupled solution). Two non-dimensional parameters, Stefan's (St) and Deborah's (De) numbers, that play a key role in determining the extent of the coupling, are isolated. The influence of the coupling and its nature have been demonstrated numerically in selected cases. Results of the parametric studies show that De and St decide the nature of the coupling. The error made by decoupling the problem can be shown graphically and regimes are identified where the coupling is important or negligible. Criteria allowing the identification of the regimes are presented. Finally, an example is presented to demonstrate the importance of the coupling for the cooling of Nylon 6-6 and PET, which exhibit fast and slow crystallization kinetics.

Dual-mechanism kinetics of polyphenylene sulfide (PPS) melt-crystallization

This investigation demonstrates that polyphenylene sulfide (PPS) crystallizes in a unique dual-mechanistic fashion in which 8% of the material by volume crystallizes instantaneously, while the remaining material crystallizes in a time dependent fashion. These rapid melt-crystallization kinetics are quantitatively modeled using a dual-mechanistic model approach which is based on the methodology first observed by Velisaris and Seferis in polyetheretherketone (PEEK) crystallization. The crystallization model is then used to accurately predict both isothermal and for the first time non-isothermal crystallization behavior over a wide spectrum of cooling rates utilizing the same model parameters. Specifically, this work identifies and models the initial fast crystallization kinetics of PPS. Additionally, the versatility of the Velisaris and Seferis dual-mechanistic model has been established with PPS, by simply showing that it is a special case of the generalized dual-crystallization kinetics methodology.

Synchrotron small-angle x-ray scattering study of crystalline structures and isothermal crystallization kinetics of poly(aryl ether ether ketones)

The crystallization behaviors at elevated temperatures and fast isothermal crystallization kinetics around ∼230°C of poly(aryl ether ether ketones) (PEEKs) were studied. The crystalline structure parameters were evaluated by means of one-dimensional correlation function analysis. The long period, the lamellar thickness, and the one-dimensional crystallinity as a function of temperature were compared between two samples which had different repeat units in the polymer backbone. for two samples, the long period and the lamellar thickness were found to increase with increasing crystallization temperature simultaneously.