Search results for "Cooling rate"
showing 10 items of 26 documents
Nucleation of quasicrystals by rapid cooling of a binary melt: A molecular-dynamics study.
1995
A binary Lennard-Jones fluid was cooled in an NPT ensemble by molecular-dynamics simulations. Depending on the cooling rate, we find a sharp transition from the melt either into a disordered structure or into a phase of icosahedral long-range order. We also observed a decagonal phase.
Molecular Dynamics Computer Simulation of Cooling Rate Effects in a Lennard-Jones Glass
1995
We present the results of a molecular dynamics computer simulation of a binary Lennard-Jones mixture. We simulate a quench of the system from a liquid state at high temperatures to a glass state at zero temperature by coupling the system to a heat bath that has a temperature that decreases linearly (with slope -γ) with time. We investigate how the residual density of the system varies as a function of the cooling rate γ and rationalize our results by means of the dependence of the coordination number of the particles on the cooling rate.
Phenomenological approach to compare the crystallization kinetics of isotactic polypropylene and polyamide-6 under pressure
2001
Reliable experimental data for semicrystalline polymers crystallized under pressure are supplied on the basis of a model experiment in which drastic solidification conditions are applied. The influence of the pressure and cooling rate on some properties, such as the density and microhardness, and on the product morphology, as investigated with wide-angle X-ray scattering (WAXS), is stressed. Results for isotactic polypropylene (iPP) samples display a lower density and a lower microhardness with increasing pressure over a wide range of cooling rates (from 0.01 to 20 °C/s). Polyamide-6 (PA6) samples exhibit the opposite behavior, with the density and microhardness increasing at higher pressur…
The role of radiative losses in the late evolution of pulse-heated coronal loops/strands
2012
Radiative losses from optically thin plasma are an important ingredient for modeling plasma confined in the solar corona. Spectral models are continuously updated to include the emission from more spectral lines, with significant effects on radiative losses, especially around 1 MK. We investigate the effect of changing the radiative losses temperature dependence due to upgrading of spectral codes on predictions obtained from modeling plasma confined in the solar corona. The hydrodynamic simulation of a pulse-heated loop strand is revisited comparing results using an old and a recent radiative losses function. We find significant changes in the plasma evolution during the late phases of plas…
Evidence of Mechanisms Occurring in Thermally Induced Phase Separation of Polymeric Systems
2014
Thermally induced phase separation is a fabrication technique for porous polymeric structures. By means of easy-to-tune processing parameters, such as system composition and demixing temperature, a vast latitude of average pore dimensions, pore size distributions, and morphologies can be obtained. The relation between demixing temperature and morphology was demonstrated via cloud point curve measurement and foams fabrication with controlled thermal protocols, for the model system poly-l-lactide–dioxane–water. The morphologies obtained at a temperature lower than cloud point showed a closed-pore architecture, suggesting a “nucleation-and-growth” separation mechanism, which produced larger po…
Non-isothermal crystallization kinetics of PET
2000
The crystallization kinetics of poly(ethylene terephthalate) was studied using constant cooling rate, isothermal and quenching experiments. A non-isothermal crystallization kinetics equation based on a single mechanism was used to analyze the data. Different mechanisms of crystallization at low, intermediate, and high cooling rates were hypothesized based on deviation of the experimental data from the single mechanism model.
The X-ray determination of the amounts of the phases in samples of isotactic poly(propylene) quenched from the melt at different cooling rates
1997
A new procedure for the determination of the amounts of phases in samples of isotactic poly(propylene) quenched at different cooling rates from the same melted polymer is described. According to the procedure, all the patterns corresponding to the same quenching series are simultaneously analyzed for the amounts of phases so that reliable phase fractions relative to the different samples of the series are achieved. The analysis of the results points out that for increasing cooling rates above 30°C/s a remarkable increase of the mesomorphic phase settles, mainly at the expense of the α-monoclinic one.
Design, build-up and optimization of a fast quenching device for polymeric thin film
2014
In this work an innovative apparatus for the characterization of polymer solidification under very high cooling rates (up to thousand of K/s) is described, according to the continuous cooling transformation approach adopted in metallurgy for studying structure development in metals. The proposed model experiment is addressed to design a method for the characterization of non-isothermal solidification behaviour, encompassing typical cooling conditions of polymer processing. Only temperature history determines the structure formed, as melt solidification takes place in quiescent conditions. With respect to the device previously developed by the authors [1, 3] the present equipment presents th…
Effect of pressure on the PVT behaviour of iPP as revealed by dilatometric measurements
2002
Isotactic Poly-propylene samples, previously prepared under known conditions of pressure and cooling rate by means of a special apparatus designed and set-up by the authors, were subjected to several isobaric runs at low cooling and heating rate in a confining fluid dilatometer (by GNOMIX). The effect of the previous thermo-mechanical histories and the effect of pressure in the dilatometry on specific volume of the samples was studied. Results show that the initial specific volume depends upon the previous thermo-mechanical histories, which however cancels out after the first heating run. Moreover the reported dilatometric experimental data support the evidence that an increase of pressure …
Thermoanalytical studies on phases of D-mannitol
1993
Abstract D-mannitol exists in several polymorphic crystalline forms. The conditions of crystallization are not well-defined, and in some cases mixtures of the different forms are obtained. In the DSC study the different forms melted nearly at the same temperature (166±°C). The heat of fusion of the k form was lower than those of the other forms. With slow heating rate (2 ° C min ) the δ form changed to k between 140 and 165 °C. The crystallization of D-mannitol from the melt gave from one to seven peaks in the DSC between 95 and 126 °C depending on cooling rates and the amounts of sample.