Search results for "quench"
showing 10 items of 306 documents
First-principles study of the amorphous In3SbTe2phase change compound
2013
Ab initio molecular dynamics simulations based on density functional theory were performed to generate amorphous models of the phase change compound In${}_{3}$SbTe${}_{2}$ by quenching from the melt. In-Sb and In-Te are the most abundant bonds with only a minor fraction of Sb-Te bonds. The bonding geometry in the amorphous phase is, however, strongly dependent on the density in the range 6.448--5.75 g/cm${}^{3}$ that we investigated. While at high density the bonding geometry of In atoms is mostly octahedral-like as in the cubic crystalline phase of the ternary compound In${}_{3}$SbTe${}_{2}$, at low density we observed a sizable fraction of tetrahedral-like geometries similar to those pres…
Structure evolution and reaction mechanism in the Ni/Al reactive multilayer nanofoils
2014
Abstract The extremely rapid gasless reactions in binary Ni/Al reactive multilayer nanofoils (RMNFs) are investigated both experimentally and theoretically. The quenching technique is used to study the dynamics of structural transformation on the micro- and nanoscales. The experimentally obtained patterns of structural evolution related to the heterogeneous reactions are compared with the results of molecular dynamics simulations carried out for the same reactive system. Based on the obtained data, the intrinsic mechanism of the reaction in Ni/Al RMNF is considered, which adequately explains the unusual parameters of a gasless combustion wave in such a system.
Modeling the interactions between light and crystallizing polymer during fast cooling
2004
In this work, an experimental set-up able to quench thin polymer films whilst recording the sample thermal history as well as the overall and depolarized light intensities of a laser beam emerging from the sample is described. The interactions between the light beam and the crystallizing material have been modeled accounting for absorption and scattering phenomena. The proposed model was found to be able to reproduce the ex- perimentally observed behavior of light intensities and it was validated by comparison with conventional DSC analysis. On the basis of this model, a method to obtain crystallinity evo- lution is proposed and applied to some fast cooling runs. The method was applied to q…
On the Nature of the Plateau in Two-Step Dinuclear Spin-Crossover Complexes
2004
A remarkable feature of the spin-crossover process in several dinuclear iron(II) compounds is a plateau in the two-step transition curve. Up to now, it has not been possible to analyse the spin state of dinuclear pairs that constitute such a plateau, due to the relative high temperatures at which the transition takes place in complexes investigated so far. We solved this problem by experimentally studying a novel dinuclear spin-crossover compound [[Fe(phdia)(NCS)(2)](2)(phdia)] (phdia: 4,7-phenanthroline-5,6-diamine). We report here on the synthesis and characterisation of this system, which exhibits a two-step spin transition at T(c1)=108 K and T(c2)=80 K, displaying 2 K and 7 K wide therm…
Microgel regions in dilute agarose solutions: the notion of non-gelling concentration, and the role of spinodal demixing
1991
Abstract Freely drifting microgel regions are found in aqueous solutions of agarose, a representative biostructural polysaccharide, at concentrations between 0.01% and 0.05% w/v when quenched from 100°C to lower temperature. The size of these domains depends on the quench temperature and agarose concentration. The results agree with recent findings on the role that fluctuations within or close to the instability region of solution have as the initial step towards the self-assembly of supramolecular structures, and throw a new light on the notion of the lowest solute concentration needed for gelation.
Kinetics of phase separation in polymer blends for deep quenches
1986
Electro microscopy was used to study the phase separation kinetics of a polystyrene/polyvinylmethylether system subjected to a critical deep quench. The size of the phase-separated domains was found to increase linearly with time, implying that hydrodynamic effects control the rate of growth of the domains in the time scale and temperature range under consideration. From these measurements the growth velocity and approximate diffusion constants can be determined for three different temperatures. Comparison of these results with those obtained by light scattering on other systems and with theoretical predictions is possible by replotting in dimensionless units.
Competition between intrinsic and extrinsic effects in the quenching of the superconducting state in FeSeTe thin films
2015
We report the first experimental observation of the quenching of the superconducting state in current-voltage characteristics of an iron-based superconductor, namely, in FeSeTe thin films. Based on available theoretical models, our analysis suggests the presence of an intrinsic flux-flow electronic instability along with non-negligible extrinsic thermal effects. The coexistence and competition of these two mechanisms classify the observed instability as halfway between those of low-temperature and of high-temperature superconductors, where thermal effects are respectively largely negligible or predominant.
Effect of sintering process and additives on the properties of cordierite based ceramics
2013
It is possible to obtain cordierite ceramics with high temperature synthesis using both synthetic and raw natural materials. This paper discusses the possibilities to obtain cordierite ceramics, replacing part of required oxides with raw materials from various Latvian deposits of dolomite and clay. The obtained raw cordierite powders were ground in two modes (3 and 12 hours) and fired at 1200 °C. Ceramic samples were characterized by hydrostatic weighting method; crystalline phase composition was studied by XRD. Obtained samples were evaluated by their mechanical (compressive) strength and linear coefficient of thermal expansion (CTE). Thermal shock resistance was tested using water quenchi…
Lifetime of the metastable 6P 3/2 level of PbII
1989
Pb+-ions were stored in a r.f.-quadrupole trap. Short laser pulses at a 710-nm M1-transition excited the ions to the metastable 6P 3/2 level. Time-resolved registration of the subsequent decay photons at the same wavelength directly gives the lifetime of that state. No dependence of the decay rate on the density of different buffer gases up to 10−5 mbar pressure was observed and from this we deduced upper limits to the quenching cross section. We have observed, however, a small dependence on the stored ion number. The final result for the lifetime is 41.2 ± 0.7 ms in agreement with the result of a previous calculation.
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.