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91.
Differential scanning calorimetry (DSC) was utilized to study the behavior of six Ge-Se glasses containing 0, 5, 10, 15, 17.5
and 20 at.% Ge during the glass transition. These alloys readily form glasses and can be prepared by quenching in air. Moreover,
their behavior depends greatly on the composition. This work reveals that two additional properties must be considered: the
variation in the glass transition temperature and different structural relaxation. The quantity used to quantify the relaxation
was the enthalpy relaxation as this measures the heat lost by the glass during annealing. Given the complexity of the relaxation
process, the experimental results were analysed by means of the empirical Kohlrausch-Williams-Watts relaxation model.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
92.
Gerzon E. Delgado Asilo J. Mora Jorge Uzctegui Ali Bahsas Alexander Briceo 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(8):o448-o450
The crystal structure of the title compound, C10H10N2O2·H2O, also known as l ‐5‐benzylhydantoin monohydrate, is described in terms of two‐dimensional supramolecular arrays built up from infinite chains assembled via N—H...O and O—H...O hydrogen bonds among the organic molecules and solvent water molecules, with graph‐set R33(10)C(5)C22(6). The hydrogen‐bond network is reinforced by stacking of the layers through C—H...π interactions. 相似文献
93.
J. J. Suñol N. Clavaguera M. T. Mora 《Journal of Thermal Analysis and Calorimetry》1998,52(3):853-862
The low-temperature parts of the temperature-heating rate-transformation (T-HR-T) and temperature-time transformation (T-T-T)
diagrams were obtained for crystallization processes. A knowledge of the kinetic model governing crystallization is not needed
because both transformation curves can be obtained from non-isothermal calorimetric experiments. The calorimetric study was
performed by means of differential scanning calorimetry. The method was applied to analyse crystallization processes of Fe-Ni-based
amorphous alloys prepared by melt spinning. The compositions studied were Fe40Ni40P14Si6, Fe40Ni40P10Si10 and Fe40Ni40P6Si14.
A good concordance was observed between the experimental T-HR-T curves obtained by calculation and the experimental data,
which verifies the reliability of the method. In the T-T-T diagrams, the agreement was good in process B1, while in processes
A1 and C1 there are small differences that could be related to different crystallization products obtained in isothermal/non-isothermal
experiments.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
94.
The study of the energetics of the accepted intradimer diamond growth mechanism over (100) diamond surface is presented. The calculations were made in a density functional approach with the DGauss code using a DZVP2 basis set and a BLYP interchange and correlation potential. A simple 9-carbon cluster modeling the (100) diamond surface was used; its validity is discussed in relation with other calculations that used larger model clusters. The mechanism, presented in six steps, is based in the Harris and Garrison's work that considers the methyl radical as the main growth precursor agent and the breaking of the dimer surface bond with the corresponding methylene radical formation as a prior step to the formation of a CH2-bridge structure, which is a feasible step; in contrast to these molecular dynamics results, Huang and Frenklach, using semiempirical methods, consider the breaking of the dimer surface bond and the formation of a CH2-bridge structure as one step and this step as the energetically determinant of the mechanism. They also found an activation energy barrier for the interaction between a radical surface center with a H and CH3. The present work tries to discern between these two ideas by calculating the activation barriers and the reaction energies for each step of the Harris and Garrison's mechanism in a density functional approach and comparing them to the results of Huang and Frenklach. The energy calculations point toward the scission of the dimer bond (step 4) as the determinant step; this step is endothermic, with an energy barrier of 50.43 kcal-mol–1. On the other hand, the formation of the CH2-bridge structure (step 5) is a feasible step with an energy barrier of 13.57 kcal-mol–1. The adsorption of CH3 (step 2) and H (step 6) species over radical surface sites did not involve any energy barriers, as it would be hoped. These steps were strongly exothermic and are close to the thermodynamic values for C—C and C—H bond energies. The removal of methylic hydrogen (step 3) did not show any problem because the activation barrier is only 3.68 kcal-mol–1 less than the removal of a surface hydrogen (step 1), which has an energy barrier of 19.59 kcal-mol–1. All steps, except number 4, were exothermic. 相似文献
95.
Mahedero MC Díaz NM Muñoz de la Peña A Espinosa Mansilla A Gónzalez Gómez D Bohoyo Gil D 《Talanta》2005,65(3):806-813
A widely employed compound for honey treatment, sulfathiazole (ST), was determined in commercial honey samples, employing a combination of photochemically induced fluorescence excitation-emission matrices (EEMs) and chemometric processing of the recorded second-order data. Parallel Factor Analysis (PARAFAC) and Self-Weighted Alternating Trilinear Decomposition (SWATLD) methods were used for calibration. An appropriately designed calibration with a set of standards composed of 18 samples, coupled to the use of the second-order advantage offered by the applied chemometric techniques, allowed quantitation of sulfathiazole in spiked commercial honey samples. No previous separation or sample pretreatment steps were required. The results were compared with other calibration methods such as N-PLS and PLS-1 that produced good results on synthetic samples but not on the investigated commercial honey samples. 相似文献
96.
An eigenexpansion solution of the time-independent Brownian motion Fokker-Planck equation is given for a situation in which the external acceleration is a step function. The solution describes the heavy-species velocity distribution function in a binary mixture undergoing a shock wave, in the limit of high dilution of the heavy species and negligible width of the light-gas internal shock. The diffusion solution is part of the eigenexpansion. The coefficients of the series of eigenfunctions are obtained analytically with transcendentally small errors of order exp(–1/M), whereM 1 is the mass ratio. Comparison is made with results from a hypersonic approximation. 相似文献
97.
98.
99.
Lithium-ion batteries are promising energy storage technology devices. They possess many advantages, including high energy density, flexible and lightweight construction and considerable durability. The rapid development of nanotechnologies can further improve their capacity, cycle life and safety. In this experiment, Li-ion diffusion in an all-solid lithium-ion battery (ASSLiB) was studied using the Neutron Depth Profiling (NDP) nuclear analytical technique. The thin ASSLiB system was synthesised by RF magnetron sputtering. The experiment showed that NDP is a very efficient experimental tool for direct analysis of Li distribution in Li batteries. It has been found that the depth profile of Li strongly depends on the state of charge of the battery. About one-third of the total number of Li in ASSLiB can move between the electrodes during charging / discharging. It has been also shown, using the multipixel detectors, that the lateral distribution of Li in ASSLiB is not homogeneous. This can mean, for example, that the position of Li is affected by structural defects that may arise due to variation of the volume or stress of the battery during charging or discharging. In the work are presented first results of measurements performed on ASSLiB of a 1?µm thickness. 相似文献
100.
The study of the kinetics and mechanism of dehydrochlorination reaction of 2‐methyl benzyl chloride in the gas phase was carried out by means of electronic structure calculations using ab initio Móller‐Plesset MP2/6‐31G(d,p), and Density Functional Theory (DFT) methods: B3LYP/6‐31G(d,p), B3LYP/6‐31++G(d,p), MPW1PW91/6‐31G(d,p), MPW1PW91/6‐31++G(d,p)], PBE/6‐31G(d,p), PBE/6‐31++G(d,p). Investigated reaction pathways comprise: Mechanism I, a concerted reaction through a six‐centered cyclic transition state (TS) geometry; Mechanism II, a 1,3‐chlorine shift followed by beta‐elimination and Mechanism III, a single‐step elimination with simultaneous HCl and benzocyclobutene formation through a bicyclic type of TS. Calculated parameters ruled out Mechanism III and suggest the elimination reaction may occur by either unimolecular Mechanism I or Mechanism II. However, the TS of the former is 20 kJ/mole more stable than the TS of the latter. Consequently, the Mechanism I seem to be more probable to occur. The rate‐determining process is the breaking of C‐Cl bond. The involvement of π‐electrons of the aromatic system was demonstrated by NBO charges and bond order calculations. The reaction is moderately polar in nature. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 537–546, 2011 相似文献