乙二胺盐酸盐的低温热容和热化学性质

合成了乙二胺盐酸盐, 并表征了其晶体结构. 测定了其在78~370 K温度区间的低温热容, 通过最小二乘法拟合得到热容对温度的多项式方程. 设计了合理的热化学循环, 测定了所设计反应的反应物和产物的溶解焓, 得到反应焓. 利用Hess定律计算出乙二胺盐酸盐的标准摩尔生成焓为-(540.74±1.33) kJ/mol. 利用紫外-可见光谱和折光指数的结果检验了所设计热化学循环的可靠性.     

Numerical Simulation of Diesel Spray Evaporation in a “Stabilized Cool Flame” Reactor: A Comparative Study

The major objective of this work is to numerically investigate the interacting physical and chemical phenomena that characterize the flow in a stabilized cool flame diesel fuel spray evaporation system. A two-phase RANS computational fluid dynamics code has been developed and used to predict the characteristics of the developing turbulent, multiphase, multi-component, reactive flow-field. The code employs a Eulerian–Lagrangian approach, taking into account the mass, momentum, thermal and turbulent energy exchange between the phases. A variety of physical phenomena, such as turbulent dispersion, droplet evaporation, droplet-wall collision, conjugate heat transfer, drift correction, two-way coupling are taken into account by implementing respective sub-models. Two alternative modelling approaches for the simulation of cool flame reactions have been validated and evaluated by comparing numerical predictions with experimental data from two atmospheric pressure, evaporating Diesel spray, Stabilized Cool Flame reactors. Both models have achieved good quantitative agreement in the majority of the considered test cases. The results have been used to estimate the local physical and chemical characteristic time scales of the occurring phenomena, thus allowing, for the first time, the classification of stabilized cool flames.     

氦气提纯技术发展现状与应用分析

为实现氦气资源的循环利用,有必要对氦气进行回收纯化。文中对目前国内外氦气的提纯技术发展现状进行了分析介绍,并综合分析比较了这些方法的应用原理、优缺点及发展趋势,针对各自的使用特点,给出了几种详细的提纯工艺实现方法,为促进我国氦气提纯技术的发展提供了新的思路。     

Direct numerical simulations of rich premixed turbulent n-dodecane/air flames at diesel engine conditions

Rich premixed turbulent n-dodecane/air flames at diesel engine conditions are analyzed using direct numerical simulations. The conditions correspond to a parametric variation of the Engine Combustion Network Spray A (pressure 60 atm; oxidizer oxygen level and temperature 21% and 900 K, respectively; fuel temperature 363 K). Three simulations with equivalence ratios of 3, 5, and 7 are performed with a Karlovitz number (Ka, based on flame time) of order 100 to match the estimated Ka of the rich premixed combustion region in Spray A. At these conditions, the reference laminar flames exhibit a complex structure which involves both low-temperature chemistry (LTC) and high-temperature chemistry over a wide range of length scales. In the presence of turbulence, the flame structure is strongly affected in physical space and the reaction zone exhibits a very complex structure in which broken, distributed, and thin regions co-exist, especially for the leanest case. However, the contribution of the LTC pathway is only weakly affected by turbulence. In progress variable space, the mean flame structure, including the chemical source terms, is found to match remarkably well that of the corresponding unity Lewis number laminar flame, particularly for the $?=$ 3 and 5 cases. This behavior is attributed to the strong turbulent mixing occurring throughout the flames/reaction zones, which suppresses differential diffusion effects. Nevertheless, large conditional fluctuations around the mean chemical source terms are identified. These are found to correlate very well with radical species mass fractions such as OH. In addition, a similar functional dependence is obtained from counterflow laminar flames. As such, it appears from these results that laminar flame models have a potential to be used to represent the thermochemical state of rich premixed turbulent flames under diesel engine conditions.     

Synthesis of 3-fluoro-3-methyl-3-silatetrahydropyran and its conformational preferences in gas and solution by GED,NMR and theoretical calculations

The 3,3-disubstitued 3-silaheterocyclohexane with an electronegative substituent at silicon, 3-fluoro-3-methyl-3-silatetrahydropyran 1, was synthesized, and its molecular structure and conformational properties studied by gas-phase electron diffraction (GED) and low temperature ¹³C and ¹⁹F NMR spectroscopy. Quantum-chemical calculations were carried out both for the isolated species and H-complexes in gas and in polar medium. The predominance of the 1-F_eqMe_ax conformer (1-F_eq:1-F_ax ratio of 65:35, ΔG°?=?0.37?kcal/mol) determined from GED is close to the theoretically estimated conformational equilibrium, especially at the DFT level. In solution, low temperature NMR spectroscopy showed no decoalescence of the signals in ¹³C (down to 95?K) and ¹⁹F NMR spectra (down to 123?K). However, the calculated ¹⁹F chemical shift of ?173.6?ppm for the 1-F_eqMe_ax conformer practically coincides with the experimentally observed value (?173 to ?175?ppm) as distinct from that for the 1-F_axMe_eq conformer (?188.8?ppm), suggesting compound 1 to be anancomeric in solution, in compliance with its theoretical and experimental preference in the gas phase.     

Structural development and kinetic analysis of PbTiO3 powders processed at low-temperature via new sol-gel approach

The synthesis of crystalline lead titanate powder by a generic low-temperature sol-gel approach is developed. Acetoin was added as ligand, instead of the commonly used alkanolamines, to ensure total dissolution of the precursor compounds. The feasibility of the acetoin-Ti isopropoxide complex as a new precursor of PbTiO₃ perovskite particles via sol-gel method has been demonstrated. No excess lead has been introduced. Nanometric PbTiO₃ crystallites have been formed at 400 °C under atmospheric pressure from titanium isopropoxide and lead acetate in alcoholic solution by remarkably low activation energy of crystallization process of 90 kJ mol⁻¹. The powders show tetragonal lattice and dendritic morphology. In addition to the effect of heat-treatment temperature, time, and atmosphere, the sol chemistry particularly influenced the phase composition, particle size, and particle morphology. The use of different ligands significantly modified powder morphology. The extent of the crystallization was quantitatively evaluated by differential thermal analysis and analyzed by Johnson-Mehl-Avrami approach. The crystallization followed two rate regimes depending on the interval of the crystallized fraction.     

A combined temperature-dependent electron and single-crystal X-ray diffraction study of the fresnoite compound Rb2VV2O8

High-purity Rb₂V₃O₈ has been grown and temperature-dependent electron and single-crystal X-ray diffraction used to carefully investigate its fresnoite-type reciprocal lattice. In contrast to other recently investigated representatives of the fresnoite family of compounds, Rb₂V₃O₈ is not incommensurately modulated with an incommensurate basal plane primary modulation wave vector given by q∼0.3 〈110〉^*. A careful low-temperature electron diffraction study has, however, revealed the existence of weak incommensurate satellite reflections characterized by the primitive primary modulation wave vector q₁∼0.16c^*. The reciprocal space positioning of these incommensurate satellite reflections, the overall (3+1)-d superspace group symmetry, as well as the shapes of the refined displacement ellipsoids determined from single-crystal XRD refinement, are all consistent with their arising from a distinct type of condensed rigid unit modes (RUMs) of distortion of the Rb₂V₃O₈ parent structure.     

Shpol'skii spectroscopy at the interface of two non-polar microenvironments: a novel approach for the analysis of polycylic aromatic compounds

This article presents a thorough investigation of quantitative parameters for the analysis of polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and polychlorinated dibenzofurans (PDBFs) partitioning between an octadecyl silica extraction membrane and microliters of an n-alkane solvent spiked on the surface of the membrane. Shpol'skii spectrometry is directly performed on the surface of the membrane with the aid of a cryogenic fiber optic probe. The analyte concentration in the layer of Shpol'skii solvent follows a linear relationship with the analyte concentration in the water sample and the same is observed for the phosphorescence signal of the cryogenic probe. The accuracy and precision needed for quantitative analysis in aqueous samples is demonstrated. The analytical figures of merit show the feasibility to determine organic pollutants at the parts-per-trillion level with minimum solvent consumption.     

Low-temperature synthetic route based on the amorphous nature of giant species for preparation of lower valence oxides

We examined low-temperature synthetic route based on the amorphous nature of giant species to succeed to prepare Cs blue bronze (Cs_0.3MoO₃), which has never obtained by usual high-temperature methods, at ca. 680 K. Solid solutions (K_1−xRb_x)_0.28MoO₃ and (Li_1−xNa_x)_0.9Mo₆O₁₇ were also obtained at lower temperatures (ca. 670 K). For the latter system consisting of non-isostructural end members, Li_0.9Mo₆O₁₇-structure type solid solution was formed even when 0.25<x<0.70, unlike the case by the usual high-temperature methods. Metastable mixed oxides Ln₂Mo₃O₉ (Ln=La, Gd) were obtained, but not as single phases.     

Photochemistry of Transition-Metal Atoms: Reactions with Molecular Hydrogen and Methane in Low-Temperature Matrices

Reactions of metal atoms with molecular hydrogen and alkanes are prototypical of more complex systems involving metal-mediated reactions in solution, on supports, and on surfaces. The simplicity of metal-atom reactions makes them particularly attractive for fundamental experimental and theoretical studies. Following the first reports of H₂ and CH₄ activation by photoexcited metal atoms in cryogenic matrices, the behavior of a number of transition-metal atoms in their ground and selected electronically excited states has been examined with molecular hydrogen, methane, and ethane. A wealth of structural, electronic, reactivity, and selectivity information is emerging from these studies and it is now becoming possible to recognize the controlling factors at work in these fundamental chemical reactions. In this article, some experimental results for a number of metal-atom systems, in particular, those involving silver, copper, manganese, and iron atoms, are presented along with a discussion of the factors that are believed to be important in the understanding of the observed physical and chemical behavior.