Diffusional effect of pores on the densification in microgravity liquid phase sintered FE-CU alloys

OLiPSE-02 Fe-Cu samples, which were liquid phase sintered under 10 m 5 torr in microgravity for 20, 30, 60, and 330 min for each composition, were analyzed in this article. The compositions of the samples are 80% Fe/Cu, 70% Fe/Cu, 60% Fe/Cu, and 50% Fe/Cu by volume. The experimental results of distortion and densification were presented. During the microgravity processing, liquid ejection occured for the long duration samples with compositions 70% Fe/Cu and 60% Fe/Cu. Measurements of the weights and dimensions of all the beads were made and their distributions were presented. One of the beads that are about the average weight and size from the 70% Fe/Cu long duration sample was chosen to be mounted, polished, etched, and analyzed under an optical microscope. The iron in the bead appeared as iron grains and its grain size was smaller than that in the mother sample with the same composition. Discussions of the bead and its iron grain formations are provided.     

Diffusional Creep Mechanisms

Creep extension without dislocation movement across grains may be obtained in polycrystalline aggregates by diffusion through the grains (Nabarro-Herring) or through grain boundaries (Coble). These mechanisms are compared with a suggestion that creep can occur by grain-boundary sliding controlled by diffusion which can lead to movement along the boundary of grain-boundary protrusions and can be accommodated by diffusion around triple points.     

液相法甲醇合成的平衡收率

对液相法甲醇合成系统进行了热力学分析，建立了求解该系统相平衡和化学平衡问题的非线性方程组。在此基础上，分别对以四甘醇二甲醚和角鲨烷为液相介质的反应热力学平衡进行了计算，结果表明液相介质具有提高甲醇平衡收率的作用。研究了液相介质的性能、用量、温度、压力及原料气组成对甲醇平衡收率的影响。     

Supported liquid phase catalysis in selective oxidation

The application of supported liquid-phase catalysis (SLPC) to selective oxidation examples is discussed to provide valuable alternatives to the purely homogeneous or heterogenous processes. Specific examples discussed are the Wacker type ethylene oxidation on heterogenous catalysts and the vinyl acetate production by ethylene acetoxylation. The potential industrial application of SLPC for these oxidations and the possible extensions of this technology to other oxidation processes are also discussed.     

Theory of liquid phase dispersion in packed columns

Dispersion in the liquid phase for trickle or two-phase flow in packed columns has two important contributions, local dispersion in the packing, and axial dispersion due to the differences in liquid flow conditions between the wall and bulk regions of packing. A three-dimensional axisymmetric formulation of dispersion within the column is analysed and compared to a one-dimensional formulation in the axial co-ordinate. It is shown that the one-dimensional formulation is correct for the limit of long dispersion times. For other times the coefficient for total dispersion within the column is found to be a function of local dispersion, differences in flow between the wall and bulk regions, and dispersion time. An analytical relationship is given between the coefficient for total dispersion, and contributing factors, in local dispersion and column flows.     

纳米技术与纳米材料(Ⅸ)--纳米TiO2的液相合成

综述了液相法合成纳米TiO2，比较了各种液相法的优缺点，详细讨论了液相法合成纳米TiO2的研究进展和发展趋势。认为以TiCl4、TiOSO4和H2TiO3为原料时，产品成本较低。低温液相合成纳米TiO2的生产工艺由于省去了高温煅烧工序而最具竞争力。并指出过滤和防团聚是液相法规模化生产纳米TiO2需要重点解决的问题。     

Solidification structure in pure zirconia liquid molten phase

Up to now few studies concerning the crystallographic features of zirconia materials (HZ) used as refractory material have been performed. The elaboration process through raw material fusion followed by a controlled cooling step lead to a material containing 94 wt.% of dendritic monoclinic zirconia. During cooling, ZrO₂ passes through three different structural phase transitions (SPTs), inducing formation of a complex microstructure made of different crystallographic domains called variants. This study focus on formation of these different monoclinic variants in a non-doped zirconia based material and the possibility to reconstruct initial cubic parent crystals formed at high temperature using optical microscopy and Electron Back Scattering Diffraction (EBSD). EBSD experiments allow to identify 24 monoclinic variants issued from tetragonal parent crystal and to highlight the contours of the parent cubic crystal. Then, the microstructure appearing during the first steps of the solidification of the material can be evidenced.     

Polyethyleneglycol catalytic dehydration kinetics in the liquid phase

Eleven representative polyethyleneglycol (25322–68–3) catalytic dehydration reactions have been studied in the liquid phase at atmospheric pressure. The aim of this research is to build a kinetic model representative of the polyethyleneglycol dehydration process. Three types of reaction take place simultaneously in the process: cyclisation, condensation and alcoholysis. Activation energies and frequency factors are given, and the relationships between kinetic parameters and chain length of reactants and products are discussed according to the reaction type.     

A fundamental approach in liquid phase adsorption kinetics

Liquid-solid adsorption kinetic data are mostly interpreted by a limited number of rate equations, (pseudo-first, pseudo-second order and Elovich). Besides, a fundamental tool in heterogeneous reactions, the Langmuir theory of adsorption, is used almost exclusively to model equilibrium isotherms but, surprisingly, not kinetics. Considering the limited applicability of the mentioned kinetic models, especially in estimating kinetic constants and predicting adsorption mechanism, it seems more reasonable to apply the Langmuir kinetic equation in modeling the liquid phase adsorption. In the diffusion-free regime, by constructing the experimental equilibrium isotherm of a system, one can easily check the validity of the Langmuir model. Afterwards, kinetic constants can be readily calculated and used to predict adsorption performance under different operating conditions. The proposed procedure was tested in the experimental results of cyanide adsorption in activated carbon to verify the applicability of the Langmuir adsorption mechanism and estimate the equilibrium and kinetic constants.     

Micro-segregations in liquid phase sintered silicon carbide ceramics

The densification behaviour of LPSSiC ceramics with different amount of secondary phases was investigated during Field Assisted Sintering (FAST). In the densified materials micro-segregations were found with dimensions of several 100 μm. Sometimes such segregations were found in gas pressure sintered materials. The investigation of the state of crystallisation by EBSD and XRD revealed that these micro-segregations are connected with the formation of large YAG (Yttrium aluminium garnet) crystals. The mobility of yttrium in the grain boundaries was investigated by measuring concentration profiles in diffusion couples. The high diffusion coefficient determined at 1850 °C (10^?6 cm/s) indicates that the observed segregations are caused by the crystallisation kinetics of the secondary phases during cooling.     

MD simulation of phase transformations in liquid carbon

The supercooled liquid of carbon is investigated by means of molecular-dynamics simulation. The dynamics of a glass and a supercooled liquid is compared and the glass transition temperature is determined by two methods: analyzing (i) the temperature dependence of thermodynamic coefficients and (ii) relaxation time of liquid. The pressure dependences of the glass transition temperature and the diamond melting temperature are found. The percolation properties of structures of sp³ atoms formed in liquid carbon with different numbers of embedded diamond crystallites are investigated. It is shown that the percolation cluster of 4-fold coordinated atoms forms when their total concentration in structure reaches a value close to 0.38 irrespective of the number of embedded crystallites. It turns out that the stability of diamond crystallites embedded into supercooled carbon liquid correlates with the presence of the percolation cluster of 4-fold coordinated atoms. The correspondence of diamond crystallite stability with percolation disappears at a temperature more than 5000 K. The topological criterion for the definition of tetrahedral amorphous carbon is proposed: amorphous carbon is tetrahedral if a percolation cluster exists in it and the embedded diamond crystallites are stable.     

聚酯液相热媒系统

热媒管道是聚酯工程中非常重要的工艺管线,它的施工安装质量将直接影响聚酯工程正常生产和产品的品质。介绍了液相热媒系统的工作流程,并分析了一些关键的设计要点;如热媒膨胀槽,管道中气体分离器、排气管道及温度计套管的布置及讨点。指出聚酯装置中热媒循环系统的设计应当严格按要求设计,以保证聚酯装置及纺丝装置的正常运行。     

两液相生物反应器研究进展

介绍了两液相反应器的进展及存在问题，两液相反应器仍处于试验阶段，其主要问题是生物催化剂在界面的聚集损失活性等。     

环己烷液相氧化工艺研究进展

介绍了近年来环己烷液相空气均相和非均相催化氧化、光诱导催化氧化、无催化氧化、纯氧氧化等的研究进展 ,并对今后的研究发展方向进行了分析。     

Diffusional Creep and Kinetic Demixing in Yttria-Stabilized Zirconia

The creep behavior of fine-grained yttria-stabilized zirconia with 25 mol% Y₂O₃ has been characterized as part of an investigation of kinetic demixing in solid-solution oxides which are subjected to a nonhydrostatic state of stress. At temperatures between 1400° and 1600°C, the steady-state strain rate of (Zr_0.6Y_0.4)O_1.8 samples with average grain sizes between 2.5 and 14.5 μm can be summarized by the flow law ɛ= 6.5 × 10⁻⁷σ^1.2 exp[−550 (kJ/mol)/ RT ] d ^−2.2 (s⁻¹) for stresses in the range 8 to 60 MPa, where σ is in pascals and d is in meters. This flow law indicates that deformation occurs by a Nabarro-Herring creep mechanism in which the creep rate is limited by cation lattice diffusion. Kinetic demixing was not observed in deformed polycrystalline samples even though diffusional creep was rate limited by cation lattice diffusion. This result can be explained if the cation diffusivities are approximately equal or if extensive grain rotation occurs during diffusional creep.     

Diffusional deposition of particles in a model alveolus

Particle deposition by Brownian diffusion in a lung model alveolus during breathing is studied numerically. The transient and steady-state fractional deposition are obtained for different particle sizes.     

Diffusional resistances to oxygen transfer in whole blood

The present work investigates the resistance to oxygen transfer from the red blood cell by a modified rapid flow technique. If is found that the transfer of oxygen in the boundary layer surrounding the red blood cell can account for all of the transport resistance found in these experiments.     

Enhanced Diffusional Separation in Liquids by Sinusoidal Oscillations

Abstract

A general analysis of the problem of enhanced diffusional separation of dilute liquid solutions contained within open ended capillary tubes and subjected to axial oscillations is presented. Results show that the mass diffusion flux of the various components is equal to the product of the molecular diffusion coefficient of the species in question, the magnitude of the species axial concentration gradient, the square of the ratio of the tidal displacement to the capillary radius, and a function of the Womersley number. The earlier results of Dryer are shown to be correct for small oscillation frequencies and tube diameters, but predict effective diffusion coefficients which are too low at higher Womersley numbers. Differential diffusion separation fluxes some six orders of magnitude larger than possible with the same geometry in the absence of axial oscillations appear to be achievable for typical aqueous solutions.     

固液搅拌槽内液相湍流特性

采用粒子图像测速系统研究搅拌槽内固液二相湍流运动的流场分布规律,结果表明,液相速度随着颗粒体积分数的增加,先增加后变小,在颗粒体积分数为0.5%时有最大值。湍流动能和耗散率大的区域分布在桨叶尖端右下方,随着加入颗粒后,桨叶下方液相湍流动能和耗散率都比清水时大。湍流动能在颗粒体积分数为0.9%时有最大值,湍流动能耗散率在颗粒体积分数为1.3%时有最大值。