Preparation and microstructure of in-situ(ZrB_2+Al_2O_3+Al_3Zr)_p/A356 composite synthesized by melt direct reaction

（ZrB2＋Al2O3＋Al3Zr）/A356 composites were synthesized by melt direct reaction from A356-（K2ZrF6＋KBF4＋Na2B4O7） system.The phase compositions and the microstructures of the as-prepared composites were investigated by XRD,SEM and TEM.The results show that the reinforcements are composed of ZrB2 and Al2O3 ceramic phase particles and Al3Zr intermetallic particles.The ZrB2 particulates are easy to join together to form some particle clusters and distribute along the α（Al） grain boundary.The morphologies of the ZrB2 particulates are in hexagon-shape with the size of about 50 nm.The TEM investigation results of Al3Zr indicate that Al3Zr grows in the form of facet with the length-diameter ratio of about 20.The morphologies of Al2O3 particles are in rectangular-shape and ellipsoidal-shape,with the size of about 0.1 μm.In addition,the interfaces of the matrix and particles are net and no interfacial outgrowth is observed.

Preparation of Al-Al_3Ti in situ composites by direct reaction method

Al-Al3Ti composites were prepared by a direct reaction method, in which Al3Ti was formed by the reaction of Ti and Al in aluminum alloy melt. The morphology of Al3Ti changes apparently from the fine particle, needle-like to large block with the increase of Al3Ti content. The addition of magnesium can markedly change the morphology of Al3Ti and reduce their size. Short rod-like Al3Ti was formed and homogeneous distribution was obtained with the addition of 3 wt.% Mg. The effect of Al3Ti and Mg on the microstructure of Al-Al3Ti composites and the mechanism were also discussed.

Kinetics of the direct reaction between ozone and phenol by high-gravity intensified heterogeneous catalytic ozonation

In this study,high-gravity intensified heterogeneous catalytic ozonation is utilized for treatment of phenol-containing wastewater,and the kinetics of the direct reaction between ozone and phenol in the presence of excess tertiary butanol(TBA)is investigated.It is revealed that the direct reaction between ozone and phenol in the rotating packed bed(RPB)follows the pseudo-first-order kinetics with a reaction rate constant higher than that in the conventional bubbling reactor(BR).Under different conditions of temperature,initial pH,high-gravity factor,and gaseous ozone concentration,the apparent reaction rate constant varies in the range of 0.0160–0.115 min-1.An empirical power-exponential model is established to characterize the effects of these parameters on the direct reaction between ozone and phenol by high-gravity intensified heterogeneous catalytic ozonation.

PHASES AND STRUCTURE OF PREFORM DURING PREPARING PROCESS OF Al／TiCp COMPOSITES BY DIRECT REACTION SYNTHESIS

Direct reaction synthesis(DRS), based on the principle of self-propagating hightemperature synthesis (SHS), is a new method for preparing particulate metal matrix composites (PMMCs). The effects of the temperature of the aluminum melt and the aluminum content in the preform on the phases and structure of the reacted preform have been investigated by X-ray diffraction and scanning electron microscopy.It has been shown that TiC phase is prone to be synthesized with the increasing of the temperature of the aluminum melt and the decreasing of the aluminum powder content in the preform, and that the size of TiC particle becomes fine with the increasing of the temperature and the decreasing of the aluminum powder content.

Direct Electrochemical Reaction of Horseradish Peroxidase Immobilized on the Surface of Active Carbon Powders

It is reported for the first time that horseradish peroxidase (HRP) immobilized on the active carbon can undergo a direct quasi-reversible electrochemical reaction. In addition, the immobilized HRP showed the stable bioelectrocatalytic activity for the reduction of H2O2.

In-situ Preparation of Al/TiAl_3(P) Composite by Direct Reaction between Molten Al and TiO_2 Powder

TiAl3 particle reinforced pure Al composite has been made by direct reaction among molten Al, TiO2 and a flux. The composite exhibits high Synthetically properties. The strength and hardness are higher than those of pure Al matrix by 71.5% and 134% respectively However, the elongation is 20.36%, slightly lower than that of the Al matrix.

Direct asymmetric aldol reaction using MBHA resin-supported peptide containing L-proline unit

MBHA resin-supported tripeptide catalyst system containing L-proline unit has been developed for use in the direct asymmetric aldol reaction of acetone and aldehydes, which afford the corresponding products with satisfactory isolated yields and enantiomeric excesses. 2009 Hong Bin Zou. Published by E]sevier B.V. on behalf of Chinese Chemical Society. All rights reserved.

DFT Study on the (S)-Proline-catalyzed Direct Aldol Reaction between Acetone and 4-Nitrobenzaldehyde

DFT/6-31G^＊ calculations were applied to study the direct aldol reaction between acetone and 4-nitrobenzaldehyde catalyzed by （S）-proline. Four transition states associated with the stereo-controlling step, corresponding to syn and anti arrangements of methylene moiety related to the carboxylic acid group in enamine intermediate and re and si attacks to the aldehyde carbonyl carbon have been obtained. The solvent effect of DMSO was investigated with polarized continuum model. The computed energies of transition states reveal the stereo-selectivity of the reaction.

高Cr铸造镍基高温合金K4648与陶瓷型芯的界面反应研究

采用金相显微镜、扫描电镜及能谱、电子探针和X射线衍射对高Cr铸造镍基高温合金K4648等轴晶和定向凝固铸件的合金/陶瓷型芯界面反应进行了系统研究,获得反应时间与反应量关系的界面反应动力学曲线、不同反应时间的反应界面形貌及产物的种类。结果表明:高Cr铸造镍基高温合金K4648与铝基型芯不易发生反应,而与硅基陶瓷型芯发生剧烈的界面反应,反应产生金属瘤状凸起物,造成铸件内腔破坏。此外,白色的硅基型芯内部变成黑色,黑色反应区内含有一定量的Cr,Al,Ti元素。在反应的中、后期型芯黑色反应区内还存在着灰色区,该区的Cr,Al,Ti含量远高于黑色反应区。高Cr铸造镍基高温合金K4648合金与硅基陶瓷型芯反应分为:(1)富Cr,Al,Ti熔体向型芯内的渗入阶段;(2)富Cr,Al,Ti熔体与陶瓷型芯SiO2基体的反应;(3)富Cr,Al,Ti的熔体与型芯中Zr-SiO4颗粒反应三个阶段。反应过程中型芯存在局部液化现象。K4648合金/硅基陶瓷型界面反应产物主要为层状或树枝状Al2O3,块状Cr3Si金属间化合物、ZrO2,富Cr,Zr,Al,Ti的复合氧化物、共晶形态的富Cr,Si,Al,Ti的复合氧化物、块状或树枝状的富Ti,Al,Zr,Cr复合氧化物。反应产物中的Cr,Al,Ti元素来自合金熔体而Zr,Si,O来自陶瓷型芯。

In-medium nucleon-nucleon elastic cross-sections determined from the nucleon induced reaction cross-section data

Within the framework of the improved quantum molecular dynamics model, the medium modifications of the free nucleon-nucleon elastic cross-sections are investigated. By using various in-medium nucleon-nucleon elastic cross-sections in the model, the nucleon induced reactions on various targets are simulated, and the excitation functions of reaction cross-sections in the energy range from 25 MeV to 1 GeV are calculated. By comparing the calculations with the experimental data, the isospin, density, and momentum dependence of the medium correction factors of free nucleon-nucleon elastic cross-sections are determined.

Highly Enantioselective Direct Asymmetric Aldol Reaction Catalyzed by 4,5-Methano-L-proline

The 4,5-methano-L-proline was used as chiral organocatalysts in direct asymmetric aldol reactions.Under the optimal conditions,excellent enantioselectivities(up to 99%ee)were obtained with high chemical yields(up to 95%)for a series of aldehydes using only 5 mol%catalyst loading.To show the practicality of the method,the reaction was tested at a large scale.The reaction was complete in 16 h,and the aldol product was obtained in 86%yield and 93%ee.

Effect of nuclear deformation on direct capture reactions

Direct radiative capture processes are well described by a spherical potential model. Since most nuclei are not spherical, and in order for the model to explain direct radiative captures more accurately, the effect of nuclear deformation has been analyzed with q-deformed Woods-Saxon potential in this work. The results imply that nuclear deformation largely affects the direct radiative capture, and it should be taken into account when discussing direct capture reactions.

DFT Study on the Origin of the Enantioselectivity of （S）-4-Hydroxylproline-Catalyzed Direct Aldol Reaction between Acetone and 4-Nitrobenzaldehyde

DFT-B3LYP calculations were carried out to study the enantioselectivity of the （S）-4-hydroxylproline-catalyzed direct aldol reaction between acetone and 4-nitrobenzaldehyde. Four transition structures associated with the stereo-controlling step of the reaction have been determined. They are corresponding to the anti and syn arrangements of the methylene moiety related to the carboxylic acid group in enamine intermediate and the si and re attacks to the aldehyde carbonyl carbon. The effect of DMSO solvent on the stereo-controlling step was investigated with polarized continuum model （PCM）. The computed energies of the transition states reveal the moderate enantioselectivity of the reaction.