Mesoscopic simulation of the impregnating process of unidirectional fibrous preform in resin transfer molding

The resin transfer molding has gained popularity in the preparation of fiber-reinforced polymer-matrix composites because of its high efficiency and low pollution. The non-uniform inter-tow and intra-tow flows are regarded as the reason of void formation in RTM. According to the process characteristics, the axisymmetric model was developed to study the interaction between the flow in the inter-tow space and that in the intra-tow space. The flow behavior inside the fiber tows was formulated using Brinkman's equation, while that in the open space around the fiber tows was formulated by Stokes' equation. The volume of fluid (VOF) method was applied to track the flow front, and the effects of filling velocity, resin viscosity, inter-tow dimension and intra-tow permeability on fluid pressure and flow front were analyzed. The results show that the flow front difference between the inter-tow and intra-tow becomes larger with the decrease of intra-tow permeability, as well as the increase of filling velocity and inter-tow dimension.

Preparation of highly active Pt/C cathode electrocatalysts for DMFCs by an improved aqueous impregnation method

An improved aqueous impregnation method was used to prepare 40 wt% Pt/C electrocatalysts. TEM analysis of the samples showed that the Pt particles impregnated for a short time have a very narrow size distribution in the range of 1-4 nm with an average size of 2.6 nm. UV-vis spectroscopy measurements verified that the redox reaction between PtCl62- and formaldehyde took place with a slow rate at ambient temperature via a two-step reaction path, where PtCl42- serves as an intermediate. The use of the short-time-impregnated 40 wt% Pt/C as cathode electrocatalysts in direct methanol fuel cells yields better performance than that of commercial 40 wt% Pt/C electrocatalyst. Experimental evidence provides clues for the fundamental understanding of elementary steps of the redox reactions, which helps in guiding the design and preparation of highly dispersed Pt catalyst for fuel cells.

Highly active PtRu catalysts supported on carbon nanotubes prepared by modified impregnation method for methanol electro-oxidation

A simple and rapid synthesis method (denoted as modified impregnation method, MI) for PtRu/CNTs (MI) and PtRu/C (MI) was presented. PtRu/CNTs (MI) and PtRu/C (MI) catalysts were characterized by transmission electron microscopy (TEM) and X-ray diffractometry. It was shown that Pt-Ru particles with small average size (2.7 nm) were uniformly dispersed on carbon supports (carbon nanotubes and carbon black) and displayed the characteristic diffraction peaks of Pt face-centered cubic structure.

High activity PtRu/C catalysts synthesized by a modified impregnation method for methanol electro-oxidation

A modified impregnation method was used to prepare highly dispersive carbon-supported PtRu catalyst (PtRu/C). Two modifications to the conventional impregnation method were performed: one was to precipitate the precursors ((NH4)(2)PtCl6 and Ru(OH)(3)) on the carbon support before metal reduction: the other was to add a buffer into the synthetic solution to stabilize the pH. The prepared catalyst showed a much higher activity for methanol electro-oxidation than a catalyst prepared by the conventional impregnation method. even higher than that of current commercially available, state-of-the-art catalysts. The morphology of the prepared catalyst was characterized using TEM and XRD measurements to determine particle sizes, alloying degree, and lattice parameters. Electrochemical methods were also used to ascertain the electrochemical active surface area and the specific activity of the catalyst.

Infraciliature and myoneme system of Campanella umbellaria (Protozoa, Ciliophora, Peritrichida)

The infraciliature and myoneme system of Campanella umbellaria were revealed using the protargol impregnation technique. The main characteristics of the infraciliature are the peristomial ciliary rows (haplokinety and polykineties), which make four and a half turns around the peristomial disc before plunging into the infundibulum, and the aboral infraciliature, which is made up of the aboral ciliary wreath (trochal band) and the scopula. The myoneme system is composed of: 1) longitudinal fibers, which include 60-84 (mean 72.3) short longitudinal fibers, 40-56 (mean 45.8) medium-length longitudinal fibers, and numerous long longitudinal fibers; and 2) circular fibers, which include 8-12 (mean 9.3) peristomial ring fibers, linking fibers, support fibers, and peristomial disc fibers. The various fibers in C. umbellaria are interconnected to form a single myoneme system that may act as a cell skeleton as well as providing the mechanism by which the zooid contracts and relaxes. (C) 2004 Wiley-Liss, Inc.

MoNi/gamma-Al2O3 Catalyst: Preparation and Catalytic Activity for Acetic Acid Hydrotreating

MoNi/gamma-Al2O3 catalysts were prepared by the impregnation method. The catalyst samples were characterized by XRD and TPR. The effects of Mo promoter content and the catalyst reducing temperature Oil hydrotreatment activity of the catalyst were studied under 200 degrees C and 3 MPa hydrogen pressure using acetic acid as the model compound. The XRD results indicate that the addition of Mo promoter is beneficial to the uniformity of nickel species on the catalyst and decreases the Interaction between nickel species and the support Which results in the decrease the of NiAl2O4 spinel formation. The addition of Mo promoter also decreases the reducing temperature of the catalyst. After the catalyst of 0.06 MoNi/gamma-Al2O3 being reduced Under the atmosphere of H-2/N-2(5/95, V/V), nickel oxide was reduced to Ni-0. The reaction was promoted obviously upon the addition of the MoNi/gamma-Al2O3 catalyst reduced at 600 degrees C. The Mo-modified Ni/gamma-Al2O3 catalyst reduced at 600 degrees C displayed the highest activity during the reaction, the conversion of acetic acid reached the highest point of 33.2%. The products included ethyl acetate and water.

聚乳酸烟用过滤嘴制备工艺及若干基础问题的研究

本论文适应聚乳酸烟用过滤嘴工业化的需要，针对烟用过滤嘴特殊的工艺和技术要求，进行了相关问题的基础研究。 在自制模型小纺丝机上进行了小试研究。研究了干燥条件、树脂水分含量、树脂规格、添加助剂、纺丝温度、纺丝速度，后处理等对聚乳酸可纺性、纤维性能的影响，确定了中试纺丝条件。在聚丙烯烟用丝束国产线上进行了中试研究，研究了纺丝速度，牵倍，牵伸温度，松弛热定型温度和时间对聚乳酸纤维力学性能、热学性能、粘接性能、开松性能、过滤性能的影响，进一步明确了树脂规格和纺丝条件，研发出适合聚乳酸香烟滤材的粘接剂，并且初步得到了吸阻和硬度符合接烟要求的过滤嘴棒。在卷烟厂进行了过滤嘴的香烟接装实验，结果表明聚乳酸香烟过滤嘴可以满足高速接烟的需要。 在实验室和卷烟厂分别进行了聚乳酸滤材吸附/过滤性能研究：1）在实验室，进行了聚乳酸纤维对烟气中典型的烟气成分的静态吸附实验；2）在卷烟厂，对接装聚乳酸香过滤嘴的香烟进行了烟气分析和品吸。结果表明聚乳酸烟用丝束对极性和非极性烟气成分气体有较高的吸附/吸收能力，但对烟碱的吸附却很少。因而聚乳酸过滤嘴的香烟可能有自己独特的吸味风格。聚乳酸香烟过滤嘴具有同二醋酸纤维素过滤嘴相近的过滤能力，可以有效的过滤烟气中的有害物质，过滤效果优于聚丙烯。 针对聚乳酸在熔体纺丝过程中热稳定性差这一关键问题，深入系统地研究了添加有聚碳化二亚胺聚乳酸的流变学行为、热学性能、热降解行为、力学性能、酶降解行为和稳定机制。实验结果表明在聚乳酸中添加抗水解稳定剂能显著提高聚乳酸的加工热稳定性，表现为经过熔体加工后，分子量较少下降，熔融指数增加不多，力学性能基本维持不变。改性的原因是聚碳化二亚胺在加工的过程中与残留的或加工过程中形成的乳酸和/或水分子反应，消除或减少了聚乳酸的水解，阻止了乳酸对聚乳酸水解的催化作用；与聚乳酸的端羟基或端羧基发生了化学反应，从而减少了通过端基“反咬”形成丙交酯而降解的可能性，甚至将端基偶联，使分子量增大。 通过高压静电纺丝制备具有不同三醋酸甘油酯（GTA）含量的聚乳酸超细纤维毡，场发射扫描电镜、示差扫描量热仪、水接触角和力学性能测试表明，随着GTA含量的增加，纤维之间趋于粘连，形成立体网状结构，纤维毡的断裂伸长率、回弹率、拉伸强度可分别达到200%、85%、4.24MPa，比不改性的聚乳酸超细纤维毡有显著地提高。当GTA含量在40%以下时，纤维粘毡表现出超疏水特性，表面表观水接触角约在130°左右，当GTA含量高于50%，水能迅速浸润和渗入纤维毡，表观水接触角为0°。

A mechanism for enhanced photocatalytic activity of silver-loaded titanium dioxide

In this paper, silver-loaded TiO2 photocatalyst was prepared by photochemical impregnation method and characterized by transmission electron microscopy (TEM), diffuse reflectance spectra (DRS), photooxidation of phenol and photoreduction of Cr(VI). Electron paramagnetic resonance (EPR) was used to detect photoproduced paramagnetic radicals. The correlation of photocatalytic activity and photogenerated reactive species was discussed, and the mechanism of silver-loaded TiO2 for enhancement of photocatalytic activity was elucidated. The results show that deposited silver on TiO2 Surface acts as a site where electrons accumulate. The better separation between electrons and holes on the modified TiO2 surface allowed more efficiency for the oxidation and reduction reactions. The enhanced photocatalytic activity was mainly attributed to the increased amounts of O-2(.-) reactive species and surface Ti3+ reactive center on silver-loaded TiO2 photocatalyst. (C) 2004 Published by Elsevier B.V.

Synthesis and characterization of carbon black supported Pt-Ru alloy as a model catalyst for fuel cells

A set of bimetallic Pt-Ru catalysts prepared by co-impregnation of carbon black with ruthenium(III) chloride hydrate and hydrogen hexachloroplatinate(IV) hydrate were investigated by temperature-programmed reduction (TPR), chemisorption of hydrogen, transmission electron microscopy (TEM), microcalorimetry of adsorbed CO and a structure-sensitive reaction (n-hexane conversion). The results showed that the volumetric capacities for CO and H-2 adsorption is influenced in the bimetallic Pt-Ru catalysts by the formation of a Pt-Ru alloy. The n-hexane reaction revealed that the reaction mechanism for the pure Pt catalyst mainly occurs via cyclic isomerization and aromatization due to the presence of bigger Pt surface ensembles, whereas the Pt-Ru catalysts exhibited predominantly bond-shift isomerization by the diluting effect of Ru metal addition. The differential heats of CO chemisorption on Pt-Ru catalysts fell between the two monometallic Pt and Ru catalysts extremes. (C) 2004 Elsevier B.V. All rights reserved.

Structure and acidity of Mo/H-MCM-22 catalysts studied by NMR spectroscopy

A comprehensive study on physical and chemical properties of Mo/MCM-22 bifunctional catalysts has been made by using combined analytic and spectroscopic techniques, such as adsorption, elemental analysis, and Xe-129 and P-31 NMR of adsorbed trialkylphosphine oxide probe molecules. Samples prepared by the impregnation method with Mo loadings ranging from 2-10 wt.% have been examined and the results are compared with that obtained from samples prepared by mechanical mixing using MoO3 or Mo2C as agents. Sample calcination treatment is essential in achieving a well-dispersed metal species in Mo/MCM-22. It was found that, upon initial incorporation, the Mo species tend to inactivate both Bronsted and Lewis sites locate predominantly in the supercages rather than the 10-membered ring channels of MCM-22. However, as the Mo loading exceeds 6 wt.%, the excessive Mo species tend to migrate toward extracrystalline surfaces of the catalyst. A consistent decrease in concentrations of acid sites with increasing Mo loading < 6 wt.% was found, especially for those with higher acid strengths. Upon loading of Mo > 6 wt.%, further decreases in both Bronsted and Lewis acidities were observed. These results provide crucial supports for interpreting the peculiar behaviors previously observed during the conversion of methane to benzene over Mo/MCM-22 catalyst under non-oxidative conditions, in which an optimal performance was achieved with a Mo loading of 6 wt.%. The effects of Mo incorporation on porosity and acidity features of the catalyst are discussed. (C) 2004 Published by Elsevier B.V.