Metal encapsulation in zeolite particles: A rational design of zeolite-supported catalyst with maximum site activity

Zeolite-supported metal catalysts have been proven effective in many important catalytic reactions, such as hydrogenation, Fisher-Tropsch synthesis, automobile exhaust catalysis, selective catalytic reduction and many others. Despite the successful preparation of the catalyst through widely adopted methods, including ion exchange and impregnation, the metal dispersion over the zeolite is lack of control with high randomness. This renders the so-called “catalytic performance” an overall contribution from the metal sites located inside the zeolite micropores and those located on the external surface. This is exceptionally true for small to medium pore zeolites with typical free apertures of 0.3–0.6 nm (such as LTA and MFI). A more rational design of zeolite-supported metal catalysts is by encapsulating the metal nanoparticles or clusters within zeolite pores prior to the zeolite formation. Encapsulation of metals in zeolite prevents them from sintering and sulphur poisoning by cage confinement and molecular exclusion (via well-defined pore size and shape), respectively. This paper gives a new perspective on using metal clusters and nanoparticles as catalysts and the design of an effective zeolite-supported catalytic system.     

Feature-based metal stamping part and process design. Part I: stampability evaluation

It is essential to devise a representation scheme for the metal stamping part design which allows the designer to capture and reason the design information, and ultimately, to take various considerations into account and make evaluation decisions. In our research, the feature-based approach is used to represent the metal stamping part, and feature-based metal stamping part and process design has been studied and presented in a two-part paper. This is the first of a two-part paper focusing on stampability evaluation. In Part II a feature-based stamping process planning approach is investigated. This paper presents a feature- and knowledge-based stampability evaluation system. Tasks of this research include identification of the aims, criteria, and procedure of stampability evaluation, as well as the formalization of the stampability evaluation knowledge. Stampability evaluation is classified into stampability verification and stampability measurement. Stampability verification is used to determine whether a part design is stampable or not. Stampability measurement can be employed to select a best design from stampable candidate designs. Based on the stamping design feature definition, a stampability-coding scheme with incorporated knowledge has been developed to enable comprehensive stampability evaluation. Finally, a case study demonstrates the feasibility of such stampability evaluation system.     

Sol-gel preparation and characterisation of mixed metal tin oxide thin films

Mixed metal oxide stannates were prepared by sol-gel methods and coated onto solid titanium substrates as thin films using spin and dip coating methods. Metal oxides such as Sb₂O₅, ZrO₂, CuO, MnO_x and PdO were introduced into a SnO₂ host matrix using sol-gel technology. The mixed metal tin oxide materials prepared via the sol-gel route were extensively characterised in terms of surface characterisation and chemical composition. Thermogravimetric analysis was performed to confirm that at 600 °C (the calcination temperature) no further structural changes due to mass loss occur. UV spectroscopy of the liquid gels allowed the determination of the band gap energy. The surface morphology of the thin film electrodes were characterised by atomic force microscopy and scanning electron microscopy and the effect of the coating method employed i.e. spin or dip coating could be clearly seen in the estimated values of surface roughness. These techniques were also able to confirm the thickness of the films in the nano range. Combined nuclear beam techniques such as Rutherford backscattering spectroscopy and particle induced X-ray emission provided some insight into the chemical composition of the mixed metal tin oxides and confirmed the presence of the dopant element in the SnO₂ host material.     

A methodology for evaluation of metal forming system design and performance via CAE simulation

In the current metal forming product development paradigm, product cost, time-to-market and product quality are three overriding issues, which determine the competitiveness of the developed products. In the up front design process, the first 20% of design activities commits to about 80% of product development cost and product quality issues. How to conduct ‘right the first time’ design is critical to ensure low development cost, high product quality and short time-to-market. To address these issues, state of the art technologies are needed. Traditionally, computer-aided design (CAD) and computer-aided manufacturing (CAM) technologies provide solutions for representation of design intent and realization of design solution physically. However, it is difficult to address some critical issues in the design of forming process, tooling structure, material selection and properties configuration, and finally the product quality control and assurance. Computer-aided engineering (CAE) technology fills this gap as it helps practitioners generate, verify, validate and optimize design solutions before they are practically implemented and physically realized. In this paper, a methodology for evaluation of metal forming system design and performance via CAE simulation is developed. The concept of metal forming system and its design is first articulated and how the CAE technology helps design and design solution evaluation is then presented. To assess and evaluate the performance of metal forming systems, quantitative design evaluation criteria are developed. Through industrial case study, how the developed methodology helps metal forming system design and evaluation is illustrated and its efficiency and validity is finally verified.     

Recent advances in metals and metal oxides as catalysts for vanadium redox flow battery:Properties,structures,and perspectives

Vanadium redox flow battery(VRFB)is a kind of battery with wide application prospect.Electrode mate-rial is one of the key components of VRFB,and its stability directly affects the performance of battery.Among all kinds of electrode materials,carbon-based material has the best comprehensive properties.However,carbon-based electrodes still have disadvantages such as poor hydrophilicity and low electro-chemical activity which need to be improved.One of the effective ways to improve the performance of electrode is to modify carbon-based material with metals and metal oxides.The metal catalysts have excellent electrical conductivity and high catalytic activity.The metal oxide catalysts have the advan-tages of low cost,wide variety and strong oxidizing properties.This work introduced the application of metal and metal oxide modified electrodes in VRFB in recent years,classified the catalysts,studied their catalytic performance and mechanism.The metal catalysts were reviewed from precious metals and base metals.The metal oxide catalysts were classified and discussed according to the similar proper-ties of the same group elements.This work compared different modification methods,summarized the research progress of metal and metal oxide modification,and proposes the future development direction of electrodes and catalysts.     

木质素基树脂的制备及其对重金属离子的吸附性能

以木质素磺酸钠为原料,利用反相悬浮聚合技术,成功制备木质素基树脂.研究了木质素基树脂的制备工艺及其对重金属离子Pb2+、Cd2+的吸附性能.结果表明,优化的聚合条件为:液体石蜡与反应水溶液的相比为3:1、分散剂占有机相百分含量为2%、温度为90℃、盐酸浓度为3mol/L、甲醛占木质素磺酸钠百分含量为9%、聚合时间为2h.30℃时,所制备的树脂对Pb2+、Cd2+的饱和吸附量分别达到33.6523mg/g和30.12mg/g.所制备的木质素基树脂有大量羟基和磺酸基等含氧基团存在,非常有利于它对重金属离子的吸附.木质素基树脂的比表面积为0.0963m2/g,孔容为0.002389cm3/g,平均孔径为99.2208nm,表明该树脂具有大孔树脂的结构特点.     

锂离子电池用多孔电极结构设计及制备技术进展

随着人们对锂离子电池需求的日益增加, 高能量密度和高功率密度锂离子电池技术成为研究热点之一。材料改性及新材料开发能有效提高电池的能量密度, 除此以外, 孔隙率、孔径大小与分布、曲折度及电极组分分布等电极的微观结构参数也是决定电极及电池性能的关键因素。通过优化电极结构设计提升高比能电池的性能逐渐成为人们关注的焦点。本文综述了锂离子电池多孔电极结构设计优化的研究进展, 总结了多孔电极结构设计要素及制备方法, 最后对电极结构设计优化以及推动新型制备技术的规模化应用在高比能锂离子电池领域的未来发展前景进行展望。     

Ultrasonic vibration-assisted machining:principle,design and application

Ultrasonic vibration-assisted(UVA) machining is a process which makes use of a micro-scale high frequency vibration applied to a cutting tool to improve the material removal effectiveness.Its principle is to make the tool-workpiece interaction a microscopically non-monotonic process to facilitate chip separation and to reduce machining forces.It can also reduce the deformation zone in a workpiece under machining,thereby improving the surface integrity of a component machined.There are several types of UVA machining processes,differentiated by the directions of the vibrations introduced relative to the cutting direction.Applications of UVA machining to a wide range of workpiece materials have shown that the process can considerably improve machining performance.This paper aims to provide a comprehensive discussion and review about some key aspects of UVA machining such as cutting kinematics and dynamics,effect of workpiece materials and wear of cutting tools,involving a wide range of workpiece materials including metal alloys,ceramics,amorphous and composite materials.Some aspects for further investigation are also outlined at the end.     

Electrokinetic recovery of Cd, Cr, As, Ni, Zn and Mn from waste printed circuit boards: Effect of assisting agents

The printed circuit boards (PCBs) contains large number of heavy metal such as Cd, Cr, As, Ni, Zn and Mn. In this study, the use of electrokinetic (EK) treatment with different assisting agents has been investigated to recover the heavy metals from waste PCBs, and the effectiveness of different assisting agents (HNO₃, HCl, citric acid) was evaluated. The PCBs were first pre-treated by supercritical water oxidation (SCWO) process, then subjected to EK process. The heavy metal speciation, migration and recovery efficiency in the presence of different assisting agents during EK process were discussed. The mass loss of Cd, Cr, As and Zn during the SCWO process was negligible, but approximately 52% of Ni and 56% of Mn were lost in such a process. Experimental results showed that different assisting agents have significant effect on the behavior and recovery efficiency of different heavy metals. HCl was highly efficient for the recovery of Cd in waste PCBs due to the low pH and the stable complexation of Cl⁻. Citric acid was highly efficient for the recovery of Cr, Zn and Mn. HNO₃ was low efficient for recovery of most heavy metals except for Ni.     

Grinding behavior of WO3, NiO,Fe2O3 by ultrasonic milling parameters control and preparation of nanocomposite powder

Tungsten-based alloys have been widely applied in various industries due to their excellent mechanical properties. Tungsten-based alloys have a high sintering temperature due to the high melting point of tungsten, so the coarse particles negatively affect the mechanical properties of the alloy. This problem can be solved by increasing the densification by reducing the sintering temperature and time by adding nanoparticles with high surface energy. Herein, we fabricated nanoparticle-sized metal oxides by ultrasonic milling to minimize the influx of impurities to improve the densification of tungsten alloys. The main parameters of the ultrasonic milling experiments were ball density and ball layer. Metal oxides prepared by ultrasonic milling showed an average particle size distribution of less than 200 nm, and metal composite powders prepared through subsequent hydrogen reduction also showed nanoparticle size distributions. We believe that this approach will enable the production of improved sintered tungsten-based alloys.     

Heavy metal ions adsorption and photodegradation of remazol black XP by iron oxide/silica monoliths: Kinetic and equilibrium modelling

The adsorption of heavy metal ions (Cr³⁺, Pb²⁺ and Cd²⁺) by metal oxide monoliths (Fe₂O₃ and Fe₂O₃/SiO₂) synthesized via nanocasting method using SiO₂ monoliths as a template was studied. The adsorption experiments were performed in different batches by varying key parameters and the equilibrium between the adsorbents and metal ion solution was achieved in ～120?min at pH 6. The maximum monolayer adsorption efficiency for Pb (II), Cr (III) and Cd (II) ions was 850, 770 and 690?mg/g, respectively, for the magnetic Fe₂O₃/SiO₂ monoliths. The experimental data show best fit with the pseudo-second-order reaction type. The adsorption data found to be well fitted using Freundlich and Langmuir adsorption isotherms. The adsorption process was exothermic and spontaneous in nature, as confirmed by the thermodynamic parameters. Furthermore, the photocatalytic degradation of an industrial dye e.g., remazol black XP (RxP) by Fe₂O₃/SiO₂ monoliths was done from wastewater and the photocatalytic efficiency of the monoliths (using different amount) has been evaluated under visible light source which gives the best results (97.8%) for the monolith concentration 0.10?g/L.     

层次孔炭材料的设计制备及其在储能领域的应用

层次孔炭材料呈合理的微孔-中孔/大孔结构及孔径分布,具有高的电化学活性表面、极短的扩散距离和较高的传质速率,在用作储能器件电极材料时,表现出优异的功率特性.通过综述近来年层次孔炭材料的设计制备及其在储能领域的应用进展,重点介绍了本课题组自2008年以来的研究成果,进而展望了层次孔炭材料的发展方向.指出:层次孔炭材料主要通过模板法或模板-活化联合法制备.这两种方法可以实现炭材料纳米结构的精确调控.最近,开发出来的更简易的免模板法展现出较好的应用前景.     

Thin-film photo-catalytic TiO2 phase prepared by magnetron sputtering deposition, plasma ion implantation and metal vapor vacuum arc source

This study utilizes three methods, magnetron sputtering deposition (MSD), plasma ion implantation (PIII), and metal vapor vacuum arc (MeVVA), to prepare a thin-film TiO₂. The formation of stoichiometrical TiO₂-polymorphs as a layer is regularly relevant to the characteristic of the photo-catalytic effect. TiO₂-polymorphs created at the outermost surface and initiated by efficient photons are still capable to produce superficial hydroxyl groups for subsequent photo-catalytic reactions. The MSD-treated surface with the majority of TiO₂-anatase (101) surface is presently photo-catalytic. The PIII or MeVVA treatment results in an ion-implanted layer of different Ti / O ratios along with the detecting depths, whereas the Ti and O elements in TiO₂ phase at the outermost surface of the layer can be distinguished. Although the PIII- or MeVVA-treated surface is relatively insignificant in photo-catalytic reactions assessed by water droplet contact angle, the consumption of methylene blue in water and antibacterial test, it is still potential to adjust their surface chemistry by improving the quality of the ion-implanted layer, roughening the contact surface area, and increasing the efficiency to regenerate the photo-catalytic reactions. In addition, the ion implantation methods do not alter the size and dimension of a substrate that is a great advantage to employ them for various advanced applications.     

Mechanical and magnetic properties of metal fibre networks, with and without a polymeric matrix

Bonded networks of metal fibres are highly porous, permeable materials, which often exhibit relatively high strength. Material of this type has been produced, using melt-extracted ferritic stainless steel fibres, and characterised in terms of fibre volume fraction, fibre segment (joint-to-joint) length and fibre orientation distribution. Young’s moduli and yield stresses have been measured. The behaviour when subjected to a magnetic field has also been investigated. This causes macroscopic straining, as the individual fibres become magnetised and tend to align with the applied field. The modeling approach of Markaki and Clyne, recently developed for prediction of the mechanical and magneto-mechanical properties of such materials, is briefly summarised and comparisons are made with experimental data. The effects of filling the inter-fibre void with compliant (polymeric) matrices have also been explored. In general the modeling approach gives reliable predictions, particularly when the network architecture has been characterised using X-ray tomography.     

Effects of secondary phases on the damping behaviour of metals, alloys and metal matrix composites

An understanding of the precise correlation between the presence of secondary phases and material damping has eluded investigators, partly as a result of the fact that often there are various mechanisms involved. As a step towards the clarification of damping phenomena in metals and alloys, this paper provides a systematic review of the studies that have been completed on the damping mechanisms present in metals and alloys, with particular emphasis on precipitation. The damping mechanisms associated with secondary phases in metals and alloys have been subdivided into four categories, namely interface damping theory, thermal mismatch-induced dislocation damping theory, interaction damping theory and the rule of mixtures damping theory. A number of alloy systems are discussed to demonstrate the applicability of the four types of theory and the level of understanding of these complex mechanisms. As an extension of precipitation damping theory, the damping behaviour and mechanisms in particle-reinforced metal matrix composites are extensively discussed.     

Laser,tungsten inert gas,and metal active gas welding of DP780 steel: Comparison of hardness,tensile properties and fatigue resistance

The microstructural characteristics, tensile properties and low-cycle fatigue properties of a dual-phase steel (DP780) were investigated following its joining by three methods: laser welding, tungsten inert gas (TIG) welding, and metal active gas (MAG) welding. Through this, it was found that the size of the welded zone increases with greater heat input (MAG > TIG > laser), whereas the hardness of the weld metal (WM) and heat-affected zone (HAZ) increases with cooling rate (laser > TIG > MAG). Consequently, laser- and TIG-welded steels exhibit higher yield strength than the base metal due to a substantially harder WM. In contrast, the strength of MAG-welded steel is reduced by a broad and soft WM and HAZ. The fatigue life of laser-and TIG-welded steel was similar, with both being greater than that of MAG-welded steel; however, the fatigue resistance of all welds was inferior to that of the non-welded base metal. Finally, crack initiation sites were found to differ depending on the microstructural characteristics of the welded zone, as well as the tensile and cyclic loading.     

The Gibson-Ashby model for additively manufactured metal lattice materials: Its theoretical basis,limitations and new insights from remedies

The Gibson-Ashby (G-A) model has been instrumental in the design of additively manufactured (AM-ed) metal lattice materials or mechanical metamaterials. The first part of this work reviews the proposition and formulation of the G-A model and emphasizes that the G-A model is only applicable to low-density lattice materials with strut length-to-diameter ratios greater than 5. The second part evaluates the applicability of the G-A model to AM-ed metal lattice materials and reveals the fundamental disconnections between them. The third part assesses the deformation mechanisms of AM-ed metal lattices in relation to their strut length-to-diameter ratios and identifies that AM-ed metal lattices deform by concurrent bending, stretching, and shear, rather than just stretching or bending considered by the G-A model. Consequently, mechanical property models coupling stretching, bending and shear deformation mechanisms are developed for various lattice materials, which show high congruence with experimental data. The last part discusses new insights obtained from these remedies into the design of strong and stiff metal lattices. In particular, we recommend that the use of inclined struts be avoided.     

Numerical simulation of metal matrix composites and polymer matrix composites processing by infiltration: a review

The injection of a liquid metal through a fibrous preform is one of the techniques used to manufacture metal matrix composites (MMCs). The flow of metal through fibrous preform is a problem of fluid mechanics in porous medium. Numerical simulations of this process were developed in particular for non-isothermal infiltrations which take into account the phenomena of phase change. In addition, numerical models were developed to predict the appearance of defects in the end product and to study the evolution of the deformation of the fibrous preform during metal infiltration. After pointing out the analogous numerical studies devoted to the Resin Transfer Moulding (RTM) process, we give a progress report on the models developed to date for MMCs.     

Standard free energy change of formation per unit volume: a new parameter for evaluating nucleation and growth of oxides, sulphides, carbides and nitrides

 The present paper introduces a thermodynamic parameter, the standard free energy changes of formation of oxide, sulphide, carbide and nitride per unit volume, as a criterion for comparing the formation tendency of these compounds. The diagrams for the standard free energy change of formation of common oxides, sulphides, carbides and nitrides per unit volume vs temperature have been calculated and established based on the available thermodynamic data. It is believed that these diagrams can provide better explanations to some oxidation phenomena including the effects of reactive elements on the selective oxidation of Cr₂O₃ and Al₂O₃. Received: 12 September 1997 / Accepted: 16 September 1997     

Adsorption and diffusion of oxygen on metal surfaces studied by first-principle study:A review

First-principle calculations,especially by the density functio nal theory(DFT),is used to study the structure and properties of oxygen/metal interfaces.Adsorption of oxygen molecules or atoms on metal surfaces plays a key role in surface science and technology.This review is dedicated to the adsorption of oxygen molecules or atoms on metal surfaces and diffusion behavior from first-principle investigation.We hope that this review can provide some useful contributions to understa nd the study of adsorption properties and diffusion behavior on a metal surface at an atomic-scale,especially for those interested in catalytic oxidation and application of corrosion.