金属玻璃研究简史

金属玻璃的发明和研究已经整整50年了.半个世纪以来,金属玻璃不但成为性能独特的新材料,同时也是研究材料科学和凝聚态物理中一些重要问题的模型体系.金属玻璃的研究已经成为凝聚态物理的一个重要分支.文章简要介绍了金属玻璃的研究历史以及最新的进展,并扼要介绍了这门学科的发展前景.     

Influence of using nanoobjects as filler on functionality-based energy use of nanocomposites

The goal of our study was to investigate the potential benefits of reinforcing polymer matrices with nanoobjects for structural applications by looking at both the mechanical properties and environmental impacts. For determining the mechanical properties, we applied the material indices defined by Ashby for stiffness and strength. For the calculation of environmental impacts, we applied the life cycle assessment methodology, focusing on non-renewable energy use (NREU). NREU has shown to be a good indicator also for other environmental impacts. We then divided the NREU by the appropriate Ashby index to obtain the ‘functionality-based NREU’. We studied 23 different nanocomposites, based on thermoplastic and thermosetting polymer matrices and organophilic montmorillonite, silica, carbon nanotubes (single-walled and multiwalled) and calcium carbonate as filler. For 17 of these, we saw a decrease of the functionality-based NREU with increasing filler content. We draw the conclusion that the use of nanoobjects as filler can have benefits from both an environmental point of view and with respect to mechanical properties.     

Scanning probe microscopy of graphene

A material with novel fundamental properties that challenge our current understanding is always exciting for research. If the novel properties extend to the realm of device engineering and promise a revolution in applications, then the scope of its research knows no bounds. The story of graphene, the two dimensional form of carbon, has followed this path. Graphene has been the subject of numerous experimental and theoretical investigations since 2004 when an elegant and a simple technique to make monolayer graphene set the stage for extensive research. Many other techniques to make graphene were developed in parallel to this technique. As graphene is replete with unique structural and electronic properties scanning probe microscopy has proved to be an exciting and a rewarding venture. In this review we discuss the findings of scanning probe microscopy and how it has served as an indispensable tool to understand the properties of graphene and further graphene research.     

Tailoring electronic properties of two-dimensional antimonene with isoelectronic counterparts

Using ab initio density functional theory calculations, we explore the three most stable structural phases, namely, α,β, and cubic(c) phases, of two-dimensional(2D) antimonene, as well as its isoelectronic counterparts SnTe and InI. We find that the band gap increases monotonically from Sb to SnTe to InI along with an increase in ionicity, independent of the structural phases. The band gaps of this material family cover the entire visible-light energy spectrum, ranging from 0.26 eV to 3.37 eV, rendering them promising candidates for optoelectronic applications. Meanwhile, band-edge positions of these materials are explored and all three types of band alignments can be achieved through properly combining antimonene with its isoelectronic counterparts to form heterostructures. The richness in electronic properties for this isoelectronic material family sheds light on possibilities to tailor the fundamental band gap of antimonene via lateral alloying or forming vertical heterostructures.     

Experimental fatigue performance of laser-formed components

Much knowledge has been gained with respect to the forming of sheet material by laser technology since its inception during the mid-1980s. However, many press-formed sheet metal components are subjected to cyclic loading conditions during their service life. It is from this standpoint that the work reported in this paper originates. This work deals with some aspects of the structural integrity of laser-formed plate samples that were formed to a radius of curvature of approximately 125 mm. Furthermore, a comparison is drawn between laser-formed and stock plate samples fatigue tested under reverse-bending cyclic conditions. The results indicate that the fatigue life of the laser-formed samples was substantially enhanced when compared to that of the stock plate samples. This observed improvement in fatigue life is attributed to the laser-hardening mechanism, i.e., the phase transformation and rate of cooling of the material from above the A₃ temperature, i.e. approximately 1200 °C. This aspect of improved fatigue life is considered to be beneficial to the motor manufacturing industry that could result in the possible use of thinner gauge material.     

Materials Research with X-ray Micro-beams at the Advanced Photon Source

X-ray scattering has had a rich and prominent place in the history of materials research. For samples that are large single crystals, X-ray diffraction provides very detailed, high-quality information about the atomic structure of almost every kind. However, most engineering materials are not a large single crystal, but mixtures of materials or a poly-crystalline material. Still, X-ray diffraction using X-ray beams significantly larger than the structures being investigated has produced much excellent information. Examples of this are powder diffraction, texture analysis, strain analysis, etc. While these types of analyses have been very useful in providing a microscopic understanding, they do not provide the microscopic information that we really want. What we really want to have is this useful X-ray diffraction information for every volume element in our sample; not just the diffraction information about small volume elements, but all of the volume elements, exactly where they are in our sample, and how each one diffracts. This detailed spatial and structural information is what is needed for a full understanding of the source of the properties that we find in engineering materials.     

Welding of thermoplastics by ultrasound

Industrial applications of power ultrasound in joining of thermoplastics are reviewed. Current uses include welding of rigid parts, forming operations such as staking and metal-in-plastic insertion, spot-welding, and continuous joining of films and synthetic fabrics. Process variables, equipment and applications are discussed.     

The strong piezoelectricity in polyvinylidene fluroide (PVDF)

Polymers have been playing an important role already for a long time in electronic engineering as dielectrics. Recently a search has been made for polymers with unusual properties: organic semiconductors or photoconductors, electrets, and polymeric piezo — and pyroelectrics have been developed. And now, polyvinylidene fluroide (PVDF), a new piezoelectric film material is being produced on an industrial scale.^1,2 In this article, recent developments and applications of piezoelectric polymers are surveyed.     

高温高压下闪锌矿相GaN结构和热力学特性的分子动力学研究

利用分子动力学方法和Buckingham经验势模型对重要半导体材料GaN立方闪锌矿相的晶格常数、相变压力(从闪锌矿到岩盐结构)、热膨胀、等温体模量、定压热容等结构和热力学特性在300—3000K的温度范围和0—65GPa的压力范围内进行了研究.研究表明，闪锌矿相GaN常态下的结构和热力学参数的模拟结果与实验数据及其他理论结果相符.同时在所选作用势模型可靠性检验的基础上，对等温体模量、定压热容诸非谐性参量在高温高压下的热力学行为进行了预测.所得结果在材料科学等领域的研究中具有一定的应用背景和参考价值. 关键词： GaN Buckingham势 分子动力学模拟 高温高压     

The present status of Si/ SiO2 superlattice research into optoelectronic applications

Due to the potential applications in optoelectronic areas, Si/SiO₂ superlattices have been focused on extensively in the last few years. The work spans a wide range from theory to experiment, investigating mechanisms and structural, electronic and optical properties of the material, and also including deposition technologies and analytical methods; it has led to a much better understanding of the material and a series of fruitful results have been obtained. This paper centers on reviewing the progress and present status of Si/SiO₂ superlattice research—for the first time, to our knowledge. The present work gives the authors’ assessment of the area of Si/SiO₂ superlattice deposition, including deposition technologies, characterization methods, film properties and potential applications. Finally, some existing problems and other related Si based structures with potential optoelectronic applications are summarized.     

Effect of the mode of combustion on the service life of the combustion chamber material

The effect of the characteristics of intrachamber combustion (the pressure and the temperature of combustion products) on the service life of the material of the combustion chamber of a thermal engine is examined. The problem is studied with the help of the Zhurkov kinetic approach based on model examples of spherical and cylindrical shells subjected to the action of cyclically varying pressure and temperature of the gas in the chamber. An analogy between the influence of stress and temperature on the service life of material is demonstrated. It is shown that periodic variations of the intrachamber characteristics can lead to an appreciable shortening of the service life of the shell in comparison with the service life at a constant pressure and temperature equal to the corresponding mean values. Thus, in the case of pressure and temperature variations (of the harmonic type), small in amplitude, the effect of the accelerated aging of the material per cycle of loading is proportional to the square of the amplitude of variations. In this case, a relative increase in the deterioration of material during one period of loading does not depend on the value of the period of loading. The problem of the effective medium stress with a periodically varying loading of random type is discussed. The theoretical results obtained are illustrated for aluminum shells and other construction materials, as examples.     

Experimental and theoretical study of multiscale damage-failure transition in very high cycle fatigue

Multiscale mechanisms of failure of metals (Armco iron, titanium, aluminum) are studied for high cycle and very high cycle fatigue. By correlating with the results of structural studies, a theoretical approach is developed to describe fatigue crack kinetics in damaged material under high cycle and very high cycle fatigue loading conditions. Stages of crack nucleation and propagation are analyzed using the profilometry data from the fracture surface. The scale invariance of fracture surface roughness is established, which allows an explanation of the self-similar nature of fatigue crack kinetics under high cycle and very high cycle fatigue. Variation of elastic-plastic properties of Armco iron under very high cycle fatigue is studied using an acoustic resonance method. It is found that the material density decreases during fatigue damage accumulation, with the minimum of the material density in the bulk of the specimen.     

Social and place-focused communities in location-based online social networks

Thanks to widely available, cheap Internet access and the ubiquity of smartphones,millions of people around the world now use online location-based social networkingservices. Understanding the structural properties of these systems and their dependenceupon users’ habits and mobility has many potential applications, including resourcerecommendation and link prediction. Here, we construct and characterise social andplace-focused graphs by using longitudinal information about declared social relationshipsand about users’ visits to physical places collected from a popular online location-basedsocial service. We show that although the social and place-focused graphs are constructedfrom the same data set, they have quite different structural properties. We find that thesocial and location-focused graphs have different global and meso-scale structure, and inparticular that social and place-focused communities have negligible overlap.Consequently, group inference based on community detection performed on the social graphalone fails to isolate place-focused groups, even though these do exist in the network. Bystudying the evolution of tie structure within communities, we show that the time periodover which location data are aggregated has a substantial impact on the stability ofplace-focused communities, and that information about place-based groups may be moreuseful for user-centric applications than that obtained from the analysis of socialcommunities alone.     

The sol-gel mixed oxide Cr0.11V2O5.16: An attractive cathodic material for secondary lithium batteries

Preliminary results of the properties of a new mixed oxide Cr_0.11V₂O_5.16 which was synthesized by a sol-gel process and may be used as cathode material for secondary lithium batteries are presented in this paper. The electrochemical properties are investigated and compared with those exhibited by the sol-gel vanadium pentoxide V₂O₅. The results are discussed with respect to the structural data available from these compounds. The presence of Cr³⁺ and additional O^2- ions in the structure notably emphasizes the attractive performances of the material both in terms of specific capacity and cycle life. In particular, a high capacity is still available even for the pure material used without addition of electronic conductor. The cyclability, as well as the behaviour at high discharge rates are found to be significantly better than for the parent oxide V₂O₅. These results are consistent with structural considerations from which less severe structural deformations are expected during lithium insertion. Paper presented at the 4th Euroconference on Solid State Ionics, Connemara, Galway, Ireland, Sept. 13–19, 1997     

Improvements to laser forming through process control refinements

Laser forming is a process that uses the energy of relatively high powered lasers to cause permanent deformation to components by inducing localised thermal stresses. It is envisaged that this material processing technique will find a number of commercial applications. This paper briefly discusses laser forming and the development of a basic process monitoring and control system used to overcome variability problems due to the complex nature of the lasers themselves and the manner in which they interact with material. It then goes on to show how the basic control system was modified, using increased feedback data sampling, time delays and a modified control algorithm which takes account of the forming rate in addition to the error. The effect of these developments is then illustrated by a series of tests which show the modifications significantly improve process tolerances.     

Synthesis, crystal growth and characterization of a metal-organic nonlinear optical tri-allylthiourea mercury chloride single crystals

Metal-organic nonlinear optical material tri-allylthiourea mercury chloride single crystal was grown using low temperature solution growth method. The growth parameters such as pH and temperature were optimized for getting colorless single crystals. The X-ray rocking curve measurement shows that the grown crystal was free from internal structural grain boundaries. The structural, spectral, optical and thermal properties of the grown specimen were studied using various characterization techniques. The defects present in the grown crystals were studied with chemical etching analysis. The results show that the grown crystals are suitable candidates for nonlinear optical applications.     

Finite element simulation of laser tube bending: Effect of scanning schemes on bending angle, distortions and stress distribution

Laser forming has received considerable attention in recent years. Within laser forming, tube bending is an important industrial activity, with applications in critical engineering systems like micro-machines, heat exchangers, hydraulic systems, boilers, etc. Laser tube bending utilizes the thermal stresses generated during laser scanning to achieve the desired bends. The parameters to control the process are usually laser power, beam diameter, scanning velocity and number of scans. Recently axial scanning has been used for tube bending instead of commonly used circumferential scans. However the comparison between the scanning schemes has involved dissimilar laser beam geometries with circular beam used for circumferential scanning and a rectangular beam for the axial scan. Thermal stresses generated during laser scanning are strongly dependent upon laser beam geometry and scanning direction and hence it is difficult to isolate the contribution made by these two variables. It has recently been established at the Corrosion and Protection Centre, University of Manchester, that corrosion properties of material during laser forming are affected by the number of laser passes. Depending on the material, the corrosion behaviour is either adversely or favourably affected by number of passes. Thus it is of great importance to know how different scanning schemes would affect laser tube bending. Moreover, any scanning scheme which results in greater bending angle would eliminate the need for higher number of passes, making the process faster. However, it is not only the bending angle which is critical, distortions in other planes are also extremely important. Depending on the use of the final product, unwanted distortions may be the final selection criteria. This paper investigates the effect of scanning direction on laser tube bending. Finite-element modelling has been used for the study of the process with some results also validated by experiments.     

Efficient spin injector scheme based on Heusler materials

We present a rational design scheme intended to provide stable high spin polarization at the interfaces of the magnetoresistive junctions by fulfilling the criteria of structural and chemical compatibilities at the interface. This can be realized by joining the semiconducting and half-metallic Heusler materials with similar structures. The present first-principles calculations verify that the interface remains half-metallic if the nearest interface layers effectively form a stable Heusler material with the properties intermediately between the surrounding bulk parts. This leads to a simple rule for selecting the proper combinations.     

Microscopical and physical characterization of microwave and microwave-hydrothermal synthesis products

Application of microwave energy for materials processing is emerging as an innovative technology with many advantages over the conventional processing, and the rapid progress in this field suggests that microwave material processing (e.g., microwave and microwave-hydrothermal process) will play an outstanding role in the broad field of nanoscience and nanotechnology. This review article gives an up-to-date overview of the current microscopical and physical characterization of the products synthesized by microwave and microwave-hydrothermal process, particularly for oxide nanomaterials because they are indispensable for nanotechnological innovations due to their combinations of infinite variety of structural motifs and properties with manifold morphological features. Basic principles, advantages, and limitations of microwave and microwave-hydrothermal processes are first introduced, and then their recent applications in the synthesis of different classes of functional materials especially for oxide nanomaterials are critically reviewed. Next, the recent progress on the structural and physical characterizations is summarized and discussed. Finally, prospects for future researches within this field are elaborated.