Modified cellulose morphologies and its composites; SEM and TEM analysis

The complex, multi-level super molecular architecture of cellulose has been the subject of interest for several decades. The mechanical, physical, and environmental properties of cellulose depend on the molecular, supramolecular and morphological structure of the cellulose. This paper gives a brief overview to micro structural analysis of cellulose, as studied using transmission electron microscopy and scanning electron microscopy. The application of these techniques to study the diverse morphology of cellulose and its composites is illustrated using several examples.     

三角波加载下金属铝动态破坏现象的微观模拟

采用嵌入原子势模型和分子动力学方法, 模拟研究了三角波加载下金属铝动态破坏的微观过程和动力学性质. 根据原子中心对称参数变化给出了样品微结构演化过程, 解读了熔化前后破坏过程的形态差异; 基于Virial定理统计了样品中压力和温度等力学量波形, 分析了熔化前后材料的强度变化. 通过不同碰撞速度的模拟, 讨论了破碎区内物质形态和密度分布的变化, 给出了材料破坏深度的变化规律. 研究还发现, 熔化后材料的动态拉伸强度已显著降低, 而此时由声学近似推算的材料拉伸强度已明显高于内部应力直接计算结果. 关键词： 破坏 分子动力学 冲击     

Improved microstructure and mechanical properties in gas tungsten arc welded aluminum joints by using graphene nanosheets/aluminum composite filler wires

In the present study, different amounts of graphene nanosheets (GNSs) were added to the 4043 aluminum alloy powders by using the mechanical alloying method to produce the composite filler wires. With each of the produced composite filler wires, one all-weld metal coupon was welded using the gas tungsten arc (GTA) welding process. The microstructure, mechanical properties and fracture surface morphology of the weld metals have been evaluated and the results are compared. As the amount of GNSs in the composition of filler wire is increased, the microstructure of weld metal was changed from the dendritic structure to fine equiaxed grains. Furthermore, the tensile strength and microhardness of weld metal was improved, and is attributed to the augmented nucleation and retarded growth. From the results, it was seen that the GNSs/Al composite filler wire can be used to improve the microstructure and mechanical properties of GTA weld metals of aluminum and its alloys.     

Effects of microstructure on the properties of ferroelectric lead zirconate titanate (PZT) thin films

Lead zirconate titanate (PZT) thin films were prepared with pulsed laser deposition and sol–gel techniques. The PZT films fabricated by these two techniques have similar randomly oriented single perovskite phases, but the film derived from the pulsed laser deposition exhibits a more compact and flat morphology. The dielectric, ferroelectric, and piezoelectric properties of the two kinds of films are comparatively characterized and discussed. It is observed that a denser microstructure would lead to a significantly higher dielectric constant and remanent polarization and a much lower coercive electric field, but only a relatively slight enhancement on the piezoelectric constant. The film with a looser microstructure could have a substantially higher piezoelectric voltage constant g₃₃ due to the much lower dielectric constant. Our results and discussion provide a better understanding of the relationship between the microstructure and the film properties, which is essential in order to tailor the microstructure and hence determine the performance aiming at a specific application. PACS 68.55.Jk; 77.22.-d; 77.65.-j     

Material microstructures analyzed by using gray level Co-occurrence matrices

The mechanical properties of materials greatly depend on the microstructure morphology. The quantitative characterization of material microstructures is essential for the performance prediction and hence the material design. At present,the quantitative characterization methods mainly rely on the microstructure characterization of shape, size, distribution,and volume fraction, which related to the mechanical properties. These traditional methods have been applied for several decades and the subjectivity of human factors induces unavoidable errors. In this paper, we try to bypass the traditional operations and identify the relationship between the microstructures and the material properties by the texture of image itself directly. The statistical approach is based on gray level Co-occurrence matrix(GLCM), allowing an objective and repeatable study on material microstructures. We first present how to identify GLCM with the optimal parameters, and then apply the method on three systems with different microstructures. The results show that GLCM can reveal the interface information and microstructures complexity with less human impact. Naturally, there is a good correlation between GLCM and the mechanical properties.     

The effect of gamma irradiation and shelf aging in air on the oxidation of ultra-high molecular weight polyethylene

This study has investigated the effect of shelf aging, for up to one year in air, on the properties of gamma-irradiated ultra-high molecular weight polyethylene (UHMWPE). A variety of techniques were used to characterize the properties of treated samples. Differential scanning calorimetery (DSC) was used to characterize the morphology. The extent of cross-linking in a polymer network was detected by swelling measurements. The durometer hardness test was used to measure the relative hardness of this material, and changes in density were also measured. Results from all these measurements were combined to explain the changes in the microstructure of the aged, irradiated UHMWPE. This study shows that crystallinity is increased with radiation dose and with aging due to chain scission, which leads to a reduction in the molecular weight of the material. This allows the chains to rearrange to form crystalline regions. Positron annihilation lifetime spectroscopy confirms these conclusions. Fractional free volumes have been deduced from lifetime parameters, which correlate with the data obtained by the other techniques.     

Micro-structural characterization of precipitation-synthesized fluorapatite nano-material by transmission electron microscopy using different sample preparation techniques

Fluorapatite is a naturally occurring mineral of the apatite group and it is well known for its high physical and chemical stability. There is a recent interest in this ceramic to be used as a radioactive waste form material due to its intriguing chemical and physical properties. In this study, the nano-sized fluorapatite particles were synthesized using a precipitation method and the material was characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM). Two well-known methods, called solution-drop and the microtome cutting, were used to prepare the sample for TEM analysis. It was found that the microtome cutting technique is advantageous for examining the particle shape and cross-sectional morphology as well as for obtaining ultra-thin samples. However, this method introduces artifacts and strong background contrast for high-resolution transmission electron microscopy (HRTEM) observation. On the other hand, phase image simulations showed that the solution-drop method is reliable and stable for HRTEM analysis. Therefore, in order to comprehensively analyze the microstructure and morphology of the nano-material, it is necessary to combine both solution-drop and microtome cutting techniques for TEM sample preparation.     

Influence of slight microstructural gradients on the surface properties of Ti6Al4V irradiated by UV

Ti6Al4V alloy is one of the most widely used materials for biomedical implants. Among its properties, it is remarkable the photoactivity displayed by its passive layer, which is mainly composed by titanium dioxide. However, variations in the processing conditions may yield to differences in the microstructure which can be reflected on the surface properties of the machined product. From contact angle measurements taken on different zones of samples removed from a commercial bar of Ti6Al4V, it has been shown that the modifications of the surface Gibbs energy suffered by the alloy under UV irradiation have a radial dependence. This behaviour is related to slight microstructural changes of the alloy, particularly with an increase in the volume fraction of the β-phase when moving to the interior of the sample, which alters the composition and/or microstructure of the passive layer along its radius. This study shows that gradients in the microstructure and physical properties are sample size dependent and are likely related to thermal gradients during processing.     

Neutrons for fuel cell membranes: Structure, sorption and transport properties

A molecular level understanding of structure and transport properties in fuel cell ionomer membranes is essential for designing new electrolytes with improved performance. Scattering techniques are suited tools for this purpose. In particular, neutron scattering, which has been extensively used in hydrogen-containing systems, is well adapted to investigate water-dependent complex polymeric morphologies. We report Small-Angle Neutron Scattering (SANS) studies on different types of fuel cell polymers: perfluorinated, radiation-grafted and sulfonated polyphosphazene membranes. We show that contrast variation methods can be efficiently employed to provide new insights on membrane microstructure and reveal ionic condensation effects. Neutrons have been used also as non-intrusive diagnosis tool to probe water properties and distribution inside membranes. Recently, in-situ neutronography and SANS experiments on operating fuel cells have been reported. In-plane cartography of water distribution at the surface of bipolar plates and water profiles across membrane thickness have been obtained and studied as a function of operating conditions. The last section of the article is devoted to the use of Quasi-Elastic Neutron Scattering to study water dynamics at molecular scale. We show that analysis with an appropriate sophisticated diffusion model allows to extract diffusion coefficients, characteristic times and length-scales of molecular motions. This quantitative information is fruitfully integrated in multi-scale modelling and usefully compared with numerical simulations. QENS also permits to compare alternative polymers and relate dynamical properties to chemical composition and membrane nanostructure.     

形貌依赖的ZnO阴极射线发光性质研究

采用溶剂热法,通过调节水和乙醇混合液的比例制备了多种形貌的ZnO微米结构。利用扫描电子显微镜（SEM）对ZnO微米结构的形貌及尺寸进行了观察。采用可以实现纳米级微观区域光谱采集的阴极射线发光（CL）技术,对不同形貌的单个粒子的光谱进行精细表征,获得了位置依赖的ZnO阴极射线发光数据。实验结果表明：ZnO材料的发光性质与形貌有关,由于形貌差异导致其局部结晶质量、界面缺陷、表面电荷分布、表面晶面等方面的差异,几种因素共同作用决定其最终的发光性质。     

Microstructural Degradation of the AlMo0.5NbTa0.5TiZr Refractory Metal High-Entropy Superalloy at Elevated Temperatures

Refractory metal high-entropy superalloys (RSA), which possess a nanoscale microstructure of B2 and bcc phases, have been developed to offer high temperature capabilities beyond conventional Ni-based alloys. Despite showing a number of excellent attributes, to date there has been little consideration of their microstructural stability, which is an essential feature of any material employed in high temperature service. Here, the stability of the exemplar RSA AlMo_0.5NbTa_0.5TiZr is studied following 1000 h exposures at 1200, 1000 and 800 °C. Crucially, the initial nanoscale cuboidal B2 + bcc microstructure was found to be unstable following the thermal exposures. Extensive intragranular precipitation of a hexagonal Al-Zr-rich intermetallic occurred at all temperatures and, where present, the bcc and B2 phases had coarsened and changed morphology. This microstructural evolution will concomitantly change both the mechanical and environmental properties and is likely to be detrimental to the in-service performance of the alloy.     

Growth induced anisotropy of cobalt in cobalt/organic semiconductor films

We present the study of Co/organic semiconductor (OS) stacks both from the morphological and magnetic point of view. Co has been successfully used up to now as top contact of hybrid vertical devices. While the properties of Co grown on amorphous layers are well established, its deposition on soft materials presents critical aspects such as interfacial damage that affects its electrical and magnetic properties. In this work we focus on the influence of the morphology of the organic underlayer in the magnetic behavior of a Co thin film: tris(8-hydroxyquinoline) aluminum (Alq₃) grown in different conditions by molecular beam evaporation have been considered. A further considered aspect is the effect of the presence of a thin oxide barrier (Al₂O₃) on the Co magnetic properties.     

Factors affecting the microstructure and mechanical properties of Ti-Al3Ti core-shell-structured particle-reinforced Al matrix composites

This work studied the effects of matrix powder and sintering temperature on the microstructure and mechanical properties of in situ formed Ti–Al₃Ti core–shell-structured particle-reinforced pure Al-based composites. It has been shown that both factors have significant effects on the morphology of the reinforcements and densification behaviour of the composites. Due to the strong interfacial bonding and the limitation of the crack propagation in the intermetallic shell during deformation by soft Al matrix and Ti core, the composite fabricated using fine spherical-shaped Al powder and sintered at 570 °C for 5 h has the optimal combination of the overall mechanical properties. The study provides a direction for the optimum combination of high strength and ductility of the composites by adjusting the fabrication parameters.     

Controlled synthesis of porous nickel oxide nanostructures and their electrochemical capacitive behaviors

Achieving precise control over the synthesis and properties of porous nanostructured materials has been garnering considerable recent research attention. In the work presented here, nickel oxalate nanostructures with controllable shapes were synthesized through a simple and facile wet-chemistry route without any surfactant. An interesting shape evolution process from 2D nanoflakes to 1D nanorods has been illustrated on the basis of time-dependent experimental studies. Subsequent calcination at 380 °C yielded porous NiO nanostructures that retained the morphologies of their predecessors. The phase composition, morphology, and structure of the as-obtained products were studied by various tools. Electrochemical properties of the NiO electrodes were carried out using cyclic voltammetry and galvanostatic charge–discharge measurements by a three-electrode system. Electrochemical studies reveal that the as-prepared mesoporous NiO nanostructures have good specific capacitance and exhibit excellent capacity retention for more than 1,000 cycles due to its porous character and morphology. The results suggest that mesoporous NiO nanostructures are a promising supercapacitor electrode material.     

Effect of gun current on the microstructure and crystallinity of plasma sprayed hydroxyapatite coatings

Hydroxyapatite (HA) is a bioactive material because its chemical structure is close to the natural bone. Its bioactive properties make it attractive material in biomedical applications. Gas tunnel type plasma spraying (GTPS) technique was employed in the present study to deposit HA coatings on SUS 304 stainless steel substrate. GTPS is composed of two plasma sources: gun which produces internal low power plasma (1.3-8 kW) and vortex which produces the main plasma with high power level (10-40 kW). Controlling the spraying parameters is the key role for spraying high crystalline HA coatings on the metallic implants. In this study, the arc gun current was changed while the vortex arc current was kept constant at 450 A during the spraying process of HA coatings. The objective of this study is to investigate the influence of gun current on the microstructure, phase crystallinity and hardness properties of HA coatings. The surface morphology and microstructure of as-sprayed coatings were examined by scanning electron microscope. The phase structure of HA coatings was investigated by X-ray diffraction analysis. HA coatings sprayed at high gun current (100 A) are dense, and have high hardness. The crystallinity of HA coatings was decreased with the increasing in the gun current. On the other hand, the hardness was slightly decreased and the coatings suffer from some porosity at gun currents 0, 30 and 50 A.     

A TEM study on lithium zinc ferrite thin films and the microstructure correlation with the magnetic properties

Sputtered lithium zinc ferrite films were studied using transmission electron microscopy to investigate the microstructure morphology and its correlation with the observed magnetic properties as a function of annealing temperature and time. The present study showed that the films contain nanocrystallites. The observed magnetic order in the films is because of inter granular coupling through low angle grain boundaries. The anomalous magnetic properties observed earlier in these films can be explained on the basis of the presence of large grain boundary volume.     

极性分子的激光冷却及囚禁技术

分子由于其不同于原子的特殊性质,在原子、分子和光物理研究中有其独特的地位.冷分子研究已经开展了二三十年,取得了很多重大的进展.但是以斯塔克减速器为代表的传统冷却方案遇到瓶颈,很难进一步提高分子的相空间密度.将原子中成熟的激光冷却技术拓展到极性分子中是本领域近年来的重大突破,使得冷却和囚禁分子的范围得以大大扩展,分子的相空间密度也得以提高.本文对国内外激光冷却极性分子的最新成果进行综述,并以BaF分子为例介绍激光冷却极性分子的相关理论和技术,包括分子能级结构分析及精密光谱测量,采用缓冲气体冷却进行态制备和预冷却,以及通过冷分子束研究激光与BaF分子间的相互作用.这些为后续开展激光冷却与囚禁实验研究奠定了基础,也为开展其他新的分子冷却实验提供了参考.     

Nanotechnology in the Chemical Industry – Opportunities and Challenges

The traditional chemical industry has become a largely mature industry with many commodity products based on established technologies. Therefore, new product and market opportunities will more likely come from speciality chemicals, and from new functionalities obtained from new processing technologies as well as new microstructure control methodologies. It is a well-known fact that in addition to its molecular structure, the microstructure of a material is key to determining its properties. Controlling structures at the micro- and nano-levels is therefore essential to new discoveries. For this article, we define nanotechnology as the controlled manipulation of nanomaterials with at least one dimension less than 100nm. Nanotechnology is emerging as one of the principal areas of investigation that is integrating chemistry and materials science, and in some cases integrating these with biology to create new and yet undiscovered properties that can be exploited to gain new market opportunities. In this article market opportunities for nanotechnology will be presented from an industrial perspective covering electronic, biomedical, performance materials, and consumer products. Manufacturing technology challenges will be identified, including operations ranging from particle formation, coating, dispersion, to characterization, modeling, and simulation. Finally, a nanotechnology innovation roadmap is proposed wherein the interplay between the development of nanoscale building blocks, product design, process design, and value chain integration is identified. A suggestion is made for an R&D model combining market pull and technology push as a way to quickly exploit the advantages in nanotechnology and translate these into customer benefits.     

Electrospray deposit structure of nanoparticle suspensions

Electrospray atomization has unique capabilities for deploying colloidal suspensions to create nanoparticle films and coatings. This technique can deliver precise quantities of particles in a dry state to a target substrate and overcomes many limitations of other printing and coating technologies. Since the structure of a nanoparticle layer governs its functionalities, it is essential to understand the relationship between the key operating parameters and the macro- and microstructure of an electrospray deposit. We investigated the role of three key parameters on the deposit structure: electrospray time, the target substrate electrical properties, and the polydispersity of the colloidal suspension. The macrostructure of the nanoparticle deposits was similar for all spray times and substrates. In particular, the deposited particles segregate to the center and edge of a deposit, leaving a depletion region in between. We speculate that the mutual Coulombic forces due to the space charge inside the plume play a key role in governing the trajectory of the nanoparticles and the ensuing deposit morphology. Since particles emitted by electrospray are highly charged, the microstructure of a deposit was strongly influenced by the electrical conductivity of the target substrate. By maintaining a net charge, particles deposited on to a dielectric substrate could influence the deposition of subsequent in-flight particles, which opens new routes for exerting control over the deposit structure.