Chemical Processing of Nanostructured Cemented Carbide

Chemical processing is becoming a vital component in the economic development of advanced engineering materials. Our research group on chemical processing has been focussed on the development of process to produce nanophase cemented carbide. It is a much more direct route for making WC/Co than traditional processing methods, and offers the potential for lower cost production of novel materials with homogeneous nanophase microstructures and improved properties. This paper addresses the scientific and technical issues relating to the chemical processing of nanophase WC/Co composite powder and their sintering.     

A RUNNER-GATE DESIGN SYSTEM FOR DIE CASTING

Various analytical finite element method (FEM) tools have been developed for flow processes, including die casting, but they only give information about whether the predetermined die design is correct. Current shop practice uses trial-and-error methods to determine new die designs. This article describes development of a computer-aided die design system for die casting. The computer-assisted design (CAD) system was written using Auto LISP with a personal computer. This system was developed to present algorithms for automation of die design, especially a runner-gate system using three-dimensional geometry. This system quantifies practical knowledge and experiences in die design as the formulating procedure. The system allows engineers to make automatic and efficient designs and it will result in reduction of required expenses and time. The system is composed of selection of cast alloy and product design, and uses the runner-gate design. In addition, specific rules and equations for the system are presented. An example is applied to a cap-shaped casting using the proposed system.     

Characteristics and link structure of a national scholarly Web space: The case of South Korea

This study performs a webometric analysis to explore the communication characteristics of scientific knowledge in a national scholarly Web space comprising top ranking universities and government supported research institutions in South Korea. We found significant differences in scholarly communication activity as well as linking behavior among different subspaces in addition to institutional differences. We also found the usefulness of the ADM approach in analyzing the metric data containing extreme outliers and discovered the directory model as the most appropriate. Page counts were found significantly correlated with inlinks as well as with outlinks at the directory level in the whole scholarly Web space.     

Enhanced green emission from Tb-Bi co-doped GdAlO3 nanophosphors

Bi³⁺ and Tb³⁺ ions co-doped GdAlO₃ (GAP) nanophosphors have been synthesized by means of solvothermal reaction method. The XRD pattern of GAP phosphor confirms their orthorhombic phase. The luminescence properties of these phosphors have been explored by analyzing their excitation and emission spectra along with their decay curves. The excitation spectra of GAP:Tb³⁺, Bi³⁺ phosphors consist of a broad band in the shorter wavelength region due to the 4f⁸ → 4f⁷5d¹ transition of Tb³⁺ ions overlapped with the 6s² → 6s¹6p¹ (¹S₀ → ³P₁) transition of Bi³⁺ ions and some sharp peaks in the longer wavelength region due to f → f transitions of Tb³⁺ ions. The present phosphors exhibit green color due to strong ⁵D₄ → ⁷F₅ transition of Tb³⁺ ions. The emission intensity was enhanced by co-doping with Bi³⁺ ions under 292 nm excitation, which indicate that the efficient energy transfer occurred from Bi³⁺ to Tb³⁺ ions.     

Different shape of GaAs quantum structures under various growth conditions

We report the influences of growth parameters on the characteristics of GaAs quantum rings (QRs) and quantum dots (QDs) formed on AlGaAs/GaAs by the droplet epitaxy (DE) method. After forming Ga droplets on the AlGaAs/GaAs surface, varying amounts of arsenic (As) flux were introduced to fabricate the GaAs quantum structures. By decreasing the As flux from 8 × 10^− 5 to 3 × 10^− 5 Torr, the shape of the GaAs quantum structures was changed from QDs to elongated QRs. With further decreasing As flux, the shape of the elongated QRs became symmetric. The formation characteristics of the GaAs QRs from the QDs with the amount of As flux were discussed in terms of migration behaviors of the gallium (Ga) atoms on the GaAs(001)-c(4 × 4) surface. The effects of the amount of Ga supply and the growth temperature for the deposition of Ga droplets on the formation of the GaAs quantum structures were also considered.     

Synthesis of Uniquely Structured Yolk–Shell Metal Oxide Microspheres Filled with Nitrogen‐Doped Graphitic Carbon with Excellent Li–Ion Storage Performance

Novel structured composite microspheres of metal oxide and nitrogen‐doped graphitic carbon (NGC) have been developed as efficient anode materials for lithium‐ion batteries. A new strategy is first applied to a one‐pot preparation of composite (FeO_x‐NGC/Y) microspheres via spray pyrolysis. The FeO_x‐NGC/Y composite microspheres have a yolk–shell structure based on the iron oxide material. The void space of the yolk–shell microsphere is filled with NGC. Dicyandiamide additive plays a key role in the formation of the FeO_x‐NGC/Y composite microspheres by inducing Ostwald ripening to form a yolk–shell structure based on the iron oxide material. The FeO_x‐NGC/Y composite microspheres with the mixed crystal structure of rock salt FeO and spinel Fe₃O₄ phases show highly superior lithium‐ion storage performances compared to the dense‐structured FeO_x microspheres with and without carbon material. The discharge capacities of the FeO_x‐NGC/Y microspheres for the 1st and 1000th cycle at 1 A g^?1 are 1423 and 1071 mAh g^?1, respectively. The microspheres have a reversible discharge capacity of 598 mAh g^?1 at an extremely high current density of 10 A g^?1. Furthermore, the strategy described in this study is generally applied to multicomponent metal oxide–carbon composite microspheres with yolk–shell structures based on metal oxide materials.     

Shape-dependent cytotoxicity of polyaniline nanomaterials in human fibroblast cells

The toxicity of polyaniline (PANI) nanomaterials with four different aspect ratios on human lung fibroblast cells was investigated by cell viability assay, cytotoxicity assay, apoptosis/necrosis measurement, and reactive oxygen species production. The toxicity increased with decreasing aspect ratio of PANI nanomaterials. In contrast, the highest aspect ratio PANI nanomaterials showed similar results with bulk PANI materials. The adverse effect of PANI nanomaterials was also concentration- and time-dependent. Low aspect ratio PANI nanomaterials induced more necrosis and more reactive oxygen species than others. These results provide new understanding of shape-dependent toxicity of nanomaterials.     

Effects of Surface Morphology and Composition Modification on Spectral Emissivity and Thermal Diffusivity Profile at High Temperatures

A new all-spectroscopic method for depth-resolved thermal diffusivity measurement of metallic specimens has been demonstrated. The method entails measurement of the mass entrained into a laser-produced plasma (LPP) plume in such a manner that the plume is representative of the specimen in elemental composition. Both the abundance of matter and its elemental composition are measured by time-resolved spectroscopy for each LPP plume. In order to delineate the morphology versus composition basis of the depth dependence, a new study on a Nichrome ribbon specimen heated by ohmic heating in a vacuum is presented. A set of depth-resolved thermal diffusivity measurements is carried out, while noting the attendant changes in the spectral emissivity and elemental composition at succeeding ablation layers. Additional measurements are carried out after the specimen has been treated under varying heating conditions. Preferential diffusion of chromium at high temperatures has been found to contribute to the dynamics of surface thermophysical properties at high temperatures. Representative LPP ablation is well suited for removal of surface impurities prior to thermophysical property measurements by the pulse heating technique.     

One‐Dimensional Nanostructures: Synthesis,Characterization, and Applications

This article provides a comprehensive review of current research activities that concentrate on one‐dimensional (1D) nanostructures—wires, rods, belts, and tubes—whose lateral dimensions fall anywhere in the range of 1 to 100 nm. We devote the most attention to 1D nanostructures that have been synthesized in relatively copious quantities using chemical methods. We begin this article with an overview of synthetic strategies that have been exploited to achieve 1D growth. We then elaborate on these approaches in the following four sections: i) anisotropic growth dictated by the crystallographic structure of a solid material; ii) anisotropic growth confined and directed by various templates; iii) anisotropic growth kinetically controlled by supersaturation or through the use of an appropriate capping reagent; and iv) new concepts not yet fully demonstrated, but with long‐term potential in generating 1D nanostructures. Following is a discussion of techniques for generating various types of important heterostructured nanowires. By the end of this article, we highlight a range of unique properties (e.g., thermal, mechanical, electronic, optoelectronic, optical, nonlinear optical, and field emission) associated with different types of 1D nanostructures. We also briefly discuss a number of methods potentially useful for assembling 1D nanostructures into functional devices based on crossbar junctions, and complex architectures such as 2D and 3D periodic lattices. We conclude this review with personal perspectives on the directions towards which future research on this new class of nanostructured materials might be directed.