Byoung-Kee Kim

Fabrication of W–20 wt % Cu composite nanopowder and sintered alloy with high thermal conductivity

Abstract The reduced W–20% Cu powder with W particle sizes of about 30–100 nm and uniform distribution of components was successfully synthesized by mechano-thermochemical process. This process consists of three steps: the producing of oxide powder, the wet ball milling of oxide powder and the final reduction. W/Cu composite oxide clusters with a spherical shell structure were prepared by spray drying of aqueous solution of Cu and W salts with subsequent oxidation at 750 °C for 2 h. These oxide clusters were fragmented to fine oxide powders by wet milling and reduced at 600–800 °C in hydrogen. The sintering behavior of composite powder and thermal conductivity of sintered alloys were also investigated. This composite powder showed higher sinterability comparatively with conventional blended powders. The thermal conductivity of W–20% Cu alloys prepared by this work is 239±5.0 W/mK, which is equal to the theoretical value. Superior properties of the present powder are due to the homogeneous mixing state of nanosized W and Cu particles in powder, homogeneous redistribution of W solid particles in liquid Cu and high purity of powder. This alloy did not contain such impurities as Fe and Co that can be easily introduced in powder in conventional processing.

Gene–gene interaction between interleukin‐4 and interleukin‐4 receptor α in Korean children with asthma

Background Interleukin‐4 receptor α (IL‐4Rα), which binds IL‐4 and IL‐13, is involved in signal transduction of those cytokines that lead to IgE production, and is also a key functional component of the Th2 lymphocyte phenotype.

Combined effect of tumour necrosis factor‐α and interleukin‐13 polymorphisms on bronchial hyperresponsiveness in Korean children with asthma

Background TNF‐α and IL‐13, two pivotal pro‐inflammatory cytokines, are increased in asthmatic airways and may be linked to asthma susceptibility and/or bronchial hyperresponsiveness (BHR).

Manufacturing of aluminum flake powder from foil scrap by dry ball milling process

A feasibility study for producing aluminum flake powder from aluminum foil scrap by dry ball milling under an inert argon with a few % of oxygen was carried out. It was found that the pieces of aluminum foil scrap were laminated to each other, elongated by micro-forging of the falling balls, fragmented into small pieces of foil and finally formed into flake powder, during the ball milling. A larger ball is more beneficial to the milling of aluminum foil into the flake powder due to the large impact energy during the falling of the ball. Intermediate stops during the ball milling produced a finer aluminum flake powder than non-stop milling for up to 25 h due to cooling of the vial. A larger amount of stearic acid reduces friction between the foil or the balls and vial wall, thus give less milling efficiency, 3 wt.% of stearic acid as additive being verified as the optimum content. The aluminum flake powder produced by the dry ball milling of aluminum foil scrap can be applied to fingerprint detection or to aerate light-weight concrete. # 2000 Elsevier Science S.A. All rights reserved.

Effect of Active Smoking on Asthma Symptoms, Pulmonary Function, and BHR in Adolescents

Active smoking is known to increase asthma symptoms and bronchial hyper‐responsiveness (BHR) while decreasing pulmonary function in adults, but few studies have addressed these issues in adolescents.

Effects of lifter bars on the ball motion and aluminum foil milling in tumbler ball mill

Effects of lifter bars on the ball motion during ball milling and characteristics of aluminum flake powders prepared by the ball milling of aluminum foil scraps were studied. When rotation speed of milling jar without lifter bar is below 75% of critical revolutions per minute (rpm), balls slide in the jar. As rotation speed of milling jar increases up to 93% and 140%, the mode of balls motion changes to cascading and cataracting type, respectively. By setting even one lifter bar in the jar, balls move as cascading mode and cataracting mode at 37% and 56% of critical rpm, respectively. As number of lifter bars increases, the necessary rotation speeds of milling jar for cascading mode and cataracting mode decrease drastically. The aluminum foils scrap was milled in the milling jar with four lifter bars and without lifter bar under the rotation speeds of jar corresponding to cascading and cataracting modes. That result shows that it is possible to achieve same quality of milled fine powder by using lifter bars even under the significantly lower rotation speeds of jar.

Cyclosporine treatment decreases the percentage of cutaneous lymphocyte antigen (CLA)(+)CD4(+) T cells in children with severe atopic dermatitis.

Skin-homing T cells expressing cutaneous lymphocyte antigen (CLA) are important in the pathogenesis of atopic dermatitis (AD) (1). Cyclosporine, which controls cytokine production by T cells and regulates their activation, is safe and effective in the treatment of severe AD (2, 3). The effect of this drug on circulating CLA+ T cells in AD, however, is not known. We therefore evaluated the effect of cyclosporine treatment on clinical outcome and CLA+ T cells in children with AD. Ten children with severe, lichenified skin lesions [severity scoring of atopic dermatitis (SCORAD) index >50], refractory to topical steroid therapy were treated with cyclosporine (5 mg/kg/day), while 10 children with AD were treated with thymopentin (50 mg, 3 times/week), for 6 weeks. None of these 20 patients had used any systemic steroids for at least 6 months prior to the study. They were compared with 11 healthy children as ageand sex-matched controls, with no history, symptoms or signs of AD or any other respiratory allergic disease. Clinical outcome was monitored by the SCORAD index (4). Peripheral blood T-lymphocyte subpopulations, including CLA+ T cells, were assayed by flow cytometry. The percentages of peripheral blood CD4+CLA+ and CD3+CLA+ T cells were significantly higher in children with AD before treatment than in controls. The SCORAD index was decreased significantly after treatment with cyclosporine or thymopentin. Cyclosporine treatment significantly reduced the percentages of CD4+CLA+ (Fig. 1) and CD3+CLA+ T cells (P < 0.05), but not the percentages of CD3+, CD4+, CD8+, and CD8+CLA+ T cells. In contrast, treatment with thymopentin did not affect CLA+ T cells. In this study, we demonstrated that the percentage of CD4+CLA+ T cells was significantly higher in peripheral blood mononuclear cells (PBMCs) of children with severe, chronic AD than in those of healthy children. CLA participates in selective transendothelial migration of memory/effector T cells by binding to E-selectin on endothelial cell layers after activation by proinflammatory cytokines (5, 6). Although CD4+ T cells have been regarded as important in the pathogenesis of AD, we found that the percentage of peripheral blood CD4+ T cells did not differ between AD children and healthy children. We also found, in combination with markedly improved clinical symptoms, a significant decrease of CD3+CLA+ and CD4+CLA+ T cells after treatment with cyclosporine, except for CD8+CLA+ T cells, although treatment with thymopentin did not affect

Thermo-mechanical improvement of Inconel 718 using ex situ boron nitride-reinforced composites processed by laser powder bed fusion

Hexagonal boron nitride-reinforced Inconel 718 (h-BN/IN718) composites were fabricated using a laser powder bed fusion (LPBF) technique to treat a nanosheet-micropowder precursor mixture prepared in a mechanical blending process. Tailoring the BN in IN718 enhanced the thermal resistance of the composites, thereby dampening the sharpness of the melting temperature peak at 1364 °C. This is because the presence of the BN reinforcement, which has a low coefficient of thermal expansion (CTE), resulted in a heat-blocking effect within the matrix. Following this lead, we found that the BN (2.29 g/cm3) was uniformly distributed and strongly embedded in the IN718 (8.12 g/cm3), with the lowest alloy density value (7.03 g/cm3) being obtained after the addition of 12 vol% BN. Consequently, its specific hardness and compressive strength rose to 41.7 Hv0.5·cm3/g and 92.4 MPa·cm3/g, respectively, compared to the unreinforced IN718 alloy with 38.7 Hv0.5·cm3/g and 89.4 MPa·cm3/g, respectively. Most importantly, we discovered that the wear resistance of the composite improved compared to the unreinforced IN718, indicated by a decrease in the coefficient of friction (COF) from 0.43 to 0.31 at 2400 s. This is because the BN has an exfoliated surface and intrinsically high sliding and lubricating characteristics.

High Temperature Oxidation Behavior of Ni based Porous Metal

【This study investigated the high temperature oxidation behavior of Ni-22.4%Fe-22%Cr-6%Al (wt.%) porous metal. Two types of open porous metals with different pore sizes of 30 PPI and 40 PPI (pore per inch) were used. A 24-hour TGA test was conducted at three different temperatures of

Enhanced Oxidation Resistance of Iron Nanoparticles via Surface Modification in Chemical Vapor Condensation Process

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