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        검색결과 637

        321.
        2007.06 KCI 등재 구독 인증기관 무료, 개인회원 유료
        Properties of carbon blacks and carbon black/SBR rubber composites filled by surface modified carbon blacks were examined. Although the specific surface area of carbon blacks increased after the surface modifications with heat, acid, and base, there were no obvious changes in resistivity. The composites filled by heat treated carbon blacks showed a higher tensile strength and elongation than those filled by raw blacks. The acid and base treated carbon blacks filled composites also showed higher tensile strength but similar elongation values with those filled by raw blacks. With increasing loading ratio, both tensile strength and elongation increased, and appeared a maximum value at 30-40 phr. Modulus at 300% strain remained increasing with further loading of carbon blacks. At the same loading, the heat treated black filled composites showed similar modulus values with composites filled by raw blacks but for base and acid treated black filled composites much higher values were obtained. After the surface modification, the functional groups which played an important role in reinforcement action were changed.
        4,000원
        322.
        2007.06 KCI 등재 구독 인증기관 무료, 개인회원 유료
        In this work, activated carbon (AC) after HNO3 modification was used as the support during the production of supported TiO2 to increase the high deposition efficiency and the photocatalytic activity. The results of N2 adsorption showed that the BET surface area of samples decreased with an increasing of the concentration of HNO3 due to the penetration of TiO2. From XRD data, a single crystal structure of anatase peak was observed in diffraction patterns for the AC coated with titanium complexes. From the SEM results, almost all particles were aggregated with each other at the carbon surface and AC was covered with TiO2 particles in all of the samples. The EDX spectra show the presence of C, O, Ti and other elements. It was also observed a decreasing of amount of C content with increasing Ti and O content from the EDX. The results of FT-IR revealed that the modified AC contained more surface oxygen bearing groups than that of the original AC. The effect of surface acidity and basity calculated from Boehm titration method was also evaluated from correlations as a function of NaOH, NaHCO3, and Na2CO3 uptake. The surface modification of AC by HNO3 leads to an increase in the catalytic efficiency of AC/TiO2 catalysts, and the catalytic efficiency increases with increasing of HNO3 concentration.
        4,000원
        323.
        2007.06 KCI 등재 구독 인증기관 무료, 개인회원 유료
        Bulk metallic glass (BMG) composite was fabricated by consolidation of milled metallic glass composite powders. The metallic glass composite powder was synthesized by a controlled milling process using the Cu-based metallic glass powder blended with 30 vol% Zr-based metallic glass powders. The milled composite powders showed a layered structure with three metallic phases, which is formed as a result of mechanical milling. By spark plasma sintering of milled metallic glass powders in the supercooled liquid region, a fully dense BMG composite was successfully synthesized.
        4,000원
        324.
        2006.12 KCI 등재 구독 인증기관 무료, 개인회원 유료
        The experimental data from the central composite design runs were utilized for mathematical models far the drilling characteristics containing linear, quadratic and interactive effects of the parameters such as volume fraction of TiC in the composites, drill speed, feed rate and drill diameter. The models were developed via stepwise selection where the insignificant effects were removed using t-test. The models were subjected to optimization of maximizing drill life and satisfying the other constraints.
        4,000원
        326.
        2006.10 KCI 등재 구독 인증기관 무료, 개인회원 유료
        Electronic packaging involves interconnecting, powering, protecting, and cooling of semiconductor circuits fur the use in a variety of microelectronic applications. For microelectronic circuits, the main type of failure is thermal fatigue, owing to the different thermal expansion coefficients of semiconductor chips and packaging materials. Therefore, the search for matched coefficients of thermal expansion (CTE) of packaging materials in combination with a high thermal conductivity is the main task for developments of heat sink materials electronics, and good mechanical properties are also required. The aim of this work is to develop copper matrix composites reinforced with carbon nanofibers. The advantages of carbon nanofibers, especially the good thermal conductivity, are utlized to obtain a composite material having a thermal conductivity higher than 400 W/mK. The main challenge is to obtain a homogeneous dispersion of carbon nanofibers in copper. In this paper, a technology for obtaining a homogeneous mixture of copper and nanofibers will be presented and the microstructure and properties of consolidated samples will be discussed. In order to improve the bonding strength between copper and nanofibers, different alloying elements were added. The microstructure and the properties will be presented and the influence of interface modification will be discussed.
        4,000원
        327.
        2006.09 구독 인증기관·개인회원 무료
        The type, volume fraction, size, shape and arrangement of embedded particles influence the mechanical properties of the particle reinforced metal matrix composites. This presents the investigation of the SiC particle and porosity distributions in various aluminum matrix composites produced by cold- and hot-pressing. The microstructures were characterized by optical microscopy and stereological parameters. SiC and porosity volume fractions, and the anisotropy distribution function were measured to establish the influence of the consolidation method.
        328.
        2006.09 구독 인증기관·개인회원 무료
        Sintered composites of Al-8wt%Cu-10vol%SiCp were deformed by repressing or equal channel angular pressing(ECAP) at room temperature, and . Repressing produced more densification than ECAP but resulted in much lower transverse rupture strengths. In both cases, deformation at room temperature and , resulted in much lower strengths than deformation at , and also caused the fracturing of some SiC particles. The higher bend strengths and less SiC fracturing at are attributable to the presence of an Al-Cu liquid phase during deformation. The employment of copper coated SiC instead of bare SiC particles for preparing the composites was found not improving the properties.
        329.
        2006.09 구독 인증기관·개인회원 무료
        Various reactions and the in-situ formation of new phases can occur during the mechanical alloying process. In the present study, Al powders were strengthened by AlN, using the in-situ processing technique during mechanical alloying. Differential thermal analysis and X-ray diffraction studies were carried out in order to examine the formation behavior of AlN. It was found that the precursors of AlN were formed in the Al powders and transformed to AlN at temperatures above . The hot extrusion process was utilized to consolidate the composite powders. The microstructure of the extrusions was examined by SEM and TEM. In order to investigate the mechanical properties of the extrusions, compression tests and hardness measurements were carried out. It was found that the mechanical properties and the thermal stability of the Al/AlN composites were significantly greater than those of conventional Al matrix composites.
        330.
        2006.09 구독 인증기관·개인회원 무료
        Considering the idea that some properties, especially the mechanical properties of at ambient temperature can be improved by adding of some substitutional/interstitial elements, our goal was to obtain these materials starting from mechano-composites powders. In this aim, using mechanical alloying techniques three type of mechano-composite powders starting from elemental powders were obtained. Then, by reactive sintering in argon atmosphere at temperature over , alloyed materials were realized. This paper presents our research results regarding the microstructural aspects and phase formation in obtained materials.
        332.
        2006.09 구독 인증기관·개인회원 무료
        Attempts have been made to describe the influence of production process parameters on the microstructure and properties of W-Ag and Mo-Ag composites. The compositions of powder mixtures are W+30% Ag and Mo+30%Ag. Silver additions assists densification during sintering by a liquid phase sintering process. The main goal of this work is to compare properties and microstructure of as-sintered and as-infiltrated composites.
        333.
        2006.09 구독 인증기관·개인회원 무료
        Influences of machining on magnetic properties of soft magnetic composites (SMC's) with addition of two kinds of binder, i.e., organic binder and inorganic one, were investigated. Machining does not affect DC magnetic properties of the SMC compacts. This can be ascribed to their particular structure in which the ironpowder particles are highly isolated by the binder. On the other hand, decrease in resistivity and resultant increase in eddy current loss was confirmed in the machined compacts containing inorganic binder. It is supposed that the brittleadditive binder existing between the iron particles is partly broken, and iron-to-iron contact is formed on the machined surface.
        335.
        2006.09 구독 인증기관·개인회원 무료
        Several boride sintered bodies such as , , and were previously reported. In the present study, the sinterability and physical properties of chromium boride containing chromium carbide sintered bodies were investigated in order to determine its new advanced material. The samples were sintered at desired temperature for 1 hour in vacuum under a pressure by hot pressing. The relative density of sintered bodies was measured by Archimedes' method. The relative densities of addition of 0, 5, 10, 15 and 20 mass% composites were 92 to 95%. The Vickers hardness of the with 10 and 15 mass% composites were about 14 and 15 GPa at room temperature, respectively. The Vickers hardness at high temperature of the addition of 10 mass% composite decreased with increasing measurement temperature. The Vickers hardness at 1273 K of the sample was 6 GPa. The Vickers hardness of addition of composites was higher than monolithic sintered body. The powder X-ray diffraction analysis detected CrB and phases in containing composites.
        336.
        2006.09 구독 인증기관·개인회원 무료
        Silicon nitride - silicon carbide composite was developed by using an abrasive SiC powders as a raw material. The composites were prepared by mixing abrasive SiC powder with silicon, pressing and sintering at under nitrogen atmosphere in atmosphere controlled vacuum furnace. The proportion of silicon in the initial mixtures varied from 20 to 50 wt%. After sintering, crystalline phases and microstructure were characterized. All composites consisted of and as the bonding phases in SiC matrix. Their physical and mechanical properties were also determined. It was found that the density of the obtained composites increased with an increase in the content formed in the reaction.
        337.
        2006.09 구독 인증기관·개인회원 무료
        Carbon nanotube (CNT) reinforced hydroxyapatite (HAp) composites were fabricated by using the spark plasma sintering process with surfactant modified CNT and HAp nano powder. Without the dependency on sintering temperature, the main crystal phase existed with the HAp phase although a few contents of (Tri calcium phosphate) phase were detected. The maximum fracture toughness, was obtained in the sample sintered at and on the fracture surface a typical intergranular fracture mode, as well as the pull-out pmhenomenon of CNT, was observed.
        338.
        2006.09 구독 인증기관·개인회원 무료
        In this investigation, based ceramic composites were fabricated by in-situ reaction hot pressing using , TiC SiC powder as starting materials. The reaction synthesized composites by hot pressing at was found to posses very high relative density. The reaction synthesized composites comprise , , SiC and graphite by the reaction between TiC and . The newly formed and graphite was embedded both inside grain and at grain boundary . The mechanical properties of reaction synthesized -graphite composites were more enhanced compared to those of monolithic .
        339.
        2006.09 구독 인증기관·개인회원 무료
        The aging behavior of sintered Al composites with various ceramic contents was investigated. 2xxx series blended powder was used as the starting powder. Ceramic contents were 0wt.% and 5wt.%. The blended powders were compacted at 250MPa. The sintering process was performed at for 60min in a atmosphere. Each part was solution-treated at for 60min and aged at . The Rockwell hardness at the peak aging time increased with ceramic contents. However, the peak aging time at maximum hardness was reduced with increased ceramic contents.
        340.
        2006.09 구독 인증기관·개인회원 무료
        Mechanical properties of 7xxx series Al metal matrix composite (MMC) powders containing different amounts of ceramic were investigated. The ceramic contents of the starting powders were 5 wt.% or 10 wt.%. The powders were uniaxially cold compacted using a cylindrical die with a compacting pressure of 250 MPa and were sintered at in a dry atmosphere for 60 min. For the heat treatment, sintered parts were solution treated at and aged at . Compression tests were conducted to reveal the effect of particle content on the mechanical properties of the composites. Fractography was examined using a scanning electron microscope.