Designing, Processing and Properties of Advanced Engineering Materials

Volumes 449-452

doi: 10.4028/www.scientific.net/MSF.449-452

Paper Title Page

Authors: Young Jae Lee, Jae Hyung Kim, Jang Soon Kim, Dong Bok Lee, Jae Chun Lee, Yun Jung Chung, Yun Soo Lim
Abstract: Activated carbon fibers were prepared from stabilized PAN-based fibers by chemical activation using potassium hydroxide at different concentration. The experimental data showed variations in specific surface area, microstructure by the activated carbon fibers. Specific surface area of about 2545 m2/g was obtained in the KOH/stabilized PAN-based fiber ratio of 1:1 at 800°. An abrupt reduction of specific surface area was observed in the experiments with the ratio of 3:1 of OH/stabilized PAN-based fiber, being dissimilar with the result of KOH/fiber ratios of 1:1 and 2:1 in the similar experiments. The high concentration of KOH led to the destruction of micropore walls instead of forming mesopores.
217
Authors: Nobumitsu Shohoji
Abstract: Elementary carbon in solid state might exist in variety of allotropic forms including graphite, diamond and amorphous carbon. Among them, graphite is in the stable form with chemical carbon activity a(C) = 1 whereas diamond is in meta-stable state and amorphous carbon is in un-stable state with a(C) higher than 1. Experimental evidences showed that carbide and carbo-nitride being in equilibrium with carbon possessing a(C) higher than 1 was with higher C content than the corresponding ones in equilibrium with graphite. In case of gaseous ammonia NH 3, higher nitrogen activity a(N)and higher hydrogen activity a(H) than the ones corresponding to the equilibrium partial pressure levels, p(N 2) and p(H 2), might be gained by suppressing its dissociation to a level away from the equilibrium state for the given temperature T by flowing. Thus, under flowing NH 3 gas, nitride or carbo-nitride with N content higher than that in equilibrium with N 2 gas at p(N 2) anticipated from the dissociation equilibrium at the given T might be obtained. Chronological development of this line of work started by Prof. Masahiro Katsura in early seventies at Osaka University is reviewed in this paper as I was one of collaborators involved in this very exciting research work from the early stage of its development.
221
Authors: Yoshinobu Motohashi, Kazuyoshi Waseda, Kazuhiko Kitahora
Abstract: A sinter-bonding method for a typical structural ceramic, Si3N4, has been studied by making good use of 3Y-ZrO2/Al2O3 composites powder as an interlayer. During the process of the sinter-bonding, the sintering of the inserted powder as well as the bonding of the interfaces, Si3N4/ inserted powder /Si3N4, progressed imultaneously. Since superplasticity in the 3Y-ZrO2/AlO3 composites can arise after, even during, the sintering process under proper bonding temperature and stress conditions, the surface roughness of the Si3N4 to be bonded can be filled up mainly by the material flow of the interlayer even though the surfaces are uneven and have curvatures. It was found that the sinter-bonding of the polycrystalline Si3N4 specimens was completed at temperatures ranging from 1573 to 1813 K with bonding stresses ranging from 4 to 10 MPa, at which superplastic flow of the inserted material would arise, whereas the Si3N4 showed no permanent deformation. The bonded Si3N4 specimens showed the bending strength of more than 300MPa at room temperature.
225
Authors: Kazuo Osumi, Hideki Kita, Tateoki Iizuka, Takene Hirai
Abstract: In this study, we developed silicon nitride with low friction, low wear and high strength for wear resistance parts. And this work is to study the basic synthetic process for ultra fine particles reinforced silicon nitride composites and the fabrication processes of wear resistance parts. The following results were obtained: 1) The basic synthetic and fabrication process for wear parts were almost established, 2) In engine durability test, it has confirmed that the wear resistance could be improved by using developed silicon nitride.
229
Authors: Jun Suh Yu, B.S. Lee, Sung Churl Choi, Ji Hun Oh, Jae Chun Lee
Abstract: Electrically conductive porous Si/SiC fiber media were prepared by infiltration of liquid silicon into porous carbon fiber preforms. The series rule of mixture for the effective electrical conductivity was applied to the disc shaped samples to estimate their silicon content, effective electrical conductivity and porosity. The electrical conductivity was estimated by assuming the disc sample as a plate of equivalent geometry, i.e., same thickness, electrode distance and volume. As the volumetric content of silicon in a sample increases from 0.026% to 0.97%, the estimated electrical conductivity increases from 0.17 S/cm to 2.09 S/cm. The porosity of the samples measured by Archimedes principle was in the range of 75~83% and 1~4% less than the one estimated by the series rule of mixture for the effective electrical conductivity.
233
Authors: Hyun Jae Yoo, Yong Ho Park, Ik Min Park
Abstract: The bulk (Bi0.2iSb0.8)2Te3 thermoelectric alloys added with Ag up to 2.0 mass% were prepared by mechanical alloying and pulse discharge sintering (MA-PDS). Microstructures of the sintered samples were investigated. In the two samples with 1.0 and 2.0 mass% Ag, an abnormal growth of the (Bi,Sb)2Te3 phase, manifested by the formation of coarse crystals that are visible with eye, has been revealed during the PDS process of the alloyed powders. The local temperature rise in the compact induced by the compositional fluctuation as a result of Ag addition was suggested to be responsible for the observed abnormal growth. In addition, the electrical transport properties, i.e., electrical resistivity and Seebeck coefficient, of the sintered samples were studied.
237
Authors: Jung Hwan Kim, Ki Gang Lee, Y. Kim, S.K. Kang
Abstract: Brick samples were prepared through vitrification process with two different kinds of EAF dust. Leaching concentrations of various metal ions and anions for the bricks(20wt% EAF dust-80wt% clay) were evaluated by ICP and IC analysis. The results of leaching test showed that the concentration of ions leached from bricks were proportional to the square root of time and saturated with leaching time. The saturated concentrations of alkali and alkali-earth metal ions were 0.1-250ppm; on the other hand, the heavy metal ions were 0-0.084ppm. The efflorescence mechanism of EAF dust-clay bricks was studied by quantitative analysis for the effects of various metal ions and anions. Efflorescence formed on the brick surfaces which were immersed in DI water and dried slowly in the air were characterized by SEM, EDS and XRD. The results of EDS and XRD showed that the main component of the efflorescence was water soluble Na2SO4 .
241
Authors: Yun Chuan Yang, Chang Jiang Liu, Guo Kang Li
Abstract: With the help of the scanning electron microscope, the superfine powders produced from 8 kinds of materials by Jet Mill were experimentally investigated and were qualitatively analyzed based on the stress wave theory and the crystallography theory. It was found that the crystal structure had a decisive influence on the shape of particles, and the shape of non-crystal particles occurred at random. The particle materials produced from intensive impulsive loading maintained their original roperties. The unbalanced crack extension, which caused by the defects of materials or other factors, was the main factor of material destruction.
245
Authors: Jung Il Lee, Tae Whan Hong, Il Ho Kim, Soon Chul Ur, Young Geun Lee, Sung Lim Ryu
Abstract: High silicon Al-Si alloy powders having nanocrystalline structures have been produced by mechanical alloying process. Microstructures in mechanically alloyed Al-Si powders were investigated by scanning electron microscopy and transmission electron microscopy. X-ray diffraction analyses were also carried out to characterize lattice constant, crystallite size and misfit strain. Effective milling time for the formation of nanocrystalline microstructure was thought to be approximately 12 hours, and the sizes of Al and Si crystallites in mechanically alloyed powders after longer than 12 hours of milling were reduced to about 30nm and 70nm respectively, in Al-70 mass% Si alloy system. The misfit strains increased with milling time up to 240 hours, and saturated to 5.73×10-3 and 4.39×10-3 for Al and Si crystallites, respectively.
249
Authors: Chung Hyo Lee, S.H. Lee, S.Y. Chun, Sang Jin Lee, Young Soon Kwon
Abstract: Nanocomposite formation of metal-metal oxide systems by mechanical alloying (MA) has been investigated at room temperature. The systems we chose are the Fe 2O 3-M(M=Al,Ti,Zn,Cu), where pure metals are used as reducing agent. It is found that nanocomposite powders in which Al 2O 3 and TiO 2 are dispersed in Fe matrix with nano-sized grains are obtained by mechanical alloying Fe 2O 3 with Al and Ti, respectively. However, the reduction of Fe 2O 3 with Cu by MA is not occurred. And the system of Fe 2O 3-Zn results in the formation of FeO plus ZnO after 120 h of milling. It is also shown that the magnetic evidence for the solid state reduction by mechanical alloying through changes in saturation magnetization and coercivity.
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