Eco-Materials Processing & Design VII

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Authors: S.H. Lee, H.Y. Jung, Jung Mann Doh, Jin Kook Yoon, H.N. Lim
Abstract: Effects of 0.5 wt% Indium addition on the oxidation of Au-Pt-Cu alloy, the interfacial microstructure and bonding strength between porcelain and Au-Pt-Cu-xIn alloys(x = 0, 0.5wt%) were investigated using scanning electron microscopy, X-ray diffractometry, transmission electron microscopy, and a tensile tester. The bonding strength of the Au-Pt-Cu and Au-Pt-Cu-0.5In alloys with porcelain was about 24.6 MPa and 49.5 MPa in average, respectively. This higher bonding strength in the Au-Pt-Cu-0.5In alloy compared with the Au-Pt-Cu alloy without In is ascribed to the formation of In2O3 at the interface between porcelain and Au-Pt-Cu-0.5In alloy. Especially, the formation of In2O3 at the interface between porcelain and Au-Pt-Cu-0.5In alloy leads to enhancing chemical bonding between In2O3 and various oxides in porcelain, and also to improving the anchoring effect.
Authors: Hao Wang, Wei Min Wang, Zheng Yi Fu, Tohru Sekino, Koichi Niihara
Abstract: Mullite-based nanocomposites with embedded FeCr alloy nanoparticles were synthesized by reduction of sol-gel prepared Al5.4(Fe0.8Cr0.2)0.6Si2O13 solid solution in hydrogen. The feature of the formation of FeCr alloy is characterized by XRD analysis. Structural characterization revealed that the intragranular FeCr alloy nanoparticles along with inter-granular iron grains were obtained in as reduced sample. After acid washing, the intergranular metal grains were eliminated. The static magnetic properties of nanocomposite powders were studied using Magnetic Property Measurement System. It is found that part of the intra-granular metal nanoparticles have superparamagnetic behavior at room temperature.
Authors: Pyuck Pa Choi, Ji Soon Kim, O.T.H. Nguyen, Dae Hwan Kwon, Young Soon Kwon
Abstract: Al-La-Ni-Fe alloys of three different compositions (Al82La10Ni4Fe4, Al85La9Ni3Fe3 and Al88La6Ni3Fe3) were prepared high-energy milling in a planetary ball-mill (AGO-2). Complete amorphization was observed for the Al82La10Ni4Fe4 alloy after milling for 350 h at a rotational speed of 300 rpm. In contrast, the Al85La9Ni3Fe3 and Al88La6Ni3Fe3 powders contained the FCC Al phase even for prolonged milling. The amorphization tendency was found to increase in the order of Al88La6Ni3Fe3 < Al85La9Ni3Fe3 < Al82La10Ni4Fe4, which may well be ascribed to the increasing atomic size mismatch of the constituent elements on La addition. DSC analyses of amorphous samples revealed two-stage crystallization processes for all three alloys, however, with strong variations in the thermal stability upon compositional changes. As observed by SEM, amorphous powders consisted of particles with nearly spherical shape and diameters ranging from 5 to 20 µm.
Authors: Si Young Sung, Young Jig Kim
Abstract: Alpha-case formations between investment molds and TiAl alloys were investigated for economic TiAl alloys net-shape forming. The α-case reactions between mold and TiAl alloys were characterized by using optical microscopy and a hardness tester. In the case of TiAl alloys, there were no α-case formation reactions. The α-case was formed not only by interstitial oxygen elements but also by substitutional metallic elements dissolved from mold materials. There were neither interstitial nor substitutional α-case formations since TiAl alloys have both negligible solubility of oxygen and low activity in molten states. The results of the investment casting of TiAl alloys confirmed that the casting route in our study can be an effective approach for the economic net-shape forming of TiAl alloys automotive parts.
Authors: Byung Geel Yu, Ye Lim Kim, Kae Myung Kang, Si Young Chang
Abstract: Plasma electrolytic oxide coatings were produced on both pure magnesium and binary Mg-Al alloys containing 3, 6, 7 wt% Al, and the effect of Al on the characteristics of coatings was investigated under the processing conditions of various coating times and current. The coatings on Mg-Al alloys showed porous microstructure and some volcano top-like pores on the surface, and they consist of MgO and Al2O3. The surface roughness became larger with increasing coating time, while it was unchanged with increasing Al content. The thickness increased with increasing coating time and showed slight dependence on Al content. The hardness was almost unchanged with increasing coating time and Al content in the coatings grown with the ratio of current, C1:C2=100:75.
Authors: Sang Won Myoung, Jin Ho Kang, Seong Hwan Park, Seoung Soo Lee, Dong Won Joo, Yeon Gil Jung
Abstract: A novel process in the synthesis of SiC microtubes is proposed, based on modified CVD process. This process was adopted to siliconize the carbon fibers that perform with relatively small surface area, either partially or completely, into the SiC microtubes with large surface area. An oxidic vapor generated from a metal reacts with a carbon solid preform, which leads to a carbide possessing with a unique morphology. The carbon fiber preforms have been unidirectionally arranged into alumina tube, and then a solid-vapor reaction between carbon fiber preforms and SiO vapor originated from the mixture powder pack of Si and SiO2 has been carried out in restoration atmosphere (argon gas/hydrogen gas = 80/20) at 1450°C. The synthesized SiC.C composites were re-sintered with the modified mixture powder pack of Si, SiO2, Al, and Al2O3 at the same condition, in which amounts of Al and Al2O3 employed as a impurity have been controlled under 1 wt% with different mole ratios (Al2O3 : Al = 1:1, 2:1, 3:1). Two kinds of SiO and AlO vapors are generated in the second step reaction process, which react with carbon residuals. The quantitative and qualitative properties of the SiC micorotubes were analyzed by using TGA, SEM, and XRD. The inner morphology of the SiC micorotubes is dependent on the impurity concentration and the gas nature, showing the grains grown with membrane type in the second reaction process because of the impurity.
Authors: Xiao Ning Zhang
Abstract: A metallic modification technique on fabric is put forward in this paper. Morphologies and element analysis of modified fabric samples with copper and nickel-iron double films were carried out by using SEM and EDX. Shielding effectiveness (SE) on the samples was tested within 0.1~1000MHz and 1.5~18GHz. Within 0.1~1000MHz, modified fabric SE is between –93dB and –110dB. Two nickel-plated methods were compared. The measurement results of two modified fabric indicate that nickel-iron alloy films are better than nickel film on SE. With the advantages of low cost, flexibility , high electromagnetic protection characteristics, the modified fabric has a widely applicable foreground.
Authors: Si Young Sung, Bong Jae Choi, Sang Hwa Lee
Abstract: The aim of this study is to investigate the applicability of titanium matrix composites (TMCs) sleeve to Al alloys die-casting. Ti and 1.88 mass% B4C were prepared for the synthesis of 10 vol% (TiC+TiB) hybrid TMCs. In-situ synthesis and net-shape forming of TMCs were carried out in a vacuum induction melting furnace. The synthesized (TiC+TiB) TMCs were examined using scanning electron microscopy, an electron probe micro-analyzer, X-ray diffraction and transmission electron microscopy. The resistance-ability of (TiC+TiB) TMCs to molten Al alloys attack was also examined. Their reactions were carried out in a furnace at 993 K for times varying from 0 to 1200 s. In the case of conventional sleeve material, H13 steel, there were severe interfacial reactions and erosion after 60 s. On the other hand, the resistance of (TiC+TiB) TMCs to interfacial reactions and erosion by molten A380 alloy was significantly increased.
Authors: Sook Young Moon, Myung Soo Kim, Yun Soo Lim
Abstract: OXI-PAN fibers, Kynol fibers, and rayon fibers were used as precursors for the preparation of activated carbon fibers (ACFs) by chemical activation with KOH at 800°C. The effects of different precursor fibers and fiber/KOH ratios on the final ACFs are discussed. The precursor fibers used were appropriate for the ACFs in a single stage pyrolysis process. The OXI-PAN fibers, which were activated with KOH of 2.0M, showed a specific surface area of 2328m2/g, however, lost the fiber shape because of low yields. The Kynol fibers and Rayon fibers showed the high yields, but lower specific surface areas of 900m2/g and 774m2/g, respectively, at KOH of 1.5M. The OXI-PAN fibers, which were activated with KOH of 1.5M, have a specific surface area of 1028m2/g and higher micro-pore volumes and lower yields rather than Kynol-1.5 and Rayon-1.5 samples. This phenomenon is attributed to higher chemical resistance of the Kynol and Rayon fibers rather than OXI-PAN fibers. However, the Kynol fibers were the best precursors on KOH activation at 800°C when carbon yields, surface areas, and micropore volumes are condisered.
Authors: Tae Hyun Nam, Cheol Am Yu, Dae Won Jung, Kwon Koo Cho
Abstract: The microstructure of Ni sulfides prepared by thermal sulfidation of pure Ni and their dependence of fabrication parameters were investigated by means of scanning electron microscopy and X-ray diffractions. Sulfidation was made by isothermally annealing Ni with the sulfur in vacuum sealed glass ampoules at 673 K for 120 – 600s under the sulfur pressure of 100 and 220 kPa. The sulfide layers formed in the early stage were found to consist of spherical particles smaller than 0.5um, which were grown and agglomerated with increasing annealing temperature. Thickness of sulfides developed on Ni substrate was found to increase with increasing annealing time and sulfur pressure. It was also found that compositions of dominant Ni sulfides changed with varying annealing time. At the initial stage, only Ni3S2 sulfide was formed on pure Ni, which was tightly bonded to Ni substrate. On increasing annealing time, NiS sulfide was formed. On further increasing annealing time, NiS1.97 sulfide was formed, which always coexisted with NiS sulfide. A mechanism for sulfidation of Ni is proposed as follows: 3Ni + 2S  Ni3S2, Ni3S2 +S  NiS, NiS + S  NiS1.97

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