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ONLINE ISSN: 1347-5320
PRINT ISSN: 1345-9678

MATERIALS TRANSACTIONS Vol. 42 (2001), No. 12

  • Phase Relation and Thermodynamic Properties of NaCl-Na2CO3 System as a Basic System for Secondary Fly Ash in Incineration Processes of Municipal Wastes

    Kokoro Iwasawa, Shu Yamaguchi, Masafumi Maeda

    pp. 2480-2486

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    DOI:10.2320/matertrans.42.2480

    Abstract

    The thermodynamic properties and phase relation of an alkali metal-oxychloride system were examined; this is a basic model system of secondary fly ash generated in the volume reduction process of bottom ash and fly ash from incineration processes. The phase diagram for the NaCl–Na2CO3 system and its thermodynamic properties have been examined by a hot filament method and electromotive force (EMF) method using Na β-Al2O3 as a solid electrolyte from 500°C to 900°C. The liquidus lines and the eutectic temperature show good agreement with previous reports. Activities of Na2CO3 for the NaCl–Na2CO3 system obtained in this study are compared with the data from the phase diagram.

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  • Recycling of Rare Earth Magnet Scraps: Part I Carbon Removal by High Temperature Oxidation

    Kazutaka Asabe, Akihiko Saguchi, Wataru Takahashi, Ryosuke O. Suzuki, Katsutoshi Ono

    pp. 2487-2491

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    DOI:10.2320/matertrans.42.2487

    Abstract

    In the recycling of the permanent Nd–Fe–B magnet, the carbon such as free carbon and carbides at the grain boundary segregation in the magnet scrap are elements that are harmful and which obstruct the magnet performance. The removal of the carbon is currently a major problem. Remelting of scraps should, therefore, be done on condition that the carbon content is lowered to an appropriate level prior to melting. The aim of this work was to open the route for decarburization of the Nd magnet powder scraps with high carbon, as well as of the sintered body scraps with moderate carbon concentration. Decarburization via oxidation in air allowed the removal of not only free carbon but also grain boundary carbides at temperatures higher than 1273 K down to 300 mass ppm. However, an increase in the oxygen content is inevitable with the high temperature oxidation. The next step was then to reduce the iron oxide by heating it in a hydrogen atmosphere at 1273 K and subsequently to eliminate the oxygen combined with the rare-earth constituent using calcium which has a strong affinity with oxygen. The basic technology for the recycling process of the permanent Nd–Fe–B magnet scraps was discussed.

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  • Recycling of Rare Earth Magnet Scraps: Part II Oxygen Removal by Calcium

    Ryosuke O. Suzuki, Akihiko Saguchi, Wataru Takahashi, Takashi Yagura, Katsutoshi Ono

    pp. 2492-2498

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    DOI:10.2320/matertrans.42.2492

    Abstract

    Powder scraps of neodymium-iron-boron permanent magnet were deoxidized by using calcium vapor, liquid or CaCl2 melt at 1223–1273 K . Because the scraps react with the acidic solutions during leaching of the byproduct CaO, the methods for removal of the excess amount of Ca and CaO were studied. When pH was controlled at about 8 during several times leaching, the dissolution of rare earth elements could be minimized. Ca vapor deoxidation could not supply enough amount of Ca through CaO layer. When a large amount of CaCl2 was added, the dissolution rate of CaO into the aqueous solution became faster, but some amounts of rare earth components were lost. The deoxidation by Ca liquid and 5 mass%CaCl2 and the subsequent leaching in distilled water with pH>8 gave the better result so that oxygen, even in heavily oxidized scraps, could be lowered to 0.7 mass%.

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  • Numerical Analysis of Multi-Smelter for Melting Metal Waste

    Xinghe Zhang, Reijiro Takahashi, Jun-ichiro Yagi

    pp. 2499-2505

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    DOI:10.2320/matertrans.42.2499

    Abstract

    In view of the limited natural resources and the protection of the global environment, a process for treating the waste materials discharged from industrial production and human life is strongly requested to be developed. A multi smelter was proposed, which consists of coke packed bed in the lower part and free board where fine materials are fluidized during operation in the upper part. It can reduce significantly the volume, eliminate toxicity and recover some materials such as metals, because it has high temperature that can melt waste and reducing atmosphere. Many melting tests were done successfully from February 1999 using the multi-smelter constructed at Osaka Prefecture University. This reactor can treat the waste materials of 1 ton/day. In this operation test, industrial waste materials like used TV sets, air conditioners and refrigerators was melted without secondary emission of dangerous materials like dioxin. In this multi-smelter, the packed bed part seems to play an important role for melting metallic wastes effectively and for achieving a stable operation. On the basis of this foresight, a two-dimensional mathematical model has been proposed, which considered transport phenomena of heat, mass and momentum together with melting and chemical reactions in the high temperature packed bed for processing waste materials. Numerical simulation was conducted to investigate in-furnace phenomena and effects of operating conditions on the process stability. As the results, the process characteristics such as distributions of gas concentration, temperature and velocity have been obtained; they are useful to evaluate the performance of the multi-smelter and to improve the operations leading to less energy consumption and more waste materials treatment. The results showed the multi-smelter is a useful process for melting some kind of waste materials like used refrigerators, air-conditioners, the major part of which were originally made from iron and plastics.

  • Recycling of Solid Wastes from Integrated Steelmaking Plant: A Sustainable Alternative

    Cyro Takano, Ramiro Conceicao Nascimento, Guilherme Frederico B. Lenz e Silva, Dener Martins dos Santos, Marcelo Breda Mourão, Jose Deodoro Trani Capocchi

    pp. 2506-2510

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    DOI:10.2320/matertrans.42.2506

    Abstract

    Worldwide, the iron and steelmaking industry generates around 30 million tons of the recyclable wastes per year. They are generated at different phases of the production with different types and characteristics. Within these are: sludge of the Blast Furnace; coke fines; fine and coarse fractions from oxygen converters; sludge from water treatment at rolling mill unit; and others. In this paper the above dusts and sludges were physically and chemically characterized. The obtained results allowed defining self-reducing pellets using these materials. The high temperature behaviors of the pellets were evaluated. Good results, with no decrepitation and swelling, and high yield of reduction, show that it is feasible to recycle them, as self-reducing pellets, in oxygen steelmaking converter, with a net benefit of US$ 20 per ton of these dusts.

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  • A Mineralogical Study of the Reductive Roasting of Zinc Ferrite Residues — A Potential Zinc Recycling Technology

    Tzong Chen, John Dutrizac

    pp. 2511-2518

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    DOI:10.2320/matertrans.42.2511

    Abstract

    A stockpiled zinc ferrite residue from Noranda Inc., CEZinc consists mostly of ZnFe2O4 and Fe2O3, together with trace amounts of a number of other phases including Mn-bearing oxides and Sr sulphate. Reductive roasting of the zinc ferrite residue for 2 h at 800°C resulted in the extensive conversion of the ZnFe2O4 to (Fe, Zn)O and ZnO; the (Fe, Zn)O phase contains about 16 mass%Zn. The particle sizes and shapes after reductive roasting are similar to those in the unroasted feed, but the roasted material may be slightly more porous. The copper impurity in the ferrite residue is reduced to an Ag-bearing copper alloy which occurs as inclusions along the grain boundaries of the (Fe, Zn)O phase. Some of the Sr sulphate present in the zinc ferrite residue is reduced to a Zn–Fe–Sr sulphide phase, and all of the initially present Fe2O3 is reduced to (Fe, Zn)O . Reductive roasting converts the zinc ferrite residue into species which are soluble in dilute acid or alkaline media, thereby allowing the potential recycling of the Zn, Cu and Ag values.

  • Extraction of Metals from Disposed Fragmented Portable Telephones by Various Leaching Solution

    Liu Kejun, Atsushi Shibayama, Wan Tai Yen, Toshio Miyazaki, Toyohisa Fujita, Kenji Murata

    pp. 2519-2522

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    DOI:10.2320/matertrans.42.2519

    Abstract

    The extraction Au, Pd, Ag and Cu from electronic disposed portable telephone fragmented by explosive in water using several leaching solution was studied in this investigation. The metals extraction by three kinds of leaching solution, thiosulfate, iodine, and aqua regia, were compared. The best metals extraction was obtained from a 30 mass% aqua regia solution. The efficiency of metals extraction from the samples fragmented in different extents was compared with the 10 mass% aqua regia solution. The recovery of 91.97% Au, 97.69% Pd and 90.87% Cu could be achieved by a 30 mass% aqua regia solution at the retention of 54 h.

  • Thermodynamic Consideration on the Kiln Dust Generated from Eco-cement Production

    Keiichi Miura, Kouichiro Sato, Tsutomu Suzuki, Takaaki Oogami, Akira Yazawa

    pp. 2523-2530

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    DOI:10.2320/matertrans.42.2523

    Abstract

    Eco-cement is expected to provide a solution for both the municipal and industrial problems caused by limited availability of landfill sites. The heavy metals in wastes are vaporized through the sintering process and caught as kiln dust in the bag filter. For the purpose of recycling the metals, the usefulness of thermodynamic calculation in regard to the Eco-cement production process was confirmed, and the behavior of Zn, Cu and Pb components in Eco-cement production was analyzed by means of simulation. Consequently, the results can be summarized as follows: (1) As the volatilization ratio of metals at 1400°C, which is the sintering temperature of Portland cement type Eco-cement, Pb is the highest, followed by Cu and Zn is the lowest. (2) Each component reacts with CaCl2 and is vaporized mainly as ZnCl2, CuCl and PbCl2 in an oxidizing atmosphere of 1400°C. (3) It was found that the volatilization behavior of Cu and Zn are different depending on the employed atmosphere whether oxidizing or reducing. The volatilization ratio of the Cu component is higher than that of the Zn component under an oxidizing condition. On the other hand, that of Zn component is much higher under a reducing condition.

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  • Measurement of Thermodynamic Functions of Solid Phase for DD, DF, OCDD and OCDF, and Estimation of Thermodynamic Functions of Gas Phase for PCDD/Fs Using Molecular Orbital Method with Density Functional Theory

    Etsuro Shibata, Satoru Yamamoto, Hirotaka Koyo, Takashi Ikeda, Eiki Kasai, Masafumi Maeda, Takashi Nakamura

    pp. 2531-2536

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    DOI:10.2320/matertrans.42.2531

    Abstract

    In this study, heat capacities of solid phase, melting points and enthalpies of fusion for DD, DF, OCDD and OCDF were measured by a modulated differential scanning calorimeter. Thermodynamic functions of gas phase such as heat capacity, entropy and standard enthalpy of formation for PCDD/Fs were calculated by the molecular orbital method with density functional theory, which is viewed as the one of the most accurate methods at present. The temperature dependences of enthalpies of formation for DD, DF, OCDD and OCDF can be estimated in the range from the solid phase to the gas phase using the data obtained in this study and reference data.

  • Catalytic Roles of Copper on Chlorination of Precursor Phenol for Dioxins Using Ab Initio Molecular Orbital Method

    Mitsuhito Hirota, Takashi Araki, Akio Fuwa

    pp. 2537-2542

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    DOI:10.2320/matertrans.42.2537

    Abstract

    In this study, we have clarified the chlorination mechanism of precursor phenol in the homogeneous and heterogeneous phase using ab initio molecular orbital calculation. Simultaneously, we have analyzed the catalytic roles of copper on this chlorination reaction. The results obtained in this study are as follows: (1) the chlorination of precursor phenol in the homogeneous phase progresses via the direct condensation of phenol and Cl2, whereby desorbing HCl, (2) the chlorination of precursor phenol in the heterogeneous phase occurs via the adsorption and surface reaction of precursor phenol. The catalytic role of copper on the chlorination of precursor phenol is that Cl–Cl bond strength is weakened due to the back donation from copper surface.

  • Mechanical Properties of Diffusion Bonding Joint of SiC and Al-Sn Alloys at Elevated Temperatures

    Houhong Pan, Isao Itoh, Masaaki Matsubara

    pp. 2543-2547

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    DOI:10.2320/matertrans.42.2543

    Abstract

    Aluminum alloys were selected to bond to SiC by diffusion bonding in the atmosphere for researching their bondability. Diffusion bonding was carried out at 873 K for 3.6 ks and 7.2 ks under bonding pressures of 2 MPa, 4 MPa and 8 MPa. The mechanical properties of SiC/Al–0.5Sn joints and SiC/Al–0.5Sn–1Mg joints at elevated temperatures were examined by shear test, and the fracture surfaces of joints were investigated using SEM and EPMA . The results indicate that (1) pure aluminum cannot be bonded to SiC . Adding 0.5%Sn into aluminum can improve bondability. The compound addition of 0.5%Sn and 1%Mg into aluminum can improve both the shear strength and the elevated temperature properties of joint. (2) In the case of SiC/Al–0.5Sn diffusion bonding, the fracture fully occurs on bonding surfaces. In the case of SiC/Al–0.5Sn–1Mg diffusion bonding, the fracture partly occurs in the side of SiC . (3) The optimum bonding pressure is 4 MPa and 8 MPa for SiC/Al–0.5Sn and SiC/Al–0.5Sn–1Mg diffusion bonding, respectively. In optimum bonding condition, the maximum shear strength of SiC/Al–0.5Sn–1Mg joint is 51.7 MPa.

  • Modeling of Solvent Extraction of Zinc from Sulphate Solutions with D2EHPA

    Man-Seung Lee, Jong-Gwan Ahn, Seong-Ho Son

    pp. 2548-2552

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    DOI:10.2320/matertrans.42.2548

    Abstract

    A thermodynamic model based on chemical equilibria with mass and charge balance equations has been developed for the solvent extraction system consisting of ZnSO4–H2SO4–H2O-D2EHPA-kerosene. The activity coefficients of all solutes in the aqueous phase were calculated by Pitzer’s equation. By applying this model, the equilibrium concentrations of solutes were calculated from the concentration of zinc and pH . The extracted metal species was ZnHA3 and extraction equilibrium constant was found to have a value of 9.77×10−2 from the slope of the equilibrium extraction data. The predicted distribution coefficients of zinc were in good agreement with experimental results.

  • Nanometer-Size Polycrystallization in bcc→hcp+C15 Structural Change of a Ti-30 mol%Cr Alloy

    Akihiko Hirata, Makoto Tanimura, Yasumasa Koyama

    pp. 2553-2558

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    DOI:10.2320/matertrans.42.2553

    Abstract

    The crystallographic features of a bcc→hcp+C15 structural change in a Ti–30 mol%Cr alloy have been examined by transmission electron microscopy. When the alloy was annealed at 873 K below the eutectoid temperature, the structural change occurred in the following five steps: bcc→bcc+Zone I→bcc+Zone II→bcc+Zone II+hcp→bcc+hcp+C15→hcp+C15. The interesting features of the change are that the diffuse ω state is present in the metastable bcc matrix, and that in the fourth step the C15 grains with a size of about 2 nm appear in the bcc matrix around the hcp region. As a result of these extremely small C15 grains, the final microstructure, which was obtained from the 5-h-and 100-h-annealed samples, consists of the hcp and C15 grains with an average size of about 100 nm. On the basis of these results, the physical origin of the nm-size polycrystallization in the appearance of the C15 phase is discussed in relation to both the presence of diffuse ω state in the metastable bcc matrix and the formation of the complex coordinated polyhedra in the C15 structure.

  • Effect of Joining Compressive Stress on Solid State Bonding of Graphite to Nickel

    Hidekazu Sueyoshi, Tomoyuki Nishida

    pp. 2559-2566

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    DOI:10.2320/matertrans.42.2559

    Abstract

    Graphite was bonded to nickel in a vacuum using an RF-induction furnace with temperature, keeping time and joining compressive stress as variables. The bending strength of graphite/nickel joints, the changes of microstructure and hardness of nickel near the interface were investigated. Thermal stress induced in the joints was estimated by means of finite element analysis. On the basis of these results, the influences of joining compressive stress on bonding were examined. Joining compressive stress and joining temperature are important factors for close contact and strong bonding between the joining surfaces of graphite and nickel. At a high joining temperature, nickel is plastically deformed even under low joining compressive stress so that full contact and strong bonding are accomplished. At a low joining temperature, strong bonding was not achieved when joining compressive stress is low, because plastic deformation of nickel is restrained. The plastic deformation of nickel plays an important role in enabling good contact and strong bonding. The strength of the joints increased with joining compressive stress. The plastic deformation of nickel near the joining interface increases with the joining compressive stress so that graphite is elastically deformed during annealing. Therefore, compressive stress is retained on the graphite surface near the joining interface. Thermal tensile stress induced on the graphite surface after cooling is relaxed by this compressive stress.

  • A Kinetic Study on the Fe-Zn-P Coatings by Electrodeposition

    Jong-Gwan Ahn, Jae-Woo Ahn, Man-Seung Lee

    pp. 2567-2571

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    DOI:10.2320/matertrans.42.2567

    Abstract

    A kinetic study on the electrodeposition of Fe–Zn–P ternary alloys onto steel in chloride solutions was carried out using a rotating disc geometry. Mass transfer through diffusion layer controlled the deposition rates of zinc onto steel, and those of iron and phosphorus were controlled by the rates of both electrochemical reaction and mass transfer. The zinc content in the Fe–Zn–P alloy increased with stirring speed and voltage. However, iron content in the Fe–Zn–P alloy decreased with speed and voltage. The phosphorus content is almost constant with respect to stirring speed in the lower voltage range but decreased slightly with stirring speed in the higher voltage range.

  • Preparation and Magnetic Properties of Co-based Bulk Glassy Alloys

    Hisato Koshiba, Akihisa Inoue

    pp. 2572-2575

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    DOI:10.2320/matertrans.42.2572

    Abstract

    This paper deals with the formation and soft magnetic properties of Co(Fe)-M-B (M=transition Metals) glassy alloys in thin sheet and bulk ring forms prepared by single role melt spinning and copper mold casting methods. This multicomponent system was found to exhibit a distinct glass transition and a wide supercooled liquid region (ΔTx) exceeding 70 K before crystallization. The high thermal stability of the supercooled liquid has enabled us to produce the bulk glassy alloys. The Co–Fe–Ta–B alloy samples with a ring form of φ7 mm×φ3 mm×t1 mm consist of a single glassy phase. These bulk amorphous samples exhibit excellent soft magnetic properties, which are nearly the same as those of the corresponding melt-spun glassy thin sheets: the coercivity (Hc) and saturation magnetic flux density (Bs) are 0.25 A/m and 0.49 T, respectively. These good soft magnetic properties suggest structural homogeneity resulting from its high glass-forming ability. The excellent soft magnetic properties are useful for industrial application.

  • Morphology and Crystallography of β-Mg2Si Precipitation in Al-Mg-Si Alloys

    Yasuya Ohmori, Long Chau Doan, Yoshitsugu Matsuura, Sengo Kobayashi, Kiyomichi Nakai

    pp. 2576-2583

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    DOI:10.2320/matertrans.42.2576

    Abstract

    The exothermic reaction occurring after β′′ precipitation in Al–Mg–Si alloys has been investigated by means of differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). The reaction peak height observed in DSC increases with increasing excess Mg or decreasing excess Si content from Al–Mg2Si quasi-binary composition. It was confirmed that this reaction peak arises from the precipitation of cuboid β-Mg2Si particles related to the matrix with the cube-cube orientation relationship. At the later stage of ageing, thin β-Mg2Si plates nucleate at the cuboid β-phase particles. The orientation relationship of them is rotated 45° or 18.4° in the further aged specimens about the direction normal to the {001}Al||{001}β habit plane from the cube-cube relationship. The changes in morphology and the crystallography of the β-Mg2Si precipitates with the progress of ageing can be explained qualitatively in terms of coherency and interface energy of the precipitates.

  • Quality Improvement by Annealing for Flash-evaporated Thin InSb Films

    Md Abu Taher, Yumiko Haga, Yoshio Nakamura, Osamu Nittono

    pp. 2584-2589

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    DOI:10.2320/matertrans.42.2584

    Abstract

    Thin InSb films were prepared at room temperature by a rapid vacuum evaporation (flash evaporation) method using indium antimonide compound as a source material. The characteristics of the films such as microstructure and electrical properties were investigated in terms of heat treatment procedure. The as-deposited InSb films were found to have polycrystalline structure, and their stoichiometry was much better at higher deposition rates. Their characteristics were strongly influenced by successive annealing. The evaporation of Sb from the film caused by annealing led to poor electrical properties of the films. In order to avoid the evaporation of Sb from the film, an attempt was made to cap an as-deposited film with SiO2 layer before annealing. The microstructures as well as the galvanomagnetic properties were improved by introducing such capped-annealing. The highest Hall mobility of 2.1×104 cm2/Vs was obtained in an InSb film of 1.0 \\micron thick, when it was prepared with a deposition rate of 10 nm/s and followed by capped-annealing at 773 K.

  • Biocompatibility of Surface-Treated Pure Titanium and Ti-6Al-4V Alloy

    Byung Il Kim, Min Ho Lee, Woo Yong Chon, Dong Joo Yoon, Tae Sung Bae, Hyeoung Ho Park, Hyun Wook Cho

    pp. 2590-2596

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    DOI:10.2320/matertrans.42.2590

    Abstract

    In the present study, commercial purity Ti and Ti–6Al–4V alloy specimens with and without alkali- and heat-treatments were implanted in the abdominal connective tissue of mice. Conventional SUS 316L stainless steel was also implanted for comparison. After three months, their biocompatibility was evaluated by in vitro and in vivo experiments. When immersed in Hank’s solution, which has ion concentrations similar to that of human blood, an apatite layer, which accelerates the connection with bone, formed easily on the alkali-treated specimens compared to the non-treated specimens. The number of macrophages, which is known to increase as the inflammation reaction proceeds, is much lower for the alkali-treated specimens than for other samples. The average thickness of the fibrous capsule formed around the implant is much thinner for the alkali-treated specimens than for the others. These results show that the alkali- and heat-treatments performed in the present study will be very effective for the improvement of biocompatibility.

  • Surface Modification of SKD 61 during EDM with Metal Powder in the Dielectric

    Biing Hwa Yan, Yan Cherng Lin, Fuang Yuan Huang, Chen Hung Wang

    pp. 2597-2604

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    DOI:10.2320/matertrans.42.2597

    Abstract

    This study investigates the influence of process parameters of electrical discharge machining (EDM) on machining performances with the addition of Al and Cr powder into kerosene. In addition, the effects of powder addition on surface fine-finish and modification are also discussed. The machining process parameters of this empirical investigation included peak current, pulse duration, as well as the type of powder added, its grain size, and mixing ratio. The machining performance, characterized by material removal rate (MRR), electrode wear rate (EWR) and surface roughness, was monitored as a function of process variables. Moreover, surface modifications were also explored thoroughly. The experimental results demonstrate that addition of Al and Cr powders into the dielectric enlarges the gap distance and divides discharge current, which promotes better EDM performance. Restated, adding a mixture of Al and Cr powders into dielectric yields the best results. Moreover, during EDM, the added powder migrates and penetrates the machined surface. Test results reveal that the corrosion resistance and surface hardness was improved by adding the proper powder into dielectric.

  • A Simple Semi-empirical Method for Calculating Electronic Structures in Molecules and Amorphous Materials

    Shuji Obata

    pp. 2605-2612

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    DOI:10.2320/matertrans.42.2605

    Abstract

    A simple semi-empirical method is developed with a valence bond theory for calculating electronic structures, which is applicable for from molecules to condensed matters. Matrix elements in terms of the overlap integrals and the Hamiltonians are determined semi-empirically with a σ bond basis set. Molecular states are calculated using block matrix transformations based on the Green’s function theory. The bulk state calculations are performed by means of the clustered recursion method. The electronic structures in molecules CH4, C2H6, diamond like clusters and diamond are presented as examples, which are compared with ionization spectrum data. Complex number atomic orbitals obtained directly from the Schrödinger equations are handled for approximating effective interactions in valence bond systems.

  • Effect of Si Content on SiO2 Particle Erosion of Spheroidal Graphite Cast Iron

    Fei-Yi Hung, Li-Hui Chen, Truan-Sheng Lui

    pp. 2613-2621

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    DOI:10.2320/matertrans.42.2613

    Abstract

    The effect of Si content on SiO2 particle erosion wear of spheroidal graphite cast iron was studied. The present erosion tests were performed to provide an understanding of erosion wear resistance of spheroidal graphite (S.G.) cast iron, which is required for improving weather resistance by raising silicon content. An increased Si content promoted a decrease in the amount of the pearlite phase, thus decreasing the erosion resistance of as cast S.G. cast iron. An increased Si content hardens the ferrite phase, thereby improving the erosion resistance. The erosion rate of full pearlitic S.G. cast iron tends to increase as the Si content increases. The wear surface and subsurface morphologies which reflect the erosion wear process, an increase in erosion wear rate could be caused either by changes in the microstructure or by the variation of silicon content which almost did not alter the impact angle of maximum erosion rate of S.G. cast iron. It should be noted that the dominant factor on the erosion resistance was the presence of the pearlite structure in the materials despite the fact that the specimens may have different silicon contents.

  • Room-Temperature Magnetic Refrigerate System Gadolinium-Terbium-Neodynium

    Zhang Xiyan, Yang Ling, Zhou Shijie, Qi Linlin, Liu Zhinong

    pp. 2622-2624

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    DOI:10.2320/matertrans.42.2622

    Abstract

    A system of magnetic materials suited for a room temperature magneto-refrigeration, Gd–Tb–Nd, has been investigated. Samples were melted in an argon-protected high-frequency magnetic induction furnace. Magnetization curves were measured with a vibrating-sample magnetometer, in order to obtain the magnetic entropy change. Experimental results show that the Curie temperature (Tc) of the present system is near room temperature and decreases as the Tb and Nd contents increase. By addition of a small amount of Nd, the magnetic entropy change is comparable with that of Gd–Tb, and the transition temperature changes greatly. Therefore Nd can be used as a working temperature regulator. The Gd–Tb–Nd system is a prospect for realizing a large-scale room-temperature refrigeration in low magnetic fields.

  • Dependence of Corrosion Rate of Alumina-Chromia on Properties of Molten Slags

    Takehiko Hirata, Akio Deguchi, Satoshi Ohta, Tatsuo Morimoto, Minoru Ike, Nozomu Uchida

    pp. 2625-2629

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    DOI:10.2320/matertrans.42.2625

    Abstract

    Al2O3 based conventional ceramic materials used for incineration at power generation plants can be seriously corroded by molten oxide mixture. Therefore, it has been necessary to determine the ceramics component that makes Al2O3 based ceramics more stable in molten slag. We found that Cr2O3–Al2O3 based ceramic materials exhibited superior corrosion resistance in the molten slag even though their durability is still insufficient. The aim of this study is to develop a more stable ceramic material in molten oxides. The corrosion behavior of the candidate material Cr2O3–Al2O3 ceramics was investigated in detail in CaO–SiO2–B2O3 melts, especially as a function of the basicity and viscosity of the melt. The basicity and viscosity represent the chemical and physical properties of the oxide melt, respectively.

  • A Model for the Prediction of Reaction Diffusion Paths in Multicomponent Systems with Limited Solubility

    Bernard Hallemans, Patrick Wollants, Jozef R. Roos, Bart Blanpain

    pp. 2630-2636

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    DOI:10.2320/matertrans.42.2630

    Abstract

    A numerical method to compute the reaction diffusion process in multicomponent systems exhibiting limited solubility in their compounds has been developed. The method combines a description of local thermodynamic equilibrium at the moving interfaces with a phenomenological description of the diffusion process in every phase, taking their specific solubility features into account. There is no formal restrictions on the number of components or phases. The algorithm software can be used for the systematic study of the influence of different system variables such as free energies of formation and mobilities on the stable diffusion path, as well as for the prediction of the actual diffusion path in technologically important contacts. As an example calculations in a hypothetical ternary system are shown.

  • Icosahedral and Amorphous Phases in Melt-Spun Ti-Zr-Ni-Cu Alloys

    Limin Wang, Akihisa Inoue

    pp. 2637-2640

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    DOI:10.2320/matertrans.42.2637

    Abstract

    Structure of melt-spun Ti60Zr15Ni25−xCux (x=0, 5, 10, 15, 20 and 25) alloys and crystallization behavior of the amorphous alloys have been studied. The alloys have different structures depending on cooling rate. An icosahedral quasicrystal phase (I-phase) is formed directly upon cooling at a wheel velocity of 20 m/s for x=0–15, and at wheel velocities of 40 and 60 m/s for x=0. The high cooling rate at 60 m/s for x=5–25 causes the formation of a single amorphous phase. DSC traces of the amorphous alloys obtained during continuous heating to 1000 K showed distinct exothermic peaks. The first exothermic reaction at low temperatures for x=5, 10 and 15 is due to the precipitation of I-phase, and the following reactions at higher temperatures result from the formation of α-Ti and Ti2Ni or Ti2Cu phases. The simultaneous addition of Cu and Ni to Ti–Zr base alloys can enhance the forming ability of I-phase as well as amorphous phase.

  • Velocity of Sound in Liquid Simple Metals near the Melting Point

    Isao Yokoyama

    pp. 2641-2645

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    DOI:10.2320/matertrans.42.2641

    Abstract

    In this paper we report comparisons between theoretical and experimental values of the velocity of sound in twenty liquid simple metals near the melting point. We used three model theories, namely, (1) an improved Rosenfeld’s approach, (2) Ascarelli’s approach and (3) a modified Ascarelli’s approach. For alkali metals, the three model theories give much the same predictions in the velocity of sound. For polyvalent metals, electrons play an important role when the valency is increased. For noble metals, the degree of agreement between theory and experiment is improved by taking into account the effects of the ionic core due to the s-d hybridization.

  • Grain Morphology of Recrystallized Polycrystalline-Si Film by Excimer Laser Annealing

    Naoto Matsuo, Tomoyuki Nouda, Naoya Kawamoto, Ryouhei Taguchi, Yoshio Miyai, Hiroki Hamada

    pp. 2646-2648

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    DOI:10.2320/matertrans.42.2646

    Abstract

    Grain morphology of recrystallized polycrystalline(poly)-Si by excimer laser annealing (ELA) was investigated for both SiO2 (50 nm)/SiN (50 nm)/glass substrate and quartz substrate. The Raman peak of the poly-Si on the SiN substrate was shifted to the higher frequency side than that on the quartz substrate. The disk-shaped grains were observed on the quartz substrate, while they were not observed on the SiN substrate. The poly-Si grains with a uniform grain size were observed, and kept constant in a range of the present energy density and the shot number on the SiN substrate. To understand these phenomena, the crystal growth model relating to the concentration of hydrogen atoms in the film is discussed.

  • Electron Beam Welding of Zr-Based Bulk Metallic Glass to Crystalline Zr Metal

    Yoshihito Kawamura, Shinya Kagao, Yasuhide Ohno

    pp. 2649-2651

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    DOI:10.2320/matertrans.42.2649

    Abstract

    We have tried an electron-beam welding of a Zr-based bulk metallic glass plate to a polycrystalline Zr metal one for a Zr41Ti14Cu12Ni10Be23 (at%) bulk metallic glass having an excellent glass forming ability. We have succeeded in butt-welding the bulk metallic glass and pure Zr metal plates with a thickness of 3 mm. Invisible defect or clack was detected around the bead and heat-affected zone. The bulk metallic glass around the interface kept the amorphous state. Formation of any crystalline phases except for hcp-Zr was not detected in the interface. The interface of the successfully welded sample exhibited enough toughness and joining strength to endure the bending through 90 degrees by hammering.

  • Processing of Ductile Magnesium Alloy under Dynamic Tensile Loading

    Toshiji Mukai, Masashi Yamanoi, Kenji Higashi

    pp. 2652-2654

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    DOI:10.2320/matertrans.42.2652

    Abstract

    Polycrystalline magnesium generally fractures intergranuarly under dynamic loading, and exhibits limited ductility owing to its HCP structure. In this study, improvement of tensile mechanical properties under dynamic loading has been demonstrated for a commercial magnesium alloy of AZ31. A commercial AZ31 alloy was subjected to simple shear processing through ECAE (equal-channel-angular-extrusion) followed by annealing to develop a texture that differs from directly-extruded alloy. During the dynamic tensile test, elongation-to-failure was more than twice as high than that of the directly-extruded alloy. Inspection of the fracture surface on the dynamically deformed sample revealed that the ECAE processed alloy followed by annealing fractured with the development of ductile dimples and few macro cracks, which is often observed on the fracture surface of magnesium alloys.
  • © 2001 The Japan Institute of Metals and Materials

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