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

MATERIALS TRANSACTIONS Vol. 48 (2007), No. 12

  • Recent Ecomaterial Developments and Environmental Achievements of Major Industries in Japan

    pp. 3036-3042

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    DOI:10.2320/matertrans.MK200706

    The research was made on how ecomaterials have been developed and are used currently in Japan. All the information was obtained from the web-sites 2001–2005 year version environmental reports of over two hundred and sixty companies mainly with more than 5000 employees and listed on Japanese stock markets. The researched ecomaterials were classified into the six categories proposed by Japanese “Ecomaterials Forum”. The number of ecomaterials nearly doubled between 2001 and 2003, and has been on the yearly increase ever since. Each industry is considered to have its individual problems to tackle and has developed its peculiar ecomaterials in response to such problems and requirements year by year. Moreover, many remarkable achievements in eco-products, eco-systems and ecological techniques utilizing ecomaterials are proudly shown in the environmental reports. The spread of these ecomaterials and eco-products will be quite effective for the saving of energy and also contribute greatly to the improvement of environment. Meanwhile, given the use of a large quantity of resources in these days, it is necessary for us to pay attention to and conduct researches into environmental problems including preventive measures against exhaustion of rare resources from a broader perspective and a bird’s-eye view approaches.
  • Eco-MCPS: a Newly Developed Web-Based Database for Eco-Materials in Japan

    pp. 3043-3049

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    DOI:10.2320/matertrans.MK200710

    A novel Web-based database on eco-materials was constructed by the database subcommittee of Ecomaterial Forum. Enquiries were made to companies to obtain about 800 product data, and the data were organized into the Web-based database- “Eco-M·C·P·S” (more simply denoted as Eco-MCPS), which was implemented by PostgreSQL (RDBS) and PHP (server side script). Eco-materials and related products can be searched by the product category or the environmental category. Some products are indexed by key categories, and are related with each other by the key, which makes the products comparable or associated with other products. The products or companies can be searched in the search page by typing in case-sensitive free keywords, such as “RoHS”, and the search can be refined by adding product categories or environmental categories. Searches can be made for eco-labeled products. Association rules which may reflect social interest level on ecomaterials were found by data mining the access log data of the database.
  • Proposal of Index of Cyclic Material Use in Green Environmental Profiles

    pp. 3050-3055

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    DOI:10.2320/matertrans.MK200711

    The author has developed a method for evaluating green environmental profiles. In the definition of eco-efficiency, the factors responsible for any kind of environmental burden were clarified. The eight evaluation criteria - new processes to eliminate emissions of hazardous substances; greenhouse gases; environmental emission in the atmosphere, water, and soil; industrial water; exhaust heat; and final disposal - can be used to evaluate each environmental burden. Emission targets were also specified in order to measure their achievements. The evaluation criteria include DfE (Design for Environment) support information for manufacturing, recycling, and disposal processes in the eco-efficiency equation. Achievement in every criterion is classified using an evaluation sheet developed for the purpose.
  • Thermal Treatment of Municipal Sewage Sludge Aiming at Marketable P-Fertilisers

    pp. 3056-3061

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    DOI:10.2320/matertrans.MK200707

    Municipal sewage sludge is a carrier of nutrients – most important phosphorus (P) – but also contains organic pollutants and heavy metals. A two steps thermal treatment is suggested based on 1. mono-incineration of sewage sludge under destruction of organic pollutants and 2. thermochemical treatment of the resulting ashes to remove heavy metals and increase P-bioavailability. The targeted products are marketable P-fertilisers. The thermochemical treatment was investigated in a gas tight lab-scale rotary furnace. Seven sewage sludge ashes of different origin and composition and one residue from gasification of sewage sludge were mixed with a chlorine donor (e.g. MgCl2) and thermochemically treated under systematic variation of operational parameters. The distributions of the heavy metals between solid and gas phase were determined. The heavy metals concentrations of the treated ashes met the legislative limits in most cases. The products from thermochemical treatment are suited raw materials for P-fertiliser production. Relevant process parameters such as temperature, type and concentration of Cl-donor and retention time were optimised for the thermochemical treatment step.
  • Unburned Carbon Behavior in Sintered Coal Fly-Ash Bulk Material by Spark Plasma Sintering

    pp. 3062-3065

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    DOI:10.2320/matertrans.MK200702

    Coal fly-ash bulk materials were prepared by spark plasma sintering (SPS). The as-received coal fly ash produced by Misumi Power Station (The Chugoku Electric Power Co., Inc.), had an average particle size of 19 μm and contained about 2% carbon from unburned coal. The sintering temperature was 1000°C for 10 min. The mass density of the sintered compact was 2.4×103 kg/m3. After three-point flexural testing of the compact, the average flexural strength and Young’s modulus were 25.6 MPa and 23.0 GPa, respectively. From the flexural strength, the Weibull modulus was found to be m=6.13, indicating that the compact was a typical ceramics. Fractographic examination indicated that in all specimens the fracture origin was located on the bottom surface and was not an intrinsic flaw. Vickers indentation test showed that the fracture toughness was 0.61 MPa·m0.5 and the calculated critical flaw size, c0, was 0.18 mm. This c0 value was larger than that of the voids and unburned carbon on the fracture surface. It is noteworthy that the mechanical strength of the sintered compact was not affected by the voids and unburned carbon.
  • Sintering Properties of Functionally Graded Materials Using Coal Fly Ash and NiCr-Based Alloy Powder

    pp. 3066-3069

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    DOI:10.2320/matertrans.MK200703

    Functionally graded materials (FGMs) were prepared by spark plasma sintering using coal fly ash and NiCr alloy powder. The coal fly ash was produced by Misumi coal thermal power station (Chugoku Electric Power Co., Inc.), and 80 mass% nickel and 20 mass% chromium (Fukuda Metal Foil & Powder Co., Ltd) were used as source materials. The sintering was done at 1000°C in a graphite die. X-ray diffraction patterns of the sintered coal fly ash materials indicated that the mullite (3Al2O3·2SiO2) and silica (SiO2) phases were predominant. Direct joining of coal fly ash and NiCr causes a fracture at the interface due to a mismatch of thermal expansion. Cracks in the FGMs were observed between the two layers when the difference of linear thermal expansion coefficient (α) was over 4.2×10−6 K−1, while no cracks were detected in stable FGMs when the difference was less than 4.0×10−6 K−1.
  • Stabilization of Mine Waste Using Paper Sludge Ash under Laboratory Condition

    pp. 3070-3078

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    DOI:10.2320/matertrans.MK200705

    The leaching of potentially toxic elements or the generation of acidity from mine waste often creates significant environmental pollution. A great deal of research has been undertaken to find an effective solution to the problem of acid mine drainage. An attractive solution has been proposed, not only efficient but also economical, as it uses another waste material. The objective of this study was to investigate the feasibility of stabilizing acidic mine waste using alkaline industrial waste, paper sludge ash, produced by the pulp and paper industry, under laboratory conditions. By mixing mine waste with paper sludge ash (the weight ratio of mine waste to paper sludge ash is 10: 4), the eluted solution became neutral, and the concentrations of almost all metals dropped below the Japanese effluent standard. The inhibition of acid mine drainage with addition of PSA is sustainable. Although Radish sprouts did not grow on mine waste, they could be grown on the waste mixed with paper sludge ash. These results suggest that it is possible to use paper sludge ash for afforestation of a mine waste site.
  • Interaction between Phosphorus Micro-Segregation and Sulfide Precipitation in Rapidly Solidified Steel—Utilization of Impurity Elements in Scrap Steel

    pp. 3079-3087

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    DOI:10.2320/matertrans.MK200704

    Copper is one of the main residual elements in steel, especially in recycled scrap steel. Sulfur and phosphorus are two of the main impurities in steel, and it may result in a large emission of slag and CO2 to remove them from steel. Utilization of these elements has been an important and difficult matter for metallurgist. In the present paper, the as-cast steels containing different concentrations of copper, sulfur and phosphorus are prepared by strip casting process or laboratory rapid solidification process. The effect of phosphorus addition on sulfide precipitation is investigated and discussed with respect to the morphology, size, and composition of sulfide. Both experimental results and mathematical calculation showed that the addition of phosphorus retards the sulfide precipitation at high temperature, promotes more copper bearings and smaller sulfides precipitation at low temperature. On the other hand, sulfide precipitates are shown to reduce the micro-segregation degree of phosphorus in steel, which may be because some phosphorus dissolves in sulfide and sulfide particles provide more interfaces for phosphorus to distribute.
  • Effects of Thermo-Mechanical Treatment on the Tensile and Compressive Properties of a Glass-Balloon-Dispersed Aluminum Alloy Composite

    pp. 3088-3094

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    DOI:10.2320/matertrans.MK200712

    A repeated thermomechanical treatment (RTMT) was adopted to control the microstructure of a glass-balloon-dispersed aluminum alloy (AC3A) composite. The RTMT, which involves the repetition of a multi-step process and followed by heat treatment, was applied to a cast plate of the composite. The composite was successfully worked into a rod or sheet by either swaging or flat rolling. The porous glass balloons were deformed or cracked so that the composite could be worked easily. The swaged material exhibited higher tensile strength, Young’s modulus, and elongation as compared to the cast material. The composite materials also exhibited excellent energy absorption properties.
  • Process Parameters Optimization in Preparing High-Purity Amorphous Silica Originated from Rice Husks

    pp. 3095-3100

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    DOI:10.2320/matertrans.MK200715

    Rice husk, one of the main agricultural disposals in Japan, China, India, and South-east Asian countries, is employed as useful renewable resources to produce energy and high-purity silica (SiO2), because it consists of 70% organics and about 20% SiO2. The latter, SiO2 is obtained by burning rice husks in air. The purity of rice husk ashes, however, is reduced by the remains of both carbon contents originated in organics and original metallic impurities such as K, Na, Ca, P, Al, etc. In the previous works, the utilization of the leaching methods by strong acids with a high concentration for both the remove the metallic impurities and the fragmentation of silica structural network was suggested. As their results, the thermal resolution mechanism of organics was discussed by using TGA showing the mass loss behavior during heating. The objective in this study is to clarify the mechanism of the removal of organic components when applying a dilute H2SO4 leaching treatment with 1∼5% solution concentration. In particular, from a viewpoint of the investigation on molecule structural changes of organics, GCMS (Gas Chromatograph Mass Spectrometer) analysis is carried out on acid-leached rice husks. When using only 1% concentration H2SO4 solution leaching, a change of cellulose of polysaccharides to levoglucosan via glucose of monosaccharide by hydrolysis and condensation reactions occurred. This reaction accompanied with dehydration always served en endothermic heat, which was found in DTA profile of acid leached rice husk materials. It was also clarified that such a low concentration H2SO4 solution was enough to remove alkali metal elements contained in husks. By optimizing the combustion temperature of rice husks after acid leaching, completely amorphous silica ashes, composing of 99.3% SiO2 and 0.04% carbon, were obtained.
  • Corrosion Protection of AZ91D Magnesium Alloy by Anodization Using Phosphate Electrolyte

    pp. 3101-3108

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    DOI:10.2320/matertrans.L-MRA2007881

    Mechanism of corrosion protection obtained by anodization for die-cast plates of ASTM AZ91D (Mg-9 mass%Al-0.7Zn) magnesium alloy has been studied. Anodization was conducted by conventional Dow17 which utilizes chromium oxide (VI), ammonium fluoride and phosphoric acid, and by environment-friendly Anomag whose electrolyte consists of phosphate and ammonium salt. The anodized surface obtained in Dow17 showed local corrosion in salt spray test (SST) after ∼500 ks to form corrosion products consisting of magnesium hydroxides. On the other hand, the surface anodized in Anomag was covered with amorphous film, showed only discoloring in SST and corrosion product was scarcely observed. When the anodized surfaces were trenched with ceramic knife to form locally exposed substrate, corrosion product was formed on the trench in the case of Dow17, but corrosion was well suppressed by formation of new type of protective film in the case of Anomag. Anodic polarization curves indicate that the surface anodized in Dow17 is protected by passive substances through which electrolyte can easily reach the substrate, and that in Anomag show sacrificial function where the anodized layer dissolves quite slowly into the electrolyte prior to the substrate. The excellent corrosion protectivity obtained in Anomag is considered to be based on the formation of a new type of protective film as well as sacrificial function of the original amorphous anodized layer.
  • Heat Capacity of La1−XSrXFeO3−δ from 2 K to 1340 K

    pp. 3109-3117

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    DOI:10.2320/matertrans.MRA2007146

    Isobaric heat capacities, Cp, of LaXSr1−XFeO3−δ solid solutions from near absolute zero Kelvin (2 K) to high temperature (1340 K) were measured by a relaxation method and differential scanning calorimetry. Also, their Debye temperatures, ΘD, were determined from the measured Cp values below 10 K and isochoric heat capacities, CV, were calculated by inserting the ΘD values into Debye functions, followed by calculating the isochoric entropies of vibration, Δ0TSV. From the measured Cp values, it was found that oxygen vacancy (VO••) formed by a self-compensating reaction by doping of Sr′La decreased the onset temperatures of the magnetic and structure phase transitions, broadening the temperature ranges of such phase transitions. The entropies of vibration of oxygen vacancy, ΔfSTVvib.(VO••), estimated by differentiation of Δ0TSV with the VO•• content at 298 K and 800 K were 58.65 J·K−1·mol−1 and 64.59 J·K−1·mol−1, respectively. Such a large ΔfSTVvib.(VO••) appears to be one of important reason for foming VO••.
  • Environmentally Friendly Composite Film of Anodizing and Electrodeposition Coating Having a High Corrosion Resistance on Magnesium Alloy AZ91D

    pp. 3118-3125

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    DOI:10.2320/matertrans.MRA2006632

    In this study, we compared and examined the corrosion resistance of the magnesium alloy with the composite film of 2 kinds of coating on 3 kinds of surface treated film as the substrate treatment. 3 kinds of surface treated film stands for conventional DOW17 anodized film (DAF), chemical conversion treatment JISA3-type MX3 film (CCF), which contain hexavalent chromium, fluorine and phosphorus compounds, and environmentally friendly silicate anodized film (SAF) containing no hazardous substances and 2 kinds of coating stands for organic coating and electrodeposion coating. As a result of the analysis, we could observe that it was extremely effective for magnesium alloy AZ91D to apply the composite film of environmentally friendly SAF with cationic electrodeposition coatings to obtain superior corrosion resistance to that of the composite film of conventional DAF or CCF with organic spray coating. At the same time we could take an action for the environment countermeasure by using the environmentally friendly SAF with the water base cationic electrodeposition coatings as a countermeasure for VOC (Volatile Organic Compound) regulations.
  • Unusual Wetting of Liquid Bismuth on a Surface-Porous Copper Substrate Fabricated by Oxidation-Reduction Process

    pp. 3126-3131

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    DOI:10.2320/matertrans.MRA2007179

    The unusual wetting phenomenon of liquid Bi on surface-porous copper has been studied. A porous layer was prepared at the surface of a copper substrate and the wetting behavior of liquid Bi on this layer was investigated and compared with that on a flat solid copper substrate. A surface-oxidized copper substrate was reduced at 473 K in H2 to prepare a porous layer at the surface. Since the contact angle of liquid Bi on the flat solid copper substrate was gradually declining with increasing temperature, the behavior of liquid Bi on solid copper was shown to have good-wettability. In addition, the unusual wetting behavior of liquid Bi was observed on surface-porous copper substrate. This result is evidence that the pores in the porous layer are 3-dimensionally inter-connected. This usual wetting phenomenon of liquid Bi was then applied in the joining of copper wire with the surface-porous copper substrate. Bonding was successfully achieved with a minimized weld overlay at the joining point.
  • Reduction Kinetics and Mechanisms of NiFe2O4 with Synthesis of Nanocrystalline Fe-Ni Alloy

    pp. 3132-3139

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    DOI:10.2320/matertrans.MRA2007191

    Nickel ferrite (NiFe2O4) powder was prepared through the ceramic route by calcination of a stoichiometric mixture of nickel oxide and iron oxide. The produced powders of NiFe2O4 were isothermally reduced in pure hydrogen at 800–1100°C. Based on thermogravimetric analysis, the reduction behavior of nickel ferrite and the kinetics reaction mechanism were studied. The initial ferrite powder and the various reduction products were characterized by XRD, SEM, TEM and reflected light microscope to reveal the effect of hydrogen reduction on composition and microstructure of produced Ferronickel alloy. Microstructure of partially and completely reduced samples was studied and the activation energy values were calculated from Arrhenius equation. The approved mathematical formulations for the gas solid reaction were applied and it was found that the reaction is controlled by the combined gaseous diffusion and interfacial chemical reaction mechanisms at both of the initial and the final reaction stages. Complete reduction of NiFe2O4 was almost achieved with 95.5–100% reduction extent at 800–1100°C respectively. The FCC Fe(0.7−0.64)-Ni(0.3−0.36) alloy was synthesized with nanocrystalline size ranged from 24 nm at 800°C to 16.1 nm at 1100°C respectively.
  • Feasibility of Friction Stir Welding for Joining and Microstructure Refinement in a ZK60 Magnesium Alloy

    pp. 3140-3148

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    DOI:10.2320/matertrans.MRA2007177

    Feasibility of FSW to produce defect-free welds and for microstructure refinement in a ZK60 magnesium alloy has been examined over wide ranges of rotational and welding speeds. The results showed that joined-state was affected very much by the thickness of plates to be joined: for “thin” 3-mm thick plates, FSW was successful in a relatively wide range of welding conditions, whereas all “thick” 6-mm welds were found to be defective irrespective of rotational and welding speeds used. We have demonstrated that FSW is a very effective tool for microstructure refinement in the ZK60 alloy plates: A coarse, mm-scale, original grain structure was efficiently refined down to fine-grained range. It appears that second-phase particles containing Zr play an important role in the grain refinement.
  • Preparation of Hydroxyapatite and Calcium Phosphate Films by MOCVD

    pp. 3149-3153

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    DOI:10.2320/matertrans.MRA2007145

    Ca-P-O films were prepared by MOCVD using Ca(dpm)2 and (C6H5O)3PO precursors. The crystal phase changed with changing deposition conditions of substrate temperature (Tsub), total pressure (Ptot) and molar ratio of Ca and P precursors (RCa/P). α-tricalcium phosphate (α-Ca3(PO4)2) in a single phase was obtained at Tsub=973 K, RCa/P<0.3 and Tsub=1073 K, RCa/P=0.1 to 0.5. Hydroxyapatite (Ca10(PO4)6(OH)2) in a single phase was first prepared by MOCVD at Tsub=973 K, RCa/P=0.5 and Tsub=1073 K, RCa/P=0.8 to 1. The maximum deposition rate of α-TCP and HAp films in a single phase were 6.0 and 4.0 nm s−1 at Ptot=0.8 kPa and Tsub=1073 K, respectively.
  • Thermodynamic and Magnetic Properties of Pd0.93Ag0.07 Hydride

    pp. 3154-3159

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    DOI:10.2320/matertrans.MRA2007150

    Thermodynamic and magnetic properties of the Pd0.93Ag0.07 hydrides were measured. The isotherms of Pd0.93Ag0.07 -H and -D systems in the temperature range 373–523 K showed the plateau regions to be within 0.05 < [Q (Q=H or D)]/[Pd0.93Ag0.07] < 0.4. From an investigation of the thermodynamic isotope effect for the formation and decomposition of hydride, the enthalpy changes, ΔH°β→α, for desorption of hydrogen and deuterium were evaluated to be 43.0 kJ/molH2 and 36.4 kJ/molD2, respectively. It was observed that the magnetization of Pd0.93Ag0.07Hx at ambient temperature increased with increasing magnetic field. Since the magnetization was not saturated up to 7 T, it can be concluded that Pd0.93Ag0.07Hx is paramagnetic. The magnetic susceptibility of Pd0.93Ag0.07Hx progressively decreased with increasing hydrogen content and vanished at [H]/[Pd0.93Ag0.07] = 0.4. The disappearance of the susceptibility coincided with the termination of the plateau region of the isotherms. This fact can be explained by the rigid band model, according to which the vacant part of d-band of Pd0.93Ag0.07 can accept electrons from absorbed hydrogen atoms.
  • Effects of Ag Addition on Microstructure and Thermoelectric Properties of NaxCo2O4 Synthesized by Citric Acid Complex Process

    pp. 3160-3163

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    DOI:10.2320/matertrans.MRA2007171

    A thermoelectric NaxCo2O4/Ag composite was synthesized by citric acid complex process using CH3COOAg as an Ag source. The powder precursor after calcination was composed of plate-like NaxCo2O4 grains and Ag particles. The Ag addition deteriorated crystallographic anisotropy of the sintered body. However, the electrical resistivity and the Seebeck coefficient of this composite were significantly smaller and slightly larger, respectively, than those of the sample without Ag, resulting in lager power factor. The Ag phase dispersed in the NaxCo2O4 matrix contained about 5–17 at.% Co, which is considered to cause the increase in Seebeck coefficient.
  • Enhancement of Biocompatibility on Bioactive Ti-Nb-Based Alloy by High-Density Plasma Modification

    pp. 3164-3169

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    DOI:10.2320/matertrans.MER2007160

    The formations and characteristics of oxides on the surfaces of the plasma-treated Ti-Nb-Hf alloys were investigated by employing X-ray photoelectron spectroscopy, X-ray powder diffractometer and scanning electron microscopy. Further, the non-treated and plasma-treated specimens were incubated in phosphate-buffered saline (PBS) containing albumin to evaluate their biocompatibility. The results indicate that through O2-plasma treatment, the thickness of the oxide layer increases, and the surface roughness improves, exhibiting little protuberances and numerous micropores and cavities on the treated surface. The compositions of the oxide layers in the specimen without O2-plasma treatment consist of TiO, Ti2O3 and TiO2, and the oxides transform to mainly TiO2 as the specimen is treated with O2-plasma. In addition, the formation of nitrides by allylamine plasma treatment can provide amino-group linkings for the attachment of albumin. Plasma oxidation and polymerization are believed to improve biocompatibility and therefore promote osseointegration.
  • Hydrogen Absorption Performance of Mechanically Alloyed (Mg2Ni)100−xTix Powder

    pp. 3170-3175

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    DOI:10.2320/matertrans.MER2007169

    The hydrogen storage alloy (Mg2Ni)100−xTix (x=0, 2.5, 5.0, 7.5 and 10.0 at%) powders were synthesized from elemental powder mixture by mechanical alloying (MA) under an Ar atmosphere. The as-milled powders were examined as a function of titanium addition by X-ray diffraction and synchrotron X-ray absorption near-edge structure (XANES) techniques at various milling time. The hydrogen absorption kinetics of the 15 h as-milled powders were evaluated. The maximum hydrogen absorption content of 15 h as-milled Mg2Ni powders can be improved from 3.14 mass% to 3.88 mass% when 5.0 at% of titanium was added. The hydrogenation rate of the Mg2Ni powder was also obviously enhanced by introducing the titanium into Mg2Ni lattices. More than 20% improvement of hydrogen absorption for Mg2Ni intermetallic powders was achieved by adding titanium.
  • Viscous Flow Workability of Ni-Cr-P-B Metallic Glasses Produced by Melt-Spinning in Air

    pp. 3176-3180

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    DOI:10.2320/matertrans.MER2007624

    We prepared the Ni80−xCrxP16B4 (x=3, 6, 9, 12, 15, 18, 21, 24, 27 and 30 at%) alloy ingots in an Ar flow atmosphere and then produced the alloy ribbons by melt-spinning. The thermal stability was examined and the alloy composition was optimized.
    A supercooled liquid state was observed in the alloys with Cr contents above 9 at% and the Tg and Tx increased with increasing Cr content. There is a tendency for ΔTx to increase with increasing Cr content up to 18 at%. The largest ΔTx is about 45 K and remains almost unchanged in the Cr content range above 15 at%. The groove-forming tests were performed for the alloy with optimized compositions. The Ni65Cr15P16B4 glassy alloy was heated up to Tg and was deformed by hot-pressing with dies in the supercooled liquid state. The alloy possessed a single glassy phase and the thermal stability parameters, Tg, Tx and ΔTx of the alloy did not change even after the hot-pressing. Thus, the Ni-based glassy alloy was not thermally affected by the hot-pressing treatment in the present experimental condition. Finally, we successfully produced the metallic glassy separator for Proton Exchange Membrane Fuel Cell (PEMFC) by hot-pressing in the supercooled liquid state.
  • Diagnosis and Analysis of Oxide Films in Cast Magnesium Alloys by Ultrasonic-Vibration Treatment

    pp. 3181-3189

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    DOI:10.2320/matertrans.MER2007213

    Magnesium alloys with low density are important light metals, widely used in the aerospace and automotive industries and in the manufacture of communication devices, consumer-electronics appliances and computers products in recent years. However magnesium and magnesium alloys are the most reactive metals so that oxide films easily form on them during the melting or pouring process. These films are difficult to observe by optical micrograph. In this study we propose a simple method to observe oxide films entrapped in cast magnesium alloys. The oxide films are fractured as a result of cavitation erosion on the sample surface that occurs during ultrasonic-vibration treatment. The eroded areas become visible as differently shaped foggy marks. This method of observing and identifying foggy marks is shown to be useful in the diagnosis of oxide films in cast magnesium alloys. In addition, the presented method in the diagnosis of oxide films that formed on magnesium and aluminum alloys are also compared.
  • Production of Zr55Cu30Ni5Al10 Glassy Alloy Rod of 30 mm in Diameter by a Cap-Cast Technique

    pp. 3190-3192

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    DOI:10.2320/matertrans.MRP2007164

    In order to produce bulk glassy alloys with diameters above 1 cm, various cast techniques have been developed. The maximum diameter of Zr55Cu30Ni5Al10 alloy achieved was 16 mm by the copper metallic mold cast technique and 20 mm by the tilt cast technique. In order to produce a much larger sized bulk glassy alloy, a cap-cast technique, leading to the achievement of a higher cooling rate even in an upper region, was developed through the modification of the tilt casting technique. This paper presents the production of a glassy Zr55Cu30Ni5Al10 alloy rod with a diameter of 30 mm.
  • High Specific Strength and Improved Ductility of Bulk (Mg0.65Cu0.25Gd0.1)100−xTix Metallic Glass Composites

    pp. 3193-3196

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    DOI:10.2320/matertrans.MRP2007181

    The monolithic Mg65Cu25Gd10 bulk metallic glass always shows brittle fracture with a plastic strain of near zero even under a compressive load. Improved ductility and enhanced compressive strength were simultaneously achieved at room temperature in (Mg0.65Cu0.25Gd0.1)100−xTix (x=0, 2.5, 5 and 7.5 at%) metallic glass composites. The compressive strength (σf) reached 940 MPa, and a plastic strain (εp) of about 0.8% was undergone for the bulk metallic glass composite at x=5. The glass composites were formed by doping Mg65Cu25Gd10 bulk metallic glass with adequate lightweight titanium with a density near that of Mg65Cu25Gd10 bulk metallic glass. The composite sustains the features of lightweight and very high specific strength which are the same as those of the Mg-based bulk metallic glass. Thus, the addition of Ti does not cause distinctly harmful influence on the glass-formation ability of the matrix glass.
  • Evaluation of Electric Properties for Niobium Capacitors

    pp. 3197-3200

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    DOI:10.2320/matertrans.MRP2007619

    In order to evaluate the applicability of niobium powder, which was manufactured by the external continuous supply method, as a capacitor, the present study measured capacitor performance evaluation factors such as leakage current, permittivity loss (tanδ), capacitance, impedance, equivalent series resistance, etc.
    Capacitance decreased significantly from 156 μF in electrolyte (wet cap) to 130 μF after carbon (C)/silver (Ag) solution coating, and around 105 μF after aging, falling within the capacity tolerance of tantalum capacitors. If capacitance was converted to CV/g, it was around 81,000 CV/g. Permittivity loss (tanδ) decreased significantly from 12.9% after C/Ag coating to 7.7% after aging, satisfying the general standard level of 10% or less. Leakage current was 2.41 μA after C/Ag coating and 2.93 μA after aging, both less than the standard level of 6.3 μA. As a whole, the niobium capacitor showed somewhat more unstable characteristics than commercial tantalum capacitors but can be considered applicable as a substitute for tantalum capacitors in the future.

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