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

MATERIALS TRANSACTIONS Vol. 53 (2012), No. 3

  • New Growth Mechanism of Cubic Rh Clusters Composed of 8–12 Atoms Found by the Method of Euclidean Designs

    Makoto Tagami, Yunye Liang, Yoshiyuki Kawazoe, Motoko Kotani

    pp. 459-462

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    DOI:10.2320/matertrans.N-M2011859

    Abstract

    “Euclidean Design” a newly developed mathematical design theory has been used to reveal a heretofore hidden mechanism in the growth of cubic Rh clusters composed of eight to twelve atoms. This is the first application of this advanced mathematics to atomic cluster science as a powerful tool to optimize the geometrical structure. In the usual first principles calculation, initial structures have been given rather ad-hoc way by trial and error basis. The method proposed in the present paper is systematic and theoretically without any limitation on the number of atoms. For Rh clusters this report corrects the previously proposed structures [Y.-C. Bae, H. Osanai, V. Kumar and Y. Kawazoe: Phys. Rev. B 70 (2004) 195413], and shows that an eight atom cluster is a cube and that adding atoms on one side of the cubic cluster, growing to reach finally the two cube connected structure of a twelve atom Rh cluster.

  • Structure and Photocatalysis of TiO2/ZnO Double-Layer Film Prepared by Pulsed Laser Deposition

    Lei Zhao, Maosheng Xia, Yuhua Liu, Biju Zheng, Qing Jiang, Jianshe Lian

    pp. 463-468

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    DOI:10.2320/matertrans.M2011345

    Abstract

    Nanocrystalline double-layer film of TiO2/ZnO was prepared by pulsed laser deposition on quartz substrate and their microstructure, optical property and photocatalysis were investigated. The first/bottom ZnO layer grew on its [001] direction of the wurtzite structure, while the second/top TiO2 layer consisted of nanorods grown on the [001] direction of its anatase structure. The TiO2/ZnO film showed improved photo-absorption in visible light in the UV–visible absorption spectrum; and showed weaken UV emission and enhanced deep level emission in the photoluminescence spectrum. By the degradation of methyl orange and methylene blue, the TiO2/ZnO film exhibited evident enhanced photo-degradation efficiency in a wide wavelength range. That can be explained by the enhanced wavelength response in visible range, more effective use of irradiation light and the retarded recombination of electron–hole pairs in the double layer films.

  • Effects of Strain Rate and Temperature on Shear Properties and Fracture Characteristics of 316L Stainless Steel

    Woei-Shyan Lee, Tao-Hsing Chen, Chi-Feng Lin, Zong-Yun Li

    pp. 469-476

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    DOI:10.2320/matertrans.M2011274

    Abstract

    The dynamic shear deformation behaviour and fracture characteristics of 316L stainless steel are investigated using a split-Hopkinson torsional bar system at temperatures of −150, 25 and 300°C and strain rates ranging from 1000 to 3000 s−1. The results show that the flow stress, shear fracture strain, work hardening rate, and strain rate sensitivity all increase with increasing strain rate for a given temperature, but decrease with increasing temperature given a constant strain rate. The activation energy decreases with increasing shear stress for a constant shear strain, but increases with increasing shear strain given a constant shear stress. Optical microscopy observations reveal that localized plastic flows occur in the shear deformation region. Moreover, the flow angle increases with increasing strain rate and temperature. Scanning electron microscopy observations show that the fracture surfaces are characterized by a dimple-like structure, which indicates a ductile failure mode. The morphology and density of the dimple-like structures are highly sensitive to the strain rate and temperature conditions. Overall, the microstructural observations show that the shear response of 316L stainless steel is directly related to the effects of the strain rate and temperature on the evolution of the sheared microstructure.

  • Use of Chlorine to Remove Magnesium from Molten Aluminum

    Estéfano Aparecido Vieira, Jose Roberto de Oliveira, Gianni Ferreira Alves, Denise Crocce Romano Espinosa, Jorge Alberto Soares Tenório

    pp. 477-482

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    DOI:10.2320/matertrans.M2011256

    Abstract

    Removal of Mg from aluminum scraps, known as demagging, has been widely applied in the aluminum industry. This work discusses bubble-formation theories and magnesium kinetic removal from aluminum scraps using chlorine and inert gas fluxing. The interfacial area of the bubbles and residence time were estimated using a mathematical model. To inject gaseous chlorine, three types of nozzles were used with varying internal diameter. In addition, a porous plug, as well as varying input chlorine flow and concentration were used. The use of lower chlorine concentration improves efficiency because the interfacial tension is reduced therefore, more and smaller bubbles are formed. The model proposed herein is consistent with the experimental data.

  • Compression Behavior of Entrapped Gas in High Pressure Diecasting

    Yasushi Iwata, Shuxin Dong, Yoshio Sugiyama, Hiroaki Iwahori

    pp. 483-488

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    DOI:10.2320/matertrans.F-M2011858

    Abstract

    Die castings generally contain a large quantity of porosities due to the entrapment of air or gas in molten metal during mold filling. Although the entrapped air or gas is compressed by high casting pressure during pressurization, it will eventually remain in the castings as defects after solidification. Therefore, it is important to clarify the relation between the volume of gas defects and the pressure applied to the molten metal so as to optimize the casting design.
    In this study, we investigated the compression behavior of entrapped gas during casting. We determined the volume of gas defects and gas content in die castings by density measurement and vacuum fusion extraction method respectively. Then we calculated the gas pressure in the defects from the above volume of defects and gas content, and compared with the die casting pressure. The calculated gas pressure in the defects was found to be not equal to the die casting pressure, but equal to the pressure of the molten metal just before it dropped abruptly due to the complete blocking of the liquid metal channel by solidification. From the experimental results, the behavior of the entrapped gas can be inferred as follows. Immediately after the mold was filled with molten metal, the entrapped gas was instantly compressed. After that, the pressure of molten metal decreased gradually with the progress of solidification of the molten metal channel, and the volume of entrapped gas increased correspondingly until the pressure of the molten metal dropped abruptly. Then the volume of the entrapped gas showed a slight expansion equal to the solidification shrinkage of the enclosed molten metal.
    The above inference was verified by measuring the volume of the entrapped gas defects in castings made with intentional depressurization carried out at the time when mold filling just finished or halfway through the solidification of the molten metal channel.

  • Metal Surface Modification with Vibration-Aided Micro-Forging

    Yang Bai, Kenji Nishikawa, Ming Yang

    pp. 489-494

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    DOI:10.2320/matertrans.M2011254

    Abstract

    A vibration-aided micro-forging was performed on various metallic foils under different conditions to obtain a reliable surface that has low surface roughness values. When micro-forged it with vibration under proper experimental conditions, the surface roughness value was found to be decreased by more than 70%. However, no so significant improvement on the surface roughness can be obtained without vibration. Based on this experimental study, the surface asperities variation was approximately proportional to the forming energy W, which increases the ability of dislocations to overcome the forming resistance in micro-forging.

  • Continuous Casting of Magnesium Alloy Sheet Using Semisolid Slurry

    Futoshi Kido, Tetsuichi Motegi

    pp. 495-499

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    DOI:10.2320/matertrans.M2011252

    Abstract

    In our semisolid casting method, magnesium alloy slurry was made using an inclined cooling plate instead of electromagnetic or mechanical stirring during solidification. The semisolid slurry was fed into a twin-roll caster and continuously cast into 2 to 3 mm thick sheets with a maximum width of 200 mm. The microstructures of the sheets contained refined and globular primary crystals. The most important factors are casting temperature and twin-roll speed that influences sheet casting. The sheet obtained by this process was examined for roll workability, hardness, and Erichsen value. The results were excellent; thus, the casting sheet is suitable for deep drawing.

  • Effect of Minor Sn Additions on the Formation and Properties of TiCuZrPd Bulk Glassy Alloy

    Shengli Zhu, Guoqiang Xie, Fengxiang Qin, Xinmin Wang, Akihisa Inoue

    pp. 500-503

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    DOI:10.2320/matertrans.M2011281

    Abstract

    The minor addition is fundamental to controlling the formation, manufacture and properties of metallic materials by controlling nucleation during solidification. In the present work, we investigated the effect of minor addition of Sn on glass-forming ability, thermal stability and mechanical property of TiZrCuPd bulk glassy alloy system. The substitution of Cu by 2% Sn improves the glass-forming ability significantly. The Ti40Zr10Cu34Pd14Sn2 bulk glassy alloy rod with a diameter of 12 mm was fabricated by copper mold casting. The Ti40Zr10Cu34Pd14Sn2 bulk glassy alloy exhibits higher energy for crystallization activation (334.3 kJ/mol). The addition of 2–4% Sn can enlarge the supercooled liquid region, indicating good thermal stability. TiZrCuPdSn bulk glassy alloys exhibit high compressive strength about 2000–2050 MPa.

  • Effects of High Pressure Heat Treatment on Microstructure and Micro-Mechanical Properties of Cu77.96Al22.04 Alloy

    Lailei Wu, Lin Liu, Jianhua Liu, Ruijun Zhang

    pp. 504-507

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    DOI:10.2320/matertrans.M2011296

    Abstract

    The hardness, elastic modulus, and friction coefficient of the Cu77.96Al22.04 alloy before and after treatment at 750°C and 5 GPa for 15 min were measured by nanoindenter. Effects of high pressure heat treatment on its micromechanical properties were discussed. The results show that high pressure heat treatment can refine the microstructures of the Cu77.96Al22.04 alloy, increase its hardness and elastic recovery rate, and decrease its friction coefficient. It also shows that high pressure treatment has little effect on the elastic modulus. As a result, the deformation resistance and the anti-indentation creep of the alloy are improved effectively.

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  • Formation of Amorphous TiO2 Film on Ti Using Anodizing in Concentrated H3PO4 Aqueous Solution and Its Osteoconductivity

    Dai Yamamoto, Takanori Iida, Kensuke Kuroda, Ryoichi Ichino, Masazumi Okido, Azusa Seki

    pp. 508-512

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    DOI:10.2320/matertrans.M2011234

    Abstract

    Anodizing of Ti specimens were performed in concentrated H3PO4 aqueous solutions with a purpose to incorporate a large amount of phosphate ion into anodized coatings, and their osteoconductivity was evaluated in in vivo test. Ti specimens were anodized in 0.1–11 M H3PO4 aqueous solutions up to 200 V at a rate of 0.1 V s−1. Anodized coatings were evaluated with SEM, TEM, XRD, XPS, and laser microscope. Anodized specimens were implanted in rats’ tibia for 14 d, and then extracted.
    When anodized in concentrated (≥2 M) H3PO4 aqueous solutions under spark discharge, crystallized anatase transformed to amorphous anatase by containing a large amount of PO43− in crystal lattice of TiO2. The amorphous anatase coatings had better osteoconductivity than the crystallized anatase coatings. It is not exactly clear what was the intrinsic factor for the high osteoconductivity, but the crystallinity of anatase and/or PO43− in the film is considered to be responsible for the difference in bone-forming ability of TiO2 films.

  • Hydrogenation Properties of Ternary Intermetallic Compounds Mg2−xPrxNi4

    N. Terashita, K. Sakaki, S. Tsunokake, Y. Nakamura, E. Akiba

    pp. 513-517

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    DOI:10.2320/matertrans.M2011334

    Abstract

    Ternary intermetallic compounds, Mg2−xPrxNi4 (0.6 ≤ x ≤ 1.4) were synthesized by induction melting and investigated with respect to hydrogenation properties and structural changes. These compounds have a cubic C15b-type Laves structure (space group F-43m), where Mg and Pr have an ordered arrangement. The lattice parameters increased from a = 0.70101(3) nm to a = 0.71726(8) nm with increase of the Pr content. Mg1.4Pr0.6Ni4 and Mg1.2Pr0.8Ni4 absorbed and desorbed hydrogen up to ∼0.7 H/M reversibly through one plateau in the p-c isotherms. The stoichiometric MgPrNi4 showed two plateaus and its maximum hydrogen content reached to ∼1.0 H/M at 35 MPa. The enthalpy changes of hydrides formation of Mg1.4Pr0.6Ni4 and Mg1.2Pr0.8Ni4 were estimated to be −39.2 and −40.3 kJ/mol H2 respectively. The enthalpy changes of hydrides formation of MgPrNi4 at the lower and higher plateaus were estimated to be −42.4 and −19.6 kJ/mol H2 respectively. The metal sublattice of hydrides Mg1.4Pr0.6Ni4H∼4 and Mg1.2Pr0.8Ni4H∼4 had cubic ordered C15b-type Laves structure same as the crystal structure before hydrogenation while hydride at the lower plateau of the stoichiometric MgPrNi4 had an orthorhombic structure. The hydrogenation of Mg0.8Pr1.2Ni4 and Mg0.6Pr1.4Ni4 led to amorphization.

  • Pin-On-Disc Wear of Precipitation Hardened Titanium–Copper Alloys Fabricated by Powder Metallurgy

    Tachai Luangvaranunt, Patchara Pripanapong

    pp. 518-523

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    DOI:10.2320/matertrans.M2011293

    Abstract

    Titanium–2 mass%Cu and Ti–10 mass%Cu alloys were fabricated by powder metallurgy. The alloys were precipitation hardened to observe effect of heat treatment to their wear property. It was found that hardness of the two alloys increased after solution treatment to 320 and 526 HV, and after aging to 441 and 612 HV. However, wear resistance, as characterized by friction coefficient and mass loss in a pin-on-disc wear test deteriorated. In term of wear resistance, a lamellar morphology of eutectoid αTi/Ti2Cu was favorable to the homogenized morphology of heat treated alloys. Lowest specific wear rate was found in as-sintered Ti–10 mass%Cu, having a value of 1.16 × 10−13 m3/N·m.

  • Preparation of Nanoporous Ruthenium Catalyst and Its CO Oxidation Characteristics

    Masataka Hakamada, Junichi Motomura, Fumi Hirashima, Mamoru Mabuchi

    pp. 524-530

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    DOI:10.2320/matertrans.M2011326

    Abstract

    Anodic polarization measurements for various ruthenium (Ru) alloys revealed that hexagonal close-packed nanoporous Ru (np-Ru) can be fabricated by dealloying or selective dissolution of manganese (Mn) from Ru–Mn alloy. The pore size and specific surface area of fabricated np-Ru were 3 nm and 51.5 m2 g−1, respectively. An electron diffraction pattern suggested a polycrystalline nature of the fabricated np-Ru, which is perhaps due to the change in the crystal structure during dealloying. The oxidation of carbon monoxide (CO) was efficiently catalyzed by the np-Ru. The activation energy was 82 kJ mol−1 which is comparable to that of the polycrystalline RuO2/Ru catalyst. The present np-Ru is a novel candidate as a recoverable Ru catalyst.

  • Fabrication of Ultrafine-Grained Ti66Nb18Cu6.4Ni6.1Al3.5 Composites with High Strength and Distinct Plasticity by Spark Plasma Sintering and Crystallization of Amorphous Phase

    Weiping Chen, Xuemei Wu, Chao Yang, Xiaoqiang Li, Mindan Chen, Yuanyuan Li

    pp. 531-536

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    DOI:10.2320/matertrans.MD201110

    Abstract

    Ductile ultrafine-grained composites in Ti66Nb18Cu6.4Ni6.1Al3.5 alloy with high Nb/Ti ratio were fabricated by spark plasma sintering and crystallization of amorphous phase. Microstructure observations shows that all alloys encompass body-centered cubic β-Ti and face-centered cubic (Cu, Ni)-Ti2 regions but display different microstructures. The alloys exhibit a high fracture strength as high as 2365 MPa as well as distinct fracture strain of ∼7.6%. The results obtained provide a promising method for fabrication of two-phase composites with good combination of strength and ductility by powder metallurgy.

  • Crystal Grain Morphology Evolution over Ti, V, Nb and Ta Surface Heated in N2 Gas Environment to 2000°C by Filtered Concentrated Solar Beam in a Solar Furnace at PROMES-CNRS

    Fernando Almeida Costa Oliveira, Luís Guerra Rosa, Gilles Peraudeau, Bernard Granier, Jorge Cruz Fernandes, Teresa Magalhães, Nobumitsu Shohoji

    pp. 537-545

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    DOI:10.2320/matertrans.M2011299

    Abstract

    In recent attempts of reacting d-group transition metals with N2 gas under irradiation of concentrated solar beam at temperatures around 2000°C using a standard setup with graphite specimen holder, reaction products obtained were carbo-nitrides rather than targeted nitrides on account of yield of C2 radical plume from the graphite crucible. To suppress the interference of C2 radical possessing high carbon chemical activity a(C) in nitriding d-group transition elements in solar furnace, we investigated effectiveness of inserting colour filters in the solar beam path. Two readily available colour filters, Sky blue and Medium yellow filters, were tested for this purpose. As reported in our earlier publications, XRD (X-ray diffraction) phase identification results indicated that insertion of the Sky blue filter was effective for suppressing C2 radical yield under solar beam radiation to synthesize carbo-nitride with comparatively high N content. On the other hand, insertion of the Medium yellow filter did not result in so remarkable effect for suppressing carburization as the one detected with the Sky blue filter. In the present work, aspects of microstructures developed for Ti, V, Nb and Ta surfaces heated to 2000°C under exposure to colour-filtered solar beam in N2 gas environment are reviewed. The present experimental evidences indicated that, by insertion of the Sky blue filter, appreciable crystallite grain size refinement was realized for the synthesized M(C,N) with high N content while, by insertion of the Medium yellow filter, certain extent of influence on the morphological development, that varied depending on the substrate material, was unmistakably discernible.

  • Influence of Dislocation Separation on Dynamic Strain Aging in a Fe–Mn–C Austenitic Steel

    Motomichi Koyama, Takahiro Sawaguchi, Kaneaki Tsuzaki

    pp. 546-552

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    DOI:10.2320/matertrans.M2011342

    Abstract

    The influences of deformation temperature and strain rate on the serrated flow behavior of a Fe–17Mn–0.3C alloy with a low stacking fault energy were investigated by the tensile tests in a temperature range of 273 to 523 K. Three regions were found when the deformation temperature was plotted against the critical strains for the onset of serrations. The critical strain decreased in the region of 273 to 323 K, increased in that of 323 to 423 K, and decreased again in that of 423 to 523 K with increasing temperature. The first two regions are well known. However, the third region corresponding to that of high temperature has not been reported, and this region could be interpreted by separately considering the interactions of solute atoms with leading and trailing partials. Since the velocity of the leading partials is assumed to be significantly higher than that of the trailing partials, the critical strains in the first and third regions were concluded to result from trapping the trailing partials and the leading partials, respectively.

  • Effects of Grafting Densities of Comb-Like Copolymer on the Dispersion Properties of Concentrated Cement Suspensions

    Jiaping Liu, Qianping Ran, Changwen Miao, Min Qiao

    pp. 553-558

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    DOI:10.2320/matertrans.M2011344

    Abstract

    Effects of grafting densities of comb-like copolymer on the dispersion properties of concentrated cement suspensions are investigated systemicly in this paper. For comb-like copolymers the adsorbed amount increases at the same dosages as the grafting density decreases, while the efficiency of dispersion is improved by increasing the grafting densities. Based on the theory of Flatt at level of scaling law, the molecule size and the occupied surface area of the comb-like polymers with different grafting densities are calculated. The comb-like polymers with higher grafting density has bigger molecular size. For comb-like polymer dispersant, the steric repulsion provided by the side chains is the main drive of the dispersion, so the Flory energy is employed to explore the relationship between steric repulsion and grafting density. The calculation tells us that higher grafting density results in higher Flory energy which represents stronger steric repulsion. The calculation method based on the scaling law and Flory theory is successfully used to interpret the dispersion mechanism, and it is anticipated that this method can be applied to explain the effect of other parameters of PCE comb-like polymers on the dispersion properties of cement suspensions, ceramics suspensions, slurries and so on.

  • Formation of Black Ceramic Layer on Aluminum Alloy by Plasma Electrolytic Oxidation in Electrolyte Containing Na2WO4

    I. J. Hwang, K. R. Shin, J. S. Lee, Y. G. Ko, D. H. Shin

    pp. 559-564

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    DOI:10.2320/matertrans.M2011263

    Abstract

    The formation of black ceramic layer produced by plasma electrolytic oxidation (PEO) coating has been investigated as a function of coating time. A series of PEO coatings was carried out on aluminum alloy sample in a phosphate electrolyte containing sodium tungstate (Na2WO4) with four different coating times, i.e., 20, 100, 200 and 300 s. As the coating time increased, the amount of tungsten element in the ceramic layer increased, resulting in the black ceramic layer. This phenomenon was discussed based on the electrochemical reaction assisted by micro sparks to form WO3 compounds in the ceramic oxide layer.

  • Bone Loss and Reduced Bone Quality of the Human Femur after Total Hip Arthroplasty under Stress-Shielding Effects by Titanium-Based Implant

    Yoshihiro Noyama, Takuya Miura, Takuya Ishimoto, Takahiro Itaya, Mitsuo Niinomi, Takayoshi Nakano

    pp. 565-570

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    DOI:10.2320/matertrans.M2011358

    Abstract

    The present work was aimed at clarifying the stress-shielding effect caused by hip-joint implantation into a femur by using a human cadaver with a cementless hip implant. In particular, bone quality was assessed from the standpoint of preferential c-axis orientation of biological apatite (BAp). Comparing the implanted side to the non-implanted side, a finite element analysis (FEA) indicated that artificial hip-joint implantation had a significant stress-shielding effect on the femur. The results also showed a marked decrease in the degree of preferential BAp orientation as well as bone loss in the medial-proximal femur. This is the first report showing a reduction in the degree of preferential BAp orientation due to a stress-shielding effect after artificial hip-joint implantation. Since preferential BAp orientation is an important index for determining bone mechanical function, these findings should be taken into account in future artificial hip-joint designs, especially those involving the stem component.

  • Characteristics of Thin-Film-Transistors Based on Zn–In–Sn–O Thin Films Prepared by Co-Sputtering System

    K. J. Chen, F. Y. Hung, T. S. Lui, S. J. Chang, T. Y. Liao

    pp. 571-574

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    DOI:10.2320/matertrans.M2011347

    Abstract

    This study presents the growth of ZITO film by co-sputtering system. By adjusting the chemical composition and electrical properties of ZITO, an amorphous ZITO (a-ZITO) matrix with a semiconducting character was used to apply in active layer for thin-film transistors (TFTs) device. The proposed a-ZITO channel layer with SiNx dielectric layer exhibited depletion mode operation. The device exhibited a subthreshold swing (SS) of 1.65 V/dec, a field-effect mobility (μFE) of 2.57 cm2 V−1 s−1, and an on/off current ratio (Ion/Ioff) of 104. The small SS and an acceptable μFE were associated with a smaller roughness and stable composition of ZITO channel layer.

  • Diffusion of Tl Ions into Glass Treated by Molten Salt Ion Exchange and Hydrogen Reduction

    Mikito Ueda, Hajime Matsunaga, Toshiaki Ohtsuka, Toshiharu Yamashita

    pp. 575-577

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    DOI:10.2320/matertrans.M2011343

    Abstract

    To investigate the diffusion behavior of Tl ions, glass was immersed in TlNO3–KNO3 molten salt at 753 K for various lengths of time. The Tl ions embedded in the glass were then reduced to metallic Tl nano-particles by hydrogen at 803 K for 1 h. The depth of the ion exchange layer down to about 140 µm in the glass was found to be proportional to a square root of the length of immersion time. It was suggested that the ion exchange process is controlled by the diffusion of Tl ions from the surface to the inside. Reduction of Tl ions to metallic Tl with the hydrogen gas occurred only at the surface down to 4 µm. The concentration profile of the metallic Tl is discussed by nucleation-nucleus growth and the diffusion of Tl ions from deeper areas.

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  • Characteristics of Graphene-Filled Solderable Isotropically Conductive Adhesive (ICA)

    Byung-Seung Yim, Seung-Hoon Oh, Jiwon Kim, Jooheon Kim, Jong-Min Kim

    pp. 578-581

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    DOI:10.2320/matertrans.M2011365

    Abstract

    A new class of functionalized graphene-filled solderable isotropically conductive adhesive (ICA) has been developed using a low-melting-point alloy (LMPA) fillers. The mechanical and electrical characteristics of formulated ICAs were investigated and compared with those of three kinds of conventional ICAs filled with Ag particles. The functionalized graphene-filled solderable ICA formed good metallurgical interconnection between upper and corresponding lower electrode. The developed ICA exhibit lower electrical resistance and higher mechanical strength compared with those of conventional ICAs. In addition, the thermal conductivity was improved about 20% by adding functionalized graphene compared with that of solderable ICA without graphene.

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  • © 2012 The Japan Institute of Metals and Materials

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