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

MATERIALS TRANSACTIONS Vol. 53 (2012), No. 12

  • Influence of Crystallographic Orientation on Fatigue Reliability of β-Sn and β-Sn Micro-Joint

    Yoshiharu Kariya, Sho Tajima, Saori Yamada

    pp. 2067-2071

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    DOI:10.2320/matertrans.MB201204

    Abstract

    Crystallographic anisotropy of static mechanical characteristics and fatigue reliability of β-Sn single crystal was investigated in this study. The static mechanical properties of β-Sn strongly depend on crystallographic orientation and yield stress is extremely high in the [001] orientation compared with other orientations. The low cycle fatigue life of β-Sn also exhibits remarkable orientation dependence and the life of β-Sn can be predicted by inelastic strain energy density regardless of crystallographic orientation. The finite element analysis based on these experimental data revealed that the thermal fatigue lives of BGA joints, in the case of β-Sn single crystal, differ remarkably as the inelastic strain energy density produced per cycle differs in conjunction with the difference in crystallographic orientation.

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  • Effect of Strain-Enhanced Microstructural Coarsening on the Cyclic Strain-Hardening Exponent of Sn–Ag–Cu Joints

    Yoshihiko Kanda, Yoshiharu Kariya, Takeshi Tasaka

    pp. 2072-2077

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    DOI:10.2320/matertrans.MB201205

    Abstract

    The effects of temperature and strain-enhanced coarsening of intermetallic compounds (IMCs) on the cyclic strain-hardening exponent of Sn–Ag–Cu microsolder joints were investigated. The effect of temperature on the exponent is described by the Arrhenius function, and the cyclic strain-hardening exponent is proportional to the reciprocal square root of the average radius of the IMCs. Ag3Sn and Cu6Sn5 IMCs coarsened with time, temperature, and inelastic strain. In the growth process with time and temperature, the phase-size exponent and activation energy for a Sn–Ag–Cu microsolder joint were ∼3 and 50 kJ/mol, respectively. Ag3Sn and Cu6Sn5 growth with isothermal aging was controlled by the diffusion of Ag and Cu in the Sn matrix. In addition, the strain-enhanced coarsening of the IMCs can be described by the growth model with consideration of isothermal aging and inelastic strain-enhanced growth. Therefore, the cyclic strain-hardening exponent decreases with temperature, and the strain-enhanced coarsening of IMCs can be described by the reciprocal square root of the average radius of the IMCs and the strain-enhanced growth model.

  • Effect of Crystal Orientation on Sn Whisker-Free Sn–Ag–Cu Plating

    Yukiko Mizuguchi, Yosuke Murakami, Shigetaka Tomiya, Tadashi Asai, Tomoya Kiga, Katsuaki Suganuma

    pp. 2078-2084

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    DOI:10.2320/matertrans.MB201202

    Abstract

    Mechanically induced Sn whiskers are a serious problem in the electronics industry because they can cause electrical short circuits in narrow gaps between electrodes such as fine pitch connector pins. The authors tried to prevent the formation of them by using one of the typical Pb-free solder materials, Sn–Ag–Cu alloy, as a plating material on connector pins. It was found that reflowed Sn–Ag–Cu plating was whisker-free even under mechanical stress. Scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) analyses revealed that Sn grains of reflowed Sn–Ag–Cu plating were extremely larger than those of whisker-prone pure Sn or Sn–Cu platings that have columnar structures. The notable feature was no obvious microstructural changes in reflowed Sn–Ag–Cu plating even after applying mechanical stress for 38 days. The present study demonstrates that reflowed Sn–Ag–Cu plating is one of the best candidates as whisker-free plating.

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  • Interfacial Bonding Behavior between Silver Nanoparticles and Gold Substrate Using Molecular Dynamics Simulation

    Tomo Ogura, Masumi Nishimura, Hiroaki Tatsumi, Wataru Takahara, Akio Hirose

    pp. 2085-2090

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    DOI:10.2320/matertrans.MB201201

    Abstract

    Molecular dynamics (MD) simulation was applied to the sintering behavior of silver nanoparticles on a gold substrate in order to elucidate the sintering mechanism of the nanoparticles on the substrate. The simulation revealed that silver atoms from 1 and 2 nm nanoparticles migrated freely because of their larger surface energy and then epitaxially reoriented to the gold substrate so as to reduce grain boundary energy. The silver nanoparticles were more spread out on the (011) gold substrate than on the (001) substrate, indicating that substrates with larger surface energy induce greater spreading rates. Consideration of the competition of neck growth and epitaxial growth in sintering of nanoparticles revealed that reduction of surface energy is the predominant driving force in the initiation of sintering of silver nanoparticles, and that the reduction of grain boundary energy is subsequently consequential.

  • Interface Structure of Cu Wire Bonding on Cu Substrate with Sn Plating

    Shinichi Fujiwara, Reinhold H. Dauskardt

    pp. 2091-2096

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    DOI:10.2320/matertrans.MB201203

    Abstract

    In previous research on copper wire bonding on a copper substrate with tin plating, suitable thickness and binding conditions for the tin plating were chosen using the peel test after the copper wire bonding. These conditions were determined to be a thickness of 10 microns, a stage temperature of 373 K, a bonding power of 500 to 700 mW and a bonding time of 30 to 50 ms. Cross-sectional observations of the bonding interface indicated that the tin layer remained between the copper wire and copper substrate after bonding under these conditions. The purpose of the present study was to evaluate the joint interface structure of the bonded copper wire on the copper substrate with the tin plating. Residual Sn exists locally at the initial bonding interface, and the locations bonded to the interstitial Sn are intermixed with the locations where the Cu wire is bonded to a Cu–Sn intermetallic compound. No oxide film layer was found at the bonding interface in the joint between the Cu wire and Cu–Sn intermetallic compound; TEM images indicated that these have metallic bonding in which Cu and Cu3Sn are directly bonded. This is in contrast to ultrasonic bonding between Cu and Sn, wherein the Cu and Sn are bonded by means of the Sn oxide film.

  • Properties Investigation on Chip-on-Film (COF) Thermosonic Bonding Using Anisotropic Conductive Films (ACFs)

    Jin Sik Jeong, Byung-Seung Yim, Seung Hoon Oh, Hojin Song, Byung Hun Lee, Jong-Min Kim

    pp. 2097-2103

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    DOI:10.2320/matertrans.MB201210

    Abstract

    Chip-on-film (COF) technology has been developed for liquid crystal displays (LCD) due to its high yield capability in fine pitch products. In this study, a new COF thermosonic (TS) bonding process using anisotropic conductive adhesive and ultrasonic vibrations will be introduced. Si chips with 16 cylindrical Cu bumps (ϕ100 µm) and polyimide (PI) film substrate with a thickness of 70 µm were prepared. For the bonding condition, the bonding temperature and ultrasonic time were varied from 413 to 453 K and from 0.5 to 1 s, respectively. Also, thermocompression (TC) bonding was conducted with a bonding temperature of 453 K and bonding time of 8 s to compare it to the bonding characteristics of TS bonding. The shear strength and electrical resistance of COF assemblies were measured to verify the feasibility of COF TS bonding using ACFs. The cross-sectional inspection and fracture surface analysis of COF joints were also conducted using field-emission scanning electron microscopy (FE-SEM). As a result, the mechanical and electrical properties of the COF assembly were improved by increasing the bonding temperature and ultrasonic dwell time. It was also determined that ultrasonic energy has a significant influence in improving the mechanical and electrical properties of the TS COF assembly.

  • Reliability Properties of Solderable Conductive Adhesives with Low-Melting-Point Alloy Fillers

    Byung-Seung Yim, Jeong Il Lee, Yuseon Heo, Jooheon Kim, Seong Hyuk Lee, Young-Eui Shin, Jong-Min Kim

    pp. 2104-2110

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    DOI:10.2320/matertrans.MB201207

    Abstract

    A solderable conductive adhesive (SCA) using low-melting-point alloy (LMPA) filler was developed to overcome the limitations of conventional electrically conductive adhesives (ECAs), which include their low electrical conductivity, increased contact resistance, and low joint strength. The SCA formed good metallurgical conduction path between the corresponding electrodes due to the rheology-coalescence-wetting behaviors of molten LMPA fillers in SCA. This study examined the reliability of SCA assembly through the thermal shock test (218 to 398 K, 1000 cycles) and the high temperature and high humidity test (358 K/85%RH, 1000 h). The electrical resistance of the SCA assembly with metallurgical interconnections was much more stable than those with conventional ICAs. Before the reliability tests, a scallop-type Cu6Sn5 (η-phase) intermetallic compound (IMC) layer was formed on the Sn-plated Cu lead/LMPA and LMPA/Cu metallization interface based on the results of interfacial microstructure observations of quad flat packages (QFPs) that were assembled with SCA. After the reliability tests, the thickness of IMC layer increased with time, and Cu6Sn5 (η-phase) and Cu3Sn (ε-phase) were formed. In addition, the fracture surface exhibited a cleavage fracture mode with the fracture propagating along the Cu–Sn IMC/Sn–Bi interface. These results demonstrate that SCA assembly with metallurgical interconnection has stable electrical and mechanical bonding characteristics.

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  • Diffusion of Al and Al-Substituting Elements in Ni3Al at Elevated Temperatures

    Md. Moniruzzaman, Hiroaki Fukaya, Yoshinori Murata, Katsushi Tanaka, Haruyuki Inui

    pp. 2111-2118

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    DOI:10.2320/matertrans.M2012218

    Abstract

    Diffusion of Ti, V, Nb, Mo and Ta in Ni3Al phase was investigated at different temperatures using Ni–Al–X (X = Ti, V, Nb, Mo, Ta) pseudo-binary diffusion couples. The magnitude of the interdiffusion coefficients was in the descending order of V, Mo, Ti, Nb and Ta at all experimental temperatures ranging from 1423 to 1573 K. Diffusion data obtained in this study was compared with those of Re and Ru available in the literature as Re and Ru are recently being added in modern Ni-based superalloys. Diffusion retardation occurred for Ti, V, Nb, Mo and Ta as compared to Ru, and this can be explained by the anti-site diffusion mechanism. The high activation energy for anti-site formation is required for β-site (Al-site) elements, such as Ti, V, Nb, Mo and Ta. However, as Ru can diffuse either by α- (Ni-site) or β-site preferences without creating local disorder, Ru diffusion is not retarded by the anti-site diffusion mechanism.

  • Wear Behaviour of Squeeze-Cast Al 2014 Alloy and In-Situ 5 vol% TiB2/2014 Composite

    J. Xue, J. Wang, Y. F. Han, B. D. Sun

    pp. 2119-2128

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    DOI:10.2320/matertrans.M2012179

    Abstract

    Dry sliding wear behaviour of gravity-cast and squeeze-cast Al 2014 alloys and in-situ 5 vol% TiB2/2014 composites has been studied. Squeeze casting at different pressures has been performed on the alloy and composite. Wear tests carried out at loads of 9.8–58.8 N on a pin-on-disc machine show that both the squeeze-cast alloy and composite are more wear resistant than their gravity-cast samples. For the squeeze-cast alloys, the sample solidified at a squeeze pressure of 60 MPa shows the least wear rate. However, in the case of the squeeze-cast composites, the wear resistance of the sample solidified at a squeeze pressure of 120 MPa is the best. The wear rates decrease with increasing hardness. A detailed SEM study of wear surface and debris is carried out to substantiate the wear results. The results indicate that the improvement in wear resistance for the squeeze-cast alloy and composite is mainly attributed to the increase in hardness and reduction in casting defects such as gas porosities and shrinkage porosities. In addition, for the squeeze-cast composite, the effect of improved dispersion of TiB2 particles on the wear resistance is also discussed.

  • Effects of Copper Addition on the Precipitation of Chromium Nitrides and the Associated Pitting Corrosion Resistance of the Hyper Duplex Stainless Steels

    Soon-Hyeok Jeon, Soon-Tae Kim, Jin-Seung Kim, Ji-Soo Kim, Kwang-Tae Kim, Yong-Soo Park

    pp. 2129-2134

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    DOI:10.2320/matertrans.M2012277

    Abstract

    To elucidate the effects of copper addition on the precipitation of chromium nitrides and the associated pitting corrosion of the hyper duplex stainless steels, a potentiodynamic test, a scanning electron microscope analysis and thermodynamic calculation were conducted. Copper addition to the base alloy facilitates the precipitation of chromium nitride and stabilizes it at elevated temperatures due to the increase of activity of Cr. With aging the alloy at 1293 K, copper added alloy reduces the resistance to pitting corrosion due to the precipitation of deleterious chromium nitrides compared with that of the base alloy. Experimental results are in good agreement with thermodynamic calculations of elemental activity and the driving force for the precipitation of chromium nitrides.

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  • Synthesis and Characterization of NiO Nanoparticles by Sol–Gel Method

    Lay Gaik Teoh, Kun-Dar Li

    pp. 2135-2140

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    DOI:10.2320/matertrans.M2012244

    Abstract

    Due to the outstanding electrical, magnetic and catalytic properties, nickel oxide (NiO) has been received considerable attention during the past decades. In this study, NiO nanoparticles were prepared by sol–gel method, which is one of the simplest and lowest-cost techniques. The synthesis was accomplished by using Poly(alkylene oxide) block copolymer as the surfactant, and Ni(NO3)2·6H2O as the inorganic precursor. The effect of experimental parameters, such as calcination temperatures and H2O concentration on the NiO nanoparticles formation were investigated. TGA, XRD, SEM, TEM and N2 adsorption–desorption isotherms were used to characterize the microstructure and specific surface area of the samples. TGA and FTIR analyses demonstrated that copolymers were expelled at 573 K. The formation of NiO nanoparticles and their structural features were greatly dependent on the calcination temperature. The sample calcined at 923 K was composed of pure NiO nanoparticles as shown by XRD. As H2O concentration was increased, the reoxidation process of metallic Ni to form NiO would reduce, but it would not affect the structural type of NiO nanoparticles. In general, the addition of water would weaken and inhibit oxidation effects. The temperature of stable metallic Ni was increased up to 823 K. The specific surface area evaluated from the N2 adsorption–desorption indicated that the samples consisting of non-porous NiO nanoparticles. Increasing H2O addition resulted in an increase of specific surface area of nanocrystalline NiO powder.

  • Preparation of Niobium Disilicide Coating by Heating Niobium in a Sodium–Silicon Melt

    Takahiro Yamada, Hiroto Sato, Hisanori Yamane

    pp. 2141-2144

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    DOI:10.2320/matertrans.MAW201213

    Abstract

    A Niobium disilicide (NbSi2) layer was formed at the surface of Nb plates by heating those plates with Si powder and a piece of Na at 1000–1200 K for 1–48 h. The thickness of the NbSi2 layer increased to 129 µm with increasing temperature and in proportion to the square root of the heating time. The activation energy of the NbSi2 layer formation evaluated from the Arrhenius plot of parabolic growth constants was 160 kJ mol−1. NbSi2-coated Nb plates retained their shapes after heating at 1100–1700 K for 10 h in air. Oxidation of the inner Nb of the plates was prevented.

  • Effects of Re Content and Fabrication Process on Microstructural Changes and Hardening in Neutron Irradiated Tungsten

    Makoto Fukuda, Takashi Tanno, Shuhei Nogami, Akira Hasegawa

    pp. 2145-2150

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    DOI:10.2320/matertrans.MBW201110

    Abstract

    The effects of the material fabrication process and rhenium (Re) content on the irradiation-induced changes in the microstructure and hardness of pure tungsten (W) and W–Re alloys were investigated. Neutron irradiation of pure W and W–Re alloys (Re concentration 3–26%) was carried out in the experimental fast reactor JOYO. The irradiation conditions were 0.44 displacement per atom (dpa) at 531°C and 0.47 dpa at 583°C for pure W and W–Re alloys, respectively. After irradiation, microstructural observations using a transmission electron microscope (TEM) and Vickers microhardness tests were performed.
    Voids and dislocation loops were observed in both pure W and W–Re alloys after irradiation. The number density of voids in pure W was higher than that in W–3%Re, W–5%Re and W–10%Re. Only in the case of W–26%Re irradiated to 0.47 dpa at 583°C were there no voids observed, but irradiation-induced fine precipitates and a few dislocation loops were observed. The irradiation hardening of pure W was greater than that of the W–Re alloys. It was considered that irradiation hardening of pure W was caused mainly by the higher number density of voids. The addition of Re suppressed void formation and irradiation hardening of the W–Re alloys. Irradiation hardening of W was also suppressed in hot-rolled W compared with arc-melted as-cast W.

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  • Influence of Substrate Temperature on the Structure and Cohesive/Adhesive Strength of Fe–Co–Si–B–Nb Metallic Glass Coating Films Produced by Thermal Spraying

    Masahiro Komaki, Tsunehiro Mimura, Saori Tsuji, Kenji Amiya, Yasunori Saotome, Tohru Yamasaki

    pp. 2151-2159

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    DOI:10.2320/matertrans.M2012282

    Abstract

    The influence of the substrate temperature on the structure, pore distribution and cohesive/adhesive strength of Fe–Co-based metallic glass coating films has been examined. The metallic glass coating films have been produced by a thermal spraying technique using our developed cylindrical nozzle on SS400 substrates. The splat morphology of the sprayed particles changed from an irregular splash to a disk shape at a transition temperature of about 300°C. When the substrate temperature increased to the transition temperature region (300–323°C), the porosity in the boundaries between the sprayed coating films and the substrates decreased. This can be produced by the strong increase in the wettability of the sprayed particles which is accompanied with a morphological change from splashed to disk-shaped particles. At temperatures ranging from 375 to 400°C, the porosity in both the boundary and inside regions decreased, and the volume fraction of the amorphous phase increased with temperature, resulting in a increase in the cohesive/adhesive strength up to about 27 MPa.

  • Thermoelectric Thin Film Device of Cross-Plane Configuration Processed by Electrodeposition and Flip-Chip Bonding

    Min-Young Kim, Tae-Sung Oh

    pp. 2160-2165

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    DOI:10.2320/matertrans.M2012265

    Abstract

    Using electrodeposition and flip-chip bonding, a cross-plane thin film device consisting of 242 pairs of the electrodeposited n-type Bi–Te and p-type Sb–Te thin film legs was successfully fabricated. The electrodeposited Bi–Te films with the thickness of 2.5–20.2 µm exhibited the Seebeck coefficients of −52 to −59 µV/K and the power factors of 5.5–5.1 × 10−4 W/m·K2. While the Seebeck coefficient of the Sb–Te film varied from 276 to 485 µV/K, the power factor was changed from 81 × 10−4 to 50 × 10−4 W/m·K2 with increasing the film thickness from 2.2 to 20.5 µm. The internal resistance of the thin film device consisting of 242 pairs of the electrodeposited n–p thin film legs was measured as 3.7 KΩ. The open-circuit voltage and the maximum output power of the thin film device were 0.294 V and 5.9 µW, respectively, with the temperature difference of 22.3 K across the hot and cold ends of the thin film device.

  • Mechanism of Localized Corrosion and Phase Transformation of Tube-to-Tube Sheet Welds of Hyper Duplex Stainless Steel in Acidified Chloride Environments

    Jin-Seung Kim, Soon-Tae Kim, In-Sung Lee, Seok-Hwan Jang, Yong-Soo Park, Kwang-Tae Kim, Young-Sub Kim

    pp. 2166-2174

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    DOI:10.2320/matertrans.M2012243

    Abstract

    The mechanism of localized corrosion and phase transformation of tube-to-tube sheet welds of hyper duplex stainless steel (HDSS) were investigated in acidified chloride environments. The HDSS tube-to-tube sheet welded with an Ar shielding gas without a filler metal, which increases the ferrite content, Cr2N and pitting resistance equivalent number (PREN) difference between the two phases, demonstrated the lower corrosion resistance than that with Ar shielding gas with a filler metal. The pitting corrosion of the weld metal (WM) in the HDSS tube-to-tube sheet welded using a pure Ar shielding gas with a filler metal occurred at the dendrite core (DC) that Cr and Mo were depleted and at the region adjacent to Mu phase that Mo and W were depleted. The localized corrosion was selectively initiated at the α-phase because the PREN value of the α-phase was much smaller than that of the γ-phase, irrespective of the chemical compositions of the shielding, and the areas of the WM, heat affected zone (HAZ) and base metal (BM) (except for the WM in the HDSS tube-to-tube sheet welded using Ar with a filler metal).

  • Recovery of Sn, Ag and Cu from Waste Pb-Free Solder Using Nitric Acid Leaching

    Kyoungkeun Yoo, Jae-chun Lee, Kwang-sek Lee, Byung-su Kim, Min-seuk Kim, Soo-kyoung Kim, B. D. Pandey

    pp. 2175-2180

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    DOI:10.2320/matertrans.M2012268

    Abstract

    The development of a hydrometallurgical process for the recycling of waste Pb-free solder based on nitric acid leaching, followed by the separation of Ag and Cu through AgCl precipitation or cementation, was investigated. Nitric acid dissolved Cu and Ag from the waste material while converting tin to stannic oxide (SnO2), which is very sparingly soluble in the HNO3 solution. More than 99% of the Ag and Cu in the waste Pb-free solder were dissolved in 2 kmol·m−3 HNO3 under the leaching conditions of 75°C, 100 kg·m−3 pulp density and stirring at 400 rpm for 120 min. The addition of NaCl or Cu powder was used to separate Ag from Cu in the solution. The addition of 2 kg·m−3 of NaCl or 125 kg·m−3 of Cu powder to the leaching solution at 30°C led to the successful recovery of 3755 g·m−3 of Ag. Thus, the results showed that Sn, Ag and Cu could be separated and recovered from waste Pb-free solder by the proposed recycling process.

  • Development of Adavanced Separation Technology of Rare Metals Using Extraction and Crystallization Stripping

    Junji Shibata, Norihiro Murayama, Masakazu Niinae, Takashi Furuyama

    pp. 2181-2186

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    DOI:10.2320/matertrans.M2012234

    Abstract

    In a present process to treat the tungsten carbide tool waste, the wastes are roasted in air and then an alkali leaching is carried out in an autoclave. An environmentally friendly process is required to recover rare metals (Co and W) from the wastes. The effect of mechano-chemical (MC) treatment on leaching of rare metals was investigated in this study. The solvent extraction and crystallization-stripping methods were applied to separate and recover tungsten and cobalt in the leached solutions.
    The MC treatment for the rare metal leaching is effective to dissolve rare metals from the wastes due to the change in crystalline structure of WC and oxidation of WC with KMnO4. Cobalt ions are extracted with D2EHPA by a cation exchange reaction. Tungsten in the leachate can be extracted by TOA (tri-octyl amine) as an extractant, because tungsten species exist as a form of anionic species in acidic solution. The rare metals in organic phase are recovered as insoluble salts such as oxalates and ammonium salts in the crystallization-stripping process.

  • Effects of Niobium on Mechanical Twinning and Tensile Properties of a High Mn Twinning-Induced Plasticity Steel

    Singon Kang, Jae-Gil Jung, Young-Kook Lee

    pp. 2187-2190

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    DOI:10.2320/matertrans.M2012273

    Abstract

    The effects of Nb on mechanical twinning and tensile deformation behavior were investigated in hot-rolled Fe–18Mn–0.6C–1.5Al twinning-induced plasticity (TWIP) steels without and with 0.1Nb. In comparison to the Nb-free TWIP steel with fully-recrystallized and equiaxed grains, the Nb-added TWIP steel showed non-recrystallized and elongated grains with well-dispersed NbC particles and a high density of dislocations. The increased yield and tensile strengths in the Nb-added TWIP steel were mainly caused by the hardening of dislocations in non-recrystallized grains rather than the precipitation hardening of NbC particles or the solid solution hardening of Nb atoms. Meanwhile, the uniform elongation and strain hardening rate of the Nb-added TWIP steel were decreased due to inactive mechanical twinning, which is probably because the dislocations interfere with the movement and dissociation of dislocations necessary for mechanical twinning.

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  • Electrostatically Controlled Enrichment of Lepidolite via Flotation

    Junhyun Choi, Wantae Kim, Woori Chae, Sang Bae Kim, Hyunjung Kim

    pp. 2191-2194

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    DOI:10.2320/matertrans.M2012235

    Abstract

    We first report flotation of lepidolite by using stearyl trimethyl ammonium chloride (STAC), one of the quaternary ammonium salts, without adding any depressant to get an insight on further advanced separation. X-ray diffraction patterns showed that the ores obtained from Boam mine, Uljin, South Korea were mainly composed of lepidolite, muscovite, quartz, calcite and albite. Zeta potential results showed that the isoelectric points (IEP) were about 2.5, 2.3 and 9.7 for quartz, albite and calcite, respectively, and that for lepidolite was determined to be less than 2. Based on the results for the electrokinetic properties of the minerals included in lepidolite ores, 3-stage flotation for the lepidolite was carried out in Denver Sub-A cells. Rougher flotation was first conducted at ca. pH 9 to separate calcite minerals, followed by first cleaner flotation over a pH range of 6.3–8.0 to find the maximum separation point of calcite gangue and second cleaner flotation over a pH range of 2–4 to maximize the removal of quartz/albite gangues. The results for the first cleaner showed that Li2O grade increased with decreasing pH while Li2O recovery tended to slightly increased with increasing pH. The trend for Li2O grade and recovery after second cleaner flotation was similar with that for the products after first cleaner flotation. Overall, Li2O grade increased with decreasing pH while the recovery slightly increased with increasing pH. Maximum Li2O grade (i.e., 2.77), which was about 3.8 times greater than the grade in the feed and around 36% of maximum threshold value (i.e., theoretical value, ∼7.7), was achieved at ca. pH 2.0. The increase in Li2O grade with decreasing pH could be attributed to the enhanced selectivity of lepidolite with decreasing pH due to the more favorable interaction of STAC with lepidolite (IEP of lepidolite < 2) relative to albite or silica (IEP of albite and silica = 2.3 and 2.5, respectively).

  • Surface Modification of Calcium Carbonate with Cationic Polymer and Their Dispersibility

    Yosep Han, Hyunjung Kim

    pp. 2195-2199

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    DOI:10.2320/matertrans.M2012236

    Abstract

    The influence of polyethylenimine (PEI) dosage on the dispersibility of precipitated calcium carbonate (PCC) particles was systematically investigated. The results for the zeta potential of PCC particles and the viscosity and turbidity of PCC suspension showed that charge reversal (negative to positive) of PCC particles occurred as the PEI concentration increased due to the specific adsorption of PEI onto the surface of the particles. Additionally, increasing the PEI concentration up to 5 mg/kg led to the reduction of the zeta potential of the PCC particles (almost neutral) and consequently a decrease in the particle stability, which was consistent with Derjaguin–Landau–Verwey–Overbeek (DLVO) interaction calculation results. However, the stability of the PCC particles gradually improved when the PEI concentration > 5 mg/kg. The trend was attributed to the enhancement of the electrostatic repulsive force between two interacting particles at low PEI concentration range (5 to 10 mg/kg). On the other hand, at high PEI concentration range (>10 mg/kg), it was found that additional repulsive forces (i.e., non-DLVO force) occurred between PEI-adsorbed PCC particles due to steric hindrance, consequently resulting in the improvement in the stability of the PCC suspension when the PEI concentration > 10 mg/kg.

  • Platinum–Nitrogen-Codoped TiO2 Photocatalyst: Effect of Acid Catalysts on Visible-Light Activity

    Jungho Ryu, Soonhyun Kim

    pp. 2200-2204

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    DOI:10.2320/matertrans.M2012294

    Abstract

    Platinum–nitrogen-codoped TiO2 (Pt–N–TiO2) was prepared by a conventional sol–gel process via the addition of different acid catalysts: nitric acid (HNO3), acetic acid (HAc) and both (HNO3–HAc). The Pt–N–TiO2 samples were then characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and UV–visible diffuse reflectance analysis. The samples successfully exhibited visible-light-induced photocatalysis for the degradation of dichloroacetate (DCA) and 4-chlorophenol (4-CP). The HAc/450 sample (following the notation “added acid catalyst/calcination temperature”) exhibited the highest visible activity for DCA degradation. This finding can be explained by the much stronger visible absorption of the calcined samples than the uncalcined samples and the slightly larger surface area of HAc/450 compared to other calcined TiO2 samples. However, the performance of 4-CP degradation was proportional to the Pt–N–TiO2 sample surface area regardless of visible absorption, which could be ascribed to the fact that 4-CP degradation can occur through a surface-complex-mediated pathway under visible irradiation.

  • Influence of Laser Remelting on Tensile Properties of Nanocomposite Ni–Al2O3 Coatings

    Chen Jinsong, Yang Jianming, Qiao Bin

    pp. 2205-2207

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    DOI:10.2320/matertrans.M2012256

    Abstract

    Ni–Al2O3 nanocomposition coatings were fabricated onto the surface of steel (grade 45) substrates using jet electroplating technology followed by laser remelting. The microstructure of the Ni–Al2O3 nanocomposite coating and the laser remelted layer were analysed. The surface composition was analysed using energy-dispersive X-ray spectroscopy (EDS). The tensile properties of the composite coating before and after laser irradiation were measured. The results show that for optimized testing parameters jet electroplating technology can produce 3.58 mass%. Ni–Al2O3 nanocomposite coatings. The tensile strength and percentage elongation of the test specimen with nanocomposite coating are better than substrate material. Laser remelting further improved the tensile strength and percentage elongation of the test-specimen.

  • The Effect of Oxygen and Hydroxide Ion on Electrochemical Leaching Behavior of Tin

    Soo-kyung Kim, Jae-chun Lee, Jinki Jeong, Kyoungkeun Yoo

    pp. 2208-2210

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    DOI:10.2320/matertrans.M2012311

    Abstract

    The dissolution of tin from waste Pb-free solder was electrochemically investigated in NaOH solution. Two oxidation peaks were observed in a cyclic voltammetry test in 1 kmol m−3 NaOH solution at less than 45°C, and the peaks indicate the oxidation of tin to Sn2+ and Sn2+ to Sn4+, whereas only one peak was observed at 75°C resulting from the direct oxidation of tin to Sn4+. The increase in NaOH concentration and the introduction of oxygen enhanced the dissolution of tin in NaOH solution with less than 0.5 kmol m−3 whereas that of tin decreased with increasing NaOH concentration further to 1.5 kmol m−3 and the decrease in the dissolution of tin was accelerated by introducing oxygen. An optimum waste solder alkaline electrolysis process was found to be at more than 75°C and around 0.5 kmol m−3 NaOH based on the cyclic voltammetry and constant current experiment.

  • Editor’s Announcement

    pp. 2212-2212

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    DOI:10.2320/matertrans.EAM2012603

  • Editor’s Announcement

    pp. 2211a-2211a

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    DOI:10.2320/matertrans.EAM2012601

  • Editor’s Announcement

    pp. 2211b-2211b

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    DOI:10.2320/matertrans.EAM2012602

  • © 2012 The Japan Institute of Metals and Materials

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