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

MATERIALS TRANSACTIONS Vol. 56 (2015), No. 6

  • Effect of pH Value on the Crack Growth Behavior of X70 Pipeline Steel in the Dilute Bicarbonate Solutions

    pp. 777-780

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    DOI:10.2320/matertrans.M2015096

    In this work, the crack growth behavior of X70 pipeline steel in the near-neutral pH and acidic solutions was investigated using in-situ crack length measurement, microscopic observation and polarization curves. The results showed that the decrease of the solution pH promoted the anodic and cathodic reactions simultaneously and accelerate the corrosion rate of X70 steel. This resulted in the blunt crack tip of X70 steel in the acidic environment. The crack growth rate of X70 steel in the acidic solution was lower than that in the near-neutral pH environment, which was attributed to the higher corrosion rate and the weaker couple effect around the crack tip.
  • Investigation of a New Method for Sheet Deep Drawing Based on the Pressure of Magnetic Medium

    pp. 781-784

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    DOI:10.2320/matertrans.M2014437

    To improve the forming performance of the deep drawing and the uniformity of wall thickness and then to improve the whole sheet quality, this paper puts the magnetic intelligent materials into the die as a force transmission medium to play a flexible back pressure role in the sheet deep drawing process, and develops a special experimental setup. The magnetic field affects the rheological properties of magnetorheological fluid (MRF) in the sheet deep drawing process, which changes the stress state and the deformation behavior. The research which takes the 304 stainless steel sheet whose thickness is 0.8 mm as an experimental object shows that, the forming performance of the sheet drawn with the MRF can be significantly improved with the increase of magnetic field intensity. Compared with conventional deep drawing, when the electric current of the coil is 2 A, the forming height limit of the sheet in the deep drawing process based on the pressure of magnetic medium increases by 26.3%, and the whole uniformity of wall thickness is improved obviously, which can effectively inhibit the possibility of the wrinkling defect in the flange. Thus, the sheet deep drawing process based on the pressure of magnetic medium is a potential research direction that may achieve the major breakthrough and progress.
  • Formation of MgCu2 from MgH2 and Cu in Pressurized Hydrogen Atmosphere

    pp. 785-789

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    DOI:10.2320/matertrans.M2014426

    We have been proposing that there are competitive two kinds of pathways in the hydrogenation of Mg/Cu super-laminate composites. The one is that Mg reacts with Cu to form Mg2Cu and then Mg2Cu is hydrogenated to form MgH2 and MgCu2. The other is that Mg is hydrogenated and then MgH2 and Cu reacts to form MgCu2 together with H2 gas, according to a hypothesis that the reaction of MgH2 + 2Cu → MgCu2 + H2 occurs. In the present study, the reaction conditions such as pressure and temperature were investigated in order to confirm that the hypothesis is true. Well-mixed MgH2 and Cu powder was compressed to a pellet at 1.73 GPa and then heated at various hydrogen pressures and temperatures. Following results were obtained from the experiments at 673 K. The above-mentioned alloying accompanied by H2 emission occurs at pressures higher than 6.6 MPa of H2 pressure, which is higher than lower limit for the hydrogenation of Mg2Cu. On the other hand, Mg2Cu is formed at 3.3 MPa which is lower than the limit. The reaction of MgH2 with Cu also occurs at 573 K in 3.3 MPa H2. But it requires very long time such as 691.2 ks, although the existence of MgCu2 is confirmed in 86.1 ks of heating time in the case of Mg/Cu super-laminate composites.
  • Giant Atomic Clusters Induced Mechanism in {10\bar{1}4} Twinning of Hexagonal Close-Packed Crystals

    pp. 790-792

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    DOI:10.2320/matertrans.M2015032

    Following the discoveries of the giant atomic clusters (GACs) induced mechanism in a series of twinning modes in hexagonal close-packed (HCP) crystals, the law of atomic motion in {10\bar{1}4} twinning is successfully revealed in this paper by using the GACs rotation model. It is found that the GACs in {10\bar{1}4} twinning (for magnesium) rotate by an angle of 20.2° without making a shifting along the longitudinal direction of the clusters. As an important parameter to judge the difficulty degree of a twinning mode to occur, the value of the relative displacement magnitude (RDM) among the adjacent atomic clusters in {10\bar{1}4} twinning (0.845a) is significantly larger than that in {10\bar{1}2}, {10\bar{1}1} and {10\bar{1}3} twinning. The discovery of the GACs induced mechanism in {10\bar{1}4} twinning in return consolidates the applicability of this mechanism in the HCP crystals.
  • Hydrogen Visualization in Steels Using Ag Decoration Method

    pp. 793-797

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    DOI:10.2320/matertrans.M2014431

    The relation between hydrogen distribution and metallographic microstructure was investigated by means of Ag decoration technique for a SUS304 austenitic stainless steel, and martensitic and spheroidized SCM440 steels precharged with hydrogen. Preferential distribution of Ag particles was seen on the slip lines of the deformed and hydrogen-charged SUS304 stainless steel, suggesting that the slip lines act as hydrogen trap sites. The martensitic SCM440 steel showed almost no selective Ag deposition, indicative of apparently homogeneous distribution of hydrogen. This is probably because the distribution of dislocations with relatively high concentration and the fine structure including lath boundaries etc. acting as hydrogen traps is homogeneous. The spheroidized SCM440 steel showed almost no Ag deposition on the coarse cementite particles and the Ag particle distribution on the other areas did not show clear selectivity. This result suggests that the hydrogen does not diffuse through the cementite particles. The smallest Ag particle size observed by means of atomic force microscope was in the order of 10 nm. Though the minimum size of the Ag particle does not necessarily indicate the resolution of the hydrogen visualization, Ag decoration technique is useful to observe the hydrogen distribution.
  • Kinetics of Reactive Diffusion in the (Sn–Cu)/Ni System at Solid-State Temperatures

    pp. 798-802

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    DOI:10.2320/matertrans.M2015059

    The kinetics of the solid-state reactive diffusion in the (Sn–Cu)/Ni system was experimentally observed to examine effects of addition of Cu into Sn on the growth behavior of compounds at the interconnection between the Sn-base solder and the multilayer Au/Ni/Cu conductor during energization heating. In this experiment, sandwich (Sn–Cu)/Ni/(Sn–Cu) diffusion couples with Cu concentrations of y = 0.01–0.03 were isothermally annealed at solid-state temperatures of T = 453–473 K for various periods up to 1972 h, where y is the mol fraction of Cu. After annealing, an intermetallic layer consisting of (Cu,Ni)6Sn5 and Ni3Sn4 was recognized between the Sn–Cu and Ni specimens in the diffusion couple. The total thickness of the intermetallic layer is proportional to a power function of the annealing time, and the exponent of the power function takes values of 0.37–0.44 at T = 453 K and those of 0.63–0.69 at T = 473 K. Thus, the growth of the intermetallic layer is controlled by boundary and volume diffusion at T = 453 K. On the other hand, at T = 473 K, interface reaction and interdiffusion contribute to the rate-controlling process of the intermetallic growth. The addition of Cu into Sn accelerates the intermetallic growth within the experimental annealing times.
  • Improvement of Uniform Elongation by Low Temperature Annealing in Al-2.5%Mg Alloy Processed by Accumulative Roll Bonding

    pp. 803-807

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    DOI:10.2320/matertrans.L-M2015806

    Al-2.5%Mg alloy (A5052) sheets were processed by accumulative roll bonding (ARB) for 1 to 7 cycles (equivalent strains from 0.8 to 5.6) at room temperature. The sheets processed by ARB for 7 cycles were then annealed isochronally for 30 min at temperatures in the range from 100°C to 400°C. Interestingly, it was found that the specimen annealed at 200°C followed by 7 cycles of ARB had the same level of yield stress (about 320 MPa) but a larger uniform elongation than the specimen processed by 3 cycles of ARB. The improvement in uniform elongation by low-temperature annealing is discussed in terms of the mechanism that the evolution of dislocation substructures inside ultra-fine grains causes plastic instability at a very early stage of the tensile test. Hardening by annealing was also observed in the specimen annealed at 100°C followed by 7 cycles of ARB.
  • Grain Size Measurement in Steel by Laser Ultrasonics Based on Time Domain Energy

    pp. 808-812

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    DOI:10.2320/matertrans.M2014445

    Laser ultrasonics, a technique based on the generation of ultrasonic waves by a pulsed laser and on their detection by a laser interferometer, can be used to determine grain sizes in steels. The absolute values of the average grain size can be calculated directly from the attenuation measurements of ultrasonic longitudinal bulk waves. The general methods of attenuation measurements are computed based on the amplitude of longitudinal waves. In fact, the amplitude as only one value is infected by the noise. Besides, the attenuation should be considered as the energy reduction. The method of time domain energy is proposed to compute the attenuation. The results indicate that time domain energy can improve the accuracy of the grain size prediction. The laser ultrasonic technique may be incorporated online for direct measurements of grain size during steel production.
  • Critical Fracture Behavior of a Cu/Al Composite Laminate via the Observation of Scanning Electron Microscope

    pp. 813-818

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    DOI:10.2320/matertrans.M2014466

    In situ fracture study of a Cu/Al composite laminate was discussed via the observation of scanning electron microscope (SEM). The experimental test was carried out by a modified miniature tensile device. With the aid of the SEM’s sample stage and a wedge block, the profile morphology of the specimen was observed. The substrate layer (1060 aluminum) and the plate layer (C11000 copper) of the specimen presented asynchronous fracture behaviors. Under a relative large strain, a mass of micro voids, cracks and connections of voids and cracks were observed in the substrate layer, accompanied with some separated copper oxide and aluminum oxide flakes. Micro cracks were also observed in the plate layer and the overall morphology of the plate layer was relatively smooth and flat. When the tensile strain increased to 0.26, the initial fracture position firstly occurred at the plate layer, and the fracture process gradually spread from the plate layer to the substrate layer. In addition, the fracture modes of the substrate layer and the plate layer mainly manifested as microvoid coalescence fracture and pure shear fracture, respectively.
  • Effects of Si on Tensile Properties Associated with Deformation-Induced ε-Martensitic Transformation in High Mn Austenitic Alloys

    pp. 819-825

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    DOI:10.2320/matertrans.M2015042

    We investigated the effect of Si on the tensile properties of Fe-33Mn, Fe-33Mn-4Si, and Fe-33Mn-6Si austenitic alloys (mass%) at 273, 294, 323, and 423 K. The Si addition promoted the deformation-induced ε-martensitic transformation, thereby enhancing the work-hardening capacity. In terms of Considère’s criterion, the enhanced work-hardening capacity can improve uniform elongation. However, the Si addition simultaneously promoted brittle cracking associated with ε-martensite, tending toward decreasing elongation. As a result of the ambivalent roles of Si related to ε-martensite, the elongation–strength balance was improved by the addition of 4%Si, but was deteriorated when the Si content increased to 6%. As an additional effect, the Si addition changed the microvoid-formation behavior, resulting in decreasing local elongations.
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  • Analysis of Run-in-Stage Wear Behavior and Contact Mechanics of Metal-on-Metal Hip Joint Bearings with Different Radial Clearances

    pp. 826-834

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    DOI:10.2320/matertrans.M2014440

    We systematically elucidate the effects of radial clearance on the wear behavior of hip joint prostheses bearings during run-in-stage. The results indicated that bearings with smaller radial clearances exhibited lower wear rate and less abrasive wear characterized by mild surface roughness and sphericity. The contact mechanics and lubrication regime of MOM bearings with different radial clearances were also analyzed, indicating that bearings with radial clearance of ∼20 µm was more beneficial for small contact pressures even the enlarged clearance made the bearings operate under a full-fluid-to-mixed lubrication during wear. The agreement between the experimental results of wear rate (mm3/Mc) and contact mechanics and lubrication analysis indicated that the radial clearance significantly affected the wear behavior of the MOM bearings.
  • Chemometric Approach for Mechanical Properties Prediction during the Electromagnetic Casting Process

    pp. 835-839

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    DOI:10.2320/matertrans.M2015058

    In this study the mechanical properties (reduction of area, S0, tensile strength, Rm, yield strength, Rp, and elongation, A) of EN AW 7075 aluminum alloy obtained by electromagnetic casting were investigated at different operating parameters: frequency (V), field strength (T) and current intensity (I). The predictive mathematical models using Response Surface Methodology, with second order polynomial (SOP) regression models, and Artificial Neural Network model (ANN), were afterwards compared to obtained experimental results. Analysis of variance and post-hoc Tukey’s HSD test at 95% confidence limit (“honestly significant differences”) have been utilised to show significant differences between various samples. SOP models showed good prediction capabilities, with high coefficients of determination (r2), 0.531–0.977, while ANN model performed even better prediction accuracy: 0.800–0.992. The optimal samples were chosen depending on mechanical properties of the product (S0 = 50.49 mm2, Rm = 405.75 N mm−2, Rp = 302.49 N mm−2, A = 6.86%), using optimal operating parameters (V = 30 Hz, I = 250 A, T = 18 × 10−3 At).
  • Effect of Loading Rate on Dynamic Fracture Morphology of a Zr-Based Bulk Metallic Glass

    pp. 840-843

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    DOI:10.2320/matertrans.M2014467

    Low-velocity plate impact experiments using a single-stage gas-gun are performed on Zr58.5Cu15.6Ni12.8Al10.3Nb2.8. Compressive fracture surfaces of the samples subjected to varying impact velocities and stress amplitudes are evaluated in order to study their loading rate dependence. Samples impacted at increasing loading rates, from increasing velocities of impact, show a larger extent of localized melting while those subjected to increasing stress show a transition from ductile to brittle fracture. These observations suggest that the mechanisms and morphology of fracture are strain-rate dependent.
  • Effects of Die Dimensions for Curvature Extrusion of Curved Rectangular Bars

    pp. 844-849

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    DOI:10.2320/matertrans.P-M2015805

    The effects of die dimensions on curvature-extrusion curved rectangular bars were investigated by experiments and numerical simulations. We conducted simulations and experiments of rectangular bar production using various die dimensions. The calculated trend of curvature showed good agreement with the experiment results, thereby validating the numerical simulation results. The curvature increases concomitantly with increasing exit height and exit width. The exit height ratio affects the curvature about 2.1 times more than the exit width ratio does. The effect of die thickness on curvature is slight. Regarding the conditions of die dimensions, the exit height is the most important factor that affects the curvature. The curvature increases when the difference in exit velocity becomes large. The generation of a dead metal area, along with container configurations, affects the curved rectangular bar curvature. Results show that the curvature is determined by the difference in exit velocity, in conjunction with the die dimensions.
  • Staggered Anvil and Rotation Processes for Refining and Homogenizing Centimeter-Scale Grains during FM Forging of Superheavy Ingots

    pp. 850-857

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    DOI:10.2320/matertrans.M2014446

    Typically, the microstructure of superheavy ingots weighing more than 300 tons consists of centimeter-scale grains. In this study, a forging method for refining and homogenizing such grain structure is proposed on the basis of modeling and simulation results. After a superheavy ingot has been subjected to a single deformation process during FM forging, different areas of the ingot exhibit variations in the degree of deformation and microstructure. The critical value of the equivalent strain for obtaining a fine-grained structure (∼30 µm) was calculated to be 0.16; on the basis of this, the staggered anvil process was designed in order to improve the deformation uniformity in the meridian plane of heavy forgings. Given that traditional rotation processes usually result in inhomogeneous deformation distributions in the cross-sections of heavy forgings, the quantitative relationship between the rotation angle and the reduction ratio was determined. This was done with the view of improving the rotation process to solve the problem of uneven deformation distribution close to the surfaces of heavy forgings. Using the improved rotation process should ensure a uniform microstructure across the entire cross-section.
  • Presence of a Doubly-Splitting Site and Its Effect on Thermoelectric Properties of Cu4SnS4

    pp. 858-863

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    DOI:10.2320/matertrans.E-M2015804

    Thermoelectric properties of Cu4SnS4 significantly change around 230 K along with a phase transition between a high temperature phase (HT-phase) and a low temperature phase (LT-phase). Here we particularly focus on a very low thermal conductivity of Cu4SnS4, which is even lower in HT-phase. The crystal structures of Cu4SnS4 are analyzed using synchrotron radiation. HT-phase is determined to be orthorhombic structure with the space group Pnma, as previously reported; however, the results of Rietveld refinement of HT-phase suggest that there are some Cu sites around saddle points of the double well potential. Phonon dispersion calculated by first-principles calculations indeed exhibits soft phonon modes of the Cu sites, consistent with the Rietveld analysis. The detailed analysis leads to a conclusion that the lower thermal conductivity in HT-phase results from an additional phonon scattering resonated with an anharmonic Cu vibration in the double well potential.
  • Thermoelectric and Magnetic Properties of Pr1−xSrxMnO3 (0.1 ≦ x ≦ 0.7)

    pp. 864-871

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    DOI:10.2320/matertrans.E-M2015807

    In this study, polycrystalline samples of Pr1−xSrxMnO3 (0.1 ≦ x ≦ 0.7) were synthesized using a conventional solid-state reaction method. We investigated crystal structure, magnetic susceptibility (χ), and thermoelectric properties, such as electrical resistivity (ρ), Seebeck coefficient (S), and thermal conductivity (κ), as a function of temperature (T) or Sr content (x). The crystal structure at room temperature changed from orthorhombic Pbnm phases, with x ≦ 0.4, to tetragonal I4/mcm phases, with x ≧ 0.5. The samples for x ≦ 0.5 showed the ferromagnetic-like ground state below Curie temperature. Conversely, the samples for x = 0.5, 0.6, and 0.7 showed the charge-ordering ground state below 160 K, the A-type antiferromagnetic ground state below 310 K, and the C-type antiferromagnetic ground state below 318 K, respectively. Above room temperature, all the samples exhibited adiabatic small polaron conduction in a competition between the double exchange interaction and the Jahn-Teller distortion. Although the samples for x = 0.1 and 0.2 showed a large positive S below room temperature, the carrier type changed from hole-like to electron-like behavior above 1000 K and 500 K, respectively. Thus, all the samples for 0.1 ≦ x ≦ 0.7 showed a negative S at a high temperature. The largest dimensionless figure of merit (ZT) of all the samples above room temperature was 0.085 at 1073 K for x = 0.7, by a decrease in both ρ and lattice κ, and an increase in S. In addition, we obtained the largest ZT in the p-type specimens for x = 0.1, thus, attaining a maximum value of 0.0035 at 468 K. We discuss this behavior in terms of the potentiality to fabricate the oxide thermoelectric modules consisting of the same type of elements.
  • Copper-Reductant Composite for Long-Life Electrical Contact

    pp. 872-877

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    DOI:10.2320/matertrans.M2014423

    The purpose of this paper is to develop a new long-life electrical contact. The ability of copper-reductant composite by which the reducing agent with a size of 50 nm or less was distributed inside to extend a sliding life as a slide member for electrical contact was studied. After investigating that L-ascorbic acid as a reductant reduces cupric oxide to copper at room temperature, formation of the copper-reductant composite was tried by the composite plating using the aqueous solutions of a mixed-ligand copper(II) complex with L-ascorbic acid and 1,10-phenanthroline. In the obtained composite film contact, L-ascorbic acid as a reductant and 1,10-phenanthroline were probably distributed in 20 nm or less size, and the sufficiently longer sliding life was shown in slide testing than the plated copper film contact.
  • New Bonding Technique Using Copper Oxide Materials

    pp. 878-882

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    DOI:10.2320/matertrans.M2014399

    As a bonding technique between semiconductor elements in a semiconductor device and external substrates, a reduction bonding technique has been developed that uses CuO particles several micrometers large. This technique has the following features. (1) CuO particles can be reduced in about 200°C H2 atmosphere. (2) Pure Cu particles about 50 nm in diameter form at this time. (3) The formed Cu particles form a sintered Cu layer. (4) Bonding can be achieved above 350°C. Bonding requires pressurization. The bonding strength (shear breaking strength) of this sintered Cu layer and Ni electrodes used by many semiconductor devices was evaluated. Consequently, bonding strengths were about 20 MPa at pressurization of 1.2 MPa and a heating temperature of 350°C. Moreover, in the bonded interface of a sintered Cu layer and Ni electrodes, the sintered Cu layer formed the hetero-epitaxial layer between Ni electrodes. For this reason, we confirmed that the bonded interface of a sintered Cu layer and Ni electrodes was in a strong bonding state on the metal object.
  • Evaporation Behaviors of Cu(In,Ga)Se2 Semiconductor Compound via Pyrometallurgical Chlorination Process Utilizing Ammonium Chloride

    pp. 883-888

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    DOI:10.2320/matertrans.M2015043

    The chlorination process utilizing ammonium chloride as chlorination reagent has been employed for the recovery of elements from a promising photovoltaic semiconductor material, copper indium gallium diselenide, Cu(In,Ga)Se2, through vaporization of the chlorides of the elements. It was found that the chlorination took place by heating of the model sample in the presence of ammonium chloride. The influence of process parameters, such as oxygen partial pressure in the gas phase, the composition of ammonium chloride and the reaction temperature, has been investigated. The increase in the oxygen partial pressure resulted in the substantial increase in the recovery. The chlorides of indium and gallium deposited in the temperature zone around 400 K, while selenium chloride concentrated in the lower temperature zone below 320 K, for the reaction at 673 K. Copper was detected mostly in residue. At 1073 K, on the other hand, the evaporation of copper chloride was observed. These phenomena result from the difference in vapor pressure of metal chlorides.
  • Selenium (Se) Removal from Copper Refinery Wastewater Using a Combination of Zero-Valent Iron (ZVI) and Se(VI)-Reducing Bacterium, Thaurea selenatis

    pp. 889-894

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    DOI:10.2320/matertrans.M2014457

    The copper refinery process produces Se(VI)-bearing wastewater with a high content of Cl and SO42− ions. To overcome the negative effect caused by Cl and SO42− ions on Se(VI) reduction and its following removal, this study investigated the possible synergistic effect of the combination of Se(VI)-reducing bacterium, Thaurea (T.) selenatis and zero-valent iron (ZVI). In the presence of SO42− (200 mM) and Cl (300 mM), the following was observed: (i) ZVI alone was unable to remove Se both under strictly aerobic and micro-aerobic conditions. (ii) Se(VI) reduction by T. selenatis alone was severely inhibited under anaerobic conditions (and thus no microbial growth was observed). (iii) On the other hand, T. selenatis was capable of growth and Se(VI) reduction under micro-aerobic conditions. (iv) Combining T. selenatis and ZVI under micro-aerobic conditions showed a synergistic effect on Se(VI) reduction, readily facilitating Se removal. This synergistic effect was optimized by adjusting the pH to near neutral (optimal for T. selenatis growth), but by adjusting the temperature to 35°C (sub-optimal for T. selenatis growth): Se removal of 55% by T. selenatis alone, was significantly improved to 98% by combining T. selenatis and ZVI. The proposed key process to display the synergistic effect on Se removal under micro-aerobic conditions is as follows: (i) Using the remaining dissolved O2 (DO) during the first hours, T. selenatis can overcome the inhibitory effect of Cl and SO42− by growing with more energy-gaining aerobic respiration, (ii) ZVI indirectly serves as a reducing agent to maintain low DO levels, consequently readily switching from aerobic to anaerobic Se(VI) respiration by T. selenatis. (iii) ZVI may also be acting directly for Se deposition by reducing microbially-produced intermediate Se(IV), which is more reactive than original Se(VI). The present findings could be used as a basis for developing an economically feasible and environmentally harmless bio-treatment technology for Se(VI) containing copper refinery wastewaters.
  • Synthesis and Characterization of Optically Clear Pressure-Sensitive Adhesive

    pp. 895-898

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    DOI:10.2320/matertrans.M2014425

    We synthesized Optically Clear Adhesive (OCA) polymers by free radical polymerizations and cured them as an interlayer between two polyethylene terephthalate (PET) release films. Some fundamental characteristics of OCA polymers including glass-transition temperature (Tg), molecular weight, viscosity, probe tack and peel strength were investigated with the change of methyl methacrylate (MMA) and 2-hydroxyethyl acrylate (HEA) monomers. The optical characteristics of OCA films were also investigated on the change of ripening temperature, high-temperature aging and heat-moisture aging. The resistance change rates of ITO-coated films were measured with heat-moisture treatment for two weeks. The results suggested that the OCA films can effectively protect ITO films and the synthesized OCA polymer can be expected to be applied to touch panel devices.
  • Immobilization of Nanoscale Sunscreening Agents onto Natural Halloysite Micropowder

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    DOI:10.2320/matertrans.M2015086

    Titanium dioxide (TiO2) nanoparticles contained in sunscreen products are typically smaller than 30 nm in order to enhance the efficacy of the sun protection. TiO2 nanoparticles of this size range raise toxicity concerns because of the generation of reactive oxygen species (ROS) and the ability to penetrate into the skin tissue. To solve these problems, we immobilized the nanoparticles on a natural tubular powder, halloysite. The nanoparticle-halloysite hybrid powders are prepared by two synthetic methods: an ex situ immobilization of TiO2 nanoparticles (after separate synthesis of a nanoparticle batch), and an in situ generation of TiO2 nanoparticles inside halloysite. Notably, TiO2 nanoparticles of pure rutile phase are synthesized so that the ROS generation is suppressed before immobilization. The ultraviolet-visible (UV-vis) light extinction results show that the sunscreening efficacy of the hybrid powder produced via the ex situ route appears to be 22% higher than that of the hybrid powder fabricated by the in situ method. An increase in the hybrid powder concentration results in a sunscreening efficiency equivalent to that of the bare TiO2 nanoparticles. Our results can be used to produce nanoparticle-halloysite hybrid powders suitable for UV light screening while reducing the potential toxicity concerns.

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