Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

© 2019 Elsevier Ltd Pt supported on CeO2 has various applications as a catalyst. Because chemical states of Pt are hugely significant in offering improved catalytic performance, it is necessary to understand structures of Pt on CeO2 at high temperatures. In this study, PtO2 and PtO2–CeO2 powders were prepared by precipitation in molten sodium nitrate, and their thermal decomposition in air was examined by X-ray diffraction. When PtO2 powder is heated at 600 °C, the oxide decomposes into Pt phase which is accompanied by a slight Pt3O4 phase. On the other hand, in a heat treatment of a PtO2–CeO2 powder, the formation of Pt phase is hindered and Pt3O4 phase is formed preferentially. These results suggest that supporting Pt on CeO2 contributes not only to maintenance of fine dispersion at high temperatures, but also to formation of the Pt3O4 phase, which might play an important role in catalytic reactions. Observation with transmission electron microscopy and chemical analysis with X-ray photoelectron spectroscopy were performed on the powders before and after the heat treatment to discuss the formation of Pt3O4 particles on a PtO2–CeO2 solid solution.

DOI： 10.1016/j.jpcs.2019.109097

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In the electrorefining of Cu, the precipitation of copper sulfate on the anode surface causes passivation, which decreases current efficiency. Because the presence of Sb in a Cu anode is known to accelerate passivation, this study investigated the anodic behaviors of Cu–Sb alloys in a H 2 SO 4 −CuSO 4 electrolyte by a direct observation method that combined optical microscopy with the channel flow double electrode technique. When a Cu−Sb (5 wt% Sb)anode (here denoted “Cu−5 wt%Sb”)with Sb segregation was dissolved, the Sb-rich region remained on the surface, inhibiting Cu dissolution and ion transfer and resulting in acceleration of passivation, which was observed as a drastic decrease in current density during voltammetry. However, a Cu−5 wt%Sb anode solutionized by heat treatment showed a moderate decrease in current density in some measurements, indicating prevention of passivation. It was observed that the dissolution of the solutionized Cu−5 wt%Sb anode generated an Sb-rich layer with complex sulfate compounds on its surface and accompanying pits. Copper sulfate precipitated selectively on the Sb-rich layer and grew into coarse grains, without covering the entire anode surface. These results suggest that passivation can be prevented by controlling the microstructure, even when an anode contains Sb. The results of this work are expected to contribute to the development of an efficient electrorefining process of Cu anodes containing high concentrations of Sb.

DOI： 10.1016/j.electacta.2019.03.064

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Iron and Steel Institute of Japan  

To investigate the heterogeneous nucleation of graphite on rare earth non-metallic inclusions during the solidification of cast iron, Fe-4.1mass%C-2.5mass%Si and S-added Fe-4.1mass%C-2.5mass%Si-0.01mass%S alloys are contact-melted and solidified on RE2O3 (RE
La, Yb) substrates. Regarding the Fe-4.1mass%C-2.5mass%Si alloy, XRD analysis and SEM observation results show that graphite, with an overall orientation in the [0001] direction, precipitates at the alloy/substrate interface. In addition, formation of nodular graphite with rare earth sulfides as the heterogeneous nuclei is observed in the bulk alloy. In the 0.01%S-added specimens, precipitation of graphite at the alloy/substrate interface is observed to be significantly weakened compared to reference specimens. Such precipitation behavior is considered to be due to the increased formation of nodular graphite in the bulk as a result of S addition. Based on these results, the precipitation behavior of graphite on rare earth compounds is discussed.

DOI： 10.2355/isijinternational.ISIJINT-2017-398

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER  

Solution growth of silicon carbide (SiC) using unary chromium (Cr) solvent was studied because the system enables a high solubility difference and a low degree of supersaturation, which would lead to rapid growth with a stabilized growth interface. The liquidus composition at SiC saturation in a quasi-binary Cr SiC system was studied at 1823-2173 K. The measured carbon (C) contents are in good agreement with the thermodynamic evaluation using the sub-regular solution model. In addition, growth experiments using a unary Cr solvent were performed by the bottom-seeded travelling solvent method. The obtained growth rates at 1803-1923 K with a temperature difference of 15-70 K were proportional to the solubility difference between the seed and source temperatures, indicating that the growth was controlled by the mass transfer of C in the solution. The maximum growth rate of 720 mu m/h at 1803 K was much higher than the growth rate by Si-rich solvents, suggesting that the Cr-rich solvent is suitable for the rapid growth at a low temperature.

DOI： 10.1016/j.jcrysgro.2016.12.049

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

Species evaporating from B2O3(l), B6O(s) and their mixtures were observed by a multiple Knudsen cell mass spectrometer between 1373 K and 1573 K (1100 A degrees C and 1300 A degrees C). Ions with mass-to-charge ratios of 70, 54, and 27 from the samples were observable, indicating the formations of B2O3(g), B2O2(g), and BO(g). The vapor pressures of the gas species were estimated by referring to thermodynamic information previously reported on B6O(s). Evaporation of B2O2(g) from a mixture [ = 6 Pa at 1473 K (1200 A degrees C)] was observed, and it was consistent with a preceding study by a different method.

DOI： 10.1007/s11663-015-0476-x

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

Electrochemical reduction of silicon on metal electrodes in molten silicate was studied. An iron sheet was immersed in SiO2-Li2O-MgO at 1273 K, and the electrode potential was controlled for 1 h. Formation on the iron of a Si-containing layer about 10-30 mu m thick was observed after the electrolysis, depending on the potential. When a molybdenum electrode was used, alpha-MoSi2 layer about 5 mu m thick was formed on the surface. The results suggest the applicability of molten oxide electrolysis as a synthesis method of Si-containing alloy layers. (C) 2015 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jallcom.2015.04.037

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Mass Spectrometry Society of Japan  

For the development and optimization of materials processing a collection of thermodynamic information concerning substances that participate in the reactions is important. One fundamental way to obtain such information is to measure the vapor pressure of gas species under conditions where they are in equilibrium with the condensed phases. Over the past 60 years Knudsen cell mass spectrometry has been used to identify and quantitatively determine gas species at high temperatures. This article describes thermodynamic foundation and examples of measurements in order to demonstrate the use of mass spectrometry focusing on the field of process metallurgy and recycling processes.

DOI： 10.5702/massspectrometry.S0040

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

To recover platinum group metals (PGMs) from spent automotive catalytic converters with a smaller environmental load, a Zn-vapor treatment prior to acid leaching was previously proposed. Because PGMs and Zn form alloys which dissolve easily, the pretreatment is believed to reduce the use of both chemical agents and processing time. In this study, effects of this treatment on PGM leaching were examined using simulated catalysts. Leaching tests in aqua regia demonstrated that Zn-vapor treatment enhanced the dissolution of PGMs, and was especially effective on Rh. Pretreatments were also found to enhance PGM extractions in hydrochloric acid depending on the conditions. Reactions on Zn-treated catalysts in the solution are discussed based on these results. (C) 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.hydromet.2014.04.019

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Anodic behaviors of Pd-Zn alloys in hydrochloric acid have been observed by channel flow double electrode to examine dissolution of Pd enhanced by alloying. The measurements on Pd - 40%Zn, Pd - 60%Zn and Pd - 78%Zn show that the enhancement of Pd dissolution depends strongly on the alloy compositions. A linear sweep voltammogram with a Pd - 78%Zn electrode indicates that Pd dissolved from the alloy at unusually low potentials, and this might be explained by a dissolution of unstable Pd clusters transiently formed through preferential dissolution of Zn. On the other hand, potentiostatic measurements show that Pd dissolves from Pd - 60%Zn at a higher rate than from the two other alloys. Dissolution characteristics of the alloys are discussed by considering their potential dependency and the morphological changes of the dissolving surface. (C) 2014 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.electacta.2014.04.156

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Anodic dissolutions of Pt and Zn from Pt-Zn compounds in 5 mol L-1 hydrochloric acid have been directly monitored by the channel flow double electrode method to investigate the mechanism of enhanced dissolution of precious metals by alloying with less noble metals. The enhancement of Pt dissolution shows strong dependence on the compound composition formed during the alloying process and is more prominent from r-PtZn1.7 and gamma(1)-Pt3Zn10 than upsilon-PtZn and gamma-Pt2Zn11. In addition, linear sweep voltammograms of Pt-92% Zn alloys show dissolution of Pt below 0.2 V vs SHE, which is far lower than the standard potential for the reaction (0.74 V). The result is explained by an activation of Pt through the preferential dissolution of Zn from the alloys. Such theoretically proposed "underpotential dissolution" is demonstrated for Pt-Zn alloys experimentally for the first time in the present study.

DOI： 10.1021/jp405184e

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The drying characteristics of a single coarse lignite particle in superheated steam are investigated. Spherical particles of Loy Yang lignite 30mm in diameter were used. The particles were dried with superheated steam at temperatures ranging from 110 to 170°C under atmospheric pressure, and their weights and temperatures were measured with electronic balance, thermocouples and infrared thermograph. Condensation of water droplets on the surface was observed initially, then constant drying rate period (CDRP) and decreasing drying rate period (DDRP) were observed successively. A numerical model of the drying process was developed based on the results, taking into account transfer of free water inside the particle, equilibrium moisture content and shrinkage of the lignite particle itself. © 2013 The Japan Institute of Light Metals.

DOI： 10.2320/matertrans.M-M2013817

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

A Rh-Zn compound was synthesized by exposing Rh to a fixed pressure of Zn vapor. After keeping Rh and Zn in a sealed container for 10 days at 1173 K and 1093 K (900 A degrees C and 820 A degrees C), respectively, an unreported compound was obtained. Its chemical composition was determined to be RhZn3, and X-ray diffraction analysis revealed it to have a face-centered tetragonal structure ( = = 3.78 and = 3.88 ). The dissolution rate of Rh from the RhZn3 in hydrochloric acid was measured using a channel flow, double-electrode method, and it was found to be more than 100 times greater than that from pure Rh. The result verified the possibility of a Rh recovery process in which Rh is exposed to Zn vapor prior to acid leaching to enhance its dissolution.

DOI： 10.1007/s11663-012-9637-3

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：JOHN WILEY & SONS  

The production of solar cells is increasing dramatically and the shortage of polycrystalline silicon for these cells has become a serious problem, making development of a low-cost production process for solar grade silicon essential. An electron beam melting technique is known to be effective for the removal of phosphorus from molten silicon. Although the phosphorus is removed by preferential evaporation in this process, the rate of removal is not sufficient, and its improvement requires thermodynamic information on phosphorus in the molten silicon. In this research, the vapor pressure of phosphorus in equilibrium with a silicon-phosphorus alloy was measured by double Knudsen cell mass spectrometry with a system blowing gas into the Knudsen cell. The activity of phosphorus in silicon, the Gibbs energy change of the dissolution of phosphorus in silicon, and other factors were estimated from the results. Using these data, we provided guidelines on how this process can be improved.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

This study examined the synthesis of Pt-Zn and Au-Zn compounds by applying Zn vapor. Phases of formed compounds were controlled by an isopiestic method, in which Pt or Au was heated at higher temperature than the Zn vapor source in a reaction container. The result was that gamma(1)-Pt(3)Zn(10), r-PtZn(1.7) and nu-PtZn were synthesized and the activities of Zn in these compounds were obtained. gamma(2)-AuZn(3) and beta'-AuZn were synthesized using thermodynamic information previously reported. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jallcom.2010.05.146

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELECTROCHEMICAL SOC INC  

As a part of a development of a hydrometallurgical recovery method for platinum, the anodic behavior of a Pt-Zn compound (75 atom % of Zn) in hydrochloric acid was examined. The dissolution rates of Pt and Zn from the compound were measured separately at controlled potentials by channel flow double electrode method. Zn dissolved preferentially from the compound at all tested potentials between 0.1 and 1.2 V vs standard hydrogen electrode, and its rate decayed with time due to the generation of a Pt-enriched phase on the compound surface. The dissolution of Pt from the compound was observed at potentials above 0.7 V, which is about the same as the onset potential for dissolution of pure Pt electrode. The dissolution of Pt from the compound accelerated with time, and its rate was much higher than that from pure Pt. Observation of the dissolved surface revealed that a Pt-enriched surface layer with many cracks and a low crystallinity had generated. The increase in the surface area and the low crystallinity caused by the preferential dissolution of Zn were believed to bring about the high rate dissolution of Pt from the compound.

DOI： 10.1149/1.3332468

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELECTROCHEMICAL SOC INC  

Anodic dissolution rates of Au and Zn from Au-Zn compounds (beta'-AuZn and gamma(2)-AuZn(3)) in 5 mol l(-1) hydrochloric acid were measured by channel flow double electrode method. Simultaneous dissolutions of Au and Zn were observed at potentials above 0.8 V from beta'-AuZn. The dissolution rate of Au from the compound at 1.0 V was about 10 times higher than that of pure Au. On the other hand, Zn dissolved preferentially from gamma(2)-AuZn(3) at all tested potentials between 0.1 and 1.2 V, and Au started to dissolve at around 0.9 V. Chronoamperometry at 1.0 V showed that dissolution of Au from gamma(2)-AuZn(3) was slower than that of pure Au at the earlier stage, but it accelerated gradually and eventually became faster than the dissolution of pure Au. An Au-enriched-layer consisting of beta'-AuZn and Au was generated with cracks at the compound surface during dissolution, and this morphological change explained the time variation of the dissolution rate. A more effective enhancement of Au dissolution was observed in beta'-AuZn than in gamma(2)-AuZn(3). The result demonstrated the effectiveness of a Zn vapor pretreatment for leaching of Au. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3494143] All rights reserved.

DOI： 10.1149/1.3494143

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Language：Japanese   Publishing type：Internal/External technical report, pre-print, etc.   Publisher：愛媛大学教育・学生支援機構  

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Language：English   Publishing type：Book review, literature introduction, etc.   Publisher：HINDAWI PUBLISHING CORP  

Removal methods of impurity from metallurgical-grade silicon (Si) are intensively studied to produce solar-grade silicon (SoG-Si) with a smaller economical load and lower cost. Removal of phosphorus (P) has been an important issue because of difficulties in application of conventional metallurgical methods such as solidification refining. Because P evaporates preferentially from molten Si due to its high vapor pressure, electron beam(EB) melting has been applied to the purification of Si. The evaporation of impurity P from Si is considered based on previous thermodynamic investigations here, and several research reports on EB melting of Si are reviewed.

DOI： 10.1155/2013/857196

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Language：Japanese   Publisher：JAPAN INST METALS  

The hydrometallurgical recovery process of precious metals involves a great environmental load. This is because strong oxidant and complexing agents such as aqua regia are required to dissolve these metals which have high chemical stability. To enhance the dissolution, alloying with other metals may be effective as is conventionally used in production and refinement of some precious metals. When precious metal alloys are immersed in aqueous solution, the less noble metals in them dissolve preferentially and precious metals form transient particles. Thus, the Gibbs Thomson effect, which explains the excess free energy of small particles, may contribute to the enhancement. Based on the assumption, an exposure to zinc vapor was proposed as a pretreatment for the leaching of precious metals. Precious metals form alloys or intermetallic compounds with zinc during the pretreatment, and if these products can be dissolved more easily than the pure metals, the environmental load involved in the recovery will be reduced. Dissolution rates of some precious metal zinc compounds were evaluated quantitatively by channel flow double electrode method to discuss the effect of the pretreatment.

DOI： 10.2320/jinstmet.75.602

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Language：Japanese   Publisher：分離技術会  

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