PubMed | Fuji Die Co., Osaka Prefecture University, Japan Synchrotron Radiation Research Institute and University of Tokyo
Type: | Journal: Advanced materials (Deerfield Beach, Fla.) | Year: 2016
Bifunctional electrocatalysts for oxygen evolution/reduction reaction (OER/ORR) are desirable for the development of energy conversion technologies. It is discovered that the manganese quadruple perovskites CaMn
PubMed | Japan Synchrotron Radiation Research Institute, Japan National Institute of Materials Science, National Research Nuclear University MEPhI, Tokyo Institute of Technology and 4 more.
Type: | Journal: Scientific reports | Year: 2014
Silicon dioxide has eight stable crystalline phases at conditions of the Earths rocky parts. Many metastable phases including amorphous phases have been known, which indicates the presence of large kinetic barriers. As a consequence, some crystalline silica phases transform to amorphous phases by bypassing the liquid via two different pathways. Here we show a new pathway, a fracture-induced amorphization of stishovite that is a high-pressure polymorph. The amorphization accompanies a huge volume expansion of ~100% and occurs in a thin layer whose thickness from the fracture surface is several tens of nanometers. Amorphous silica materials that look like strings or worms were observed on the fracture surfaces. The amount of amorphous silica near the fracture surfaces is positively correlated with indentation fracture toughness. This result indicates that the fracture-induced amorphization causes toughening of stishovite polycrystals. The fracture-induced solid-state amorphization may provide a potential platform for toughening in ceramics.
Osaka Prefecture University and Fuji Die Co. | Date: 2016-05-31
A catalyst for an oxygen evolution reaction has a higher and longer-life catalytic activity than that of the conventional and expensive noble metal oxide catalysts, such as RuO_(2 )and IrO_(2). An A-site ordered perovskite oxide catalyst (such as CaCu_(3)Fe_(4)O_(12 )and CaMn_(3)Mn_(4)O_(12 )etc.) as an oxygen evolution reaction catalyst is excellent in cost effectiveness. The catalyst has a high catalytic activity compared with a noble metal oxide catalyst, and a long repetition use life since it is extremely stable also under the oxidative reaction conditions. Use of the catalyst is expected to the important energy conversion reactions such as a charge reaction of a metal-air battery, an anode oxygen evolution reaction in the case of a direct water decomposition reaction by sunlight, etc.
Shoji T.,Fuji Die Co. |
Ogura T.,Fuji Die Co. |
Sasaki A.,Fuji Die Co. |
Terada O.,Fuji Die Co. |
Hayashi K.,University of Tokyo
Funtai Oyobi Fummatsu Yakin/Journal of the Japan Society of Powder and Powder Metallurgy | Year: 2010
In the commercial production of thick compact for Ti(C,N)-base cermet and WC-base cemented carbide, it is said that sintering crack tends to occur in the former, compared with in the latter. This and the inferior toughness, etc., are main reasons for the minor application of cermet to wear resistant parts that are usually thicker than cutting tools. In this study, the cause for the sintering crack was firstly investigated from various viewpoints. The sintering crack was shown to occur during de-waxing process of the compact. The main cause was suggested to be the presence of a large amount of fine particles generated by ball-milling particularly in Ti(C,N)-base mixed powders: (1) Under the presence, molten wax makes the pores among particles closed and/or their sizes further smaller, leading to strongly restrict the smooth escape of included gases through pores, and (2) the sintering crack occurs when the gas pressure (the maximum: the equilibrium evaporation pressure) increased by the restriction exceeds the fracture strength of the compact. Based on this suggestion, it was clarified that the sintering crack could be avoided by using hard-to-pulverize Ti(C,N) special-type raw powder with more uniform grain size.
Kawakami M.,Fuji Die Co. |
Kitamura K.,Fuji Die Co.
Materials Transactions | Year: 2015
The segregation of V and Cr at WC/Co and WC/WC interfaces in ultrafine-grained WC-0.7VC-1.4Cr3C2-10Co (mass%) cemented carbides produced through solid-state sintering and semi-sintering was investigated. This segregation was compared against that of a liquid-statesintered specimen to elucidate the mechanism by which WC grain growth is inhibited by Vand Cr. The Vand Cr were found to segregate at the WC/Co and WC/WC interfaces during solid-state sintering and semi-sintering, but no differences were observed in the Vand Cr concentrations at the interfaces among the liquid-state-sintered, solid-state-sintered and semi-sintered specimens. Furthermore, these concentrations were unchanged by quenching of the solid-state-sintered specimen. From these results, it was concluded that (V,W,Cr)Cx segregation layers are stably formed at the WC/Co and WC/WC interfaces at a temperature below the solidus of the Co phase, but almost dissolve in the liquid Co phase once the temperature exceeds its liquidus. Thus, the (V,W,Cr)Cx segregation layers observed at the WC/Co and WC/WC interfaces at room temperature are formed during the cooling that follows the liquid-state sintering. This supports the finding that WC grain growth is inhibited by the adsorption of dopant atoms onto steps/kinks on the WC surface during liquid-state sintering, as well as by the segregation layers formed on the WC surface during solid-state sintering. © 2015 The Japan Institute of Metals and Materials.
Kawakami M.,FUJI DIE Co. |
Kitamura K.,FUJI DIE Co. |
Terada O.,FUJI DIE Co.
Advances in Tungsten, Refractory and Hardmaterials IX - Proceedings of the 9th International Conference on Tungsten, Refractory and Hardmaterials | Year: 2014
Between 2004 and 2012, we developed 0.1 μm-grained cemented carbides with a Co content of 0-30 mass%. The mechanical properties of these 0.1 μm-grained cemented carbides, especially their transverse-rupture strength (three-point bending strength) and hardness, were proven to be superior to those of conventional cemented carbides. It was also expected that the size and number of defects in these 0.1 μm-grained cemented carbides would be very small. Thus, the transverse-rupture strength, critical defect size for fracture, and location of defects in a 0.1 μm-grained WC-0.7 mass%VC-1.4 mass%Cr3C2-10 mass%Co cemented carbide were investigated, and compared against conventional submicro-grained (0.4 and 0.5 μm) WC-XC-Co cemented carbides (where XC = VC + Cr3C2). The stress concentrated at the fracture source was calculated from the transverse-rupture strength, the defect size, the distance between the defect and the span center, and the distance between the defect and the tension surface. Through this, it was found that a linear relationship was satisfied between the inverse of this concentrated stress and the square root of half the defect size in 0.1 μm-grained cemented carbides. From the slope and intercept of this linear relation, along with the defect stress concentration factor and fracture condition equation, the strength of the alloy in the micro region surrounding a defect was calculated.
Kawakami M.,Fuji Die Co. |
Kitamura K.,Fuji Die Co.
International Journal of Refractory Metals and Hard Materials | Year: 2015
Abstract The WC/WC interface in VC-doped submicron-grained WC-Co cemented carbides was investigated using high-resolution transmission electron microscopy (HRTEM) and energy-dispersive X-ray microanalysis (XMA) spectroscopy. Both V and Co were segregated at WC(0001)/WC(0001) or WC(0001)/WC(randomly oriented plane) interfaces and were slightly segregated at WC(101¯0)/WC(101¯0) or WC(101¯0)/WC(randomly oriented plane) interfaces. The V concentrations at these interfaces were 6-14 at.% and 2-6 at.%, respectively, and the Co concentrations were 7-20 at.% and 4-28 at.%, respectively. The V concentration depended on the WC crystallographic orientation, whereas the Co concentration had a small correlation. On the basis of this result and the previous results for the WC/Co interface, it is concluded that the segregation of V at WC/WC interfaces occurs by the same mechanism as that at WC/Co interfaces. In particular, rather than equilibrium segregation occurring during the heating and holding stages of sintering, segregation onto the WC surface proceeds during the cooling stage of the sintering process. © 2015 Elsevier Ltd.