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Toyonaka, Japan

Katoh M.,ALMT Corporation | Hayashi K.,A.L.M.T. Tungsten Corporation | Araki T.,Toshiba Corporation | Yoshida M.,Panasonic | And 5 more authors.
Funtai Oyobi Fummatsu Yakin/Journal of the Japan Society of Powder and Powder Metallurgy | Year: 2011

As the starting material of molybdenum manufactured by powder metallurgy, molybdenum powder is used. To investigate the elution in water of the molybdenum powder used as a raw material, the molybdenum elution was analyzed by ion chromatography and X-ray photoelectron spectroscopy (XPS). It was clarified that the elution based on MoO4 2- takes place as determined by ion chromatography. Results of the surface measurement by XPS revealed that, the molybdenum oxidized in air on the surface exists mainly as molybdenum (VI) oxide (M0O3), which is the most stable oxide. The molybdenum (VI) oxide elutes promptly in water compared with the metal powder. The oxide on the molybdenum metal surface, which was assumed to be eluted promptly, became thin, and the elution was repeated again by oxidation in water through molybdenum (IV) (MoO2), (V) (Mo2O5) and (VI) oxides, and the solution was clarified to elute through molybdenum (VI) oxide. Source


Katoh M.,ALMT Corporation | Hayashi K.,A.L.M.T. Tungsten Corporation | Yoshida M.,Panasonic | Fukuda M.,Japan New Metals Co. | And 4 more authors.
Funtai Oyobi Fummatsu Yakin/Journal of the Japan Society of Powder and Powder Metallurgy | Year: 2010

The press process of molybdenum is done without using an organic binder when the molybdenum is manufactured at high temperature used in powder metallurgy. The decrease in the molybdenum ingot density, which was a factor in the yield decrease of the molybdenum product, is occurred because of remaining moisture and the presence of molybdenum oxide in molybdenum metal powder. To clarify the cause of the yield decrease, the uniform distribution process of the rare earth salt by wet doping into molybdenum and the molybdenum elution to water were examined. The dopants provide a unique effect on the thermal-deformation resistance of molybdenum. In solvents of purified water and tap water, the amount of elution of molybdenum was examined as dependence on molybdenum particle sizes and the temperatures of the solvent. Moreover, elution results obtained using alkali and acid water solvents were compared. As a result, it can be suggested that a steady dope manufacturing condition can be obtained by using the metallic molybdenum or MoO2 as the raw powder, as well as by the use of purified water held at a low temperature. Source


Patent
Japan New Metals Co. and Jx Nippon Mining & Metals Corporation | Date: 2010-09-28

Provided is a method for producing a high-purity tungsten powder having a phosphorus content of less than 1 wtppm; wherein an ammonium tungstate solution containing 1 wtppm or more of phosphorus as an impurity in terms of the inclusion in tungsten is used as a starting material, this solution is neutralized with hydrochloric acid at a temperature of 50 C. or less to adjust the pH at 4 or more and less than 7 so as to precipitate ammonium paratungstate undecahydrate crystals, the resulting solution is heated to 70 to 90 C. and filtered in a high-temperature state so as to obtain ammonium paratungstate pentahydrate crystals, the obtained crystals are calcined so as to form a tungsten oxide, and the tungsten oxide is subject to hydrogen reduction so as to obtain a high-purity tungsten powder. Additionally provided is a method for producing a high-purity tungsten powder having a phosphorus content of 0.4 wtppm or less; wherein the ammonium tungstate solution is neutralized with hydrochloric acid to adjust the pH at 4 or more and 6 or less, and this solution is subject to the same procedure as described above so as to obtain a high-purity tungsten powder. Consequently, the phosphorus content can be efficiently reduced.


Sugiyama I.,University of Tokyo | Sugiyama I.,Tohoku University | Mizumukai Y.,University of Tokyo | Taniuchi T.,Mitsubishi Group | And 9 more authors.
International Journal of Refractory Metals and Hard Materials | Year: 2015

Carbon content dependency of grain growth mechanism and grain growth inhibition mechanism in VC-doped WC-Co hardmetals is investigated. VC-doped WC-Co hardmetals with three different carbon contents were sintered with liquid phase and then rapidly quenched to freeze up the structure at the sintering temperature. In these samples, spatial distributions and atomic scale structures of V-rich phases are investigated using transmission electron microscopy (TEM) and related techniques. In these measurements, doped V is found in liquid phase as solute, in large (W,V)Cx precipitates and in interface segregations. Further detailed observations and discussions are carried out for the (W,V)Cx segregated at the WC grain/Co phase interfaces. These (W,V)Cx phases change their form from planar films to small islands depending on the carbon content. The WC grain/Co phase interfaces are fully covered by planar (W,V)Cx in the sample of low carbon content. On the other hand, the WC grain/Co phase interfaces are partially covered by (W,V)Cx islands in the material of high carbon content. During sintering, the WC grains in this sample grew much faster than those in the sample of low carbon content. These structural differences are discussed in terms of WC grain/(W,V)Cx interface energy. © 2015 Elsevier Ltd. All rights reserved. Source


Sugiyama I.,University of Tokyo | Mizumukai Y.,University of Tokyo | Taniuchi T.,Mitsubishi Group | Okada K.,Mitsubishi Group | And 7 more authors.
International Journal of Refractory Metals and Hard Materials | Year: 2012

The (W,V)Cx thin layers at the WC/Co interfaces in the oil-quenched WC-12mass%Co-0.5mass%VC hard metal were investigated by high resolution transmission electron microscopy. The (W,V)Cx thin layers are formed on the liquid phase sintering state, because they are observed on the micro-facets and some of them are included inside the WC grains. The grain growth rate strongly depends on whether the thickness of the (W,V)Cx layers is more than one layer or less during liquid-phase sintering. © 2011 Elsevier Ltd. All rights reserved. Source

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