Journal of the Japan Society of Powder and Powder Metallurgy

Studies on the Formation and Reduction of the Tungsten Trioxide

(II) Studies on the Process of Reduction of Tungsten Trioxide

Yungpil Ahn

1962 Volume 9 Issue 3 Pages 93-101
Published: June 25, 1962
Released on J-STAGE: May 22, 2009

DOIhttps://doi.org/10.2497/jjspm.9.93

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The process of reduction of tungsten trioxide in both dry and wet hydrogen was studied by means of the weight loss measurement, the X-ray analysis, the surface area measurement and the observation by electronmicroscope. The results obtained are as follows.
(1) The reduction rate differs from each stage of the reaction mentioned above and it also changes with the time duration of reduction. However, the reduction rate of α-tungsten oxide to metallic tungsten maintains a constant value until the reaction almost completes.
(2) The average size of the tungsten particles produced by the reduction in hydrogen is affected mainly by the reduction temperature and also by the partial pressure of water vapor in hydrogen.

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A Study on Manufacture of Copper Powder by Atomization

Kiyoshi Tamura, Toru Takeda

1962 Volume 9 Issue 3 Pages 102-108
Published: June 25, 1962
Released on J-STAGE: December 04, 2009

DOIhttps://doi.org/10.2497/jjspm.9.102

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With the object of atomizing high melting metals by some suitable design of jet using air, steam, water or other expansible fluid, the present authors newly designed ring-type atomizing nozzle, by which molten copper was atomized with air.
In the present work, the effects of certain atomizing variables upon the characteristics of the produced copper powder and its particle size distribution have been examined.
The results are as follows;
1) When other atomizing variables remain constant, the peak of particle size distribution curve always occurs at the range of 40 to 50 microns in spite of increasing compressed air pressure.
2) Molten copper atomized with air develops a powder the particles of which are substantially spherical, and this leads to powder of high apparent density-usually between 5.0 and to 5.5 g/cm³ and of good flow factor, -approximately 15 sec.
3) The microstructure of the powder shows that copper atomized with air includes Cu₂O and its concentration becomes higher with approaching outer surface, and also the smaller the particle size, the lower Cu₂O concentration.

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On the Phase Diagram of the Cr-O System at High Pressure of Oxygen and Some Properties of the Compound CrO_2+X

Yasumasa Goto, Toshio Kitamura

1962 Volume 9 Issue 3 Pages 109-113
Published: June 25, 1962
Released on J-STAGE: May 22, 2009

DOIhttps://doi.org/10.2497/jjspm.9.109

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The pressure versus temperature diagram of the chromium oxides (Cr₂O₅, CrO₂ and Cr₂O₃) was determined by the closed vessel method in the range of higher oxygen pressures up to 600 atms. Chromium pentaoxide Cr₂O₅ is comparatively stable below 200°C, but it dissociates into CrO₂ above this temperature. The stable ranges of CrO₂ and Cr₂O₃ in the diagram are separated by the dissociation pressure curve of CrO₂ which rises exponentially with increasing temperature through the points (450°C, 100 atms.) and (520°C, 600 atms.). The presence of Cr₃O₈, which had been reported to be stable at room temperature, was not confirmed above 200°C in the present experiments. The results of determination of oxygen contents in CrO₂ phase indicate that this phase is non-stoichiometric; their composition varies from CrO_1.92 to CrO_2.02 depending on the equilibrium conditions. The ratio of O/Cr increases with the fall of temperature and incresing oxygen pressure. The lattice constants of CrO_2+X (rutile type structure) decrease with increasing oxygen contents. The latter effect is quite consistent when we assume that the excess Cr ion are present as interstitials at the interlattice points of oxygen. The accurate lattice constants of stoichiometric compound CrO₂ are found to be a=4.408, c=2.910 a.u., a/c=1.51. The saturation magnetization of CrO_2+X at room temperature seems to increase with increasing O/Cr ratio. The ferromagnetic Curie point of them, how-ever, seems not to change with O/Cr ratio by more than 10°C.

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