Disintegration and Powder Formation of Nb 75 M 25 (M = Al, Si, Ga, Ge, and Sn) Due to Hydrogenation in an Arc-melting Ch
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Disintegration and powder formation of Nb75 M25 (M 5 Al, Si, Ga, Ge, and Sn) due to hydrogenation in an arc-melting chamber Xingguo Li, Akihiko Chiba, and Seiki Takahashi Department of Materials Science and Technology, Faculty of Engineering, Iwate University, Morioka, 020, Japan
Katsuhisa Ohsaki Steel and Technology Development Laboratory, Nisshin Steel Co., LTD., Ichikawa, 272, Japan (Received 23 June 1997; accepted 20 November 1997)
Nb75 M25 (M Al, Si, Ga, Ge, and Sn) alloy ingots were prepared by the conventional arc-melting method and then were directly reacted with high purity hydrogen of 0.1 MPa in an arc-melting chamber without exposing the ingots to air. As the clean surface of the arc-melted ingots is preserved, the ingots rapidly absorb a large amount of hydrogen without any activation treatments and disintegrate violently into fine particles. The disintegration of ingots depends on the M element. The collected particles are investigated by x-ray diffraction, electron microscopy, chemical analysis, and thermal analysis. The particles are hydrides of Nb75 M25 after hydrogenation and have a sharp-edged polygonal appearance. After dehydriding, fine Nb3 M powders with A15 crystalline structure are obtained except for Nb75 Si25 . In comparison with the atomized Nb3 M powders, the Nb3 M powders prepared by the present study have a smaller average particle size and lower impurity contents.
I. INTRODUCTION
The A15 intermetallic compounds Nb3 M (M Al, Si, Ga, Ge, and Sn) have been extensively studied because of their superior superconducting property and high strength at high temperature.1– 6 Powder metallurgy process is used in the fabrication of parts of Nb3 M compounds since they are extremely brittle and lacking in deformability.7–9 Therefore, it becomes important to fabricate fine Nb3 M powders. Fabrication of Nb3 M powders was carried out in several methods such as gas-atomization, mechanical alloying, laser alloying, hammer quenching, and diffusion of Nb and M powders.10 –15 Because of the strong oxidation and the large differences in melting point and specific gravity between Nb and M, fine powders with low cost, single phase, less oxidation, and stoichiometric composition are difficult to prepare in industrial scale. To solve these problems, we investigated disintegration due to reaction of Nb3 Al ingot with hydrogen in a constant reactor and found that this phenomenon can be applied to fabrication of Nb3 Al powders.16 However, for hydrogenation of Nb3 Al ingot, a surface activation in H2 of high pressure at high temperature is necessary as the surface oxygen layers retard hydrogen absorption. To avoid surface oxidation during transportation from the arc-melting chamber to the constant reactor, hydrogenation of Nb3 Al ingot was carried out directly in the arc-melting chamber without exposing it to air after arc-melting.17 Rapid 2526
http://journals.cambridge.org
J. Mater. Res., Vol. 13, No. 9, Sep 1998
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hydrogenation of Nb3 A
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