REPARATION OF FINE WIRES OF HYDROGEN STORAGE ALLOY WITH FINE CRYSTAL GRAIN BY THE IN-ROTATING-WATER SPINNING METHOD

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Studies were conducted to prepare a fine wire of hydrogen storage alloy by the In-Rotating-Water Spinning Method. In the first fiscal year, preliminary tests were conducted to melt alloy samples in a nozzle by induction heating and to eject the melt through the nozzle by argon back pressure. A Mm-Ni based alloy system and two Ti-Zr based alloy systems were employed as the test materials. A quartz nozzle with the mouth diameter of 0.25 mm was used. The capacity of a high-frequency induction heating apparatus(200 kHz, 5kW) was large enough to melt the Mm-Ni based alloy system but it was not enough for the Ti-Zr based alloy systems. The melt of Mm-Ni based alloy did not eject through the nozzle when the back pressure of 0.35 MPa was pressed by argon gas. This was due to the existence of slug in the melt formed by the reaction with the quartz nozzle. Then, nozzles made of carbon and alumina were tested. However, both of them were not satisfactory for the present purpose. A theoretical stud … More y on the occurrence of the minimum-heat-flux point that plays an important role during the rapid quenching process was also conducted. In the second fiscal year, an induction heating apparatus with a larger frequency(400 kHz, 5 kW) and a new induction coil were introduced. The mouth diameter of the quartz nozzle was changed to 0.5 mm. The test alloy was also changed to LaNi_5. The LaNi_5 alloy of 3 g was heated to 1450 ℃ in the nozzle and was completely melted. Then it was injected into the water layer of 1.5 mm in depth that was formed on the inside surface of a drum rotating at a velocity of 7 m/s and rapidly solidified. The geometrical shape of the product was about 30-cm long wires of 0.15 to 0.5 mm in diameter, ribbons with different lengths, or small droplets. The optimum back pressure for obtaining a thin wire was 0.3 MPa. The PCT diagram of the product showed a steeper pressure plateau than the ingot and the hydrogen-storage capacity decreased to about 70% of the latter. It was also found that the sample of alloy that was melted and then solidified gradually in quartz nozzle showed the PCT diagram similar to that of the product. The SEM view and the composition analysis by ESCA of the product showed that 2 μm thick layer of oxide was formed on the surface. However, this amount was small enough. Thus the bulk of the product was considered to be oxidized in the quartz nozzle during the melting process. According to the EPMA analysis, Ni was observed at the surface of the product. However, the composition of inner part was the same as the ingot. These results indicated that the reaction of the melt with the nozzle surface should be minimized to prevent the deterioration of the PCT characteristics. Less