Surface Structure and Electrochemical Characteristics of Ti-V-Cr BCC-Type Solid Solution Alloys Sintered with NI
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apparatus. Each sample was put in a stainless reactor tube. The reactor was outgassed for 1 hour at 25 °C, then hydrogen gas was admitted until 3 Mpa. The activated sample was vacuumed for 5 hours at 200 OCbefore the measurement to determine the origin. The as-cast alloys were pulverized by hydriding and then mechanically ground to prepare powder below 75 [tm. The alloy powders were covered with Ni by mixing Ni fine powder (0.03 rtm) or electroless plating. The sintering was performed in a vacuum of 0.133 Pa at various temperatures. The crystal structures were identified by X-ray diffraction measurement. The surface microstructure was examined by SEM (scanning electron microscopy) and EPMA (electron probe X-ray microanalysis). Electrochemical measurement The alloy electrodes were prepared by pressing the mixture of 0.1 g of alloy powder and 0.4
g of Cu powder into a pellet of 10 mm diameter at 3.8 ton/cm2 . The pellets were covered by Ni mesh as current corrector. The electrochemical measurements were performed in 31 wt.% KOH electrolyte at 25 °C using a half cell where the counter electrode was Ni(OH) 2. The electrodes were charged at 100 mA/g for 8 hours at first cycle and 5.5 hours from second cycle and discharged at 50 mA/g to the cut off voltage of -0.85 V vs. Ni(OH) 2 . RESULTS The hydrogen absorbing capacity of V is greatly influenced by metal purity [7]. Impurities, such as oxygen, cause the decrease of capacity. In Ti-V-Cr system alloys, the same characteristics were observed. Therefore, La and Zr with strong affinity with oxygen were added to improve the hydrogen absorbing capacity. The base composition was Ti0 .3V0 .55Cro. 15. 1.5 at.% and 2 at.% of La and Zr respectively were added and the composition of Tio. 285La0 .015V0 .55Cr0 1. 5 and Ti0 .3Zr0 .02V0 .53Cr0 1 5 were produced The PCT curves of these alloys are shown in Fig. 1. While the PCT characteristics of the alloy with Zr was almost the same as the original one, the hydrogen absorbing capacity of the alloy with La increased about H/M = 0.1. The standard enthalpy of oxide formations are -1793.7 kJ/mol for La 20 3 and -1097.5 kJ/mol for ZrO 2, and it is thought that deoxidization effect of La is larger than Zr. The obtained hydrogen absorbing capacity was almost the same as that of zonerefined V.
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Ti, 285 Lao015Vo JCr,5 . T. Ti 3Zr° 02VO 53C r° 15.]
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H/M . V0 .55Cro. 1 5, Fig.1 PCT curves of (0) Ti0 .3V0.55Cr0 .15 , (0) Ti0.285La0015 and (A) Ti0.3Zr0 .0 2V0.53Cr0 1. 5 at 343 K.
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Examination of Ni sintering conditions The alloy of Ti0 3Zr00. 2V0 .53Cr0 .J5 was mixed with 10 wt.% of Ni fine powder and sintered at various temperatures for 1 hour. The X-ray-diffraction patterns of these alloys are indicated in Fig. 2. After sintering at 600 C, the peaks of nickel has disappeared, so most of Ni seemed to be alloyed. Furthermore, the peaks of another bcc phase appeared in the high angle side of the peak of the original alloy. These were identified to be the pe
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