| Budget Amount *help |
¥2,700,000 (Direct Cost: ¥2,700,000)
Fiscal Year 2004: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 2003: ¥900,000 (Direct Cost: ¥900,000)
Fiscal Year 2002: ¥1,300,000 (Direct Cost: ¥1,300,000)
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| Research Abstract |
Ti-Cr hydrogen storage alloys easily absorb and desorb hydrogen at low temperatures below 273K. However, there are few reports of the detailed kinetic property of hydrogen absorption and mechanism of initial activation at low temperatures. Therefore, we report on the research about the following contents.
Hydrogen absorbing properties was measured from pressure, concentration and temperature about the TiCr1.7 and Ti-Cr alloys. Initial activation was annealing at 873K for 4h and Ti-Cr alloys have been activated at hydrogen gas of 0.87MPa. Influence of surface contaminations on the kinetic properties of hydrogen absorption were measured to pressure dependence and temperature dependence. The surface of the alloys were exposed to air from 30 minutes to 10 hours in low vacua.
The alkaline treatment of the surface of the alloys was made by sticking potassium (K) metal onto the alloy block surface or by immersing sample into 8M-KOH solution. In LaNi5, the improvement of the initial hydrogen abs
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orption rate was obtained by both methods. In Ti-Cr alloys, the improvement of rate was obtained by dry methods, but methods by alkaline solution could not be obtained.
Reactivities of H_2, O_2 and H_2O with the Cr Surface between 77 K and 298 K
The quantitative reactivities of H_2, O_2 and H_2O on the polycrystalline Cr surface prepared under ultra high vacuum condition were measured volumetrically at pressures ranging from 10^<-8> to 10^<-2> Pa and at 298 K. For the Cr-H_2 system, the reactivity was measured also at 77 K. In this study, the volumetric Wagener method was used to measure the reaction probability (reaction coefficient) r, the ratio of the rate of adsorption or absorption of gas molecules to the impinging rate of gas molecules on the Cr surface, as a function of the gas amount reacted with the Cr surface.
The Cr with a clean surface exhibited the highest reactivity r=1 for H_2 at temperatures at 77 K and 298 K, and for O_2 and H_2O at 298 K. The reactivity of H2 with the Cr with a clean surface at 298 K was found to be much higher than that of Ni or Co. The clean Cr surface exhibits the high reactivities as the clean Co surface does even at 298 K. These results suggest the formation of stable and complex H chemisorption states or hydride layers with high H coverages on the Cr surface at 298 K. In the H_2O reactivity with Cr, the uptake rate of H atoms from H_2 or H_2O was found very high even at 298 K. In the H_2O exposure, the change in the reactivity indicates the formation of Cr hydroxide on the surface. These results may be helpful for the understanding of the reaction mechanisms of these gases with the surface of Ti-Cr based alloys or hydrogen absorbing materials containing Cr element. Less
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