Research of reaction properties of Hydrogen storage alloys

在273K以下的低温下，Ti-Cr储氢合金容易吸附和解吸氢。然而，关于低温下吸氢的详细动力学性质和初始活化机理的报道很少。因此，我们报告了以下内容的研究。从压力、浓度和温度三个方面对TiCr1.7和Ti-Cr合金的吸氢性能进行了测试。初始活化是在873K下退火4h， Ti-Cr合金在0.87MPa的氢气下活化。测定了表面污染对吸氢动力学性质的影响，并对其进行了压力依赖性和温度依赖性测试。合金表面在低真空条件下暴露在空气中30分钟至10小时。合金表面的碱性处理方法是将金属钾(K)粘附在合金块表面或将样品浸入8M-KOH溶液中。在LaNi5中，两种方法均提高了初始氢吸附率。在Ti-Cr合金中，用干法可以提高速率，而用碱性溶液不能提高速率。H_2、O_2和H_2O在77 ~ 298 K范围内与Cr表面的反应活性。在超高真空条件下制备的多晶Cr表面上，H_2、O_2和H_2O在压力范围为10^<-8 ~ 10^<-2> Pa和298 K下的定量反应活性进行了体积测量。对Cr-H_2体系在77 K时的反应性也进行了测定。在本研究中，采用体积Wagener法测量反应概率（反应系数）r，即气体分子的吸附速率或吸收率与气体分子在Cr表面的撞击速率之比，作为与Cr表面反应的气体量的函数。表面清洁的Cr在77 K和298 K下对H_2的反应活性最高，对O_2和H_2O的反应活性r=1最高。H2与表面清洁的Cr在298 K时的反应活性远高于Ni或Co，即使在298 K时，清洁的Cr表面也表现出与清洁的Co表面相同的高反应活性。这些结果表明，在298 K时，Cr表面形成了稳定而复杂的H化学吸附态或高H覆盖率的氢化物层。在H_2O与Cr的反应中，即使在298 K时，H_2或H_2O对H原子的吸收率也很高。在H_2O作用下，反应性的变化表明表面形成了氢氧化铬。这些结果可能有助于理解这些气体与Ti-Cr基合金或含Cr元素的吸氢材料表面的反应机理。少

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 … More 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 KThe 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