Research of reaction properties of Hydrogen storage alloys

钛铬储氢合金在273K以下的低温下容易吸放氢。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。本文从压力、浓度和温度三个方面对TiCr1.7和钛铬合金的吸氢性能进行了测试。初始活化温度为873K，保温时间为4h，钛铬合金在0.87 Mpa的氢气中活化。测量了表面污染物对吸氢动力学性质的影响，包括压力依赖关系和温度依赖关系。合金表面在低真空下暴露于空气中30分钟至10小时，通过在合金块表面粘上钾(K)金属或将样品浸入8M-KOH溶液中进行碱性处理。在LaNi5中，对初氢abs…的改进两种方法均可获得较高的吸附速率。在77~298K温度范围内，H_2、O_2和H_2O与铬表面的反应活性在77~298K之间。在本研究中，用体积瓦格纳法测定了气体分子在铬表面的吸附或吸收速率与气体分子在铬表面的撞击速率的比值r，它是与铬表面反应的气体量的函数。在77K和298K温度下，清洁表面的铬对氢的反应活性最高，r=1。而对于298K的O2和H2O，在298K时，H_2与清洁表面的铬的反应活性远高于Ni或Co。清洁的铬表面表现出与清洁的Co表面一样的高反应活性。这些结果表明，在298K时，铬表面形成了稳定的复杂的H化学吸附状态或具有高H覆盖率的氢化物层。在H_2O与Cr的反应中，即使在298K时，H_2或H_2O对H原子的吸收也很高。反应性的变化表明在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钛铬基合金或含铬吸氢材料表面的反应机理。较少

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