稀土及晶体缺陷密度与TiFe系合金活化及吸放氢动力学的关联及机理研究

TiFe-system alloys with high hydrogen storage capacity and low cost of preparation have been considered as increasing application value in storage and shipping of hydrogen gas or hydrogen fuel tank, however, the poor activation performance and extreme hydriding/dehydriding kinetics conditions become obstacles to their practical application. The studied results show that activation and hydriding/dehydriding kinetics conditions were improved by the addition and substitution of elements, however, there also need long activation time and high pressure of hydrogen. It is confirmed by previous research that addition of rare earth elements and proper preparation technology can significantly improve the activation performance and hydriding/dehydriding kinetics of alloys, however, its mechanism is yet to be further investigated. In this project, we will intend to add a moderate amount of rare earth elements and introduce high crystal defect density in TiFe-system alloys by rapid quenching and high-energy ball-mill processing. The existing form of rare earth elements in the alloys and the influences of preparation technology process on the formation of crystal defects and distribution will be further investigated; the relationship between rare earth elements, content, preparation process and alloy activation performance will be formed and explaining its activation mechanism. The evolvement law about the crystal defects before and after hydriding/dehydriding will be explored and the effects of the change of structure on alloy hydriding/dehydriding will be investigated with illuminating the correlation between rare earth elements, preparation process and hydriding/dehydriding kinetics, and revealing mechanism of hydriding/dehydriding kinetics about alloy. It provides the theory basis for TiFe-system hydrogen storage alloy with excellent hydrogen absorption and desorption.

TiFe系合金吸氢量大、成本低廉，在氢气贮运或氢燃料箱中具有潜在应用价值，但其极差的活化性能和苛刻的吸放氢动力学条件成为其实际应用的障碍。有研究表明，通过元素添加或替代可改善其活化性能和吸放氢动力学条件，但活化仍需较长时间和高氢压。本项目前期证实，添加稀土元素和适当工艺处理可大幅度改善合金的活化性能及吸放氢动力学，但其机理尚待进一步研究。为此，拟以TiFe系合金中添加适量稀土元素为研究对象，结合快淬+短时间高能球磨在合金中引入高密度晶体缺陷，深入研究稀土元素在合金中存在形式及工艺制备过程对晶体缺陷形成及分布的影响，建立稀土元素及含量-制备工艺与活化性能之间的关系，并揭示其机理；探索合金的晶体缺陷在吸放氢前后的演变规律以及这种结构变化对合金吸放氢动力学的影响，阐明稀土及含量、制备工艺与吸放氢动力学之间的关联性，揭示合金的吸放氢动力学机制，为制备具有优异吸放氢的TiFe系贮氢合金提供理论依据。

TiFe系合金储氢量大、成本低廉，在氢气贮运或氢燃料箱中具有潜在应用价值，但其极差的活化性能和苛刻的吸放氢动力学条件成为其实际应用的障碍。通过元素添加或替代可改善其活化性能和吸放氢动力学条件。.本项目以TiFe基贮氢材料为研究起点，通过添加过渡金属及稀土作为活化元素，并采用快淬-球磨工艺制备出了具有高密度晶体缺陷的纳米晶超细复合贮氢材料，详细研究了其贮氢性能。通过Ni部分替代Fe，可形成TiFe相、第二相Ti2Fe和TiFe2相的多相结构，将TiFe合金的活化温度从573 K降到443 K。在Ni取代Fe的同时少量Mg取代Ti，并采用机械球磨制备了Ti1.09Mg0.01Fe0.9Ni0.1合金，合金为纳米晶和非晶结构，球磨之后粒径减小。机械球磨5 h会略微降低氢化物的稳定性。合金具有优异的脱氢动力学，可使脱氢时间由1800 s减小至400 s。制备了Ti1.1Fe0.8Mn0.2合金，合金形成TiFe、TiFe2和Ti1.3Fe相的多相结构，Mn替代后的合金的氢吸收能力显著增加到1.764 wt.%，同时合金的平均粒径减小，有利于降低气体活化条件，提高储氢能力和动力学。系统研究了稀土元素（La、Pr、Sm、Nd）替代Ti后合金的微观结构和储氢性能，发现合金中形成了TiFe相和TiFe2相、Ti相及稀土相，稀土元素的加入并没有显著改变相组成，仅对晶格参数产生影响。加入稀土元素后，合金的晶粒细化。稀土偏析相有利于提高氢化过程中成核率，从而提高吸氢动力学。稀土元素的加入使活化温度可降至423 K，同时也能削弱氢化物的稳定性。采用熔融纺丝法制备了快淬态合金，所有快淬态合金均保持单一的 TiFe相，快淬促进合金微观缺陷(如位错和晶界) 的产生，这利于氢扩散。.通过对本项目研究，掌握了高密度晶体缺陷纳米晶钛铁基贮氢材料微观形貌可控制备方法；详细阐述了过渡金属与RE对钛铁基合金吸放氢反应的活化机理，探讨了材料吸放氢反应动力学和热力学机制，确定了最优的活化性能材料体系，为钛铁基室温贮氢材料的发展提供了理论指导。