Sc/Ti基贮氢合金结构和性能研究

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	Sc/Ti基贮氢合金结构和性能研究
	李武会
学位类型	博士
导师	吴二冬
	2012
学位授予单位	中国科学院金属研究所
学位授予地点	北京
学位专业	材料物理与化学
关键词	Laves相合金氢（氘）化物晶体结构吸氢活化热力学和动力学 Laves Phase Alloys Hydrides/deuterides Crystal Structures Hydrogen Activation Thermodynamics And Kinetics
其他摘要	" 氢能作为理想的二次能源已受到世界的关注，固态贮氢也因为本身的优势而备受青睐。近年来，尽管在贮氢材料的研发上投入了大量的人力、财力和物力，但氢能贮藏的“瓶颈”仍没有解决。Sc是最轻的过渡元素和稀土元素，Ti是紧邻着Sc的过渡元素，作为贮氢材料，不管是在重力密度上，还是在催化性能上，都具有很强的优势。因此研究和开发Sc/Ti基贮氢材料，具有一定的理论意义和现实意义。基于此，本文主要在以下七个方面进行了研究：一、通过XRD和TEM确定ScCrMn合金为罕见的理想密排C14型Laves相结构，晶格常数a=5.064(1)，c=8.263(2) Å。合金室温下0.46 kPa即可吸氢，次大气压下加氢活化速率超快。合金加氢至ScCrMnH3.9导致体积膨胀27%，但氢化物的结构仍是C14型。H/M=0.66时，氢化物的ΔH和ΔS分别为-63 kJ·mol-1、-111 J·K-1·mol-1。这些结果表明ScCrMn合金氢化物的稳定性与贮氢同位素合金ZrCo和ZrTi0.2V1.8不差上下，并在相关应用方面优于后两种合金。氢化物的DSC-TG测量表明合金可以高效催化氢解离和氧化反应。二、ScMn2氢（氘）化物保持母合金C14型Laves相结构，体积膨胀约25%；ScMn2在室温常压下能与氢（氘）迅速发生反应，具有优异的活化性能；100 kPa和298 K时，ScMn2贮氢量和贮氘量H/M约是1.23和1.22；ScMn2具有较低的吸、放氢滞后临界温度、优异的平台特征以及较低的平台压，适于氢及其同位素贮存。与室温平台压对应的合金氢化物系统的ΔH和ΔS分别为-45 kJ·mol-1和-80 J·K-1·mol-1；ScMn2在113 kPa初始氢强下吸氢（氘）动力学可用JMA模型描述，反应级数为0.4，表观活化能分别为16±0.3 kJ·mol-1和19±1.7 kJ·mol-1，此动力学同位素效应有望用于氢同位素分离；钝化后氢化物在639 K时能完全放氢，激活放氢的表观活化能为141±14 kJ·mol-1；ScMn2合金氘化后，在转变温度Tsg =205 K下出现自旋玻璃态，冻结温度Tb = 135 K。三、Ti1-xScxMnCr (x=0.05, 0.10, 0.15, 0.22, 0.27和0.32)合金基本上是C14型Laves相，但由于成分差异导致晶格常数微小变化，因此组成相不唯一。除x=0.05合金外，其它合金块体在环境条件下均易活化，并在首次加氢过程中就可达到最高贮氢量。随Sc含量增加，合金贮氢量变大，但吸放氢平台压降低。多次充放氢后的合金没有发现氢致歧化现象，氢致缺陷和粉化现象也不严重。在室温和1 - 4000 KPa压强下，Ti0.78Sc0.22MnCr合金展示了最高的~ 2 wt%可逆贮氢量。四、Sc和Zr与普通成分CrMn形成Laves相合金，展示了超常的、可同Pd相媲美的活化性能。通过裂纹机制，这些合金块体具有与Pd表面修饰合金相类似的吸氢表现。其中ScCrMn的吸氢比Pd还快，ZrCrMn则显示了与Pd类似的吸氢速率和吸放氢可逆性。ScCrMn块体取得的最短活化时间、最快活化速率和最低活化压强分别是15 s、-16.6 kPa/s、0.46 kPa，在相同条件下，Pd粉分别为18s、-3.2 kPa/s、0.13 kPa。这些发现和相应磁化率测量表明：Cr和Mn同某些低价态金属合金化，其相应的电子结构极有利于氢的解离。五、探索了Sc-Mg-Cr-Mn多种手段合金化的工作，并采用XRD、SEM和EDS对制成的合金及氢化物进行了物相、形貌和成分表征。结果表明Mg-Cr-Mn没有形成Laves相，Mg只是少量地固溶在CrMn合金立方相中；初步发现了目标相Sc-Mg-Cr-Mn新合金，且该合金较ScCrMn有更大的贮氢量。六、在本课题组发现Ti-Mo合金新ε相氢化物的基础上，通过对Ti0.85Mo0.15合金饱和氢化物原位XRD测试，推测ε相氢化物成因可能与样品氧化有关；通过对Ti0.85Mo0.15合金ε相氢化物原位XRD测试和非原位测试，研究了ε相的晶格常数随着氢含量的变化规律。七、“氢致非晶化”现象是一个非常有意的研究方向，为了更深入地开展这项工作，于法国ILL的D4c上对Ti0.68Zr0.32MnCr合金进行了不同温度下充、放氘的原位中子散射。预计原始中子散射数据经CORRECT处理后，利用RMCPOW得出氘原子与氘原子间的对分布函数，以此来解释短程与长程有序的氘原子分布及结构。但由于Al样品室的影响，还需要后续实验才能完成数据的处理。"; " Hydrogen, as an ideal secondary energy carrier, has drawn worldwide attention. Solid state hydrogen storage materials are also widely studied because of its own advantages. In recent years, although a lot of human, financial and material resources have been poured into hydrogen storage materials research and development, the hydrogen storage bottleneck is still not resolved. Sc is the lightest transition element and rare-earth element. Ti neighbors on the Sc element. Alloys which include Sc/Ti have great advantages both in the gravitational density and in catalytic performance as a potential hydrogen storage material. Therefore, the research and development of Sc/Ti-based hydrogen storage materials have certain theoretical significance and practical values. Based on this, this paper contains mainly the following seven aspects. 1. The crystal structures of ScCrMn alloy and its hydride are determined by XRD Rietveld analysis and TEM examination. The ScCrMn alloy exhibits a rarely ideal close-packed C14 type hexagonal Laves phase structure with lattice parameters a = 5.064(1), c = 8.263(2) Å. The alloy can be activated at a low pressure of 0.46 kPa and exhibit very fast absorption rate at sub-atmosphere and room temperature. The hydrogenation of the alloy to ScCrMnH3.9 results in significant lattice expansion of 27%, but does not alter the matrix lattice structure. At hydrogen concentration H/M = 0.66 corresponding to a defined room temperature plateau pressure, the relative partial molar enthalpy ΔH and entropy ΔS are -63 kJ·mol-1 and -111 J·K-1·mol-1, respectively. These results manifest that the hydride stability of the ScCrMn alloy is comparable to those of the hydrogen isotope storage alloys of ZrCo and ZrTi0.2V1.8, and would be superior on relevant applications. The DSC-TG measurements of the hydride reveal that the alloy is an effective catalyst for the dissociation of hydrogen and combination of oxygen. 2. The hydride and deuteride of the ScMn2 alloy retain the C14 type Laves phase structure of the parent alloy, with the volume expansions of about 25%. ScMn2 can react quickly with hydrogen (deuterium) at room temperature and atmospheric pressure. The hydrogen (deuterium) storage capacity of ScMn2 is about 1.23 (1.22) H/M at 100 kPa and 298 K. ScMn2 has low hysteresis critical temperature for absorption and desorption, good plateau characteristics and relatively low plateau pressure, hence is suitable for storage of hydrogen isotopes. The enthalpy and entropy for formation of ScMn2 hydride at concentration corresponding to room temperature plateau pressure are -45 kJ·mol-1 and -80 J·K-1·mol-1, respectively. The hydriding kinetics of the alloy can be interpreted by Johnson-Mehl-Avrami (JMA) model, with the estimated reaction order of 0.4. The apparent activation energies for hydriding and deteuriding process are estimated to be 16±0.3 kJ·mol-1 and 19±1.7 kJ·mol-1, respectively, and the observed isotope effect on kinetics can possibly be applied to separation of hydrogen isotope. The passivated hydride can release completely at 639 K and the corresponding apparent activation energy is 144±14 kJ·mol-1. After the ScMn2 was deuterided, the spin glass state appeared at Tsg =205 Kand the blocking transformation temperature Tb is 135 K. 3. The Ti1-xScxMnCr (x = 0.05, 0.10, 0.15, 0.22, 0.27 and 0.32) alloys are basically C14 type Laves phase with slightly different lattice parameters owing to the difference in composition. Except for x = 0.05 alloy, the bulk samples of these alloys can be easily activated under ambient conditions and attain the maximum hydrogen storage capacities during the initial hydrogenation. As Sc content increases, the hydrogen storage capacity of the alloy increases whereas the pressure of the absorption/desorption plateau decreases. No hydrogen induced disproportionation is observed, and the pulverization and hydrogen induced defects are not severe after hydriding/dehydriding cycles of these alloys. The Ti0.78Sc0.22MnCr alloy exhibits the best reversible hydrogen storage capacity of ~ 2 wt% in between 1-4000 kPa at room temperature. 4. The Laves phase Sc and Zr alloys with CrMn as common components exhibit extraordinary hydrogen activation properties matching Pd. Through a cracking mechanism, the bulk samples of these alloys rapidly absorb hydrogen at sub-atmospheric pressures and room-temperature, and achieve absorption performance of those Pd surface-modified alloys. Among them, the ScCrMn exhibits significantly higher absorption rate than Pd, whereas, the ZrCrMn shows similar absorption kinetics and reversibility to Pd. The shortest initial-activation-time, highest initial-activation-rate and lowest allowed-activation-pressure achieved by ScCrMn are 15 s, -16.6 kPa/s and 0.46 kPa, respectively, in comparison with those of 18 s, -3.2 kPa/s and 0.13 kPa for Pd powder measured under equivalent conditions. The findings and associated magnetization measurements indicate that Cr and Mn upon alloying with certain lower valence metals possess surface electronic structures highly beneficial to hydrogen dissociation. 5. The Sc-Mg-Cr-Mn alloying work has been explored by many means, and the makeup phase, morphology and composition of the prepared alloys and hydrides have been characterized by XRD, SEM and EDS. The results show that the Mg-Cr-Mn samples don’t form a Laves phase, instead, a small amount of Mg precipitate into cubic phase CrMn alloy. It is initially found that the target phase Sc-Mg-Cr-Mn alloy occurred and the hydrogen capacity of the novel alloy is higher than that of ScCrMn. 6. Based on the new ε phase hydride in Ti-Mo-H system discovered by our research group, the causes of the ε phase formation are further investigated by virtue of in-situ XRD measurement for Ti0.85Mo0.15 alloy saturated hydride. It has been found that the ε phase formation is possibly related to the sample oxidation involved. Through in-situ and off-situ XRD measurement for Ti0.85Mo0.15 alloy ε phase hydride, the dependence of the ε phase lattice constants on the hydrogen concentration have been studied. 7. The “hydrogen-induced amorphization” phenomenon is an interesting study direction. In order to further develop the work, in-situ D4c neutron scattering measurement in ILL was carried out for Ti0.68Zr0.32MnCr alloy absorbing and desorbing deuterium at different temperatures. It was expected that after the raw neutron scattering data were proceeded using CORRECT program, the D-D pair distribution functions were obtained by inputting the treated data to RMCPOW program, then the deuterium atoms distribution with the short and long distance order and the structure could be explained. Unexpectedly, due to the influence of Al sample cell, the follow-up experiment to complete data processing is still required."
文献类型	学位论文
条目标识符	http://ir.imr.ac.cn/handle/321006/64455
专题	中国科学院金属研究所
推荐引用方式 GB/T 7714	李武会. Sc/Ti基贮氢合金结构和性能研究[D]. 北京. 中国科学院金属研究所,2012.