Mechanisms of hydride formation in hydrogen-absorbing alloys - with special attention to introduction of lattice defects -

吸氢合金中氢化物形成的机制 - 特别注意晶格缺陷的引入 -

• 批准号: 12450282
• 负责人: INUI Haruyuki
• 金额: $ 10.5万
• 依托单位: KYOTO UNIVERSITY
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (B)
• 财政年份: 2000
• 资助国家: 日本
• 起止时间: 2000 至 2001
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-12450282/
• 关键词: Hydrogen-absorbing alloy; Absorption pressure; Activation; Powdering; Lattice defects; Dislocation; Crack; Transmission electron microscopy

Hydrogen-absorbing alloys have attracted considerable interest since they have been used as negative electrode materials and are expected to be used as storage media of clean energy. In general, the hydrogen-absorption pressure is believed to be determined by the site energy for hydrogen atoms in the corresponding alloys. In the present study, however, we investigated whether or not there are any other important factors that influence the magnitude of absorption pressures and how importantly they plays a role in determining the absorption pressure. LaNi_5, TiMn_2 and FeTi were used in the present study. For binary and Co-alloyed LaNi_5, the absorption pressure is high only for the first cycle and it stays almost constant for the subsequent cycles. The desorption pressure these alloys does not depends on cycle number. Cracking (powdering) occurs significantly from the first cycle and the effective particle size after one cycle is comparable to that observed after ten cycles, indicating … More that the first cycle plays a decisive role in powdering of these alloys. A considerably high density of dislocations of the order of 10^<12> cm^<-2> are introduced during the first absorption cycle. Most of these dislocations are a-type edge dislocations aligned parallel to the c-axis and they are considered to be misfit dislocations formed at the interface between the matrix and hydride. Careful inspection indicates that the hydride is formed in a plate shape with the c-and one of the a-axes being contained in the plate face and a high density of dislocations are introduced only inside the hydride. This indicates that misfit the matrix/hydride interface advances by forming misfit dislocations and that misfit dislocations once formed are incorporated in the hydride during the course of hydride growth. The high absorption pressure for the first cycle is thus considered due to the over-pressure required to form dislocations and the over-pressure required to form cracks. In Al-alloyed LaNi_5 and TiMn_2, while significant cracking (powdering) occurs during the first absorption cycle, almost no dislocations are introduced in any of cycle number. As a result, the absorption pressure for the first cycle is only moderately higher than that for any other cycles. This is considered to be due to the fact that the matrix/hydride interface in these alloys is broader than that in binary and Co-alloyed LaNi_5,in terms of hydrogen concentration (lattice parameter). This implies that hydrides with intermediate hydrogen concentrations are relatively stable with respect to the matrix and hydride. Two plateaus are observed in P-C isotherms for FeTi, indicating the existence of two different hydrides. The absorption pressure for the first plateau ever decreases with cycle number. The extent of cracking during cycling for FeTi is significantly reduced when compared to the other investigated alloys. These indicates that the introduction of dislocations occurs persistently during cycling and the decrease in absorption pressure with cycle number is due to the decrease in the density of introduced dislocations with cycle number. Less

吸氢合金作为负极材料和清洁能源的储存介质，引起了人们极大的兴趣。通常，氢吸收压力被认为是由氢原子在相应合金中的位置能量决定的。然而，在本研究中，我们调查了是否有任何其他重要因素影响吸收压力的大小，以及它们在确定吸收压力方面发挥的作用有多重要。本研究采用LaNi_5，TiMn_2和FeTi。对于二元和Co合金化的LaNi_5，只有第一次循环的吸收压力较高，以后的循环吸收压力基本保持不变。这些合金的脱附压力与循环次数无关.开裂（粉化）从第一个循环开始显著发生，并且一个循环后的有效粒度与十个循环后观察到的相当，表明 ...更多信息 第一循环在这些合金的粉末化中起决定性作用。在<12><-2>第一次吸收循环期间引入了10 μ cm-1量级的相当高密度的位错。这些位错中的大多数是平行于c轴排列的a型刃位错，并且它们被认为是在基体和氢化物之间的界面处形成的失配位错。仔细检查表明，氢化物形成为板状，其中c轴和a轴之一包含在板面中，并且仅在氢化物内部引入高密度位错。这表明，失配的基体/氢化物界面的进步，形成失配位错和失配位错一旦形成的氢化物在氢化物生长过程中被纳入。因此，第一循环的高吸收压力被认为是由于形成位错所需的过压和形成裂纹所需的过压。在铝合金化的LaNi_5和TiMn_2中，虽然在第一次吸收循环中发生了明显的开裂（粉化），但在任何循环次数中几乎没有引入位错。结果，第一循环的吸收压力仅比任何其它循环的吸收压力适度地高。这可能是由于这些合金中的基体/氢化物界面比二元合金和钴合金LaNi_5中的宽。这意味着具有中间氢浓度的氢化物相对于基体和氢化物是相对稳定的。在FeTi的P-C等温线中观察到两个平台，表明存在两种不同的取向。第一个平台的吸收压力随循环次数的增加而降低。与其他研究合金相比，FeTi在循环过程中的开裂程度显著降低。这些表明，位错的引入持续发生在循环过程中，吸收压力随循环次数的减少是由于引入的位错密度随循环次数的减少。少