【作者】 吴朝玲；

【导师】 涂铭旌；

【作者基本信息】 四川大学 ， 材料学， 2003， 博士

【摘要】 本文针对NdFeB市场对Nd和汽车尾气市场对Ce大量需求的现状，充分考虑稀土资源的平衡利用，研究开发出了无钕稀土LPC系贮氢合金（LPC为提铈提钕后剩余的无钕的镧镨铈混合稀土金属的缩写），证实了无钕混合稀土金属代替全组分混合稀土金属用于制备贮氢合金的可行性，同时证明了该合金可用于Ni-MH电池。 本文同时针对生产中贮氢合金制造主要采用厚壁（10～30mm）铸造方法的现状，研究了薄壁（1～10mm）贮氢合金的铸造工艺对高钴和低钴LPC贮氢合金电化学性能的影响。结果发现：高钴贮氢合金的综合电化学性能随着铸锭厚度的增加而改善，原因可归结为三个因素：晶胞体积的增大、晶界缺陷的减少和晶格应力的降低。为进一步降低成本而引入Cu、Fe和Si部分替代Co，将使低钴LPC系贮氢合金的电化学性能总体上变得对壁厚不敏感。 本文同时也针对国内外普遍采用高温热处理（≥1000℃）处理贮氢合金的现状，研究了中温热处理工艺对高钴LPC贮氢合金电化学性能的影响。结果发现，不同壁厚的贮氢合金经中温热处理8小时后可获得更好的综合电化学性能。铸件壁越薄，热处理效果越好；退火改善贮氢合金电化学性能的主要因素是组织应力的消除和微区元素偏析的减小；壁厚越薄，组织应力影响因素越大。 本文还针对LPC混合稀土金属中Pr在生产难以调整的事实，优化研究了LPC Ni_3.55Co_0.75Mn_0.4Al_0.3合金的A侧La/Ce比对合金电化学性能的影响。结果发现含20～25％Ce的铸态和退火态无钕高钴贮氢合金具有更好的综合电化学性能。铈含量不同造成贮氢合金晶胞体积大小和氢化物平衡分解压的不同，并且Ce具有变价的特性，从而影响到贮氢合金的电化学性能。 本文首次用差热分析DTA和高温XRD相结合的方法研究了贮氢合金在退.城大母博士李位论文火加热过程中的变化，发现:在LPCNi3，55Co075Mn0.4AI众。合金的DTA曲线上呈现出5个放热峰:a一b一c一d一e。其中，b峰和c峰对冷却速度敏感，晶粒尺寸越小，峰的强度越大。晶界应力的消除对b峰贡献较大，而晶内应力的消除及微区元素偏析的减小对。峰贡献较大。d峰和e峰与冷却速度关系不大。d峰主要由再结晶产生，e峰主要由晶粒长大引起。 对热处理过程的组织变化分析，初步认为贮氢合金在245一 512℃温度范围内的升温过程中依次发生宏观应力消除一晶界应力消除^晶内应力消除和元素偏析减小^再结晶和晶粒长大。贮氢合金在退火过程中无相变发生。 把成分和工艺优化后的贮氢合金应用在Ni/MH电池和电动自行车中，得到了令人满意的结果:利用无钦稀土系贮氢合金制备的D型镍氢电池需3次活化，0.2C放电容量达到9.3从，lC放电容量为9.IAh，高倍率性能达到98%，IC循环寿命超过600次。该电池的低温电化学性能良好，无钦稀土系贮氢合金制备的D型镍氢电池在0℃可以放出96%的容量，同检的日本及国内其它电池最高只有90%;在一18℃，无钦镍氢电池可以放出92%的容量，其它电池不超过78%;在一30℃，无钦镍氢电池可以放出72%的容量，日本和国内某品牌电池几乎不能放电，国内另一品牌电池放电“%;在一40℃，无钦镍氢电池放电时间约17分钟。 利用本研究开发的D型镍氢电池在电动自行车上的跑车试验得到了满意的结果: 24VxgAh镍氢电池行驶里程达到38.3公里，36V、gAh镍氢电池行驶里程达到60公里，其性价比明显高出铅酸电池。更多还原

【Abstract】 Nd-free LPC-type hydrogen storage alloys, in which LPC represents the abbreviation of La-Ce-Pr mischmetal after the extraction of most Ce and Nd, were studied, according to the fact that Nd and Ce are respectively hunted for by magnetic material NdFeB and automotive catalyst, and considering the balanced application of rare earth resources. The possibility of the substitution of Nd-free LPC mischmetal for full-component one to make hydrogen storage alloys was demonstrated. And it was verified that this kind of alloy can be used in the manufacturing of Ni-MH batteries.As we know, the thickness of the hydrogen storage alloy ingots in practical production is popularly 10~30mm. In this study, strip casting was introduced, and the effect of the thickness of ingots within 1-10mm on the electrochemical properties of high-Co and low-Co LPC-type hydrogen storage alloys was studied. It was found that the comprehensive electrochemical properties of high-Co hydrogen storage alloy are improved with the increase of the thickness of the ingots. It is contributed to three factors: the expansion of unit cell volume, the decrease of the defects at grain boundaries, and the diminishing of internal stress.In order to reduce the cost of the hydrogen storage alloys, Cu, Fe and Si were applied to replace Co. It was found that the replacement made the electrochemicalproperties of low-Co LPC-type hydrogen storage alloy much insensitive to the thickness of ingots.It was also known that heat treatment at high-temperature ( 1000 ) is usually applied in the production of hydrogen storage alloys. In this work, the effect of heat treatment procedure at mid-temperature on the electrochemical properties of high-Co LPC-type hydrogen storage alloy was studied. It was found that the alloys with different thickness after heat-treated at mid-temperature for 8 hours could show better comprehensive electrochemical properties. The thinner the thickness of the ingots, the better the effect of the heat treatment. And the improvement of the electrochemical properties of hydrogen storage alloys by the anneal is mainly attributed to the diminishing of internal stress and the decrease of element segregation. The thinner the thickness of the ingots, the larger the effect of internal stress.The effect of the proportion of La/Ce in A-side of LPCNi3.55Co0.75Mn0.4Al0.3 alloy on the electrochemical properties was discussed, according to the fact that Pr is difficult to be adjusted in the production of LPC mischmetal. It was found that as-cast and annealed Nd-free LPC-type hydrogen storage alloys with 20-25% Ce in A-side show the best comprehensive electrochemical properties. Different Ce content in the alloys leads to different unit cell volume and equilibrium discomposed pressure of the hydride; And the valence of Ce could be changed in the hydride. Finally, they affect the electrochemical properties of the alloys.Differential thermo-analysis(DTA) and high-temperature XRD methods were applied together in this study to demonstrate the variation process of the hydrogen storage alloys during heating. It was found that there are five exothermic peaks in the DTA curve of LPCNi3.55Co0.75Mn0.4Al0.3 alloy, named a-b-c-d-e in turn. Peak b and c are sensitive to cooling rate. The smaller the grain sizes, the higher the peaks. Peak b is mainly depended on the diminishing of internal stress at grain boundaries.But peak c is primarily caused by the diminishing of internal stress within the grains and the decrease of elements segregation. Peak d and e depend less on cooling rates. Peak d is mostly introduced by re-crystallization. Peak e is mainly introduced by growth of the grains.According to the analysis results of microstructures during heating, the following variations were expected to happen in the hydrogen storage alloys from 245 to 512 : Diminishing of mechanical stress-Decrease of internal stress at grain boundaries-Decrease of internal stress within grains and decrease of elements segregation-Re-crystallization and growth of grains更多还原