【作者】 夏继红；

【导师】 王大辉；

【作者基本信息】 兰州理工大学 ， 材料加工工程， 2012， 硕士

【摘要】 70年代席卷全球的石油危机促使各国开始寻求新型的、来源充足的能源。氢能作为一种来源丰富、清洁、高能量密度的能源，引起了人们的关注。1970年荷兰菲利普实验室发现LaNi5材料具有可逆吸放氢的特性，储氢体积密度高于液氢，安全性能很高；他们还指出储氢材料具有广阔的发展前景，从而引起全球储氢材料的研究浪潮。软化学方法在合成储氢材料的应用取得了很大的发展。采用软化学合成的储氢材料具有成分均匀、纯度高、颗粒尺寸小、动力学性能好、催化性能好等优点。本文采用软化学方法合成了La-Mg储氢合金前驱体，并对其结构进行了表征。以硝酸镧和硝酸镁为原料，柠檬酸为络合剂，络合反应制得干凝胶，讨论了柠檬酸的用量对干凝胶的影响和焙烧温度对产物结构的影响，利用红外光谱、热重/差热分析、X射线衍射、扫描电镜和透射电镜对干凝胶和产物进行研究；结果表明，随着柠檬酸与金属离子的摩尔比由1:1上升到1.5:1，得到的干凝胶中羧酸盐的量随着增加。当比值为2:1时，干凝胶中羧酸盐的值增加到最大。分析表明：在溶液中柠檬酸的羧基易电离，脱氢后的羟基氧容易与金属离子形成稳定络合物（-O-M-），这些络合物之间连接起来构成三维聚合物框架，生成羧酸盐。随着柠檬酸含量的增加，络合金属离子的羧基的量也增加，从而使溶液中金属离子有更多机会被络合，导致干凝胶中羧酸盐的含量也随着增加。根据干凝胶的TG/DTA曲线制定出合适的热处理方式，在850℃以下焙烧产物有杂相，在950℃焙烧产物较纯；而且随着焙烧温度的升高，产物的结晶性能升高。XRD分析表明，产物为La₂O₃和MgO两相混合物。本文还系统的研究了溶液初始pH值对产物的影响。在pH值为0.5和1.48的酸性条件下，柠檬酸的多级电离受到抑制，柠檬酸中部分羧基没有电离；电离的羧基络合金属离子生成羧酸盐，红外光谱可以检测到未反应的羧基存在，络合效率低。在碱性条件，柠檬酸的电离加强，所有羧基全部电离，参与反应生成羧酸盐。pH值为0.5和1.48的酸性条件下，合成的干凝胶中没有形成作为燃烧助剂的NH₄NO₃，在焙烧时发生局部燃烧，燃烧时间长，使初期合成的颗粒有较长时间长大，产物粒径大小不均匀。而pH值为8.0和9.0的碱性条件下合成干凝胶由于在调节pH值时滴加了大量的氨水（NH₃·H₂O）使干凝胶中含有大量的NH₄NO₃作为燃烧助剂，干凝胶在焙烧时剧烈燃烧，燃烧时间短，形成的颗粒细小、粒径均匀。在pH值为8.0时，合成的产物粒径约30nm.更多还原

【Abstract】 Sweeping through the world in the1970s oil crisis prompted countries beganto seek new and sufficient energy. Hydrogen as a rich source of high energydensity,clean energy,would have to cause the attention. Phillips Laboratory of theNetherlands found that the LaNi5materials with reversible characteristics ofabsorption and release hydrogen in1970, and have high safety performance. Theyalso noted that the hydrogen storage materials have broad prospects fordevelopment,which cause lots of people to research on them. Soft chemicalsynthesis method has achieved great develop in prepareding hydrogen storagematerials.Soft chemical routes have been reported to prepare alloys with goodhomogeneity, high purity and sub-micron size particles, which are importantfactors for high hydrogen storgen capacityIn this article, soft chemical is adopted to synthesis La-Mg hydrogen storagealloys precursor and its structures were characterized.Nano precursor powders wereprepared by the sol-gel method using lanthanum nitrate （La（NO₃）3·6H₂O） analyticalgrade) and magnesium nitrate （Mg（NO₃）₂·6H₂O analytical grade） as startingmaterials, distilled water as solvent and citric acid （C6H8O7·H₂O） as chelatingagent.The effect of amount of citric acid and calcination temperature onmicrostructure of the nano precursors of La-Mg hydrogen storage alloy had beenstudied by Infrared Radiation （IR）,thermogravimetric and differential thermalanalysis （TG/DTA）, X-ray diffraction analyzer （XRD） and Transmission electronmicroscopy （TEM）;The results shows the molar ratio of citric acid to metal cationsincreases from1to1.5, the amount of citrate increases correspondingly, when themolar ration increases to2.0, the amount of citrate goes up to maximum. Hydrogenof hydroxyl in carboxyl is easy to run away, the COO-can form stable chelates（-O-M-）with metal cations. The chelates can easily form citrate which is of threedimensional skeleton structure.With the increase the quantity of carboxyl groups,much more carboxyl groups are used to complex metal cations and then form citrate,so the quality of citrate is increase.TG/DTA results show that with increase ofcalcination temperature the amount of impurity phase, La（OH）₃, decreasesmarkedly. There is the presence of impurity phase, La（OH）3, calcinated at750℃and850℃. When calcinate at950℃, impurity phase disappear and only La2O3andMgO two-phase mixture present and the nano powders with good crystallization.The effect of pH value on microstructure of the nano precursors of La-Mghydrogen storage alloy had also been studied. At the pH value of0.5and1.48, themulti-stage ionization of citric acid are restrained, which result that carboxyl groups complex metal cations insufficiently. In basic solution, the ionization ofcitric acid will be accelerated and the ability of citric acid complexing metalcations will be improved. At the pH value of0.5and1.48,the gel is preparedwithout the addition of ammonia or NH₄NO₃as fuel for self propagating, whichresult in local burning and longer combustion, the combustion takes place with lowrate of the flame propagation, which caused the longer combustion time and thegrain initial synthesized have long time to grow up then the non-uniform particlesize are formed. At the pH value of8.0and9.0,the grain synthesised instantly andhad no time to grow up because of the gel combustion rapidly. The average particlesize of powders is about30nm at the pH of8.0.更多还原