铸态及快淬态CeMg10Ni2合金电化学储氢热力学及动力学性能研究

为了改善CeMg₁₀Ni₂合金的电化学储氢性能,快淬技术被用来制备具有非晶纳米晶结构的CeMg₁₀Ni₂合金. 运用X射线衍射及高分辨透射电镜对合金的微观结构及其相组成进行分析. 通过恒电流充放电、高倍率放电、交流阻抗以及动电位极化测试对合金的电化学性能进行了详细研究. 研究结果表明,铸态合金由多相结构组成,经过快速凝固处理的合金内部含有大量的非晶纳米晶结构,而且增加的凝固速度可以增强合金内部的非晶纳米晶形成能力. 快速凝固处理减小了合金的热力学参数（ΔH和ΔS）,降低了合金氢化物的热稳定性,改善了电化学放电容量. 另外,快速凝固处理显著改善了合金的电化学动力学性能,合金的表观活化能变化进一步解释了这一结论.     

测量三棱镜折射率的一种新方法

本文介绍一种用移测显微镜测量三棱镜折射率的方法,该方法通过测量物点和物点在三棱镜中所成虚像之间的几何关系,可计算得到三棱镜折射率。     

二维Lagrange网格的积分守恒重映方法

研究了解决二维Lagrange网格大变形的一种有效的网格重分方法——积分守恒重映方法.详细地介绍了算法,并给出了数值实验结果.     

Role of Microstructure and Spectrum Features on the Catalysis Effect of Ce_(1-x)(Nd_(0.5)Eu_(0.5))_xO_(2-δ) Solid Solutions

Nanosized Ce_(1-x)(Nd_(0.5)Eu_(0.5))xO_(2-δ) solid solutions(x = 0.00~0.20) were synthesized by means of hydrothermal method.Then the solid solutions were ball milled with Mg_2Ni and Ni powders for 20 h to get the Mg_2Ni–Ni–5 mol% Ce_(1-x)(Nd_(0.5)Eu_(0.5))xO_(2-δ) composites.The structures and spectrum characteristics of the Ce_(1-x)(Nd_(0.5)Eu_(0.5))xO_(2-δ) solid solutions catalysts were analyzed systemically.XRD results showed that the doped samples exhibited single phase of CeO_2 fluorite structure.The cell parameters and cell volumes were increased with increasing the doped content.Raman spectrum revealed that the peak position of F_(2g) mode shift to higher wavenumbers and the peak corresponding to oxygen vacancies were observed distinctly for the doped samples.UV-Vis technique indicated that the absorption peaks of Eu~(3+) and Nd~(3+) ions appeared; the bandgap energy was decreased linearly.The electrochemical and kinetic properties of the Mg_2Ni–Ni–5 mol% Ce_(1-x)(Nd_(0.5)Eu_(0.5))xO_(2-δ) composites were measured.The maximum discharge capacity was increased from 722.3 mA h/g for x = 0.00 to 819.7 mA h/g for x = 0.16,and the cycle stability S_(20) increased from 25.0%(x = 0.00) to 42.2%(x = 0.20).The kinetic measurement proved that the catalytic activity of composite surfaces and the hydrogen diffusion rate were improved for the composites with doped catalysts,especially for the composites with x = 0.16 and x = 0.20.The catalysis mechanism was analyzed from the point of microstructure and spectrum features of the Ce_(1-x)(Nd_(0.5)Eu_(0.5))xO_(2-δ) solid solutions.     

Magnetic-Field-Induced Strains of Bonded Ni-Mn-Ga Melt-Spun Ribbons

Non-stoichiometric Ni50Mn27 Ga23 polycrystalline ribbons are prepared by melt-spinning technique. The magneticfield-induced strain （MFIS） of Ni-Mn-Ga bulk alloy prepared by bonding the melt-spun ribbons is obtained. The experimental results show that Ni50Mn27Ga23 bonded ribbons exhibit a typical thermal-elastic shape memory effect in the thickness direction. The martensitic transformation strain of bonded ribbons is an expansive strain of about 0.3% without the magnetic field and a contractive strain of about -0.46% at the magnetic field of 1 T. The field can not only enhance the value of the martensitic transformation strain of the bonded ribbons, but can also change the direction of the strain. The bonded ribbons alloy presents negative MFIS and obtains a larger value of the strain though influenced by the adhesive between the ribbons. Therefore, the preparation technique of the Ni-Mn-Ga bulk alloy by bonding melt-spun ribbons is helpful to get rid of the size restriction of the ribbon and to broaden the applications of the ribbons.     

定向凝固生长对Ni-Mn-Ga-RE (RE=TbSm)合金磁感生应变的影响

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熔体快淬对Ni-Mn-Ga合金马氏体相变特征及应变的影响

用真空快淬炉制备了名义成分为Ni₅₀Mn₂₇Ga₂₃，淬速 分别为2，4，8m/s的快淬态试样，并将部分试样热处理.研究结果表明，与铸态相比，快淬态试样马氏体相 变温度、居里温度均有所降低，经热处理后，降低的马氏体温度和居里温度会提高.快淬合 金与铸态合金相比更容易获得单相的Ni₂MnGa结构，并能使合金主衍射峰从（22 0）转向（ 400），形成织构，热处理后织构消失.快淬工艺对相变应变和磁致应变的影响表现出复杂性 ，研究发现获得织构的快淬带具有较浇铸态试样更大的相变应变和磁致应变. 关键词： 50Mn₂₇Ga₂₃')" href="#">Ni₅₀Mn₂₇Ga₂₃ 快淬 马氏体相变 应变     

汽车碰撞试验橡皮绳弹射速度回归统计分析与预测

清华大学汽车碰撞实验室利用橡皮绳弹射加速试验车进行碰撞试验。用线性回归统计的方法预测橡皮绳拉伸长度,精确地控制了开环状态的试验车的碰撞速度。这种橡皮绳弹射试验速度控制方法克服了由于阻力、环境温度等因素造成的影响,避免了造成巨大损失危险。同时对目前国内采用同类试验方法的试验室有一定的参考意义。     

A comparison study on the electronic structures,lattice dynamics and thermoelectric properties of bulk silicon and silicon nanotubes

In order to investigate the mechanism of the electron and phonon transport in a silicon nanotube(SiNT),the electronic structures,the lattice dynamics,and the thermoelectric properties of bulk silicon(bulk Si)and a SiNT have been calculated in this work using density functional theory and Boltzmann transport theory.Our results suggest that the thermal conductivity of a SiNT is reduced by a factor of 1,while its electrical conductivity is improved significantly,although the Seebeck coefficient is increased slightly as compared to those of the bulk Si.As a consequence,the figure of merit(ZT)of a SiNT at 1200 K is enhanced by 12 times from 0.08 for bulk Si to 1.10.The large enhancement in electrical conductivity originates from the largely increased density of states at the Fermi energy level and the obviously narrowed band gap.The significant reduction in thermal conductivity is ascribed to the remarkably suppressed phonon thermal conductivity caused by a weakened covalent bonding,a decreased phonon density of states,a reduced phonon vibration frequency,as well as a shortened mean free path of phonons.The other factors influencing the thermoelectric properties have also been studied from the perspective of electronic structures and lattice dynamics.     

二维三温辐射(磁)流体力学拉氏计算中的人工粘性分裂技术

针对使用边粘性和张量粘性进行二维三温辐射(磁)流体力学拉氏计算时激波处离子温度出现非物理尖峰的问题,提出一种人工粘性分裂技术,将人工粘性耗散能量按照电子压和离子压的比分成两部分,并分别加在电子内能和离子内能上.在二维三温辐射磁流体力学程序MARED上实现该技术,并对Z-pinch的内爆动力学过程进行数值模拟.消除了模拟结果中激波处离子温度的尖峰.