Effects of CNTs on the hydrogen storage properties of MgH2 and MgH2-BCC composite

MgH₂ with 10 wt.% Ti_0.4Mn_0.22Cr_0.1V_0.28 alloy (termed the BCC alloy for its body centred cubic structure) and 5 wt.% carbon nanotubes (CNTs) were prepared by planetary ball milling, and its hydrogen storage properties were compared with those of the pure MgH₂ and the binary mixture of MgH₂ and the BCC alloy. The sample with CNTs showed considerable improvement in hydrogen sorption properties. Its temperature of desorption was 125 °C lower than for the pure sample and 59 °C lower than for the binary mixture. In addition, the gravimetric capacity of the ternary sample was 6 wt.% at 300 °C and 5.6 wt.% at 250 °C, and it absorbed 90% of this amount at 150 s and 516 s at 300 °C and 250 °C, respectively. It can be hypothesised from the results that the BCC alloy assists the dissociation of hydrogen molecules into hydrogen atoms and also promotes hydrogen pumping into the Mg/BCC interfaces, while the CNTs facilitate access of H-atoms into the interior of Mg grains.     

An approach to design single BCC Mg-containing high entropy alloys for hydrogen storage applications

Mg is a lightweight element that can increase the gravimetric hydrogen storage capacity of high entropy alloys (HEAs). This work presents a new approach to design single-phase Mg-containing HEAs with attractive hydrogen storage properties. The design method is based on four calculated parameters (?, VEC, $\overline{\Delta {\text{H}}_{\infty }}$ and $\overline{\Delta {\text{H}}_{\text{f}}^{\text{o}}}$) that allow us to find alloy compositions that form single body-centered cubic (BCC) solid solutions with high hydrogen affinity. The method was tested in the Mg–Al–Ti–Mn–Nb system and the Mg₁₂Al₁₁Ti₃₃Mn₁₁Nb₃₃ alloy was selected among 1326 calculated compositions. This alloy was produced by high energy ball milling resulting in a homogeneous single-phase BCC alloy that absorbed 1.7 wt.% of H by forming a BCC monohydride. Despite its H uptake being H/M = 1, the gravimetric capacity of the lightweight Mg₁₂Al₁₁Ti₃₃Mn₁₁Nb₃₃ alloy was comparable to refractory BCC-HEAs with H uptake of H/M = 2.     

基于DEA方法的我国高技术产业创新效率研究

发展高技术产业,对推动产业结构升级,提高劳动生产率和经济效益,具有不可替代的作用。从投入产出角度构建了高技术产业技术创新效率评价指标。依据中华人民共和国科学技术部网站2000-2009年间的统计数据,利用DEA方法中的BCC模型对我国高技术产业技术创新效率进行了实证分析。结果显示,我国高技术产业的技术创新效率水平整体较高,但不够稳定,且部分决策单元创新效率不高主要是由于资源投入比例不当、资金投入存在浪费现象,以及高技术产业的利润实现情况不理想所造成。     

一种基于高级Petri网的微电网故障诊断方法

微电网拓扑结构灵活,运行方式多样,是一个相对自治系统。针对微电网拓扑结构多变导致故障诊断建模困难问题,提出基于微电网线路故障保护信息的分层Petri网分析模型。该模型以分层保护集形式处理微电网保护信息。当微电网拓扑结构改变时,只需更新相应的保护集信息,不需要重新建模,对微电网的灵活多变有较强的适应性。该模型还可以有效判别保护和断路器的拒动、误动和处理含有时序关系的保护信息。为增强诊断系统的容错性和可靠性,采用智能加权模糊Petri网理论自适应调整权值。仿真算例验证了方法的有效性。     

Modelling the zero shear viscosity of bimodal high solid content latex: Calculation of the maximum packing fraction

Different rheological tests were performed on monodisperse polystyrene latices and mixtures of two different latices with different particle sizes. A critical volume fraction φ_c was defined for each of the latices. Subsequently, a method based on the estimation of the porosity of a bed of randomly placed spherical particles was adapted to allow us to define the maximum packing fraction for any bimodal system. This method can be used for any ratio of particle diameter and volume fraction for the two populations provided one has knowledge of the critical volume fractions of related monodisperse latices (see Pishvaei et al., 2005. Polymer 46, 1235-1244). The model was tested experimentally, and rheological tests allowed us to validate the values of the critical volume fraction (φ_c) of different bimodal latices. A master curve of viscosity vs. polymer concentration was obtained using the concept of reduced volume fraction. The results prove that we can predict the viscosity of multimodal systems from the knowledge of monomodal packing fraction.     

Effect of cerium content on microstructure and hydrogen storage performance of Ti24Cr17.5V50Fe8.5Cex（x=0-1.0） alloys

Effect of Ce addition on microstructure and hydrogen storage performance of Ti24Cr17.5V50Fe8.5Cex (x=0, 0.5at.%, 0.8at.% and 1.0at.%) alloys was studied by X-ray diffraction, scanning electron microscopy and P-C-isotherm measurements. The results indicated that Ce addition was a useful way to improve the flatness of the plateau and increase hydrogen storage capacity of Ti24Cr17.5V50Fe8.5 alloy. It was indicated that both homogenization of composition and increase of hydrogen diffusion coefficient were the main reasons for improving the hydrogen storage performance of Ti24Cr17.5V50Fe8.5Cex alloys.     

Phase equilibria in the Ni–Cr–Ti system at 850°C

The isothermal cross-section through the ternary phase diagram Ni–Cr–Ti at 850°C was constructed by means of diffusion couples and equilibrated alloys. No ternary phases exist in the system at this temperature. The topology of the isotherm is largely determined by the presence of the TiCr₂-Laves phases which are in equilibrium with the binary Ti–Ni intermetallics. About 10 at.% of Ni can be dissolved in the hexagonal β-TiCr₂ at 850°C, and the solubility of nickel in cubic α-TiCr₂ is approximately 4 at.%. A small amount of nickel or chromium increases the stability of the b.c.c. β-Ti structure. At this temperature the β-Ti(Ni)-based solid solution can dissolve up to 18 at.% of Cr.     

碾压混凝土坝施工质量控制

碾压混凝土坝的施工质量控制是最终形成合格碾压混凝土坝的重要环节。为确保碾压混凝土坝的施工质量，首先要有满足设计指标要求和工作度较好的混凝土配合比作保证，然后要通过原材料、拌和系统及仓面施工这三方面的有效控制来实现施工质量的有效控制。     

Al、Ti、V和Cr促进高熵合金BCC相形成能力的研究

定量研究了Al、Ti、V和Cr促进CoFeMnNi基高熵合金形成BCC相的添加量,结合元素周期表分析了相关规律。使用真空熔炼炉炼制了CoFeMnNi基高熵合金,使用扫描电子显微镜、X射线衍射仪、显微硬度计分析了合金的组织结构和硬度。结果表明,CoFeMnNi合金为单一FCC相结构,Al、Ti、V和Cr四种元素单独添加到合金中出现BCC相的添加量分别是0.6、0.6、1和2 mol;促进BCC相形成能力的顺序是Al>Ti>V>Cr;对于元素周期表第4周期的过渡族元素,序号小于25的元素是BCC形成元素,序号越小越有利于在高熵合金中形成BCC相。当合金有BCC相形成时,合金的硬度升高;随BCC相的增加,硬度增加,合金脆性变大。合金含钛2 mol后,合金抗腐蚀能力提升明显,即使在王水腐蚀120 s仍然没有明显的腐蚀痕迹。     

基于微细菌群体趋药性算法的电压稳定裕度计算

针对电压稳定裕度计算问题,提出了一种基于菌群趋药性(bacterial colony chemotaxis,BCC)算法的新的优化算法——微细菌群体趋药性(micro bacterial colony chemotaxis,MBCC)算法。MBCC算法利用2个菌群(寻优菌群和库存菌群)来寻优,寻优菌群使用BCC算法来寻找最优解,库存菌群保证了寻优菌群的多样性。MBCC算法加快了算法收敛速度,提高了全局搜索能力,而且在寻优过程中减少了系统资源的浪费。将该算法用于电压稳定裕度的计算,与连续潮流法计算结果的比较表明,该算法切实可行并具有较高的精度。