Thermal performance and reduction kinetic analysis of cold-bonded pellets with CO and H_2 mixtures

Cold-bonded pellets, to which a new type of inorganic binder was applied, were reduced by H2–CO mixtures with different H2/CO molar ratios(1:0, 5:2, 1:1, 2:5, and 0:1) under various temperatures(1023, 1123, 1223, 1323, and 1423 K) in a thermogravimetric analysis apparatus. The effects of gas composition, temperature, and binder ratio on the reduction process were studied, and the microstructure of reduced pellets was observed by scanning electron microscopy–energy-dispersive spectrometry(SEM-EDS). The SEM-EDS images show that binder particles exist in pellets in two forms, and the form that binder particles completely surround ore particles has a more significant hinder effect on the reduction. The reduction equilibrium constant, effective diffusion coefficient, and the reaction rate constant were calculated on the basis of the unreacted core model, and the promotion effect of temperature on reduction was further analyzed. The results show that no sintering phenomenon occurred at low temperatures and that the increasing reaction rate constant and high gas diffusion coefficient could maintain the promotion effect of temperature; however, when the sintering phenomenon occurs at high temperatures, gas diffusion is hindered and the promotion effect is diminished. The contribution of the overall equilibrium constant to the promotion effect depends on the gas composition.     

Improved dehydriding property of polyvinylpyrrolidone coated Mg-Ni hydrogen storage nano-composite prepared by hydriding combustion synthesis and wet mechanical milling

In this work, polyvinylpyrrolidone(PVP) coated Mg_(95)Ni_5 nano-composites were prepared by hydriding combustion synthesis(HCS) plus wet mechanical milling(WM) with tetrahydrofuran(THF) and donated as WM-x wt% PVP(x = 1, 3, 5 and 7) respectively. The phase compositions, microstructures and dehydriding property, as well as the co-effect of PVP and THF were investigated in detail. XRD results showed that the average crystal size of MgH_2 in the milled Mg_(95)Ni_5 decreased from 23 nm without PVP to 18 nm with 1 wt% PVP. The peak temperature of dehydrogenation of MgH_2 in the milled Mg_(95)Ni_5 decreased from 293.0 ℃ without THF to 250.4 ℃ with THF. The apparent activation energy for decomposition of MgH_2 in WM-7 wt% PVP was estimated to be 66.94 kJ/mol, which is 37.70 kJ/mol lower than that of milled Mg_(95)Ni_5 without THF and PVP. PVP and THF can facilitate the refinement of particle size during mechanical milling process. Attributed to small particle sizes and synergistic effect of PVP and THF, the composites exhibit markedly improved dehydriding properties.     

Influence of minor boron on the microstructures of a second generation Nibased single crystal superalloy

Boron is added into single crystal superalloys as a micro-alloying element to strengthen low angle grain boundaries.However,systematic investigations on the effect of boron on microstructures of single crystal superalloys are limitedly reported.The effect of boron on as-cast and heat-treated microstructures was investigated in two experimental Ni-based single crystal superalloys containing 3 wt% Re.The current results indicated that the volume fraction of(γ+γ′)eutectic and M_3B_2 borides was evidently increased,while the number of micropores was evidently decreased with the addition of 0.02 wt% boron.The(γ+γ′)eutectic could not be dissolved completely due to the lower incipient melting temperature caused by the formation of M_3B_2 borides.Meanwhile,the M_3B_2 borides were found to be enriched with indispensable strengthening elements Cr,Mo,W and Re,and this may lower the strengthening effect and cause stress concentration during high temperature creep.     

Mechanical characterization and strain-rate sensitivity measurement of Ti- 7333 alloy based on nanoindentation and crystal plasticity modeling

The relationship between crystal orientations and meso-mechanical properties of β phase Ti-7333 titanium was investigated through the combination of nanoindentation experiments and simulation. The crystal plasticity finite element(CPFE) model for nanoindentation of single body-centered cubic crystal was established based on the experimental data. And the crystal plasticity constitutive law was implemented to simulate the nanoindentation process, obtaining satisfied results with an acceptable error. From the simulated pileup morphology patterns with different crystal orientations, it was found that the β phase experienced a symmetrical and orientation-related deformation process. Meanwhile, the strain-rate sensitivity(SRS) of β phase was investigated through nanoindentation tests based on continuous stiffness measurement(CSM) under different strain rates,varying between 0.2, 0.05 and 0.01 s~(-1). Two grains with different orientations exhibited similar SRS exponents,m, calculated from the experimental results.     

WO3 nanoflakes decorated with CuO clusters for enhanced photoelectrochemical water splitting

The low quantum efficiency arising from poor charges transfer and insufficient light absorption is one of the critical challenges toward achieving highly efficient water splitting in photoelectrochemical cells. Three dimensions(3D) structures and heterojunctions have received intensive research interests recent years due to their excellent ability to separate photo-generated charges as well as the enhanced light harvesting property. Herein,3 D Cu O/WO_3 structure was fabricated through a facile solvothermal method followed by chemical bath deposition. The loading of Cu O clusters on WO_3 nanoflake arrays results in a much improved photocurrent density compared with that of pristine WO_3 nanoflake arrays, which reaches 1.8 m A/cm2 at 1.23 V vs. the reversible hydrogen electrode. The electrochemical impedance spectroscopy measurement demonstrates that the improved performance of Cu O/WO_3 electrode is attributed to the accelerated charge transfer kinetics as a result of the desirable band alignment in Cu O/WO_3 heterojunction. This work demonstrates a facile strategy to construct superior WO_3 electrode, which will ultimately allow for efficient storage of solar energy into hydrogen.     

土地可持续利用管理与河北省新型城市化的发展对策

工业化与城市化的关系表明,我国的新型工业化要求城市化走新型城市化道路,新型城市化要求对土地进行可持续利用管理。目前河北省土地利用管理与新型城市化之间存在矛盾,这就要求河北省用土地可持续利用管理的措施来推进新型城市化的发展。     

用政治手段解决国际冲突的有益探索——以朝核问题六方会谈为例

中国在政治解决朝核问题的过程中扮演着作为第三方的大国斡旋者角色,从理论上讲,发挥这一角色作用有其特殊的涵义、困难性和复杂性,并因之要求中国的外交斡旋活动完成一定的调解任务。“六方会谈”是政治解决朝核问题的正确选择和有效途径,中国在促成六方会谈的成功举行并获得初步成果的过程中展示了高超的外交斡旋艺术,包括给予帮助的技术、支持冲突方互动的技术和操控技术,部分地完成了对于朝美之间冲突的调解任务。在中国积极和有效的外交斡旋努力下,朝核问题的解决沿正确的方向前行。     

Grey hematite photoanodes decrease the onset potential in photoelectrochemical water oxidation

Photoelectrochemical (PEC) water splitting for solar energy conversion into chemical fuels has attracted intense research attention.The semiconductor hematite (...     

DES算法FPGA实现的研究与比较

为满足无线网络通讯的数据安全要求,提出了用现场可编程门阵列(FPGA)实现DES加解密的方案,分别以减少器件面积和增加运算速度为目标来加以实现,并对这两种实现方法进行了比较。     

高密度电阻率法在探测多层采空区中的应用

介绍了高密度电阻率法的工作原理及野外工作方法,探讨了应用高密度电阻率方法探测多层采空区时应注意的问题,阐述了探测地下煤层多层采空区的具体步骤。