钯铜复合膜透氢性和稳定性研究进展

对钯铜复合膜透氢性和稳定性的影响因素进行了综述。阐述了透氢性能影响因素包括膜载体、膜组成及膜厚度、操作压力、操作温度;稳定性能影响因素包括扩散障碍层、金属偏析和硫化氢中毒。并详细介绍了钯铜合金复合膜硫化氢中毒现象和金属偏析现象的机理研究。

Directional migration behavior of cerium during sintering process of mischmetal doped cemented carbide

Three observation methods were used to investigate the existing form and the behavior of rare earth during the sintering process of high activity mischmetal （RE, with lanthanum and cerium） doped WC-8%Co-0.048%RE（mass fraction） alloy with low carbon-containing level by scanning electron microscopy （SEM） and energy dispersive X-ray spectroscopy （EDXS）, considering the fact that the addition amount of rare earth in the alloy is very minute. The directional migration process and mechanism of cerium were discussed. First, the sinter skin （surface） is observed. oxide on the sinter skin, and lanthanum in these cerium observed, and lanthanum containing phase/micro-zone in It is shown that there exists a dispersedly distributed cerium containing enrichment positions is very minute. Secondly, the polished section is the alloy is identified. Finally, based on the fact that the fracture of cemented carbide is resulted from the heterogeneous phase or other defects within the microstructure, the fracture surface is observed and cerium containing phase/micro-zone in the fracture source approximately 260 μm from the surface is identified. These combined observations reveal adequately the fact that lanthanum and cerium get separated and cerium predominantly migrates towards the surface during the sintering process.

DFT calculation analysis of oxygen reduction activity and stability of bimetallic catalysts with Pt-segregated surface

The stability and oxygen reduction reaction （ORR） activity of the Pt-segregated surface in various Pt-M alloys （M： transition metals） are investigated through systematic DFT calculations on the thermodynamic （alloy formation energy and Pt surface segregation energy）, surface chemical property （oxygen binding energy） and electronic （d-band center） properties. Factors af- fecting these properties, such as the atomic radii and surface energy of M and the electronic ligand interaction between Pt and M are analyzed as a function of outmost d electron numbers of M. It is shown that the electronic ligand interaction plays de- termining role in the alloy formation energy of various Pt-M alloys; the formation of Pt-segregated surface in Pt-M alloys is faw）red when alloying metals have higher surface energy and smaller radii than Pt; the oxygen binding energy on the Pt-segregated surface in Pt-M alloys varies approximately linearly with the d-band center of surface Pt atoms; the lattice strain and electronic ligand effects are simply additive in Pt-M alloys; the stain effect in Pt-M alloys nearly linearly affects the d-band center of the Pt-segregated surface in Pt-M alloys; transition metals with less than 10 d electrons mostly exhibit electron ligand effects which result in downshift of the d-band center of the segregated surface Pt atoms, while those with ten d electrons exhibit electron ligand effect upshifting the d-band center of the segregated Pt atoms.

Segregation growth of epitaxial graphene overlayers on Ni（111）

The orientation control of graphene overlayers on metal surface is an important issue which remains as a challenge in graphene growth on Ni surface. Here we have demonstrated that epitaxial graphene overlayers can be obtained by annealing a nickel carbide covered Ni（111） surface using in situ surface imaging techniques. Epitaxial graphene islands nucleate and grow via segregation of dissolved carbon atoms to the top surface at about 400 ℃. This is in contrast to a mixture of epitaxial and non-epi- taxial graphene domains grown directly on Ni（111） at 540 ℃. The different growth behaviors are related to the nucleation dynamics which is controlled by local carbon densities in the near surface region.