A Cu-50Cr alloy was treated by the high current pulsed electron beam(HCPEB)at 20 and 30 ke V with pulse numbers ranging from 1 to 100.Surface morphologies and microstructures of specimens before and after the treatmen...A Cu-50Cr alloy was treated by the high current pulsed electron beam(HCPEB)at 20 and 30 ke V with pulse numbers ranging from 1 to 100.Surface morphologies and microstructures of specimens before and after the treatments were investigated by employing scanning electron microscopy and X-ray diffraction.Results show that the HCPEB technique is able to induce remarkable surface modifications for the Cu-50Cr alloy.Cracks in Cr phases appear even after one-pulse treatment and their density always increases with the pulse number.Formation reason for these cracks is attributed to quasi-static thermal stresses accumulated along the specimen surface.Craters with typical morphologies are formed due to the dynamic thermal field induced by the HCPEB and they are found to prefer the sites near cracks or boundaries between neighboring Cr phases.Another microstructural characteristic produced by the HCPEB is the fine Cr spheroids,which are determined to be due to occurrence of liquid phase separation in the Cu-50Cr alloy.Finally,a general microstructural evolution profile that incorporates various HCPEB-induced surface features is tentatively outlined.展开更多
Controlling the surface structure and composi- tion at the atomic level is an effective way to tune the cat- alytic properties of bimetallic catalysts. Herein, we demon- strate a generalized strategy to synthesize hig...Controlling the surface structure and composi- tion at the atomic level is an effective way to tune the cat- alytic properties of bimetallic catalysts. Herein, we demon- strate a generalized strategy to synthesize highly monodis- perse, surfactant-free octahedral PtxNi1-x nanoparticles with tunable surface structure and composition. With increasing the Ni content in the bulk composition, the degree of concave- ness of the octahedral PtxNi1-x nanoparticles increases. We systematically studied the correlation between their surface structure/composition and their observed oxygen reduction activity. Electrochemical studies have shown that all the octa- hedral PtxNi1-x nanoparticles exhibit enhanced oxygen reduc- tion activity relative to the state-of-the-art commercial Pt/C catalyst. More importantly, we find that the surface struc- ture and composition of the octahedral PtxNi1-x nanoparti- cles have significant effect on their oxygen reduction activ- ity. Among the studied PtxNi1-x nanoparticles, the octahedral PtlNi1 nauoparticles with slight concaveness in its （111） facet show the highest activity. At 0.90 V vs. RHE, the Pt mass and specific activity of the octahedral PhNil nanoparticles are 7.0 and 7.5-fold higher than that of commercial Pt/C catalyst, re- spectively. The present work not only provides a generalized strategy to synthesize highly monodisperse, surfactant-free octahedral PtxNi1-x nanoparticles with tunable surface struc- ture and composition, but also provides insights to the struc- ture-activity correlation.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.51101177,51401040,51171146 and 51171216)the Natural Science Foundation of Chongqing(Grant No.CSTC2012JJA245)
文摘A Cu-50Cr alloy was treated by the high current pulsed electron beam(HCPEB)at 20 and 30 ke V with pulse numbers ranging from 1 to 100.Surface morphologies and microstructures of specimens before and after the treatments were investigated by employing scanning electron microscopy and X-ray diffraction.Results show that the HCPEB technique is able to induce remarkable surface modifications for the Cu-50Cr alloy.Cracks in Cr phases appear even after one-pulse treatment and their density always increases with the pulse number.Formation reason for these cracks is attributed to quasi-static thermal stresses accumulated along the specimen surface.Craters with typical morphologies are formed due to the dynamic thermal field induced by the HCPEB and they are found to prefer the sites near cracks or boundaries between neighboring Cr phases.Another microstructural characteristic produced by the HCPEB is the fine Cr spheroids,which are determined to be due to occurrence of liquid phase separation in the Cu-50Cr alloy.Finally,a general microstructural evolution profile that incorporates various HCPEB-induced surface features is tentatively outlined.
基金supported by the National Research Foundation,Prime Minister’s Office,Singapore under its CREATE Programmefinancial support by the Defence Acquisition Program Administration and Agency for Defence Development(UD120080GD),Republic of Korea
文摘Controlling the surface structure and composi- tion at the atomic level is an effective way to tune the cat- alytic properties of bimetallic catalysts. Herein, we demon- strate a generalized strategy to synthesize highly monodis- perse, surfactant-free octahedral PtxNi1-x nanoparticles with tunable surface structure and composition. With increasing the Ni content in the bulk composition, the degree of concave- ness of the octahedral PtxNi1-x nanoparticles increases. We systematically studied the correlation between their surface structure/composition and their observed oxygen reduction activity. Electrochemical studies have shown that all the octa- hedral PtxNi1-x nanoparticles exhibit enhanced oxygen reduc- tion activity relative to the state-of-the-art commercial Pt/C catalyst. More importantly, we find that the surface struc- ture and composition of the octahedral PtxNi1-x nanoparti- cles have significant effect on their oxygen reduction activ- ity. Among the studied PtxNi1-x nanoparticles, the octahedral PtlNi1 nauoparticles with slight concaveness in its （111） facet show the highest activity. At 0.90 V vs. RHE, the Pt mass and specific activity of the octahedral PhNil nanoparticles are 7.0 and 7.5-fold higher than that of commercial Pt/C catalyst, re- spectively. The present work not only provides a generalized strategy to synthesize highly monodisperse, surfactant-free octahedral PtxNi1-x nanoparticles with tunable surface struc- ture and composition, but also provides insights to the struc- ture-activity correlation.
