In order to improve the hydriding and dehydriding kinetics of the Mg2Ni-type alloys,Ni in the alloy is substituted by element Co. The nanocrystalline and amorphous Mg2Ni-type Mg2Ni1-xCox (x=0,0.1,0.2,0.3,0.4) alloys w...In order to improve the hydriding and dehydriding kinetics of the Mg2Ni-type alloys,Ni in the alloy is substituted by element Co. The nanocrystalline and amorphous Mg2Ni-type Mg2Ni1-xCox (x=0,0.1,0.2,0.3,0.4) alloys were synthesized by melt-spinning technique. The structures of the as-cast and spun alloys were studied with an X-ray diffractometer (XRD) and a high resolution transmission electronic microscope (HRTEM). An investigation on the thermal stability of the as-spun alloys was carried out with a differential scanning calorimeter (DSC). The hydrogen absorption and desorption kinetics of the alloys were measured with an automatically controlled Sieverts apparatus. The results demonstrate that the substitution of Co for Ni does not alter the major phase of Mg2Ni but results in the formation of secondary phase MgCo2. No amorphous phase is detected in the as-spun Co-free alloy,but a certain amount of amorphous phase is clearly found in the as-spun Co-containing alloys. The substitution of Co for Ni exerts a slight influence on the hydriding kinetics of the as-spun alloy. However,it dramatically enhances the dehydriding kinetics of the as-cast and spun alloys. As Co content (x) increases from 0 to 0.4,the hydrogen desorption capacity increases from 0.19% to 1.39% (mass fraction) in 20 min for the as-cast alloy,and from 0.89% to 2.18% (mass fraction) for the as-spun alloy (30 m/s).展开更多
Here, we report on hierarchical mechanical behavior of 500-nm-thick Conanocrystal 3D superlattices （supracrystals） induced by either the crystalline structure （nanocrystallinity） or the length of the coating agent...Here, we report on hierarchical mechanical behavior of 500-nm-thick Conanocrystal 3D superlattices （supracrystals） induced by either the crystalline structure （nanocrystallinity） or the length of the coating agent of Co nanocrystals. Increasing the nanocrystal shape anisotropy of Co nanocrystals through the control of their nanocrystallinities induces a higher level of ordering with both translational and orientational alignment of nanocrystals within the supracrystals. The hierarchy in ordering at various scales, i.e., from the atomic lattice within the nanocrystals to the nanocrystal superlattices within supracrystals, is correlated with marked changes in the Young＇s modulus of supracrystals： From 0.7 ±0.4 to 1.7 ±0.5 and to 6.6 ±1.5 GPa as the crystalline structure of Co nanoparticles changes from amorphous-Co to ε-Co and to hexagonal compact packing （hcp）-Co, respectively. Moreover, for supracrystals of 7 nm amorphous Co nanoparticles, the Young＇s modulus decreases by one order of magnitude from 0.7 ±0.4 to 0.08 ±0.03 GPa upon reducing the alkyl chain length of the ligands coating the Co nanoparticles from C18 （oleic acid） to C12 （lauric acid）. The hierarchical mechanical behavior is rationalized using a dimensional model of the stress-strain relationship in supracrystals.展开更多
基金Project(2006AA05Z132) supported by the National High-tech Research and Development Program of ChinaProjects(50871050, 50961009) supported by the National Natural Science Foundation of China+1 种基金Project(2010ZD05) supported by the Natural Science Foundation of Inner Mongolia, ChinaProject(NJzy08071) supported by the High Education Science Research Program of Inner Mongolia, China
文摘In order to improve the hydriding and dehydriding kinetics of the Mg2Ni-type alloys,Ni in the alloy is substituted by element Co. The nanocrystalline and amorphous Mg2Ni-type Mg2Ni1-xCox (x=0,0.1,0.2,0.3,0.4) alloys were synthesized by melt-spinning technique. The structures of the as-cast and spun alloys were studied with an X-ray diffractometer (XRD) and a high resolution transmission electronic microscope (HRTEM). An investigation on the thermal stability of the as-spun alloys was carried out with a differential scanning calorimeter (DSC). The hydrogen absorption and desorption kinetics of the alloys were measured with an automatically controlled Sieverts apparatus. The results demonstrate that the substitution of Co for Ni does not alter the major phase of Mg2Ni but results in the formation of secondary phase MgCo2. No amorphous phase is detected in the as-spun Co-free alloy,but a certain amount of amorphous phase is clearly found in the as-spun Co-containing alloys. The substitution of Co for Ni exerts a slight influence on the hydriding kinetics of the as-spun alloy. However,it dramatically enhances the dehydriding kinetics of the as-cast and spun alloys. As Co content (x) increases from 0 to 0.4,the hydrogen desorption capacity increases from 0.19% to 1.39% (mass fraction) in 20 min for the as-cast alloy,and from 0.89% to 2.18% (mass fraction) for the as-spun alloy (30 m/s).
文摘Here, we report on hierarchical mechanical behavior of 500-nm-thick Conanocrystal 3D superlattices （supracrystals） induced by either the crystalline structure （nanocrystallinity） or the length of the coating agent of Co nanocrystals. Increasing the nanocrystal shape anisotropy of Co nanocrystals through the control of their nanocrystallinities induces a higher level of ordering with both translational and orientational alignment of nanocrystals within the supracrystals. The hierarchy in ordering at various scales, i.e., from the atomic lattice within the nanocrystals to the nanocrystal superlattices within supracrystals, is correlated with marked changes in the Young＇s modulus of supracrystals： From 0.7 ±0.4 to 1.7 ±0.5 and to 6.6 ±1.5 GPa as the crystalline structure of Co nanoparticles changes from amorphous-Co to ε-Co and to hexagonal compact packing （hcp）-Co, respectively. Moreover, for supracrystals of 7 nm amorphous Co nanoparticles, the Young＇s modulus decreases by one order of magnitude from 0.7 ±0.4 to 0.08 ±0.03 GPa upon reducing the alkyl chain length of the ligands coating the Co nanoparticles from C18 （oleic acid） to C12 （lauric acid）. The hierarchical mechanical behavior is rationalized using a dimensional model of the stress-strain relationship in supracrystals.
