High hydrogen desorption temperature and sluggish reaction kinetics are the major limitations for the practical application of MgH_(2).In this study,Co particles with a face centered cubic(FCC)structure and a hexagona...High hydrogen desorption temperature and sluggish reaction kinetics are the major limitations for the practical application of MgH_(2).In this study,Co particles with a face centered cubic(FCC)structure and a hexagonal close packed(HCP)structure were prepared facilely and proved to be good catalysts for magnesium hydride.Co particles with FCC structure presented better catalytic effect on MgH_(2)than that with HCP structure.Both 7%(mass)Co FCC and HCP particle modified MgH_(2)decreased the initial dehydrogenation temperature from 301.3℃ to approximately 195.0℃,but 7%(mass)Co with FCC structure modified MgH_(2)has a faster desorption rate,and around 6.5%(mass)H_(2)was desorbed in 10 min at325℃.Hydrogen uptake was detected at 70℃ under 3.25 MPa hydrogen pressure and 6.0%(mass)H_(2)was recharged in 40 min at 150℃.The hydrogen desorption and absorption activation energy for 7%(mass)FCC Co modified MgH_(2)was significantly decreased to(76.6±8.3)kJ·mol^(-1) and(68.3±6.0)kJ·mol^(-1),respectively.Thermodynamic property was also studied,the plateau pressures of MgH_(2)+7%(mass)FCC Co were determined to be 0.14,0.28,0.53 and 0.98 MPa for 300℃,325℃,350℃ and375℃.The decomposition enthalpy of hydrogen(ΔH)for MgH_(2)+7%(mass)FCC Co was(80.6±0.1)kJ·mol^(-1),5.8 kJ·mol^(-1)lower than that of as-prepared MgH_(2).Moreover,cycling performance for the first20 cycles revealed that the reaction kinetics and capacity of MgH_(2)-FCC Co composite remained almost unchanged.The result of density functional theory calculation demonstrated that cobalt could extract the Mg AH bond and reduced the decompose energy of magnesium hydride.Our paper can be presented as a reference for searching highly effective catalysts for hydrogen storage and other energy-related research fields.展开更多
It is known that pure Co undergoes martensitic transformation from γ phase (fcc) to ε phase (hcp) by the movement of a/6<112> Shockley partial dislocations at around 400 ℃, however, there have been few system...It is known that pure Co undergoes martensitic transformation from γ phase (fcc) to ε phase (hcp) by the movement of a/6<112> Shockley partial dislocations at around 400 ℃, however, there have been few systematic works on the SM effect in Co and Co-based alloys. In this study, the fcc/hcp rnartensitic transformation and the SM effect were investigated in Co-A1 binary alloys(mole fraction of Al=0-16%). The γ/ε rnartensitic transformation temperatures were found from the DSC measurements to decrease with increasing Al content, while the transformation temperature hystereses were observed to increase from 60℃ at x(Al)=0 to 150℃ at x(Al) = 16%. The SM effect evaluated by a conventional bending test was enhanced by the addition of Al over 4% (mole fraction) and Co-Al alloys containing over 10%(mole fraction) exhibit a good SM effect associated with the hcpfee → reverse transformation above 200℃. The SM effect was significantly improved by precipitation of β (I32) phase and the max[real shape recovery strain of 2.2 % was obtained, which can be explained by precipitation hardening. The crystallographic orientations between the β, εand γ phases were also determined. Finally, the magnetic properties were investigated and it was found that the Curie temperature and saturation magnetization of Co-14% Al(mole fraction) are 690℃ and 120 emu/g, respectively. It is concluded that the Co-A1 alloys hold promise as new high-temperature and ferromagnetic SM alloys.展开更多
Advanced materials with superior comprehensive mechanical properties are strongly desired,but it has long been a challenge to achieve high ductility in high-strength materials.Here,we proposed a new V 0.5 Cr 0.5 CoNi ...Advanced materials with superior comprehensive mechanical properties are strongly desired,but it has long been a challenge to achieve high ductility in high-strength materials.Here,we proposed a new V 0.5 Cr 0.5 CoNi medium-entropy alloy(MEA)with a face-centered cubic/hexagonal close-packed(FCC/HCP)dual-phase ultrafine-grained(UFG)architecture containing stacking faults(SFs)and local chemical order(LCO)in HCP solid solution,to obtain an ultrahigh yield strength of 1476 MPa and uniform elongation of 13.2%at ambient temperature.The ultrahigh yield strength originates mainly from fine grain strength-ening of the UFG FCC matrix and HCP second-phase strengthening assisted by the SFs and LCO inside,whereas the large ductility correlates to the superior ability of the UFG FCC matrix to storage disloca-tions and the function of deformation-induced SFs in the vicinity of the FCC/HCP boundary to eliminate the stress concentration.This work provides new guidance by engineering novel composition and stable UFG structure for upgrading the mechanical properties of metallic materials.展开更多
By means of X-ray diffraction profile analysis of three different composition Fe?Mn?Si alloys, the relationship between stacking fault probabilityP sf with the concentrations of constituents in alloys, 1/P sf =540.05+...By means of X-ray diffraction profile analysis of three different composition Fe?Mn?Si alloys, the relationship between stacking fault probabilityP sf with the concentrations of constituents in alloys, 1/P sf =540.05+23.70× Mn wt%-138.74×Si wt%, was determined. According to the nucleation mechanism by stacking fault in this alloy, the equation between critical driving force ?G c andP sf ?G c=67.487+0.177 5/P sf (J/mol), was made. Therefore, the relationship between critical driving force and compositions was established. Associated with the thermodynamic calculation, theM s of fcc (γ)→ hcp(ε) martensitic transformation in any suitable composition Fe?Mn?Si shape memory alloys can be predicted and results seem reasonable as compared with some experimental data.展开更多
The mass limit of neutron star has still remained a mystery. The existing Tolman-Oppenheimer-Volkoff (TOV) equation for calculating the limit always gives different values, by introducing different assumptions and hav...The mass limit of neutron star has still remained a mystery. The existing Tolman-Oppenheimer-Volkoff (TOV) equation for calculating the limit always gives different values, by introducing different assumptions and having been predicted like 0.7 Mo, 3.2 Mo, 3.6 Mo, where Mo = 1.98 × 1030 Kg. There is a need of some better technique to adopt other than TOV relation to seek out the value. In this paper, a new relation between the mass of the collapsing star and its average density ρ′ has been derived and used to calculate the limit of neutron star. The conditions in radii between Schwarz Child’s radius and the actual radius of the collapsing star have been introduced to calculate the mass of star above which it will transform into a black hole and below it to a neutron star. A new constant, JN = 8.53707554 × 1039 N-3/2s-3Kg3 has been proposed with which if we introduce the average density of the collapsing neutron star, its mass limit can be calculated very easily. By putting the most possible mass density, which is the minimum required density for a collapsing star to transform into the black hole, it has been found that the mass limit of neutron star is quite higher than it has been assumed. The definition for black hole has also been re-defined on the basis of said radii conditions.展开更多
Co nanowire arrays of different crystal struc-tures have been electrodeposited into self-assembled anodic aluminum oxide (AAO) templates by varying pH value of electrolyte. The XRD results show that crystal structure ...Co nanowire arrays of different crystal struc-tures have been electrodeposited into self-assembled anodic aluminum oxide (AAO) templates by varying pH value of electrolyte. The XRD results show that crystal structure of Co nanowires is fcc structure at pH = 2.5, a mixed structure of fcc and hcp at pH = 3.0 and 3.5, and hcp structure at pH = 5.0. Magnetic measurements indicate that Co nanowire ar-rays of different crystal structures exhibit different magnetic properties. The coercivity of Co nanowire array of fcc struc-ture is larger than that of hcp structure about 900×103/4p A·m-1 along wire axis, and its squareness is also larger than that of hcp structure.展开更多
基金support from the National Natural Science Foundation of China(Grant Nos.51801078 and 21701083)the Natural Science Foundation of Jiangsu Province(Grant No.BK20180986 and BK20210884)。
文摘High hydrogen desorption temperature and sluggish reaction kinetics are the major limitations for the practical application of MgH_(2).In this study,Co particles with a face centered cubic(FCC)structure and a hexagonal close packed(HCP)structure were prepared facilely and proved to be good catalysts for magnesium hydride.Co particles with FCC structure presented better catalytic effect on MgH_(2)than that with HCP structure.Both 7%(mass)Co FCC and HCP particle modified MgH_(2)decreased the initial dehydrogenation temperature from 301.3℃ to approximately 195.0℃,but 7%(mass)Co with FCC structure modified MgH_(2)has a faster desorption rate,and around 6.5%(mass)H_(2)was desorbed in 10 min at325℃.Hydrogen uptake was detected at 70℃ under 3.25 MPa hydrogen pressure and 6.0%(mass)H_(2)was recharged in 40 min at 150℃.The hydrogen desorption and absorption activation energy for 7%(mass)FCC Co modified MgH_(2)was significantly decreased to(76.6±8.3)kJ·mol^(-1) and(68.3±6.0)kJ·mol^(-1),respectively.Thermodynamic property was also studied,the plateau pressures of MgH_(2)+7%(mass)FCC Co were determined to be 0.14,0.28,0.53 and 0.98 MPa for 300℃,325℃,350℃ and375℃.The decomposition enthalpy of hydrogen(ΔH)for MgH_(2)+7%(mass)FCC Co was(80.6±0.1)kJ·mol^(-1),5.8 kJ·mol^(-1)lower than that of as-prepared MgH_(2).Moreover,cycling performance for the first20 cycles revealed that the reaction kinetics and capacity of MgH_(2)-FCC Co composite remained almost unchanged.The result of density functional theory calculation demonstrated that cobalt could extract the Mg AH bond and reduced the decompose energy of magnesium hydride.Our paper can be presented as a reference for searching highly effective catalysts for hydrogen storage and other energy-related research fields.
文摘It is known that pure Co undergoes martensitic transformation from γ phase (fcc) to ε phase (hcp) by the movement of a/6<112> Shockley partial dislocations at around 400 ℃, however, there have been few systematic works on the SM effect in Co and Co-based alloys. In this study, the fcc/hcp rnartensitic transformation and the SM effect were investigated in Co-A1 binary alloys(mole fraction of Al=0-16%). The γ/ε rnartensitic transformation temperatures were found from the DSC measurements to decrease with increasing Al content, while the transformation temperature hystereses were observed to increase from 60℃ at x(Al)=0 to 150℃ at x(Al) = 16%. The SM effect evaluated by a conventional bending test was enhanced by the addition of Al over 4% (mole fraction) and Co-Al alloys containing over 10%(mole fraction) exhibit a good SM effect associated with the hcpfee → reverse transformation above 200℃. The SM effect was significantly improved by precipitation of β (I32) phase and the max[real shape recovery strain of 2.2 % was obtained, which can be explained by precipitation hardening. The crystallographic orientations between the β, εand γ phases were also determined. Finally, the magnetic properties were investigated and it was found that the Curie temperature and saturation magnetization of Co-14% Al(mole fraction) are 690℃ and 120 emu/g, respectively. It is concluded that the Co-A1 alloys hold promise as new high-temperature and ferromagnetic SM alloys.
基金supported by the National Natural Science Foundation of China(Nos.U1530401,52071038,51871194)the Fundamental Research Funds for the Central Universities(No.N2102008)the Innovation Research Group Project of Hebei Natural Science Foundation,China(No.E2021203011).
文摘Advanced materials with superior comprehensive mechanical properties are strongly desired,but it has long been a challenge to achieve high ductility in high-strength materials.Here,we proposed a new V 0.5 Cr 0.5 CoNi medium-entropy alloy(MEA)with a face-centered cubic/hexagonal close-packed(FCC/HCP)dual-phase ultrafine-grained(UFG)architecture containing stacking faults(SFs)and local chemical order(LCO)in HCP solid solution,to obtain an ultrahigh yield strength of 1476 MPa and uniform elongation of 13.2%at ambient temperature.The ultrahigh yield strength originates mainly from fine grain strength-ening of the UFG FCC matrix and HCP second-phase strengthening assisted by the SFs and LCO inside,whereas the large ductility correlates to the superior ability of the UFG FCC matrix to storage disloca-tions and the function of deformation-induced SFs in the vicinity of the FCC/HCP boundary to eliminate the stress concentration.This work provides new guidance by engineering novel composition and stable UFG structure for upgrading the mechanical properties of metallic materials.
基金Project supported by the National Natural Science Foundation of China (Grant No. 59671023).
文摘By means of X-ray diffraction profile analysis of three different composition Fe?Mn?Si alloys, the relationship between stacking fault probabilityP sf with the concentrations of constituents in alloys, 1/P sf =540.05+23.70× Mn wt%-138.74×Si wt%, was determined. According to the nucleation mechanism by stacking fault in this alloy, the equation between critical driving force ?G c andP sf ?G c=67.487+0.177 5/P sf (J/mol), was made. Therefore, the relationship between critical driving force and compositions was established. Associated with the thermodynamic calculation, theM s of fcc (γ)→ hcp(ε) martensitic transformation in any suitable composition Fe?Mn?Si shape memory alloys can be predicted and results seem reasonable as compared with some experimental data.
文摘The mass limit of neutron star has still remained a mystery. The existing Tolman-Oppenheimer-Volkoff (TOV) equation for calculating the limit always gives different values, by introducing different assumptions and having been predicted like 0.7 Mo, 3.2 Mo, 3.6 Mo, where Mo = 1.98 × 1030 Kg. There is a need of some better technique to adopt other than TOV relation to seek out the value. In this paper, a new relation between the mass of the collapsing star and its average density ρ′ has been derived and used to calculate the limit of neutron star. The conditions in radii between Schwarz Child’s radius and the actual radius of the collapsing star have been introduced to calculate the mass of star above which it will transform into a black hole and below it to a neutron star. A new constant, JN = 8.53707554 × 1039 N-3/2s-3Kg3 has been proposed with which if we introduce the average density of the collapsing neutron star, its mass limit can be calculated very easily. By putting the most possible mass density, which is the minimum required density for a collapsing star to transform into the black hole, it has been found that the mass limit of neutron star is quite higher than it has been assumed. The definition for black hole has also been re-defined on the basis of said radii conditions.
基金Acknowledgments This work has benefited from the use of 1） Los Alamos Neutron Science Facility at Los Alamos National Laboratory and 2） ISIS Pulsed Neutron and Muon Source at Rutherford-Appleton Laboratory. The financial support of the National Science Foundation＇s 1） International Materials Institutes （IMI） under DMR-0231320, 2） Integrative Graduate Education and Research Training （IGERT） under DGE-9987548, 3） Combined Research and Curriculum Development （CRCD） under EEC-9527527 and EEC-0203415, and 4） Major Research Instrumentation （MRI） under DMR-0231320 at the University of Tennessee with Dr HUBER C, Dr Van HARTESVELDT C J, Dr DUTTA D, Dr JENNINGS W, Dr G0LDBERG L, Ms P0ATS M, and Dr B0ULDIN C R as the Program Directors, is greatly appreciated. Additional funding for this project was gratefully received from the Tennessee Advanced Materials Laboratory, with Prof. PLUMMER E W as the Director.
文摘Co nanowire arrays of different crystal struc-tures have been electrodeposited into self-assembled anodic aluminum oxide (AAO) templates by varying pH value of electrolyte. The XRD results show that crystal structure of Co nanowires is fcc structure at pH = 2.5, a mixed structure of fcc and hcp at pH = 3.0 and 3.5, and hcp structure at pH = 5.0. Magnetic measurements indicate that Co nanowire ar-rays of different crystal structures exhibit different magnetic properties. The coercivity of Co nanowire array of fcc struc-ture is larger than that of hcp structure about 900×103/4p A·m-1 along wire axis, and its squareness is also larger than that of hcp structure.
