The exposure of Al-5Cu alloy to an external stress with normal aging was carried out. The effects of external stress-aging on the morphology and precipitation behavior of θ＂ phase were investigated by transmission e...The exposure of Al-5Cu alloy to an external stress with normal aging was carried out. The effects of external stress-aging on the morphology and precipitation behavior of θ＂ phase were investigated by transmission electron microscopy （TEM）, differential scanning calorimetry （DSC） and first principle calculation. The size of the θ＂ phase precipitated plates in stress-aging （453 K, 6 h, 50 MPa） is 19.83 nm, which is smaller than that of those present （28.79 nm） in stress-flee aging （453 K, 6 h）. The precipitation process of θ＂ phase is accelerated by loading external stress aging according to the analysis of DSC results. The apparent activation energy for the external stress-aging is 10% lower than the stress-free one. The first principle calculation results show that the external stress makes a decrease of 6% in the interface energy. The effects of the stress on aging process of the alloy are discussed on the basis of the classical theory. The external stress changes the morphology and precipitation behavior of θ＂ phase because the critical nucleation energy is decreased by 19% under stress aging.展开更多
Hydrogen evolution reaction （HER） at polycrystalline silver electrode in 0.1 mol/L HClO4 solution is investigated by cyclic voltammetry in the temperature range of 278-333 K. We found that at electrode potential φa...Hydrogen evolution reaction （HER） at polycrystalline silver electrode in 0.1 mol/L HClO4 solution is investigated by cyclic voltammetry in the temperature range of 278-333 K. We found that at electrode potential φa,app decreases with φ, while pre-exponential factor A remains nearly unchanged,which conforms well the prediction from Butler-Volmer equation. In contrast, with φ nega-tive shifts from the onset potential for HER to the potential of zero charge （PZC≈-0.4 V）, both Ea,app and A for HER increase （e.g., Ea,app increases from 24 kJ/mol to 32 kJ/mol）. The increase in Ea,app and A with negative shift in φ from -0.25 V to PZC is explained by the increases of both internal energy change and entropy change from reactants to the transition states, which is correlated with the change in the hydrogen bond network during HER. The positive entropy effects overcompensate the adverse effect from the increase in the activation energy, which leads to a net increase in HER current with the activation energy negative shift from the onset potential of HER to PZC. It is pointed out that entropy change may contribute greatly to the kinetics for electrode reaction which involves the transfer of electron and proton, such as HER.展开更多
Quick and reliable identification of the traffic state is of critical importance to traffic control systems, especially when spillovers appear. Firstly, a calculation method for the occupancy per cycle under different...Quick and reliable identification of the traffic state is of critical importance to traffic control systems, especially when spillovers appear. Firstly, a calculation method for the occupancy per cycle under different traffic conditions were presented, based on the relationship between the three basic traffic flow parameters, speed, traffic flow and density. Secondly, the times at which the stopping and starting waves approach a loop detector were confirmed using the traffic wave models modified by a kinematic equation. Then, the threshold of occupancy, which characterizes the appearance of spillovers, was determined by the premise that the stopping and starting waves had the same speed. At last, the accuracy and usability of the new method were verified by VISSIM simulation, using the ratio of misjudgment as the evaluation index. The results show that the ratio of misjudgment of the new method is about 11.36% compared to 17.65% of the previous method.展开更多
On the basis of mutual compensation of mobility and threshold voltage temperature effects, a stable CMOS band-gap voltage reference circuit was designed and fabricated in CSMC-HJ 0.6 μm CMOS technology. Operating fro...On the basis of mutual compensation of mobility and threshold voltage temperature effects, a stable CMOS band-gap voltage reference circuit was designed and fabricated in CSMC-HJ 0.6 μm CMOS technology. Operating from 0 to 85 ℃ under a supply voltage ranging from 4.5 to 5.5 V, the voltage reference circuit offers an output reference voltage ranging from 1.122 to 1.176 V and a voltage variation less than ±3.70%. The chip size including bonding pads is only 0.4 mm×0.4 mm and the power dissipation falls inside the scope of 28.3 to 48.8 mW operating at a supply voltage of 4.5 to 5.5 V.展开更多
The microstructure,mechanical properties and stress corrosion cracking(SCC)of 7136 aluminum alloy under T 6,T 79 and T 74 aging treatments were studied and the effects of microstructure on the mechanical properties an...The microstructure,mechanical properties and stress corrosion cracking(SCC)of 7136 aluminum alloy under T 6,T 79 and T 74 aging treatments were studied and the effects of microstructure on the mechanical properties and SCC were discussed.The results show that the ultimate tensile strength and yield strength of the aging 7136 alloys follow this sequence from high to low:T 6>T 79>pre-aging>T 74.For 7136 Al alloy after T 6 aging,the average diameter of the precipitates was(5.7±1.7)nm,and the diameter of 60.7%(number fraction)precipitates was 2−6 nm,leading to a good precipitation strengthening.The K_(IC)of T 74-aging alloy is 38.2 MPa·m^(1/2),which is 26.1%more than that of T 6-aging alloy and 17.5%more than that of T 79-aging alloy.The improved fracture toughness in T 74-aging alloy is mainly due to the reduction of the strength difference between intragranular and grain boundary.The SCC resistance of the aging 7136 alloys follows this sequence from high to low:T 79>T 74>T 6.After T 79 aging,the discontinuous grain boundary precipitates and narrow precipitate free zones were obtained in 7136 alloy,which was beneficial to SCC resistance.展开更多
基金Project(2012CB619506)supported by the National Basic Research Program of ChinaProject(51071177)supported by the National Natural Science Foundation of China
文摘The exposure of Al-5Cu alloy to an external stress with normal aging was carried out. The effects of external stress-aging on the morphology and precipitation behavior of θ＂ phase were investigated by transmission electron microscopy （TEM）, differential scanning calorimetry （DSC） and first principle calculation. The size of the θ＂ phase precipitated plates in stress-aging （453 K, 6 h, 50 MPa） is 19.83 nm, which is smaller than that of those present （28.79 nm） in stress-flee aging （453 K, 6 h）. The precipitation process of θ＂ phase is accelerated by loading external stress aging according to the analysis of DSC results. The apparent activation energy for the external stress-aging is 10% lower than the stress-free one. The first principle calculation results show that the external stress makes a decrease of 6% in the interface energy. The effects of the stress on aging process of the alloy are discussed on the basis of the classical theory. The external stress changes the morphology and precipitation behavior of θ＂ phase because the critical nucleation energy is decreased by 19% under stress aging.
基金ACKNOWLEDGMENTS This work was supported by the One Hundred Talents＇ Program of the Chinese Academy of Science, the National Natural Science Foundation of China （No.21073176）, and the National Basic Research Program of China National Science and Technology （No.2010CB923302）.
文摘Hydrogen evolution reaction （HER） at polycrystalline silver electrode in 0.1 mol/L HClO4 solution is investigated by cyclic voltammetry in the temperature range of 278-333 K. We found that at electrode potential φa,app decreases with φ, while pre-exponential factor A remains nearly unchanged,which conforms well the prediction from Butler-Volmer equation. In contrast, with φ nega-tive shifts from the onset potential for HER to the potential of zero charge （PZC≈-0.4 V）, both Ea,app and A for HER increase （e.g., Ea,app increases from 24 kJ/mol to 32 kJ/mol）. The increase in Ea,app and A with negative shift in φ from -0.25 V to PZC is explained by the increases of both internal energy change and entropy change from reactants to the transition states, which is correlated with the change in the hydrogen bond network during HER. The positive entropy effects overcompensate the adverse effect from the increase in the activation energy, which leads to a net increase in HER current with the activation energy negative shift from the onset potential of HER to PZC. It is pointed out that entropy change may contribute greatly to the kinetics for electrode reaction which involves the transfer of electron and proton, such as HER.
基金Project(2011AA110304) supported by the National High Technology Research and Development Program of China
文摘Quick and reliable identification of the traffic state is of critical importance to traffic control systems, especially when spillovers appear. Firstly, a calculation method for the occupancy per cycle under different traffic conditions were presented, based on the relationship between the three basic traffic flow parameters, speed, traffic flow and density. Secondly, the times at which the stopping and starting waves approach a loop detector were confirmed using the traffic wave models modified by a kinematic equation. Then, the threshold of occupancy, which characterizes the appearance of spillovers, was determined by the premise that the stopping and starting waves had the same speed. At last, the accuracy and usability of the new method were verified by VISSIM simulation, using the ratio of misjudgment as the evaluation index. The results show that the ratio of misjudgment of the new method is about 11.36% compared to 17.65% of the previous method.
文摘On the basis of mutual compensation of mobility and threshold voltage temperature effects, a stable CMOS band-gap voltage reference circuit was designed and fabricated in CSMC-HJ 0.6 μm CMOS technology. Operating from 0 to 85 ℃ under a supply voltage ranging from 4.5 to 5.5 V, the voltage reference circuit offers an output reference voltage ranging from 1.122 to 1.176 V and a voltage variation less than ±3.70%. The chip size including bonding pads is only 0.4 mm×0.4 mm and the power dissipation falls inside the scope of 28.3 to 48.8 mW operating at a supply voltage of 4.5 to 5.5 V.
基金Project(2017GK2261)supported by the Science and Technology Program of Hunan Province,ChinaProject(41423040204)supported by National Key Laboratory of Light Weight and High Strength Structural Materials Equipment Pre-research Laboratory Foundation,China。
文摘The microstructure,mechanical properties and stress corrosion cracking(SCC)of 7136 aluminum alloy under T 6,T 79 and T 74 aging treatments were studied and the effects of microstructure on the mechanical properties and SCC were discussed.The results show that the ultimate tensile strength and yield strength of the aging 7136 alloys follow this sequence from high to low:T 6>T 79>pre-aging>T 74.For 7136 Al alloy after T 6 aging,the average diameter of the precipitates was(5.7±1.7)nm,and the diameter of 60.7%(number fraction)precipitates was 2−6 nm,leading to a good precipitation strengthening.The K_(IC)of T 74-aging alloy is 38.2 MPa·m^(1/2),which is 26.1%more than that of T 6-aging alloy and 17.5%more than that of T 79-aging alloy.The improved fracture toughness in T 74-aging alloy is mainly due to the reduction of the strength difference between intragranular and grain boundary.The SCC resistance of the aging 7136 alloys follows this sequence from high to low:T 79>T 74>T 6.After T 79 aging,the discontinuous grain boundary precipitates and narrow precipitate free zones were obtained in 7136 alloy,which was beneficial to SCC resistance.
