To study the influence of aging heat treatments on the microstructure of single crystal superalloys with high content of refractory elements and optimal the aging heat treatment regimes, a single crystal superalloy co...To study the influence of aging heat treatments on the microstructure of single crystal superalloys with high content of refractory elements and optimal the aging heat treatment regimes, a single crystal superalloy containing 22 wt% refractory elements was investigated.Results show that for the experimental alloy, even the homogenization-solution heat treatment for 25 h cannot homogenize the alloying elements completely. During primary aging heat treatment, γ＇ phase grows larger and turns to regular cubes. Higher aging temperature induces larger γ＇ cubes. For specimens with primary aging heat treated at 1120 ℃,γ＇ morphology does not change apparently during secondary aging heat treatment. For specimens with primary aging heat treatment at 1150 ℃,γ＇phase in interdendrite grows obviously comparing with that in dendrites. By analyzing the precipitating kinetics of γ＇phase, it is found that owning to the dendrite segregation and different aging heat treatment temperatures, γ＇ phase at different regions grows under the control of different factors at different aging heat treatment stages. The two controlling factors that are driving forces of phase transformation and element diffusion rate induce obviously different growth rates of γ＇ phase. As a result, the γ＇-precipitating behaviors are variable based on different solute concentrations and aging temperatures. For advanced single crystal superalloys that are supposed to be used at relatively high temperatures, the final γ＇ size after aging heat treatment is suggested to be close to the crossing point of diffusion controlling curve and driving force controlling curve corresponding to the serving temperature. And then,high-temperature properties can be improved.展开更多
Precipitation of α-phase in massive and feathery microstructures was studied during aging in the single α field. It was found that the α-phase mainly precipitated along the γ-plate interfaces as laths in the feath...Precipitation of α-phase in massive and feathery microstructures was studied during aging in the single α field. It was found that the α-phase mainly precipitated along the γ-plate interfaces as laths in the feathery structure, while it nucleated at various sites in the massive structure in the form of particles and dominantly as plates. Precipitation of α-plates in the massive structure occurred by the difFusional ledge mechanism. The γm→α reaction proceeded by the growth of previously nucleated α-precipitates, and chiefly by the development of new α-plates展开更多
Solar-driven water splitting has emerged as a promising route for sustainable hydrogen generation,however,developing broad-spectrum responsive photocatalysts remains a challenge for achieving efficient solar-to-hydrog...Solar-driven water splitting has emerged as a promising route for sustainable hydrogen generation,however,developing broad-spectrum responsive photocatalysts remains a challenge for achieving efficient solar-to-hydrogen conversion.Here,we demonstrate a g-C_(3)N_(4)-based(UCN)catalyst with dispersed Ag single atoms(Ag SAs)and Ag nanoparticles(Ag NPs)for synergistically broad-spectrum photocatalytic hydrogen evolution.Experimental and theoretical results reveal that both Ag SAs and Ag NPs serve as active sites,with the Schottky junction between Ag NPs and g-C_(3)N_(4)effectively promoting charge separation,while Ag NPs induce localized surface plasmon resonance,extending the light response range from visible to near-infrared regions.The optimized catalyst Ag-UCN-3 exhibits a hydrogen evolution rate as high as 22.11 mmol/g/h and an apparent quantum efficiency(AQE)of 10.16%under 420 nm light illumination.Notably,it still had a high hydrogen evolution rate of 633.57μmol/g/h under 700 nm irradiation.This work unveils dual active sites engineering strategy that couples Ag SAs and Ag NPs with plasma and hot electrons,offering a new strategy for designing high-performance solar-driven energy systems.展开更多
Mg–Zn–Ag alloys have been extensively studied in recent years for potential biodegradable implants due to their unique mechanical properties,biodegradability and biocompatibility.In the present study,Mg–3Zn-x Ag（w...Mg–Zn–Ag alloys have been extensively studied in recent years for potential biodegradable implants due to their unique mechanical properties,biodegradability and biocompatibility.In the present study,Mg–3Zn-x Ag（wt%,x=0.2,0.5 and0.8）alloys with single-phase crystal structure were prepared by backward extrusion at 340°C.The addition of Ag element into Mg–3Zn slightly influences the ultimate tensile strength and microstructure,but the elongation firstly increases from12%to 19.8%and then decreases from 19.8%to 9.9%with the increment of Ag concentration.The tensile yield strength,ultimate tensile strength and elongation of Mg–3Zn–0.2Ag alloy reach up to 142,234 MPa and 19.8%,respectively,which are the best mechanical performance of Mg–Zn–Ag alloys in the present work.The extruded Mg–3Zn–0.2Ag alloy also possesses the best corrosion behavior with the corresponding corrosion rate of 3.2 mm/year in immersion test,which could be explained by the single-phase and uniformly distributed grain structure,and the fewer twinning.展开更多
Carbon nitride has been extensively used as a visible-light photocatalyst,but it has the disadvantages of a low specific surface area,rapid electron-hole recombination,and relatively low light absorbance.In this study...Carbon nitride has been extensively used as a visible-light photocatalyst,but it has the disadvantages of a low specific surface area,rapid electron-hole recombination,and relatively low light absorbance.In this study,single-atom Ag was successfully anchored on ultrathin carbon nitride(UTCN)via thermal polymerization,the catalyst obtained is called AgUTCN.The Ag hardly changed the carbon nitride's layered and porous physical structure.AgUTCN exhibited efficient visible-light photocatalytic performances in the degradation of various recalcitrant pollutants,eliminations of 85% were achieved by visible-light irradiation for 1hr.Doping with Ag improved the photocatalytic performance of UTCN by narrowing the forbidden band gap from 2.49 to 2.36 e V and suppressing electron-hole pair recombination.In addition,Ag doping facilitated O_(2) adsorption on UTCN by decreasing the adsorption energy from -0.2 to -2.22 e V and favored the formation of O_(2)^(·-).Electron spin resonance and radical-quenching experiments showed that O_(2)^(·-)was the major reactive species in the degradation of Acetaminophen(paracetamol,APAP).展开更多
基金financially supported by the Foundation of Beijing Institute of Aeronautical Materials (No.KJSJ150109)
文摘To study the influence of aging heat treatments on the microstructure of single crystal superalloys with high content of refractory elements and optimal the aging heat treatment regimes, a single crystal superalloy containing 22 wt% refractory elements was investigated.Results show that for the experimental alloy, even the homogenization-solution heat treatment for 25 h cannot homogenize the alloying elements completely. During primary aging heat treatment, γ＇ phase grows larger and turns to regular cubes. Higher aging temperature induces larger γ＇ cubes. For specimens with primary aging heat treated at 1120 ℃,γ＇ morphology does not change apparently during secondary aging heat treatment. For specimens with primary aging heat treatment at 1150 ℃,γ＇phase in interdendrite grows obviously comparing with that in dendrites. By analyzing the precipitating kinetics of γ＇phase, it is found that owning to the dendrite segregation and different aging heat treatment temperatures, γ＇ phase at different regions grows under the control of different factors at different aging heat treatment stages. The two controlling factors that are driving forces of phase transformation and element diffusion rate induce obviously different growth rates of γ＇ phase. As a result, the γ＇-precipitating behaviors are variable based on different solute concentrations and aging temperatures. For advanced single crystal superalloys that are supposed to be used at relatively high temperatures, the final γ＇ size after aging heat treatment is suggested to be close to the crossing point of diffusion controlling curve and driving force controlling curve corresponding to the serving temperature. And then,high-temperature properties can be improved.
文摘Precipitation of α-phase in massive and feathery microstructures was studied during aging in the single α field. It was found that the α-phase mainly precipitated along the γ-plate interfaces as laths in the feathery structure, while it nucleated at various sites in the massive structure in the form of particles and dominantly as plates. Precipitation of α-plates in the massive structure occurred by the difFusional ledge mechanism. The γm→α reaction proceeded by the growth of previously nucleated α-precipitates, and chiefly by the development of new α-plates
文摘Solar-driven water splitting has emerged as a promising route for sustainable hydrogen generation,however,developing broad-spectrum responsive photocatalysts remains a challenge for achieving efficient solar-to-hydrogen conversion.Here,we demonstrate a g-C_(3)N_(4)-based(UCN)catalyst with dispersed Ag single atoms(Ag SAs)and Ag nanoparticles(Ag NPs)for synergistically broad-spectrum photocatalytic hydrogen evolution.Experimental and theoretical results reveal that both Ag SAs and Ag NPs serve as active sites,with the Schottky junction between Ag NPs and g-C_(3)N_(4)effectively promoting charge separation,while Ag NPs induce localized surface plasmon resonance,extending the light response range from visible to near-infrared regions.The optimized catalyst Ag-UCN-3 exhibits a hydrogen evolution rate as high as 22.11 mmol/g/h and an apparent quantum efficiency(AQE)of 10.16%under 420 nm light illumination.Notably,it still had a high hydrogen evolution rate of 633.57μmol/g/h under 700 nm irradiation.This work unveils dual active sites engineering strategy that couples Ag SAs and Ag NPs with plasma and hot electrons,offering a new strategy for designing high-performance solar-driven energy systems.
基金supported by the National Natural Science Foundation of China (Nos. 51371046 and 51525101)the National Key Research and Development Program of China (No. 2016YFB0701202)the Fundamental Research Funds of the Central Universities (No. N141008001)
文摘Mg–Zn–Ag alloys have been extensively studied in recent years for potential biodegradable implants due to their unique mechanical properties,biodegradability and biocompatibility.In the present study,Mg–3Zn-x Ag（wt%,x=0.2,0.5 and0.8）alloys with single-phase crystal structure were prepared by backward extrusion at 340°C.The addition of Ag element into Mg–3Zn slightly influences the ultimate tensile strength and microstructure,but the elongation firstly increases from12%to 19.8%and then decreases from 19.8%to 9.9%with the increment of Ag concentration.The tensile yield strength,ultimate tensile strength and elongation of Mg–3Zn–0.2Ag alloy reach up to 142,234 MPa and 19.8%,respectively,which are the best mechanical performance of Mg–Zn–Ag alloys in the present work.The extruded Mg–3Zn–0.2Ag alloy also possesses the best corrosion behavior with the corresponding corrosion rate of 3.2 mm/year in immersion test,which could be explained by the single-phase and uniformly distributed grain structure,and the fewer twinning.
基金supported by the Shenzhen Science,Technology and Innovation Commission(No.JCYJ20200109142829123)the National Natural Science Foundation of China(No.52022049)。
文摘Carbon nitride has been extensively used as a visible-light photocatalyst,but it has the disadvantages of a low specific surface area,rapid electron-hole recombination,and relatively low light absorbance.In this study,single-atom Ag was successfully anchored on ultrathin carbon nitride(UTCN)via thermal polymerization,the catalyst obtained is called AgUTCN.The Ag hardly changed the carbon nitride's layered and porous physical structure.AgUTCN exhibited efficient visible-light photocatalytic performances in the degradation of various recalcitrant pollutants,eliminations of 85% were achieved by visible-light irradiation for 1hr.Doping with Ag improved the photocatalytic performance of UTCN by narrowing the forbidden band gap from 2.49 to 2.36 e V and suppressing electron-hole pair recombination.In addition,Ag doping facilitated O_(2) adsorption on UTCN by decreasing the adsorption energy from -0.2 to -2.22 e V and favored the formation of O_(2)^(·-).Electron spin resonance and radical-quenching experiments showed that O_(2)^(·-)was the major reactive species in the degradation of Acetaminophen(paracetamol,APAP).
