Formation behaviors of rod-like reactive shaped charge penetrator(RRSCP)and their effects on damage capability are investigated by experiments and numerical simulations.The pulsed X-ray technology and a spaced aluminu...Formation behaviors of rod-like reactive shaped charge penetrator(RRSCP)and their effects on damage capability are investigated by experiments and numerical simulations.The pulsed X-ray technology and a spaced aluminum/steel plate with the thicknesses of 5 mm/100 mm are used.Three types of sphericalsegment aluminum-polytetrafluoroethylene-copper(Al-PTFE-Cu)reactive liners with Cu contents of 0%,46.6%,and 66%are fabricated and tested.The experimental results show that the reactive liners can form excellent rod-shaped penetrators with tail skirts under the shaped charge effect,but the tail skirts disappear over time.Moreover,rupturing damage to the aluminum plate and penetration to the steel plate are caused by the RRSCP impact.From simulation analysis,the RRSCP is formed by a mechanically and chemically coupled response with the reactive liner activated by shock in its outer walls and bottom and then backward overturning,forming a leading reactive penetrator and a following chemical energy cluster.The unique formation structure determines the damage modes of the aluminum plate and the steel plate.Further analysis indicates that the formation behaviors and damage capability of Al-PTFE-Cu RRSCP strongly depend on Cu content.With increasing Cu content,the velocity,activation extent,and reaction extent of Al-PTFE-Cu RRSCP decrease,which contribute to elongation and alleviate the negative effects of chemical reactions on elongation,significantly increasing the length-diameter ratio and thus enhancing the capability of steel plate penetration.However,the lower activation extent and energetic density will weaken the RRSCP's capability of causing rupturing damage to the aluminum plate.展开更多
A series of ballistic experiments were performed to investigate the damage behavior of high velocity reactive material projectiles(RMPs) impacting liquid-filled tanks,and the corresponding hydrodynamic ram(HRAM) was s...A series of ballistic experiments were performed to investigate the damage behavior of high velocity reactive material projectiles(RMPs) impacting liquid-filled tanks,and the corresponding hydrodynamic ram(HRAM) was studied in detail.PTFE/Al/W RMPs with steel-like and aluminum-like densities were prepared by a pressing/sintering process.The projectiles impacted a liquid-filled steel tank with front aluminum panel at approximately 1250 m/s.The corresponding cavity evolution characteristics and HRAM pressure were recorded by high-speed camera and pressure acquisition system,and further compared to those of steel and aluminum projectiles.Significantly different from the conical cavity formed by the inert metal projectile,the cavity formed by the RMP appeared as an ellipsoid with a conical front.The RMPs were demonstrated to enhance the radial growth velocity of cavity,the global HRAM pressure amplitude and the front panel damage,indicating the enhanced HRAM and structural damage behavior.Furthermore,combining the impact-induced fragmentation and deflagration characteristics,the cavity evolution of RMPs under the combined effect of kinetic energy impact and chemical energy release was analyzed.The mechanism of enhanced HRAM pressure induced by the RMPs was further revealed based on the theoretical model of the initial impact wave and the impulse analysis.Finally,the linear correlation between the deformation-thickness ratio and the non-dimensional impulse for the front panel was obtained and analyzed.It was determined that the enhanced near-field impulse induced by the RMPs was the dominant reason for the enhanced structural damage behavior.展开更多
The shock-induced reaction mechanism and characteristics of Ni/Al system,considering an Al nanoparticle-embedded Ni single crystal,are investigated through molecular dynamics simulation.For the shock melting of Al nan...The shock-induced reaction mechanism and characteristics of Ni/Al system,considering an Al nanoparticle-embedded Ni single crystal,are investigated through molecular dynamics simulation.For the shock melting of Al nanoparticle,interfacial crystallization and dissolution are the main characteristics.The reaction degree of Al particle first increases linearly and then logarithmically with time driven by rapid mechanical mixing and following dissolution.The reaction rate increases with the decrease of particle diameter,however,the reaction is seriously hindered by interfacial crystallization when the diameter is lower than 9 nm in our simulations.Meanwhile,we found a negative exponential growth in the fraction of crystallized Al atoms,and the crystallinity of B2-NiAl(up to 20%)is positively correlated with the specific surface area of Al particle.This can be attributed to the formation mechanism of B2-NiAl by structural evolution of finite mixing layer near the collapsed interface.For shock melting of both Al particle and Ni matrix,the liquid-liquid phase inter-diffusion is the main reaction mechanism that can be enhanced by the formation of internal jet.In addition,the enhanced diffusion is manifested in the logarithmic growth law of mean square displacement,which results in an almost constant reaction rate similar to the mechanical mixing process.展开更多
By considering the joint effects of the Kelvin-Helmholtz(KH) and Rayleigh-Taylor(RT) instabilities, this paper presents an interpretation of the wavy patterns that occur in explosive welding. It is assumed that the el...By considering the joint effects of the Kelvin-Helmholtz(KH) and Rayleigh-Taylor(RT) instabilities, this paper presents an interpretation of the wavy patterns that occur in explosive welding. It is assumed that the elasticity of the material at the interface effectively determines the wavelength, because explosive welding is basically a solid-state welding process. To this end, an analytical model of elastic hydrodynamic instabilities is proposed, and the most unstable mode is selected in the solid phase. Similar approaches have been widely used to study the interfacial behavior of solid metals in high-energy-density physics. By comparing the experimental and theoretical results, it is concluded that thermal softening,which significantly reduces the shear modulus, is necessary and sufficient for successful welding. The thermal softening is verified by theoretical analysis of the increase in temperature due to the impacting and sliding of the flyer and base plates, and some experimental observations are qualitatively validated.In summary, the combined effect of the KH and RT instabilities in solids determines the wavy morphology, and our theoretical results are in good qualitative agreement with experimental and numerical observations.展开更多
In this paper the elastic constants of graphite at elevated temperature were experimentally investigated by using the virtual fields method(VFM). A new method was presented for the characterization of mechanical prope...In this paper the elastic constants of graphite at elevated temperature were experimentally investigated by using the virtual fields method(VFM). A new method was presented for the characterization of mechanical properties at elevated temperature. The three-point bending tests were performed on graphite materials by an universal testing machine equipped with heating furnace. Based on the heterogeneous deformation fields measured by the digital image correlation(DIC) technique, the elastic constants were then extracted by using VFM.The measurement results of the elastic constants at 500℃ were obtained. The effect on the experimental results was also analyzed. The successful results verify the feasibility of using the proposed method to measure the properties of graphite at high temperature, and the proposed method is believed to have a good potential for further applications.展开更多
At present,the stability of the new generation of solar cells based on hybrid perovskites is the bottleneck for their practical applications.Photochemical effects,high temperature,ultraviolet light,humidity and other ...At present,the stability of the new generation of solar cells based on hybrid perovskites is the bottleneck for their practical applications.Photochemical effects,high temperature,ultraviolet light,humidity and other known or still unknown factors might cause reduction of effectiveness or even irreversible loss of materials properties due to decomposition of functional layers within perovskite solar cells(PSCs).These factors alone have a serious impact on each component of the device,while their combinations lead to much more complicated effects and consequences.This review focuses on the stability of PSCs and the degradation of the device in a humid environment.We assess the instability factors and deep-seated principles of evolution of the device structure in a humidity environment with the emphasis on the influence on their interrelations.The related solutions are reviewed from the perspective of the encapsulation,perovskite active layer,carrier transport layer and electrodes.Combined with the latest research,we believe that the waterproof strategy of PSCs requires either tight encapsulation or thorough modifications in the device itself.Therefore,it is important to develop feasible strategies to improve the overall device stability over humid according to the target characteristics of various devices.展开更多
A phenomenon of shock wave reacceleration was studied when Ti+Si reactive powder is loaded by a high-speed flyer.The self-propagating reaction in the Ti+Si reactive powder was triggered by the high speed impaction of ...A phenomenon of shock wave reacceleration was studied when Ti+Si reactive powder is loaded by a high-speed flyer.The self-propagating reaction in the Ti+Si reactive powder was triggered by the high speed impaction of the flyer launched by a two-stage gas gun.In the process of self-propagating reaction,a strand of optical fiber and the electric pins were used to measure the velocity of shock wave propagation.The experimental results showed that the initial velocity of shock wave in the reactive powder was a few hundred meters per second,and then it decreased obviously with the increase of propagation distance.This phenomenon was also verified in the process of a pure Si powder loaded by a shock,while the phenomenon of shock wave reacceleration was not observed in the Ti+Si reactive powder.展开更多
Molecular dynamics simulations have been performed to explore the underlying synergistic mechanism of pillared graphene or non-covalent connected graphene and carbon nanotubes(CNTs) on the mechanical properties of pol...Molecular dynamics simulations have been performed to explore the underlying synergistic mechanism of pillared graphene or non-covalent connected graphene and carbon nanotubes(CNTs) on the mechanical properties of polyethylene(PE) nanocomposites. By constructing the pillared graphene model and CNTs/graphene model, the effect of the structure, arrangement and dispersion of hybrid fillers on the tensile mechanical properties of PE nanocomposites was studied. The results show that the pillared graphene/PE nanocomposites exhibit higher Young’s modulus, tensile strength and elongation at break than non-covalent connected CNTs/graphene/PE nanocomposites. The pull-out simulations show that pillared graphene by CNTs has both large interfacial load and long displacement due to the mixed modes of shear separation and normal separation. Additionally, pillared graphene can not only inhibit agglomeration but also form a compact effective thickness(stiff layer), consistent with the adsorption behavior and improved interfacial energy between pillared graphene and PE matrix.展开更多
Producing hydrogen peroxide(H_(2)O_(2))through an electrochemical oxygen reduction reaction(ORR)is a safe,green strategy and a promising alternative to traditional energy-intensive anthraquinone processes.Air and rene...Producing hydrogen peroxide(H_(2)O_(2))through an electrochemical oxygen reduction reaction(ORR)is a safe,green strategy and a promising alternative to traditional energy-intensive anthraquinone processes.Air and renewable power could be utilized for onsite and decentralized H_(2)O_(2)production,demonstrating significant application potential.Currently,single atom catalysts(SACs)have demonstrated significant advantages in the catalytic production of H_(2)O_(2)in 2e−ORR.However,the selectivity of SACs in ORR once puzzled researchers.This article reviews the research on the development and achievements of H_(2)O_(2)production by SACs catalysis in recent years.Especially,the structure-performance relationship is a guide to designing new SACs.Combining advanced characterization techniques and theoretical calculation methods,researchers have a clearer and more thorough understanding of the impact of the atomic interface of SACs on ORR catalytic performance.The coordination moiety formed between the active metal center atom and the support seriously determines the selectivity of SACs,mainly manifested in the adsorption of*OOH intermediates.Particularly,the atomic interface of metal atoms together with O/N co-coordination exhibit high selectivity and mass activity,and heteroatoms or functional groups on carbon supports present synergistic effects to promote the production of H_(2)O_(2)in 2e−ORR.Fine and accurate regulation of the atomic interface of SACs directly affects the 2e−ORR performance of the catalysts.Therefore,it is important to deeply understand the atomic interface of SACs and contribute to the development of novel catalysts.展开更多
Visible photoactive AgBr/TiO_2 was immobilized on a SiO_2@Fe_3O_4 magnetic support by solvothermal and sol-gel methods to form a AgBr-TiO_2/SiO_2@Fe_3O_4 magnetic photocatalyst.Samples were characterized by X-ray diff...Visible photoactive AgBr/TiO_2 was immobilized on a SiO_2@Fe_3O_4 magnetic support by solvothermal and sol-gel methods to form a AgBr-TiO_2/SiO_2@Fe_3O_4 magnetic photocatalyst.Samples were characterized by X-ray diffraction,high-resolution transmission electron microscopy and magnetometry.Hetero-structured AgBr/TiO_2 was well seeded on the shell-core SiO_2@Fe_3O_4 structure.The AgBr-TiO_2/SiO_2@Fe_3O_4 magnetic photocatalyst exhibited high photocatalytic activity in the degradation of methylene blue under visible light.The photocatalyst was superparamagnetic,which is beneficial for facile magnetic separation.展开更多
In this work, molecular dynamics simulations have been performed to explore the structural evolution and underlying sintering mechanism of aluminum nanoparticles. The structural evolution during sintering was firstly ...In this work, molecular dynamics simulations have been performed to explore the structural evolution and underlying sintering mechanism of aluminum nanoparticles. The structural evolution during sintering was firstly monitored through radial distribution function and atomic migration, and the underlying sintering mechanism was further quantitatively characterized in terms of average displacement, mean squared distance(MSD), radius ratio(i.e., the ratio of the neck radius to the particle radius), shrinkage and radius of gyration, crystalline orientations, particle size, etc. Results show that the surface atoms of nanoparticles are more active than the internal atoms, favoring the mechanical rotation of nanoparticles during sintering. During the sintering process, average displacement, radius ratio and the shrinkage rate have undergone three stages with increasing the temperature:(1) a slow increase and subsequent abrupt hike after reaching the sintering temperature;(2) an almost plateau region over a wide span of temperature;(3) finally a sharp increase again after reaching the melting temperature. In contrast, MSD remains basically unchanged before melting, close to zero, followed by a sudden increase after melting temperature. Although the radius of gyration also experiences three stages, nonetheless it exhibits almost completely contrary trend. It has also been found that both sintering temperature and melting temperature demonstrate an almost linear increase with the increase of nanoparticle size ranging from4.0, 6.0, 8.0 to 10.0 nm in diameter. Finally, we also found that the particle direction has limited effect on neck growth during sintering.展开更多
Tungsten is one of the best candidates for plasma-facing components in fusion reactors owing to its unique properties.But disadvantages such as its brittleness and high ductile-to-brittle transition temperature have r...Tungsten is one of the best candidates for plasma-facing components in fusion reactors owing to its unique properties.But disadvantages such as its brittleness and high ductile-to-brittle transition temperature have restricted its fusion energy application.Single-walled carbon nanotubes(SWCNTs) have the potential to be used as reinforcements due to their excellent mechanical properties.A new method of modifying the properties of tungsten by doping with SWCNTs was introduced.An efficient way of dispersing SWCNTs into the tungsten matrix with strong interfaces by heterocoagulation and ultrasonication was employed,and hot explosive compaction(HEC) technology was selected to compact and sinter the composite powders.The sintering properties,microstructure,densification effect,thermal conductivity,hardness and fracture toughness of the obtained SWCNTs/W bulk samples were tested,and compared with pure tungsten.The influences of SWCNTs on these properties and the main toughening mechanism of SWCNTs in a tungsten matrix were discussed.展开更多
基金the National Natural Science Foundation of China(No.12172052 and No.12132003).
文摘Formation behaviors of rod-like reactive shaped charge penetrator(RRSCP)and their effects on damage capability are investigated by experiments and numerical simulations.The pulsed X-ray technology and a spaced aluminum/steel plate with the thicknesses of 5 mm/100 mm are used.Three types of sphericalsegment aluminum-polytetrafluoroethylene-copper(Al-PTFE-Cu)reactive liners with Cu contents of 0%,46.6%,and 66%are fabricated and tested.The experimental results show that the reactive liners can form excellent rod-shaped penetrators with tail skirts under the shaped charge effect,but the tail skirts disappear over time.Moreover,rupturing damage to the aluminum plate and penetration to the steel plate are caused by the RRSCP impact.From simulation analysis,the RRSCP is formed by a mechanically and chemically coupled response with the reactive liner activated by shock in its outer walls and bottom and then backward overturning,forming a leading reactive penetrator and a following chemical energy cluster.The unique formation structure determines the damage modes of the aluminum plate and the steel plate.Further analysis indicates that the formation behaviors and damage capability of Al-PTFE-Cu RRSCP strongly depend on Cu content.With increasing Cu content,the velocity,activation extent,and reaction extent of Al-PTFE-Cu RRSCP decrease,which contribute to elongation and alleviate the negative effects of chemical reactions on elongation,significantly increasing the length-diameter ratio and thus enhancing the capability of steel plate penetration.However,the lower activation extent and energetic density will weaken the RRSCP's capability of causing rupturing damage to the aluminum plate.
基金supported by the Youth Foundation of State Key Laboratory of Explosion Science and Technology (Grant No.QNKT22-12)the State Key Program of National Natural Science Foundation of China (Grant No.12132003)。
文摘A series of ballistic experiments were performed to investigate the damage behavior of high velocity reactive material projectiles(RMPs) impacting liquid-filled tanks,and the corresponding hydrodynamic ram(HRAM) was studied in detail.PTFE/Al/W RMPs with steel-like and aluminum-like densities were prepared by a pressing/sintering process.The projectiles impacted a liquid-filled steel tank with front aluminum panel at approximately 1250 m/s.The corresponding cavity evolution characteristics and HRAM pressure were recorded by high-speed camera and pressure acquisition system,and further compared to those of steel and aluminum projectiles.Significantly different from the conical cavity formed by the inert metal projectile,the cavity formed by the RMP appeared as an ellipsoid with a conical front.The RMPs were demonstrated to enhance the radial growth velocity of cavity,the global HRAM pressure amplitude and the front panel damage,indicating the enhanced HRAM and structural damage behavior.Furthermore,combining the impact-induced fragmentation and deflagration characteristics,the cavity evolution of RMPs under the combined effect of kinetic energy impact and chemical energy release was analyzed.The mechanism of enhanced HRAM pressure induced by the RMPs was further revealed based on the theoretical model of the initial impact wave and the impulse analysis.Finally,the linear correlation between the deformation-thickness ratio and the non-dimensional impulse for the front panel was obtained and analyzed.It was determined that the enhanced near-field impulse induced by the RMPs was the dominant reason for the enhanced structural damage behavior.
基金supported by the State Key Program of National Natural Science Foundation of China(Grant No.12132003)State Key Laboratory of Explosion Science and Technology(Grant No.QNKT20-07)。
文摘The shock-induced reaction mechanism and characteristics of Ni/Al system,considering an Al nanoparticle-embedded Ni single crystal,are investigated through molecular dynamics simulation.For the shock melting of Al nanoparticle,interfacial crystallization and dissolution are the main characteristics.The reaction degree of Al particle first increases linearly and then logarithmically with time driven by rapid mechanical mixing and following dissolution.The reaction rate increases with the decrease of particle diameter,however,the reaction is seriously hindered by interfacial crystallization when the diameter is lower than 9 nm in our simulations.Meanwhile,we found a negative exponential growth in the fraction of crystallized Al atoms,and the crystallinity of B2-NiAl(up to 20%)is positively correlated with the specific surface area of Al particle.This can be attributed to the formation mechanism of B2-NiAl by structural evolution of finite mixing layer near the collapsed interface.For shock melting of both Al particle and Ni matrix,the liquid-liquid phase inter-diffusion is the main reaction mechanism that can be enhanced by the formation of internal jet.In addition,the enhanced diffusion is manifested in the logarithmic growth law of mean square displacement,which results in an almost constant reaction rate similar to the mechanical mixing process.
基金the National Natural Science Foundation of China(Grant Nos.12002037 and 12141201).
文摘By considering the joint effects of the Kelvin-Helmholtz(KH) and Rayleigh-Taylor(RT) instabilities, this paper presents an interpretation of the wavy patterns that occur in explosive welding. It is assumed that the elasticity of the material at the interface effectively determines the wavelength, because explosive welding is basically a solid-state welding process. To this end, an analytical model of elastic hydrodynamic instabilities is proposed, and the most unstable mode is selected in the solid phase. Similar approaches have been widely used to study the interfacial behavior of solid metals in high-energy-density physics. By comparing the experimental and theoretical results, it is concluded that thermal softening,which significantly reduces the shear modulus, is necessary and sufficient for successful welding. The thermal softening is verified by theoretical analysis of the increase in temperature due to the impacting and sliding of the flyer and base plates, and some experimental observations are qualitatively validated.In summary, the combined effect of the KH and RT instabilities in solids determines the wavy morphology, and our theoretical results are in good qualitative agreement with experimental and numerical observations.
基金supported by the National Natural Science Foundation of China(11232008,91216301,11227801,and 11172151)the Tsinghua University Initiative Scientific Research Program,and the Major Basic Research Program of Beijing Institute of Technology(2011CX01030)
文摘In this paper the elastic constants of graphite at elevated temperature were experimentally investigated by using the virtual fields method(VFM). A new method was presented for the characterization of mechanical properties at elevated temperature. The three-point bending tests were performed on graphite materials by an universal testing machine equipped with heating furnace. Based on the heterogeneous deformation fields measured by the digital image correlation(DIC) technique, the elastic constants were then extracted by using VFM.The measurement results of the elastic constants at 500℃ were obtained. The effect on the experimental results was also analyzed. The successful results verify the feasibility of using the proposed method to measure the properties of graphite at high temperature, and the proposed method is believed to have a good potential for further applications.
基金supported by funding from the National Natural Science Foundation of China(Grant No.21975028,22011540377)the Beijing Municipal Science and Technology Project(Grant No.Z181100005118002)+3 种基金the Beijing Municipal Natural Science Foundation(Grant No.JQ19008)funding support from the National Natural Science Foundation(Grant No.22005035)the China Postdoctoral Science Foundation(Grant No.2020TQ0043,2020M680012)supported by the Russian Science Foundation(Grant No.19-7330022)。
文摘At present,the stability of the new generation of solar cells based on hybrid perovskites is the bottleneck for their practical applications.Photochemical effects,high temperature,ultraviolet light,humidity and other known or still unknown factors might cause reduction of effectiveness or even irreversible loss of materials properties due to decomposition of functional layers within perovskite solar cells(PSCs).These factors alone have a serious impact on each component of the device,while their combinations lead to much more complicated effects and consequences.This review focuses on the stability of PSCs and the degradation of the device in a humid environment.We assess the instability factors and deep-seated principles of evolution of the device structure in a humidity environment with the emphasis on the influence on their interrelations.The related solutions are reviewed from the perspective of the encapsulation,perovskite active layer,carrier transport layer and electrodes.Combined with the latest research,we believe that the waterproof strategy of PSCs requires either tight encapsulation or thorough modifications in the device itself.Therefore,it is important to develop feasible strategies to improve the overall device stability over humid according to the target characteristics of various devices.
基金Supported by the National Natural Science Foundation of China(11172043)
文摘A phenomenon of shock wave reacceleration was studied when Ti+Si reactive powder is loaded by a high-speed flyer.The self-propagating reaction in the Ti+Si reactive powder was triggered by the high speed impaction of the flyer launched by a two-stage gas gun.In the process of self-propagating reaction,a strand of optical fiber and the electric pins were used to measure the velocity of shock wave propagation.The experimental results showed that the initial velocity of shock wave in the reactive powder was a few hundred meters per second,and then it decreased obviously with the increase of propagation distance.This phenomenon was also verified in the process of a pure Si powder loaded by a shock,while the phenomenon of shock wave reacceleration was not observed in the Ti+Si reactive powder.
基金the financial support from the National Key Research and Development Program of China (grant no. 2020YFA0711800)National Natural Science Foundation of China (grant no. 11802027, 51973033)+2 种基金State Key Laboratory of Explosion Science and Technology (grant no. YPJH20-6, QNKT20-01, JCRC18-01)BITBRFFR Joint Research Program (BITBLR2020018)Beijing Institute of Technology Research Fund。
文摘Molecular dynamics simulations have been performed to explore the underlying synergistic mechanism of pillared graphene or non-covalent connected graphene and carbon nanotubes(CNTs) on the mechanical properties of polyethylene(PE) nanocomposites. By constructing the pillared graphene model and CNTs/graphene model, the effect of the structure, arrangement and dispersion of hybrid fillers on the tensile mechanical properties of PE nanocomposites was studied. The results show that the pillared graphene/PE nanocomposites exhibit higher Young’s modulus, tensile strength and elongation at break than non-covalent connected CNTs/graphene/PE nanocomposites. The pull-out simulations show that pillared graphene by CNTs has both large interfacial load and long displacement due to the mixed modes of shear separation and normal separation. Additionally, pillared graphene can not only inhibit agglomeration but also form a compact effective thickness(stiff layer), consistent with the adsorption behavior and improved interfacial energy between pillared graphene and PE matrix.
基金supported by the Special Program on the Promotion of Graduate Research Level and Innovation Ability of Beijing Institute of Technology 2022(No.2022YCXZ003).
文摘Producing hydrogen peroxide(H_(2)O_(2))through an electrochemical oxygen reduction reaction(ORR)is a safe,green strategy and a promising alternative to traditional energy-intensive anthraquinone processes.Air and renewable power could be utilized for onsite and decentralized H_(2)O_(2)production,demonstrating significant application potential.Currently,single atom catalysts(SACs)have demonstrated significant advantages in the catalytic production of H_(2)O_(2)in 2e−ORR.However,the selectivity of SACs in ORR once puzzled researchers.This article reviews the research on the development and achievements of H_(2)O_(2)production by SACs catalysis in recent years.Especially,the structure-performance relationship is a guide to designing new SACs.Combining advanced characterization techniques and theoretical calculation methods,researchers have a clearer and more thorough understanding of the impact of the atomic interface of SACs on ORR catalytic performance.The coordination moiety formed between the active metal center atom and the support seriously determines the selectivity of SACs,mainly manifested in the adsorption of*OOH intermediates.Particularly,the atomic interface of metal atoms together with O/N co-coordination exhibit high selectivity and mass activity,and heteroatoms or functional groups on carbon supports present synergistic effects to promote the production of H_(2)O_(2)in 2e−ORR.Fine and accurate regulation of the atomic interface of SACs directly affects the 2e−ORR performance of the catalysts.Therefore,it is important to deeply understand the atomic interface of SACs and contribute to the development of novel catalysts.
基金financial support from the National Natural Science Foundation of China(10972025,10972039,11172043)the State Key Laboratory of Explosion Science and Technology,Beijing Institute of Technology(KFJJ11-6M)the Guangdong Provincial R&D Program(2011B090400419)
文摘Visible photoactive AgBr/TiO_2 was immobilized on a SiO_2@Fe_3O_4 magnetic support by solvothermal and sol-gel methods to form a AgBr-TiO_2/SiO_2@Fe_3O_4 magnetic photocatalyst.Samples were characterized by X-ray diffraction,high-resolution transmission electron microscopy and magnetometry.Hetero-structured AgBr/TiO_2 was well seeded on the shell-core SiO_2@Fe_3O_4 structure.The AgBr-TiO_2/SiO_2@Fe_3O_4 magnetic photocatalyst exhibited high photocatalytic activity in the degradation of methylene blue under visible light.The photocatalyst was superparamagnetic,which is beneficial for facile magnetic separation.
基金financially supported by the National Natural Science Foundation of China (Nos. 11802027 and 11521062)the State Key Laboratory of Explosion Science and Technology (Nos. JCRC1801, QNKT20-01)Beijing Institute of Technology Research Fund。
文摘In this work, molecular dynamics simulations have been performed to explore the structural evolution and underlying sintering mechanism of aluminum nanoparticles. The structural evolution during sintering was firstly monitored through radial distribution function and atomic migration, and the underlying sintering mechanism was further quantitatively characterized in terms of average displacement, mean squared distance(MSD), radius ratio(i.e., the ratio of the neck radius to the particle radius), shrinkage and radius of gyration, crystalline orientations, particle size, etc. Results show that the surface atoms of nanoparticles are more active than the internal atoms, favoring the mechanical rotation of nanoparticles during sintering. During the sintering process, average displacement, radius ratio and the shrinkage rate have undergone three stages with increasing the temperature:(1) a slow increase and subsequent abrupt hike after reaching the sintering temperature;(2) an almost plateau region over a wide span of temperature;(3) finally a sharp increase again after reaching the melting temperature. In contrast, MSD remains basically unchanged before melting, close to zero, followed by a sudden increase after melting temperature. Although the radius of gyration also experiences three stages, nonetheless it exhibits almost completely contrary trend. It has also been found that both sintering temperature and melting temperature demonstrate an almost linear increase with the increase of nanoparticle size ranging from4.0, 6.0, 8.0 to 10.0 nm in diameter. Finally, we also found that the particle direction has limited effect on neck growth during sintering.
基金the Chinese National Magnetic Confnement Fusion Program (No.2010GB109000)the National Natural Science Foundation of China (No.51172016)the Opening Research Issues of Jiangxi Key Laboratory of Advanced Copper and Tungsten Materials (No.2010-WT-04)
文摘Tungsten is one of the best candidates for plasma-facing components in fusion reactors owing to its unique properties.But disadvantages such as its brittleness and high ductile-to-brittle transition temperature have restricted its fusion energy application.Single-walled carbon nanotubes(SWCNTs) have the potential to be used as reinforcements due to their excellent mechanical properties.A new method of modifying the properties of tungsten by doping with SWCNTs was introduced.An efficient way of dispersing SWCNTs into the tungsten matrix with strong interfaces by heterocoagulation and ultrasonication was employed,and hot explosive compaction(HEC) technology was selected to compact and sinter the composite powders.The sintering properties,microstructure,densification effect,thermal conductivity,hardness and fracture toughness of the obtained SWCNTs/W bulk samples were tested,and compared with pure tungsten.The influences of SWCNTs on these properties and the main toughening mechanism of SWCNTs in a tungsten matrix were discussed.
