Electrocatalytic hydrogenation(ECH)offers a sustainable route for the conversion of biomass-derived feedstocks under ambient conditions;however,an atomic-level understanding of the catalytic mechanism based on heterog...Electrocatalytic hydrogenation(ECH)offers a sustainable route for the conversion of biomass-derived feedstocks under ambient conditions;however,an atomic-level understanding of the catalytic mechanism based on heterogeneous electrodes is lacking.To gain insights into the relation between electrocatalysis and the catalyst surface configuration,herein,the facet dependence of the ECH of furfural(FAL)is investigated on models of nanostructured Pd cubes,rhombic dodecahedrons,and octahedrons,which are predominantly enclosed by{100},{110},and{111}facets,respectively.The facet-dependent specific activity to afford furfuryl alcohol(FOL)follows the order of{111}>{100}>{110}.Experimental and theoretical kinetic analyses confirmed the occurrence of a competitive adsorption Langmuir-Hinshelwood mechanism on Pd,in which the ECH activity can be correlated with the difference between the binding energies of chemisorbed H(^(*)H)and FAL(^(*)FAL)based on density functional theoretical(DFT)calculations.Among the three facets,Pd{111}exhibiting the strongest^(*)H but the weakest^(*)FAL showed the copresence of the^(*)H and^(*)FAL intermediates on the Pd surface for subsequent hydrogenation,experimentally confirming its high ECH activity and Faradaic efficiency.The free energies determined using DFT calculations indicated that^(*)H addition to the carbonyl of FAL on Pd{111}was thermodynamically preferred over desorption to gaseous H2,contributing to efficient ECH to afford FOL at the expense of H2 evolution.The obtained insights into the facet-dependent ECH underline that surface bindings assist ECH or H2 evolution considering their competitiveness.These findings are expected to deepen the fundamental understanding of electrochemical refinery and broaden the scope of electrocatalyst exploration.展开更多
Vacuum die casting can reduce the'air entrapment'phenomenon during casting process.Based on the temperature measurements at metal-die interface with different processing parameters,such as slow shot speed(VL),...Vacuum die casting can reduce the'air entrapment'phenomenon during casting process.Based on the temperature measurements at metal-die interface with different processing parameters,such as slow shot speed(VL),high shot speed(VH),pouring temperature(Tp)and initial die temperature(Tm),inverse method was developed to determine the interfacial heat transfer coefficient(IHTC).The results indicate that a closer contact between the casting and die could be achieved when the vacuum system is used.It is found that the vacuum could strongly increase the values of IHTC and decrease the grain size in castings.The IHTC could have a higher peak value with increasing the Tp from680to720℃or the VL from0.1to0.4m/s.In addition,the influence of the VH and Tm on IHTC could be negligible.展开更多
The biocompatibility of orthopedic implants is closely related to their elastic modulus and surface properties.The objective of this study was to determine the effects of cold rolling,recrystallization and laser surfa...The biocompatibility of orthopedic implants is closely related to their elastic modulus and surface properties.The objective of this study was to determine the effects of cold rolling,recrystallization and laser surface melting(LSM)on the microstructure and mechanical properties of a biphase(α″+β)Ti-30Nb-4Sn alloy.X-ray diffraction(XRD)texture analysis of the cold-rolled substrate revealed the[302]α″//ND texture component,while analysis of the recrystallized substrate showed the[302]α″//ND and[110]α″//ND components.Theβ-phase texture could not be directly measured by XRD,but the presence of the[111]β//ND texture component was successfully predicted by considering the orientation relationship between theα″andβphases.Nanoindentation measurements showed that the elastic modulus of the cold-rolled substrate(63GPa)was lower than that of the recrystallized substrate(74GPa).Based on the available literature and the results presented here,it is suggested that this difference is caused by the introduction of crystal defects during cold deformation.The combined nanoindentation/EBSD analysis showed that the nanoindentation results are not affected by crystal orientation.LSM of the deformed alloy produced changes in hardness,elastic modulus and crystallographic texture similar to those produced by recrystallization heat treatment,creating a stiffness gradient between surface and substrate.展开更多
Anatase TiO2 nanocrystals and sub-microcrystals with truncated octahedral bipyramidal morphologies were prepared by direct calcination of TiOF2 precursors. The as-prepared TiO2 samples were thoroughly characterized by...Anatase TiO2 nanocrystals and sub-microcrystals with truncated octahedral bipyramidal morphologies were prepared by direct calcination of TiOF2 precursors. The as-prepared TiO2 samples were thoroughly characterized by X-ray diffraction, Raman spectroscopy, field-emission scanning electron microscopy, N2 adsorption-desorption isotherms, X-ray photoelectron spectroscopy, and UV-visible diffuse spectroscopy. It was found that the crystallinity, grain size, and {001}/{101} ratio of the samples can be increased by raising the calcination temperature from 500 to 800℃. The higher crystallinity and {001}/{101} facet ratio resulted in an increase in both aqueous and gas-phase photocatalytic activities, by inhibiting the recombination and separation of electrons and holes. After selecting two TiO2 samples with high crystallinity and {001}/{101} ratio, Au nanoparticles were decorated on their surfaces, and the photocatalytic activity of the resulting samples under visible light illumination was studied. It was found that the visible light-induced photocatalytic activity increased by 2.6 and 4.8 times, respectively, upon Au decoration of the samples prepared by calcination of TiOF2 at 700 and 800℃.展开更多
Molecular dynamics simulations are employed to study the nanometric machining process of single crystal nickel. Atoms from different machining zones had different atomic crystal structures owing to the differences in ...Molecular dynamics simulations are employed to study the nanometric machining process of single crystal nickel. Atoms from different machining zones had different atomic crystal structures owing to the differences in the actions of the cutting tool. The stacking fault tetrahedral was formed by a series of dislocation reactions, and it maintained the stable structure after the dislocation reactions. In addition, evidence of crystal transition and recovery was found by analyzing the number variations in different types of atoms in the primary shear zone, amorphous region, and crystalline region. The effects of machining speed on the cutting force, chip and subsurface defects, and temperature of the contact zone between the tool and workpiece were investigated. The results suggest that higher the machining speed, larger is the cutting force. The degree of amorphousness of chip atoms and the depth and extent of subsurface defects increase with the machining speed. The average friction coefficient first decreases and then increases with the machining speed because of the temperature difference between the chip and machining surface.展开更多
Colloid-colloid interactions in charge-stabilized dispersions can to The crystallization process and polymorph selection of hard-core some extent be represented by the hard-core Yukawa model. Yukawa model are studied ...Colloid-colloid interactions in charge-stabilized dispersions can to The crystallization process and polymorph selection of hard-core some extent be represented by the hard-core Yukawa model. Yukawa model are studied by means of smart Monte Carlo simulations in the region of face-centered-cubic (fcc) phase. The contact value of bard-core Yukawa potential and the volume fraction of the colloids are fixed, while the Debye screening length can be varied. In the early stage of the crystallization, the precursors with relatively ordered liquid structure have been observed. Although the crystal structure of thermodynamically stable phase is fcc, the system crystallizes into a mixture of fcc and hexagonal close-packed (hcp) structures under small Debye screening length since the colloidal particles act as effective hard spheres. In the intermediate range of Debye screening length, the system crystallizes into a mixture of fcc, hcp, and body-centered-cubic (bcc). The existence of metastable hcp and bcc structures can be interpreted as a manifestation of the Ostwald's step rule. Until the Debye screening length is large enough, the crystal structure obtained is almost a complete fcc suggesting the system eventually reaches to a thermodynamically stable state.展开更多
文摘Electrocatalytic hydrogenation(ECH)offers a sustainable route for the conversion of biomass-derived feedstocks under ambient conditions;however,an atomic-level understanding of the catalytic mechanism based on heterogeneous electrodes is lacking.To gain insights into the relation between electrocatalysis and the catalyst surface configuration,herein,the facet dependence of the ECH of furfural(FAL)is investigated on models of nanostructured Pd cubes,rhombic dodecahedrons,and octahedrons,which are predominantly enclosed by{100},{110},and{111}facets,respectively.The facet-dependent specific activity to afford furfuryl alcohol(FOL)follows the order of{111}>{100}>{110}.Experimental and theoretical kinetic analyses confirmed the occurrence of a competitive adsorption Langmuir-Hinshelwood mechanism on Pd,in which the ECH activity can be correlated with the difference between the binding energies of chemisorbed H(^(*)H)and FAL(^(*)FAL)based on density functional theoretical(DFT)calculations.Among the three facets,Pd{111}exhibiting the strongest^(*)H but the weakest^(*)FAL showed the copresence of the^(*)H and^(*)FAL intermediates on the Pd surface for subsequent hydrogenation,experimentally confirming its high ECH activity and Faradaic efficiency.The free energies determined using DFT calculations indicated that^(*)H addition to the carbonyl of FAL on Pd{111}was thermodynamically preferred over desorption to gaseous H2,contributing to efficient ECH to afford FOL at the expense of H2 evolution.The obtained insights into the facet-dependent ECH underline that surface bindings assist ECH or H2 evolution considering their competitiveness.These findings are expected to deepen the fundamental understanding of electrochemical refinery and broaden the scope of electrocatalyst exploration.
基金Project (2016YFB0301001) supported by the National Key Research and Development Program of ChinaProject (2015M580093) supported by the General Financial Grant from the China Postdoctoral Science Foundation of China
文摘Vacuum die casting can reduce the'air entrapment'phenomenon during casting process.Based on the temperature measurements at metal-die interface with different processing parameters,such as slow shot speed(VL),high shot speed(VH),pouring temperature(Tp)and initial die temperature(Tm),inverse method was developed to determine the interfacial heat transfer coefficient(IHTC).The results indicate that a closer contact between the casting and die could be achieved when the vacuum system is used.It is found that the vacuum could strongly increase the values of IHTC and decrease the grain size in castings.The IHTC could have a higher peak value with increasing the Tp from680to720℃or the VL from0.1to0.4m/s.In addition,the influence of the VH and Tm on IHTC could be negligible.
基金supported by the Brazilian Funding Agencies CAPES(Federal Agency for the Support and Improvement of Higher Education)(Grant No.33003017)CNPq(National Council for Scientific and Technological Development)(Grant No.233006/2014-1)FAPESP(Sao Paulo Research Foundation)(Grant No.2011/19982-2)
文摘The biocompatibility of orthopedic implants is closely related to their elastic modulus and surface properties.The objective of this study was to determine the effects of cold rolling,recrystallization and laser surface melting(LSM)on the microstructure and mechanical properties of a biphase(α″+β)Ti-30Nb-4Sn alloy.X-ray diffraction(XRD)texture analysis of the cold-rolled substrate revealed the[302]α″//ND texture component,while analysis of the recrystallized substrate showed the[302]α″//ND and[110]α″//ND components.Theβ-phase texture could not be directly measured by XRD,but the presence of the[111]β//ND texture component was successfully predicted by considering the orientation relationship between theα″andβphases.Nanoindentation measurements showed that the elastic modulus of the cold-rolled substrate(63GPa)was lower than that of the recrystallized substrate(74GPa).Based on the available literature and the results presented here,it is suggested that this difference is caused by the introduction of crystal defects during cold deformation.The combined nanoindentation/EBSD analysis showed that the nanoindentation results are not affected by crystal orientation.LSM of the deformed alloy produced changes in hardness,elastic modulus and crystallographic texture similar to those produced by recrystallization heat treatment,creating a stiffness gradient between surface and substrate.
基金supported by the National Natural Science Foundation of China(51772230,51461135004)the Hubei Foreign Science and Technology Cooperation Project(2017AHB059)the Japan Society for the Promotion of Science(JSPS)for an Invitational Fellowship for Foreign Researchers(L16531)~~
文摘Anatase TiO2 nanocrystals and sub-microcrystals with truncated octahedral bipyramidal morphologies were prepared by direct calcination of TiOF2 precursors. The as-prepared TiO2 samples were thoroughly characterized by X-ray diffraction, Raman spectroscopy, field-emission scanning electron microscopy, N2 adsorption-desorption isotherms, X-ray photoelectron spectroscopy, and UV-visible diffuse spectroscopy. It was found that the crystallinity, grain size, and {001}/{101} ratio of the samples can be increased by raising the calcination temperature from 500 to 800℃. The higher crystallinity and {001}/{101} facet ratio resulted in an increase in both aqueous and gas-phase photocatalytic activities, by inhibiting the recombination and separation of electrons and holes. After selecting two TiO2 samples with high crystallinity and {001}/{101} ratio, Au nanoparticles were decorated on their surfaces, and the photocatalytic activity of the resulting samples under visible light illumination was studied. It was found that the visible light-induced photocatalytic activity increased by 2.6 and 4.8 times, respectively, upon Au decoration of the samples prepared by calcination of TiOF2 at 700 and 800℃.
基金supported by the National Natural Science Foundation of China(Grant Nos,51375082)
文摘Molecular dynamics simulations are employed to study the nanometric machining process of single crystal nickel. Atoms from different machining zones had different atomic crystal structures owing to the differences in the actions of the cutting tool. The stacking fault tetrahedral was formed by a series of dislocation reactions, and it maintained the stable structure after the dislocation reactions. In addition, evidence of crystal transition and recovery was found by analyzing the number variations in different types of atoms in the primary shear zone, amorphous region, and crystalline region. The effects of machining speed on the cutting force, chip and subsurface defects, and temperature of the contact zone between the tool and workpiece were investigated. The results suggest that higher the machining speed, larger is the cutting force. The degree of amorphousness of chip atoms and the depth and extent of subsurface defects increase with the machining speed. The average friction coefficient first decreases and then increases with the machining speed because of the temperature difference between the chip and machining surface.
基金the National Natural Science Foundation of China (11172302, 11302226, 10972217)the Opening Fund of State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences, China (LNM201503)
文摘Colloid-colloid interactions in charge-stabilized dispersions can to The crystallization process and polymorph selection of hard-core some extent be represented by the hard-core Yukawa model. Yukawa model are studied by means of smart Monte Carlo simulations in the region of face-centered-cubic (fcc) phase. The contact value of bard-core Yukawa potential and the volume fraction of the colloids are fixed, while the Debye screening length can be varied. In the early stage of the crystallization, the precursors with relatively ordered liquid structure have been observed. Although the crystal structure of thermodynamically stable phase is fcc, the system crystallizes into a mixture of fcc and hexagonal close-packed (hcp) structures under small Debye screening length since the colloidal particles act as effective hard spheres. In the intermediate range of Debye screening length, the system crystallizes into a mixture of fcc, hcp, and body-centered-cubic (bcc). The existence of metastable hcp and bcc structures can be interpreted as a manifestation of the Ostwald's step rule. Until the Debye screening length is large enough, the crystal structure obtained is almost a complete fcc suggesting the system eventually reaches to a thermodynamically stable state.