TiAl alloy and 316L stainless steel were vacuum-brazed with Zr−50.0Cu−7.1Ni−7.1Al(at.%)amorphous filler metal.The influence of brazing time and temperature on the interfacial microstructure and shear strength of the r...TiAl alloy and 316L stainless steel were vacuum-brazed with Zr−50.0Cu−7.1Ni−7.1Al(at.%)amorphous filler metal.The influence of brazing time and temperature on the interfacial microstructure and shear strength of the resultant joints was investigated.The brazed seam consisted of three layers,including two diffusion layers and one residual filler metal layer.The typical microstructure of brazed TiAl alloy/316L stainless steel joint was TiAl alloy substrate/α2-(Ti3Al)/AlCuTi/residual filler metal/Cu9Zr11+Fe23Zr6/Laves-Fe2Zr/α-(Fe,Cr)/316L stainless steel substrate.Discontinuous brittle Fe2Zr layer formed near the interface between the residual filler metal layer andα-(Fe,Cr)layer.The maximum shear strength of brazed joints reached 129 MPa when brazed at 1020℃ for 10 min.The diffusion activation energies ofα2-(Ti3Al)andα-(Fe,Cr)phases were−195.769 and−112.420 kJ/mol,respectively,the diffusion constants for these two phases were 3.639×10^(−6) and 7.502×10^(−10)μm^(2)/s,respectively.Cracks initiated at Fe2Zr layer and propagated into the residual filler metal layer during the shear test.The Laves-Fe2Zr phase existing on the fracture surface suggested the brittle fracture mode of the brazed joints.展开更多
Developing low-cost and high-efficient noble-metal-free cocatalysts has been a challenge to achieve economic hydrogen production.In this work,molybdenum oxides(MoO3-x)were in situ loaded on polymer carbon nitride(PCN)...Developing low-cost and high-efficient noble-metal-free cocatalysts has been a challenge to achieve economic hydrogen production.In this work,molybdenum oxides(MoO3-x)were in situ loaded on polymer carbon nitride(PCN)via a simple one-pot impregnation-calcination approach.Different from post-impregnation method,intimate coupling interface between high-dispersed ultra-small MoO3-xnanocrystal and PCN was successfully formed during the in situ growth process.The MoO3-x-PCN-X(X=1,2,3,4)photocatalyst without noble platinum(Pt)finally exhibited enhanced photocatalytic hydrogen performance under visible light irradiation(λ>420 nm),with the highest hydrogen evolution rate of 15.6μmol/h,which was more than 3 times that of bulk PCN.Detailed structure-performance revealed that such improvement in visible-light hydrogen production activity originated from the intimate interfacial interaction between high-dispersed ultra-small MoO3-xnanocrystal and polymer carbon nitride as well as efficient charge carriers transfer brought by Schottky junction formed.展开更多
Investigation of early stages of crystal growth revealed that crystal growth in some systems may not follow the classic route.In the early stages of inorganic crystal growth,precursor molecules and/or nanocrystallites...Investigation of early stages of crystal growth revealed that crystal growth in some systems may not follow the classic route.In the early stages of inorganic crystal growth,precursor molecules and/or nanocrystallites may aggregate into large and disordered particles with the assistance of some polymers or biomolecules.Surface crystallization of these aggregates would then take place to form shells with high crystallinity and density,followed by an extension of the crystallization from surface to core.This so-called reversed crystal growth mechanism has been found in crystallization of several inorganic compounds including zeolites,perovskites,metals and metal oxides,and will be identified in more material systems.The establishment of this new crystal growth route gave us more freedom to control the morphology of crystals and to understand the formation mechanism of many natural minerals.This article gives a brief review of the recent research in this field by featuring some typical examples of the reversed crystal growth.展开更多
The development of non-precious metal-based electrocatalysts has attracted much research attention because of their high oxygen reduction reaction （ORR） activities, low cost, and good durability. By one-step in-situ...The development of non-precious metal-based electrocatalysts has attracted much research attention because of their high oxygen reduction reaction （ORR） activities, low cost, and good durability. By one-step in-situ ball milling of graphite, pyrrole, and cobalt salt without resorting to high-temperature annealing, we developed a general and facile strategy to synthesize bio-inspired cobalt oxide and polypyrrole coupled with a graphene nanosheet （Co3O4-PPy/GN） complex. Herein, the exfoliation of graphite and polymerization of pyrrole occurred simultaneously during the ball milling process. Meanwhile, the Co3O4 and Co-Nx ORR active sites were generated from the oxidized cobalt ion, cobalt-PPy, and the newly exfoliated graphene nanosheets via strong π-π stacking interactions. The resultant Co3O4-PPy/GN catalysts showed efficient electrocatalytic performances for ORRs in an alkaline medium with a positive onset and reduction potentials of -0.102 and -0.196 V （vs. Ag/AgCl）, as well as a high diffusion-limited current density （4.471 mA·cm^-2）, which was comparable to that of a Pt/C catalyst （4.941 mA·cm^-2）. Compared to Pt/C, Co3O4-PPy/GN catalysts displayed better long-term stability, methanol tolerance, and anti-CO-poisoning effects, which are of great significance for the design and development of advanced non-precious metal electrocatalysts.展开更多
基金financially supported by the National Natural Science Foundation of China(No.51674060)Collaborative Innovation Center of Major Machine Manufacturing in Liaoning province,China。
文摘TiAl alloy and 316L stainless steel were vacuum-brazed with Zr−50.0Cu−7.1Ni−7.1Al(at.%)amorphous filler metal.The influence of brazing time and temperature on the interfacial microstructure and shear strength of the resultant joints was investigated.The brazed seam consisted of three layers,including two diffusion layers and one residual filler metal layer.The typical microstructure of brazed TiAl alloy/316L stainless steel joint was TiAl alloy substrate/α2-(Ti3Al)/AlCuTi/residual filler metal/Cu9Zr11+Fe23Zr6/Laves-Fe2Zr/α-(Fe,Cr)/316L stainless steel substrate.Discontinuous brittle Fe2Zr layer formed near the interface between the residual filler metal layer andα-(Fe,Cr)layer.The maximum shear strength of brazed joints reached 129 MPa when brazed at 1020℃ for 10 min.The diffusion activation energies ofα2-(Ti3Al)andα-(Fe,Cr)phases were−195.769 and−112.420 kJ/mol,respectively,the diffusion constants for these two phases were 3.639×10^(−6) and 7.502×10^(−10)μm^(2)/s,respectively.Cracks initiated at Fe2Zr layer and propagated into the residual filler metal layer during the shear test.The Laves-Fe2Zr phase existing on the fracture surface suggested the brittle fracture mode of the brazed joints.
基金the National Natural Science Foundation of China(No.21872093)the National Key Research and Development Program of China(No.2018YFB1502001)the Center of Hydrogen Science of Shanghai Jiao Tong University。
文摘Developing low-cost and high-efficient noble-metal-free cocatalysts has been a challenge to achieve economic hydrogen production.In this work,molybdenum oxides(MoO3-x)were in situ loaded on polymer carbon nitride(PCN)via a simple one-pot impregnation-calcination approach.Different from post-impregnation method,intimate coupling interface between high-dispersed ultra-small MoO3-xnanocrystal and PCN was successfully formed during the in situ growth process.The MoO3-x-PCN-X(X=1,2,3,4)photocatalyst without noble platinum(Pt)finally exhibited enhanced photocatalytic hydrogen performance under visible light irradiation(λ>420 nm),with the highest hydrogen evolution rate of 15.6μmol/h,which was more than 3 times that of bulk PCN.Detailed structure-performance revealed that such improvement in visible-light hydrogen production activity originated from the intimate interfacial interaction between high-dispersed ultra-small MoO3-xnanocrystal and polymer carbon nitride as well as efficient charge carriers transfer brought by Schottky junction formed.
文摘Investigation of early stages of crystal growth revealed that crystal growth in some systems may not follow the classic route.In the early stages of inorganic crystal growth,precursor molecules and/or nanocrystallites may aggregate into large and disordered particles with the assistance of some polymers or biomolecules.Surface crystallization of these aggregates would then take place to form shells with high crystallinity and density,followed by an extension of the crystallization from surface to core.This so-called reversed crystal growth mechanism has been found in crystallization of several inorganic compounds including zeolites,perovskites,metals and metal oxides,and will be identified in more material systems.The establishment of this new crystal growth route gave us more freedom to control the morphology of crystals and to understand the formation mechanism of many natural minerals.This article gives a brief review of the recent research in this field by featuring some typical examples of the reversed crystal growth.
基金Acknowledgements The work is supported by the National Natural Science Foundation of China （Nos. 51273008 and 51473008）, the National Basic Research Program of China （No. 2012CB933200）, and the National High-tech R＆D Program of China （No. 2012AA030305）. L. M. D. is grateful to the support from NSF （Nos. AIR-IIP-1343270 and CMMI-1400274）.
文摘The development of non-precious metal-based electrocatalysts has attracted much research attention because of their high oxygen reduction reaction （ORR） activities, low cost, and good durability. By one-step in-situ ball milling of graphite, pyrrole, and cobalt salt without resorting to high-temperature annealing, we developed a general and facile strategy to synthesize bio-inspired cobalt oxide and polypyrrole coupled with a graphene nanosheet （Co3O4-PPy/GN） complex. Herein, the exfoliation of graphite and polymerization of pyrrole occurred simultaneously during the ball milling process. Meanwhile, the Co3O4 and Co-Nx ORR active sites were generated from the oxidized cobalt ion, cobalt-PPy, and the newly exfoliated graphene nanosheets via strong π-π stacking interactions. The resultant Co3O4-PPy/GN catalysts showed efficient electrocatalytic performances for ORRs in an alkaline medium with a positive onset and reduction potentials of -0.102 and -0.196 V （vs. Ag/AgCl）, as well as a high diffusion-limited current density （4.471 mA·cm^-2）, which was comparable to that of a Pt/C catalyst （4.941 mA·cm^-2）. Compared to Pt/C, Co3O4-PPy/GN catalysts displayed better long-term stability, methanol tolerance, and anti-CO-poisoning effects, which are of great significance for the design and development of advanced non-precious metal electrocatalysts.
