In this work,highly monodispersed Pt-Ni alloy nanoparticles were directly deposited on carbon substrate through a facile electrodeposition strategy in the solvent system of N,N-dimethylformamide(DMF).A series of carbo...In this work,highly monodispersed Pt-Ni alloy nanoparticles were directly deposited on carbon substrate through a facile electrodeposition strategy in the solvent system of N,N-dimethylformamide(DMF).A series of carbon supported Pt-Ni alloy electrocatalysts were synthesized under different applied electrode potentials.Among all as-obtained samples,the Pt-Ni/C electrocatalyst deposited at-1.73 V exhibits the optimal specific activity up to 1.850 mA cm^(-2)at 0.9 V vs.RHE,which is 6.85 times higher than that of the commercial Pt/C.Comprehensive physiochemical characterizations and computational evaluations via density functional theory were conducted to unveil the nucleation and growth mechanism of PtNi alloy formation.Compared to the aqueous solution,DMF solvent molecule must not be neglected in avoiding particle agglomeration and synthesis of monodispersed nanoparticles.During the alloy co-deposition process,Ni sites produced through the reduction of Ni(Ⅱ)precursor not only facilitates Pt-Ni alloy crystal nucleation but also in favor of further Pt reduction on the Ni-inserted Pt surface.As for the deposition potential,it adjusts the final particle size.This work provides a hopeful extended Pt-based catalyst layer production strategy for proton exchange membrane fuel cells and a new idea for the nucleation and growth mechanism exploration for electrodeposited Pt alloy.展开更多
Some TiAl3 whiskers are found to be produced simultaneously during the formation process of TiB2 Particulates fabricated by in situ reaction in molten aluminum. The thec t of temperature of molten aluminum on the morp...Some TiAl3 whiskers are found to be produced simultaneously during the formation process of TiB2 Particulates fabricated by in situ reaction in molten aluminum. The thec t of temperature of molten aluminum on the morphologies of the TiAl3 whiskers and the growth mechanism of the whiskers are studied in this paper. The results show that the aspect rutio of the TiAl3 whiskers decreases with the increase of the temperoture. The growth of the whiskers is proved to be controlled by a Vapor-LiquidSoltd (VLS) mechanism. The titanium and aluminum atoms in the catalytic droplet,however, have been coofrmed to react with each othen which is dtherent from other whlskcrs growing by a VLS mcchanism where the compostion in the catalytic droplet is a constant.展开更多
The growth mechanism of reinforcement in in situ synthesized (TiB+TiC)/Ti composites was investigated. The results show that reinforcements nucleate and grow in a way of dissolution precipitation. The morphologies of ...The growth mechanism of reinforcement in in situ synthesized (TiB+TiC)/Ti composites was investigated. The results show that reinforcements nucleate and grow in a way of dissolution precipitation. The morphologies of reinforcements are closely related to the solidification paths and crystal structure of reinforcements. TiB, as a reinforcement, is liable to grow along [010] direction and forms in short fibre shape due to its B27 structure, whereas primary TiC is liable to form composition undercooling and grow in dendritic shape. TiC phases precipitated in binary eutectic and ternary eutectic reactions grow in equiaxial shape. The addition of aluminum element refines TiB and TiC particles, and makes TiC reinforcements grow into the equiaxial particles easily. The addition of graphite adjusts the solidification paths and forms more TiC with dendritic shape. [展开更多
The AuSn20/Ni joints were prepared by the reflow soldering technology and then annealed at solid-state temperature to form diffusion couples.The interfacial reactions and the growth kinetics of the intermetallic compo...The AuSn20/Ni joints were prepared by the reflow soldering technology and then annealed at solid-state temperature to form diffusion couples.The interfacial reactions and the growth kinetics of the intermetallic compounds(IMC)at the AuSn20/Ni soldering interface were investigated by scanning electron microscopy(SEM)and electron probe microanalysis(EPMA).The results show that,the(Ni,Au)3Sn2phases are formed at the AuSn20/Ni interface after soldering at583K.The thickness l of the IMC layer monotonically increases with increasing annealing time t according to the relationship l=k(t/t0)n,where the exponent n is0.527,0.476and0.471for393,433and473K annealing,respectively.This indicates that the volume diffusion contributes to the growth of the IMC layer at the AuSn20/Ni interface at solid-sate temperature.The pre-exponential factor K0=1.23×10?7m2/s and the activation enthalpy QK=81.8kJ/mol are obtained from the results of the parabolic coefficient K by a least-squares method.展开更多
文摘In this work,highly monodispersed Pt-Ni alloy nanoparticles were directly deposited on carbon substrate through a facile electrodeposition strategy in the solvent system of N,N-dimethylformamide(DMF).A series of carbon supported Pt-Ni alloy electrocatalysts were synthesized under different applied electrode potentials.Among all as-obtained samples,the Pt-Ni/C electrocatalyst deposited at-1.73 V exhibits the optimal specific activity up to 1.850 mA cm^(-2)at 0.9 V vs.RHE,which is 6.85 times higher than that of the commercial Pt/C.Comprehensive physiochemical characterizations and computational evaluations via density functional theory were conducted to unveil the nucleation and growth mechanism of PtNi alloy formation.Compared to the aqueous solution,DMF solvent molecule must not be neglected in avoiding particle agglomeration and synthesis of monodispersed nanoparticles.During the alloy co-deposition process,Ni sites produced through the reduction of Ni(Ⅱ)precursor not only facilitates Pt-Ni alloy crystal nucleation but also in favor of further Pt reduction on the Ni-inserted Pt surface.As for the deposition potential,it adjusts the final particle size.This work provides a hopeful extended Pt-based catalyst layer production strategy for proton exchange membrane fuel cells and a new idea for the nucleation and growth mechanism exploration for electrodeposited Pt alloy.
文摘Some TiAl3 whiskers are found to be produced simultaneously during the formation process of TiB2 Particulates fabricated by in situ reaction in molten aluminum. The thec t of temperature of molten aluminum on the morphologies of the TiAl3 whiskers and the growth mechanism of the whiskers are studied in this paper. The results show that the aspect rutio of the TiAl3 whiskers decreases with the increase of the temperoture. The growth of the whiskers is proved to be controlled by a Vapor-LiquidSoltd (VLS) mechanism. The titanium and aluminum atoms in the catalytic droplet,however, have been coofrmed to react with each othen which is dtherent from other whlskcrs growing by a VLS mcchanism where the compostion in the catalytic droplet is a constant.
文摘The growth mechanism of reinforcement in in situ synthesized (TiB+TiC)/Ti composites was investigated. The results show that reinforcements nucleate and grow in a way of dissolution precipitation. The morphologies of reinforcements are closely related to the solidification paths and crystal structure of reinforcements. TiB, as a reinforcement, is liable to grow along [010] direction and forms in short fibre shape due to its B27 structure, whereas primary TiC is liable to form composition undercooling and grow in dendritic shape. TiC phases precipitated in binary eutectic and ternary eutectic reactions grow in equiaxial shape. The addition of aluminum element refines TiB and TiC particles, and makes TiC reinforcements grow into the equiaxial particles easily. The addition of graphite adjusts the solidification paths and forms more TiC with dendritic shape. [
基金Project(JPPT-125-GH-039)supported by the Ministry of Science and Technology of ChinaProject(Z109021567)supported by Fundamental Research Funds for the Central Universities,China
文摘The AuSn20/Ni joints were prepared by the reflow soldering technology and then annealed at solid-state temperature to form diffusion couples.The interfacial reactions and the growth kinetics of the intermetallic compounds(IMC)at the AuSn20/Ni soldering interface were investigated by scanning electron microscopy(SEM)and electron probe microanalysis(EPMA).The results show that,the(Ni,Au)3Sn2phases are formed at the AuSn20/Ni interface after soldering at583K.The thickness l of the IMC layer monotonically increases with increasing annealing time t according to the relationship l=k(t/t0)n,where the exponent n is0.527,0.476and0.471for393,433and473K annealing,respectively.This indicates that the volume diffusion contributes to the growth of the IMC layer at the AuSn20/Ni interface at solid-sate temperature.The pre-exponential factor K0=1.23×10?7m2/s and the activation enthalpy QK=81.8kJ/mol are obtained from the results of the parabolic coefficient K by a least-squares method.
