CoCrCuFeNi–TiO was prepared by arc melting of the pure elements and Ti_2CO powder under an Ar atmosphere. Both CoCrCuFe Ni and CoCrCuFeNi–TiO alloys are composed of a face-centered cubic(fcc) solid solution, whereas...CoCrCuFeNi–TiO was prepared by arc melting of the pure elements and Ti_2CO powder under an Ar atmosphere. Both CoCrCuFe Ni and CoCrCuFeNi–TiO alloys are composed of a face-centered cubic(fcc) solid solution, whereas the alloys of CoCrCuFeNi–TiO are basically composed of an fcc solid solution and TiO crystals. The microstructures of CoCrCuFeNi–TiO are identified as dendrite and interdendrite structures such as CoCrCuFeNi. The morphology of TiO is identified as an equiaxed crystal with a small amount of added Ti_2CO. By increasing the amount of Ti_2CO added, the TiO content was dramatically increased and part of the equiaxed crystals changed to a dendrite structure. A test of the oxidation resistance demonstrates that the oxidation resistance of CoCrCuFeNi–TiO is better than that of CoCrCu Fe Ni. However, as the TiO content increases further, a corresponding decrease is observed in the oxidation resistance.展开更多
he deactivation of highly active multicomponent oxide LiLa_0.5 Ti_0.5 O_(2+λ) cata-lyst at high reaction temperatures has been studied. The surface and bulk structureof the catalyst were characterized by means of XRD...he deactivation of highly active multicomponent oxide LiLa_0.5 Ti_0.5 O_(2+λ) cata-lyst at high reaction temperatures has been studied. The surface and bulk structureof the catalyst were characterized by means of XRD, IR, XPS, BET, O_2-TPD,SEM etc.. The results show that the deactivation of the catalyst at high reactiontemperatures is mainly due to the loss of surface lithium. As a result , the diffusionof lithium from bulk to surface leads to the decompositiqn of the active phase con-taining lithium, which lowers tlie number of oxygen vacancies and decreases themobility of lattice oxygen.展开更多
Multicomponent ultra-high temperature ceramics(UHTCs)are promising candidates for thermal protection materials(TPMs)used in aerospace field.However,finding out desirable compositions from an enormous number of possibl...Multicomponent ultra-high temperature ceramics(UHTCs)are promising candidates for thermal protection materials(TPMs)used in aerospace field.However,finding out desirable compositions from an enormous number of possible compositions remains challenging.Here,through elucidating the role of preferential oxidation in ablation behavior of multicomponent UHTCs via the thermodynamic analysis and experimental verification,the correlation between the composition and ablation performance of multicomponent UHTCs was revealed from the aspect of thermodynamics.We found that the metal components in UHTCs can be thermodynamically divided into preferentially oxidized component(denoted as MP),which builds up a skeleton in oxide layer,and laggingly oxidized component(denoted as ML),which fills the oxide skeleton.Meanwhile,a thermodynamically driven gradient in the concentration of MP and ML forms in the oxide layer.Based on these findings,a strategy for pre-evaluating the ablation performance of multicomponent UHTCs was developed,which provides a preliminary basis for the composition design of multicomponent UHTCs.展开更多
Noble metal alloy nanowires(NWs)with ultrathin diameters(2–3 nm)and precisely controllable elemental compositions have attracted dramatically growing attention for(electro)catalysis.Despites numerous achievements in ...Noble metal alloy nanowires(NWs)with ultrathin diameters(2–3 nm)and precisely controllable elemental compositions have attracted dramatically growing attention for(electro)catalysis.Despites numerous achievements in past two decades,noble metal alloy NWs are mostly synthesized with the traditional oil-phase methods that suffer from some undesirable drawbacks.Here,we report a general strategy for fast,scalable,and aqueous synthesis of multicomponent Pd-based alloy ultrathin NWs with an average diameter of 2.6 nm,ranging from bimetallic PdM(PdFe,PdCo,PdNi,PdCu,PdZn,PdRu,PdRh,PdAg,PdCd,PdIr,PdPt,PdAu)and binary PdS/PdP NWs,to trimetallic PdM1M2 NWs(PdAuCu,PdCoNi,PdCuZn,PdCuNi,PdAgCu,PdAuCu,PdRuAg,PdAuRu,and PdPtAu),and to tetrametallic PdM1M2M3 NWs(PdAuAgCu,PdCoCuNi,PdAuCuNi,PdPtAuCu,and PdIrPtAu).The key to the success of this aqueous synthesis is the utilization of N2H4 as the extremely strong reducing agent that directs the synchronous reduction and anisotropic nucleation growth of multicomponent Pd alloy NWs along nanoconfined columnar phase assembled with amphiphilic dioctadecyldimethylammonium chloride.As-resultant Pd-based alloy ultrathin NWs exhibit multiple structural and compositional synergies,which remarkably optimize the removal of poisoning ethoxy intermediates and thus improve electrocatalytic performance towards ethanol oxidation reaction(EOR).Among them,tetrametallic PdAuCuNi alloy ultrathin NWs hold a high EOR activity of 5.14 A mg-1 Pd and a low activation energy of 13.1 kJ mol^-1,both of which are much better than its counterpart catalysts alloyed with less elements.This work represents an important advance in precise aqueous synthesis of multicomponent noble metal alloy ultrathin NWs as the high-performance electrocatalysts for various targeted applications.展开更多
A theoretical treatment on the oxide-controlled dwell fatigue crack growth of aγ'strengthened nickelbased superalloys is presented.In particular,this study investigates the influence of an externally applied load...A theoretical treatment on the oxide-controlled dwell fatigue crack growth of aγ'strengthened nickelbased superalloys is presented.In particular,this study investigates the influence of an externally applied load and variations in theγ'dispersion on the grain boundary oxide growth kinetics.A dislocation-based viscoplastic constitutive description for high temperature deformation is used to simulate the stress state evolution in the vicinity of a crack at elevated temperature.The viscoplastic model explicitly accounts for multimodalγ'particle size distributions.A multicomponent mass transport formulation is used to simulate the formation/evolution of an oxide wedge ahead of the crack tip,where stress-assisted vacancy diffusion is assumed to operate.The resulting set of constitutive and mass transport equations have been implemented within a finite element scheme.Comparison of predicted compositional fields across the matrix/oxide interface are compared with experiments and shown to be in good agreement.Simulations indicate that the presence of a fineγ'size distribution has a strong influence on the predicted ow stress of the material and consequently on the relaxation in the vicinity of the crack-tip/oxide wedge.It is shown that a unimodal dispersion leads to reduced oxide growth rates(parabolic behavior)when compared to a bimodal one.Stability conditions for oxide formation are investigated and is associated with the prediction of compressive stresses within the oxide layer just ahead of the crack tip,which become progressively negative as the oxide wedge develops.However,mechanical equilibrium requirements induce tensile stresses at the tip of the oxide wedge,where failure of the oxide is predicted.The time taken to reach this critical stress for oxide failure has been calculated,from which dwell crack growth rates are computationally derived.The predicted rates are shown to be in good agreement with available experimental data.展开更多
The Biginelli-type compounds 4,5,8a-triarylhexahydropyrimido[4,5-d]pyrimidine-2,7（1H,3H）-diones were synthesized by a one-pot three-component reaction using sulfated tin oxide as a reusable catalyst. This method has...The Biginelli-type compounds 4,5,8a-triarylhexahydropyrimido[4,5-d]pyrimidine-2,7（1H,3H）-diones were synthesized by a one-pot three-component reaction using sulfated tin oxide as a reusable catalyst. This method has the advantages of high yields, short reaction time, simple starting materials and reusability of catalyst for several times.展开更多
基金supported by The National Natural Science Foundation of China(No.51564005)the Program for the Distinguished Young Scientific Talents of Guizhou[Qian Ke He Platform and Talent(2017)5633]+2 种基金the New Process Engineering Research Center of Process industry,Guizhou Province[Qian Jiao He KY(2017)021]the Key Laboratory of Light Metal Materials Processing of Guizhou Province(Qian Ke He Platform and talent[2016]5104)The Scientific&Technological Innovation Talent Team of Guizhou Province(Qian Ke He Talent Team[2015]4008)
文摘CoCrCuFeNi–TiO was prepared by arc melting of the pure elements and Ti_2CO powder under an Ar atmosphere. Both CoCrCuFe Ni and CoCrCuFeNi–TiO alloys are composed of a face-centered cubic(fcc) solid solution, whereas the alloys of CoCrCuFeNi–TiO are basically composed of an fcc solid solution and TiO crystals. The microstructures of CoCrCuFeNi–TiO are identified as dendrite and interdendrite structures such as CoCrCuFeNi. The morphology of TiO is identified as an equiaxed crystal with a small amount of added Ti_2CO. By increasing the amount of Ti_2CO added, the TiO content was dramatically increased and part of the equiaxed crystals changed to a dendrite structure. A test of the oxidation resistance demonstrates that the oxidation resistance of CoCrCuFeNi–TiO is better than that of CoCrCu Fe Ni. However, as the TiO content increases further, a corresponding decrease is observed in the oxidation resistance.
文摘he deactivation of highly active multicomponent oxide LiLa_0.5 Ti_0.5 O_(2+λ) cata-lyst at high reaction temperatures has been studied. The surface and bulk structureof the catalyst were characterized by means of XRD, IR, XPS, BET, O_2-TPD,SEM etc.. The results show that the deactivation of the catalyst at high reactiontemperatures is mainly due to the loss of surface lithium. As a result , the diffusionof lithium from bulk to surface leads to the decompositiqn of the active phase con-taining lithium, which lowers tlie number of oxygen vacancies and decreases themobility of lattice oxygen.
基金supported by the National Natural Science Foundation of China(52072410 and 51602349)Innovation-driven Project of Central South University.
文摘Multicomponent ultra-high temperature ceramics(UHTCs)are promising candidates for thermal protection materials(TPMs)used in aerospace field.However,finding out desirable compositions from an enormous number of possible compositions remains challenging.Here,through elucidating the role of preferential oxidation in ablation behavior of multicomponent UHTCs via the thermodynamic analysis and experimental verification,the correlation between the composition and ablation performance of multicomponent UHTCs was revealed from the aspect of thermodynamics.We found that the metal components in UHTCs can be thermodynamically divided into preferentially oxidized component(denoted as MP),which builds up a skeleton in oxide layer,and laggingly oxidized component(denoted as ML),which fills the oxide skeleton.Meanwhile,a thermodynamically driven gradient in the concentration of MP and ML forms in the oxide layer.Based on these findings,a strategy for pre-evaluating the ablation performance of multicomponent UHTCs was developed,which provides a preliminary basis for the composition design of multicomponent UHTCs.
基金the Natural Science Foundation of Jiangsu Province(BK20150969,BK20191366)Jiangsu Specially Appointed Professor Plan+1 种基金the Priority Academic Program Development of Jiangsu Higher Education Institutionsthe National and Local Joint Engineering Research Center of Biomedical Functional Materials。
文摘Noble metal alloy nanowires(NWs)with ultrathin diameters(2–3 nm)and precisely controllable elemental compositions have attracted dramatically growing attention for(electro)catalysis.Despites numerous achievements in past two decades,noble metal alloy NWs are mostly synthesized with the traditional oil-phase methods that suffer from some undesirable drawbacks.Here,we report a general strategy for fast,scalable,and aqueous synthesis of multicomponent Pd-based alloy ultrathin NWs with an average diameter of 2.6 nm,ranging from bimetallic PdM(PdFe,PdCo,PdNi,PdCu,PdZn,PdRu,PdRh,PdAg,PdCd,PdIr,PdPt,PdAu)and binary PdS/PdP NWs,to trimetallic PdM1M2 NWs(PdAuCu,PdCoNi,PdCuZn,PdCuNi,PdAgCu,PdAuCu,PdRuAg,PdAuRu,and PdPtAu),and to tetrametallic PdM1M2M3 NWs(PdAuAgCu,PdCoCuNi,PdAuCuNi,PdPtAuCu,and PdIrPtAu).The key to the success of this aqueous synthesis is the utilization of N2H4 as the extremely strong reducing agent that directs the synchronous reduction and anisotropic nucleation growth of multicomponent Pd alloy NWs along nanoconfined columnar phase assembled with amphiphilic dioctadecyldimethylammonium chloride.As-resultant Pd-based alloy ultrathin NWs exhibit multiple structural and compositional synergies,which remarkably optimize the removal of poisoning ethoxy intermediates and thus improve electrocatalytic performance towards ethanol oxidation reaction(EOR).Among them,tetrametallic PdAuCuNi alloy ultrathin NWs hold a high EOR activity of 5.14 A mg-1 Pd and a low activation energy of 13.1 kJ mol^-1,both of which are much better than its counterpart catalysts alloyed with less elements.This work represents an important advance in precise aqueous synthesis of multicomponent noble metal alloy ultrathin NWs as the high-performance electrocatalysts for various targeted applications.
文摘A theoretical treatment on the oxide-controlled dwell fatigue crack growth of aγ'strengthened nickelbased superalloys is presented.In particular,this study investigates the influence of an externally applied load and variations in theγ'dispersion on the grain boundary oxide growth kinetics.A dislocation-based viscoplastic constitutive description for high temperature deformation is used to simulate the stress state evolution in the vicinity of a crack at elevated temperature.The viscoplastic model explicitly accounts for multimodalγ'particle size distributions.A multicomponent mass transport formulation is used to simulate the formation/evolution of an oxide wedge ahead of the crack tip,where stress-assisted vacancy diffusion is assumed to operate.The resulting set of constitutive and mass transport equations have been implemented within a finite element scheme.Comparison of predicted compositional fields across the matrix/oxide interface are compared with experiments and shown to be in good agreement.Simulations indicate that the presence of a fineγ'size distribution has a strong influence on the predicted ow stress of the material and consequently on the relaxation in the vicinity of the crack-tip/oxide wedge.It is shown that a unimodal dispersion leads to reduced oxide growth rates(parabolic behavior)when compared to a bimodal one.Stability conditions for oxide formation are investigated and is associated with the prediction of compressive stresses within the oxide layer just ahead of the crack tip,which become progressively negative as the oxide wedge develops.However,mechanical equilibrium requirements induce tensile stresses at the tip of the oxide wedge,where failure of the oxide is predicted.The time taken to reach this critical stress for oxide failure has been calculated,from which dwell crack growth rates are computationally derived.The predicted rates are shown to be in good agreement with available experimental data.
文摘The Biginelli-type compounds 4,5,8a-triarylhexahydropyrimido[4,5-d]pyrimidine-2,7（1H,3H）-diones were synthesized by a one-pot three-component reaction using sulfated tin oxide as a reusable catalyst. This method has the advantages of high yields, short reaction time, simple starting materials and reusability of catalyst for several times.
