Microenvironment and electronic state modulation of Pd nanoparticles within MOFs for enhancing low-temperature activity towards DCPD hydrogenation

Precise control of the local environment and electronic state of the guest is an important method of controlling catalytic activity and reaction pathways.In this paper,guest Pd NPs were introduced into a series of host UiO-67 MOFs with different functional ligands and metal nodes,the microenvironment and local electronic structure of Pd is modulated by introducing bipyridine groups and changing metal nodes(Ce_(6)O_(6) or Zr_(6)O_(6)).The bipyridine groups not only promoted the dispersion Pd NPs,but also facilitated electron transfer between Pd and UiO-67 MOFs through the formation of Pd-N bridges.Compared with Zr6 clusters,the tunability and orbital hybridisation of the 4f electronic structure in the Ce_(6) clusters modulate the electronic structure of Pd through the construction of the Ce-O-Pd interfaces.The optimal catalyst Pd/UiO-67(Ce)-bpy presented excellent low-temperature activity towards dicyclopentadiene hydrogenation with a conversion of>99% and a selectivity of>99%(50℃,10 bar).The results show that the synergy of Ce-O-Pd and Pd-N promotes the formation of active Pd^(δ+),which not only enhances the adsorption of H_(2) and electron-rich C=C bonds,but also contributes to the reduction of proton migration distance and improves proton utilization efficiency.These results provide valuable insights for investigating the regulatory role of the host MOFs,the nature of host-guest interactions,and their correlation with catalytic performance.

静电纺丝制备有机盐类非线性光学材料纳米纤维

采用静电纺丝技术制备的有机非线性光学材料纳米纤维可有效控制非线性光学材料的分子取向,其生色团可实现与有机单晶类似的优化排列结构,表现出了与纯生色团分子相近的宏观二阶非线性光学性质。本文将有机盐类非线性光学材料掺杂在聚乙烯吡咯烷酮中制备出了具有各向异性结构且表面光滑、排列有序的纳米纤维薄膜,Kurtz非线性测试结果表明,随着薄膜厚度增加,其二次谐波信号强度成正比增大。

利用数字式谐波反馈实现交流磁测量磁通波形正弦

在磁通正弦条件下进行软磁合金交流磁性测量可以获得高准确度的测量结果.利用数字式谐波反馈原理,通过对磁通波形的分析获得了磁通波形中的谐波含量,然后在电源输出端补偿与磁通波形中谐波幅值相反、相位相同的谐波,使磁通波形得到了改善.通过对硅钢样品在不同磁化程度时的测量,检验这一方法.当硅钢样品磁化为1·87T时,经谐波反馈后次级电压的波形系数也能满足国家标准的要求.

New technique for preparing A356 alloy semisolid slurry and its rheo-diecast microstructure and properties

A new technique for preparing semisolid slurry,namely,distributary-confluence runner(DCR),was combined with die-casting(DC)to conduct rheological die-casting(R-DC)of A356 alloy.The mechanism of DCR for semisolid slurry preparation was determined via numerical simulations and experiments.The microstructure and mechanical properties of A356 alloys prepared via DC and R-DC were studied.High-quality slurry containing numerous primary α-Al(α1-Al)with an average size of 49μm and a shape factor of 0.81 could be prepared via DCR.Simulation results indicated that the unique flow state and physical field changes during slurry preparation were conducive to accelerating the uniformity of melt temperature and composition fields,nucleation exfoliation,and spherical growth.Compared with the alloy prepared via DC,the tensile strength,yield strength,and elongation of A356 alloy prepared via R-DC increased by 19%,15%,and 107%,respectively.

Enhanced visible-light photocatalytic oxidation capability of carbon-doped TiO_2 via coupling with fly ash

A carbon‐doped TiO2/fly ash support(C‐TiO2/FAS)composite photocatalyst was successfully synthesized through sol impregnation and subsequent carbonization.The carbon dopants were derived from the organic species generated during the synthesis of the C‐TiO2/FAS composite.A series of analytical techniques,such as scanning electron microscopy(SEM),attenuated total reflection‐Fourier transform infrared(ATR‐FTIR)spectroscopy,X‐ray photoelectron spectroscopy(XPS),and ultraviolet‐visible diffuse reflectance spectroscopy(UV‐Vis DRS),were used to characterize the properties of the prepared samples.The results indicated that C‐TiO2 was successfully coated on the FAS surface.Coupling between C‐TiO2 and FAS resulted in the formation of Si–O–C and Al–O–Ti bonds at their interface.The formation of Si–O–C and Al–O–Ti bonds gave rise to a positive shift of the valence band edge of C‐TiO2 and enhanced its oxidation capability of photogenerated holes as well as photodegradation efficiency of methyl orange.Moreover,the C‐TiO2/FAS photocatalyst exhibited favorable reusability and separability.This work may provide a new route for tuning the electronic band structure of TiO2.

Strain-induced α-to-β phase transformation during hot compression in Ti-5Al-5Mo-5V-1Cr-1Fe alloy

The dynamic phase transformation of Ti-5Al-5Mo-5V-1Cr-1Fe alloy during hot compression below theβtransus temperature was investigated.Strain-inducedα-to-βtransformation is observed in the samples compressed at 0-100 K below theβtransus temperature.The deformation stored energy by compression provides a significant driving force for theα-to-βphase transformation.The re-distribution of the solute elements induced by defects during deformation promotes the occurrence of dynamic transformation.Orientation dependence for theα-to-βphase transformation promotion is observed between{100}-orientated grains and{111}-orientated grains.Incomplete recovery in{111}-orientated grains would create a large amount of diffusion channels,which is in favor of theα-to-βtransformation.The effects of reduction ratio and strain rate on the dynamic phase transformation were also investigated.

Influence of rheo-diecasting processing parameters on microstructure and mechanical properties of hypereutectic Al-30%Si alloy

The effects of pouring temperature,vibration frequency,and the number of curves in a serpentine channel,on themicrostructure and mechanical properties of Al-30%Si alloy processed by rheo-diecasting(RDC)were investigated.The semisolidAl-30%Si alloy slurry was prepared by vibration serpentine channel pouring(VSCP)process in the RDC process.The results showthat the pouring temperature,the vibration frequency,and the number of the curves strongly affect the microstructure and mechanicalproperties of Al-30%Si alloy.Under experimental conditions of a pouring temperature of850°C,a twelve-curve copper channel anda vibration frequency of80Hz,the primary Si grains are refined into fine compact grains with average grain size of about24.6μm inthe RDC samples assisted with VSCP.Moreover,the ultimate tensile strength(UTS),elongation and hardness of the RDC sample are296MPa,0.87%and HB155,respectively.It is concluded that the VSCP process can effectively refine the primary Si grains.Therefinement of primary Si grains is the major cause for the improvement of the mechanical properties of the RDC sample.

Microstructure and properties of rheo-HPDC Al-8Si alloy prepared by air-cooled stirring rod process

A new and effective semisolid slurry preparation process with air-cooled stirring rod(ACSR)is reported,in which the compressed air is constantly injected into the inner cavity of a stirring rod to cool the melt.The slurry of a newly developed high thermal conductivity Al?8Si alloy was prepared,and thin-wall heat dissipation shells were produced by the ACSR process combined with a HPDC machine.The effects of the air flow on the morphology ofα1-Al particles,mechanical properties and thermal conductivity of rheo-HPDC samples were studied.The results show that the excellent slurry of the alloy could be obtained with the air flow exceeding3L/s.Rheo-HPDC samples that were produced with the air flow of5L/s had the maximum UTS,YS,elongation,hardness and thermal conductivity of261MPa,124MPa,4.9%,HV99and153W/(m·K),respectively.Rheo-HPDC samples show improved properties compared to those formed by HPDC,and the increasing rates of UTS,YS,elongation,hardness and thermal conductivity were20%,15%,88%,13%and10%,respectively.

Effect of Si content on interfacial reaction and properties between solid steel and liquid aluminum

The effect of Si content on the microstructures and growth kinetics of intermetallic compounds(IMCs)formed during the initial interfacial reaction(<10 s)between solid steel and liquid aluminum was investigated by a thermophysical simulation method.The influence of Si addition on interfacial mechanical properties was revealed by a high-frequency induction brazing.The results showed that IMCs layers mainly consisted ofη-Fe_(2)Al_(5)andθ-Fe_(4)Al_(13).The addition of Si reduced the thickness of the IMCs layer.The growth of theηphase was governed by the diffusion process when adding 2 wt.%Si to the aluminum melt.When 5 wt.%or 8 wt.%Si was added to aluminum,the growth was governed by both the diffusion process and interfacial reaction,and ternary phaseτ1/τ9-(Al,Si)_(5)Fe_(3)was formed in theηphase.The apparent activation energies of theηphase decreased gradually with increasing Si content.The joint with pure aluminum metal had the highest tensile strength and impact energy.

Effects of selective laser melting parameters on surface quality and densification behaviours of pure nickel

The effects of laser power and scanning speed on the forming characteristic of scanning tracks,densification behaviours and surface roughness of pure nickel fabricated with selective laser melting(SLM)were studied.The results indicate that the scanning tracks showed continuous,regular and flat surface with increasing laser power and decreasing scanning speed in a specific range,which could avoid the defects(like holes and balling structures)forming in SLM processing.The optimal process window was identified as the scanning speed of 900 mm/s and the laser power of 255−275 W by comparing the surface qualities and densification behaviours.With the suitable processing parameters,the relative density could achieve 99.16%,the tensile strength was(359.49±2.74)MPa,and the roughnesses of the top and side surfaces were(12.88±2.23)and(14.98±0.69)μm,respectively.

Relationship between amounts of low-melting-point eutectics and hot tearing susceptibility of ternary Al−Cu−Mg alloys during solidification

A systematical study on the relationship between the amounts of different eutectic phases especially the low-melting-point(LMP)eutectics and the hot tearing susceptibility of ternary Al−Cu−Mg alloys during solidification was performed.By controlling the concentrations of major alloying elements(Cu,Mg),the amounts of LMP eutectics at the final stages of solidification were varied and the corresponding hot tearing susceptibility(HTS)was determined.The results showed that the Al−4.6Cu−0.4Mg(wt.%)alloy,which contained the smallest fraction of LMP eutectics among the investigated alloys,was observed to be the most susceptible to hot tearing.With the amount of total residual liquid being approximately the same in the alloys,the hot tearing resistance is considered to be closely related to the amounts of LMP eutectics.Specifically,the higher the amount of LMP eutectics was,the lower the HTS of the alloy was.Further,the potential mechanism of low HTS for alloys with high amounts of LMP eutectics among ternary Al−Cu−Mg alloys was discussed in terms of feeding ability and permeability as well as total viscosity evolution during solidification.

Hydrogen storage behavior of nanocrystalline and amorphous La-Mg-Ni-based LaMg_(12)-type alloys synthesized by mechanical milling

Nanocrystalline and amorphous LaMg11Ni+x%Ni(x=100,200,mass fraction)alloys were synthesized by mechanicalmilling.The electrochemical hydrogen storage properties of the as-milled alloys were tested by an automatic galvanostatic system.The gaseous hydrogen absorption and desorption properties were investigated by Sievert’s apparatus and differential scanningcalorimeter(DSC)connected with a H2detector.The results indicated that increasing Ni content significantly improves the gaseousand electrochemical hydrogen storage performances of the as-milled alloys.The gaseous hydrogen absorption capacities andabsorption rates of the as-milled alloys have the maximum values with the variation of the milling time.But the hydrogen desorptionkinetics of the alloys always increases with the extending of milling time.In addition,the electrochemical discharge capacity andhigh rate discharge(HRD)ability of the as-milled alloys both increase first and then decrease with milling time prolonging.

Prediction of hot tearing susceptibility of direct chill casting of AA6111 alloys via finite element simulations

To predict hot tearing susceptibility(HTS)during solidification and improve the quality of Al alloy castings,constitutive equations for AA6111 alloys were developed using a direct finite element(FE)method.A hot tearing model was established for direct chill(DC)casting of industrial AA6111 alloys via coupling FE model and hot tearing criterion.By applying this model to real manufacture processes,the effects of casting speed,bottom cooling,secondary cooling,and geometric variations on the HTS were revealed.The results show that the HTS of the billet increases as the speed and billet radius increase,while it reduces as the interfacial heat transfer coefficient at the bottom or secondary water-cooling rate increases.This model shows the capabilities of incorporating maximum pore fraction in simulating hot tearing initiation,which will have a significant impact on optimizing casting conditions and chemistry for minimizing HTS and thus controlling the casting quality.

Cu-Al interfacial compounds and formation mechanism of copper cladding aluminum composites

Copper cladding aluminum(CCA)rods with the section dimensions of12mm in diameter and2mm in sheath thickness were fabricated by vertical core-filling continuous casting(VCFC)technology.The kinds and morphology of interfacial intermetallic compounds(IMCs)were investigated by SEM,XRD and TEM.The results showed that the interfacial structure of Cu/Al was mainly composed of layeredγ1(Cu9Al4),cellularθ(CuAl2),andα(Al)+θ(CuAl2)phases.Moreover,residual acicularε2(Cu3Al2+x)phase was observed at the Cu/Al interface.By comparing the driving force of formation forε2(Cu3Al2+x)andγ1(Cu9Al4)phases,the conclusion was drawn that theε2(Cu3Al2+x)formed firstly at the Cu/Al interface.In addition,the interfacial formation mechanism of copper cladding aluminum composites was revealed completely.

Preparation of semi-solid 6061 aluminum alloy slurry by serpentine channel pouring

The semi-solid 6061 aluminum alloy slurry was prepared by a serpentine channel pouring process. The effects of pouring temperature, bend number and bend diameter on the microstructures were investigated. Microstructural evolution mechanism of the semi-solid slurry during the pouring process was also analyzed. The results show that the grain is refined and the grain roundness is improved by controlling the pouring temperature close to the liquidus temperature, and the nucleation rate of primary α(Al) grains is effectively increased via increasing the bend number and decreasing the bend diameter. The primary grains are not only formed directly from the alloy melt via chilling nucleation and heterogeneous nucleation, but also evolved from the fractured dendrite fragments. Meanwhile, the heat exchange between the melt and the serpentine channel is increased by the “self-stirring” effect in the melt, which also promotes the refinement and spheroidization of primary α(Al) grains.

Significant influence of sharp grain boundary corner on tensile elongation of copper bars with columnar grains and its mechanism

The reason why elongation of copper bars with columnar grains drops significantly after small cold-drawing was explored. The copper bars were prepared by warm-mould continuous casting. Tensile test was interrupted at various tensile strains in order to detect crack origin. Electron backscattered diffraction（EBSD） was used to analyze dislocation slip bands. It is found that the as-cast microstructure contains sharp grain boundary（GB） corners nearly parallel to the solidification direction（SD）. Elongation of the copper bars drops significantly from 68.8% in as-cast state to 18.8% in as-drawn state. It is revealed that plastic deformation becomes severer in the vicinity of sharp GB corners. Locally accumulated internal stress even activates a slip system with very low Schmid factor of 0.17. The localized plastic deformation near sharp grain boundary corner promotes crack initiation and propagation, which eventually leads to the significant drop of elongation.

Solidification behavior of Pt-containing 718Plus superalloy

Solidification behaviors of Pt-containing 718Plus superalloys were studied by scanning electron microscopy(SEM),energy dispersive spectrum(EDS),differential scanning calorimetry(DSC)and simulation calculations.It is found that Pt increases solidification range and decreases solidus temperature of the alloy and precipitation temperature of Laves+ γ eutectic phase since Pt enlarges the region of γ phase by increasing Nb solubility.In addition,Pt segregates to the interdendritic region and increases the segregation of Nb and Ti in the interdendritic region due to the strong attractive interactions between Pt and Nb/Ti.As a result,Pt promotes the precipitation of the Laves+ γ eutectic phase andηphase around eutectic phase.The increase of solidification range and segregation degrees of Nb and Al caused by Pt also promotes the precipitation and growth of γ'+γ" phase around eutectic phase.These results provide experimental bases for understanding the mechanism of Pt in solidification behavior of superalloys.

Microstructure Evolution and Deformation Behavior of Metastable β-Titanium Alloy Ti55511 in Die Forging

The effect of die forging on the microstructure evolution and deformation behavior of metastable β-titanium alloy Ti55511 was investigated by electron backscatter diffraction.Before die forging,the alloy Ti55511 was subjected to multi-pass forging to optimize the microstructural heterogeneity(texture)which can cause mechanical behavior anisotropy of titanium alloys.Results show that after die forging,Ti55511 components exhibit different microstructures and textures in different local areas.No<100>fiber texture is found in all areas with different degrees of deformation.Dynamic recrystallization occurs in the area where large strain occurs during the early stage of die forging.Basket-weave microstructure forms in most local areas.