Shape and composition-controlled platinum alloy nanocrystals using carbon monoxide as reducing agent

The shape of metal alloy nanocrystals plays an important role in catalytic performances. Many methods developed so far in controlling the morphologies of nanocrystals are however limited by the synthesis that is often material and shape specific. Here we show using a gas reducing agent in liquid solution (GRAILS) method, different Pt alloy (Pt-M, M = Co, Fe, Ni, Pd) nanocrystals with cubic and octahedral morphologies can be prepared under the same kind of reducing reaction condition. A broad range of compositions can also be obtained for these Pt alloy nanocrystals. Thus, this GRAILS method is a general approach to the preparation of uniform shape and composition-controlled Pt alloy nanocrystals. The area-specific oxygen reduction reaction (ORR) activities of Pt(3)Ni catalysts at 0.9 V are 0.85 mA/cm(2)(Pt) for the nanocubes, and 1.26 mA/cm(2)(Pt) for the nanooctahedra. The ORR mass activity of the octahedral Pt(3)Ni catalyst reaches 0.44 A/mg(Pt).     

添加La_2O_3对搅拌摩擦加工制备Ni/Al复合材料组织和性能的影响

采用搅拌摩擦加工(FSP)方法在Al基体中添加微米级Ni粉及(Ni+La_2O_3)混合粉末,制备Ni/Al及(Ni+La_2O_3)/Al复合材料。采用SEM、EDS及XRD对复合区微观结构及相组成进行分析,采用室温拉伸试验对Ni/Al、(Ni+La_2O_3)/Al复合材料力学性能进行了测试。结果表明:Ni/Al复合材料中主要成分为Al、Al3Ni和Ni粉团聚物,Ni粉团聚物尺寸粗大,形貌呈壳-核结构,核为团聚的Ni,壳为Al3Ni增强相层;La_2O_3对Al-Ni原位反应有较大影响,能够强化Al-Ni原位反应,生成更多增强相;La_2O_3阻碍了Ni粉的相互吸附和聚拢行为,从而减少了团聚现象;(Ni+La_2O_3)/Al复合材料的抗拉强度可以达到186 MPa,与Al基体(抗拉强度72 MPa)、纯Al FSP(抗拉强度90 MPa)、Ni/Al复合材料(抗拉强度144 MPa)相比,其抗拉强度分别提高了158%、107%、29%。     

Shape‐Dependent Activity of Ceria for Hydrogen Electro‐Oxidation in Reduced‐Temperature Solid Oxide Fuel Cells

Single crystalline ceria nanooctahedra, nanocubes, and nanorods are hydrothermally synthesized, colloidally impregnated into the porous La_0.9Sr_0.1Ga_0.8Mg_0.2O_3‐δ (LSGM) scaffolds, and electrochemically evaluated as the anode catalysts for reduced temperature solid oxide fuel cells (SOFCs). Well‐defined surface terminations are confirmed by the high‐resolution transmission electron microscopy — (111) for nanooctahedra, (100) for nanocubes, and both (110) and (100) for nanorods. Temperature‐programmed reduction in H₂ shows the highest reducibility for nanorods, followed sequentially by nanocubes and nanooctahedra. Measurements of the anode polarization resistances and the fuel cell power densities reveal different orders of activity of ceria nanocrystals at high and low temperatures for hydrogen electro‐oxidation, i.e., nanorods > nanocubes > nanooctahedra at T ≤ 450 °C and nanooctahedra > nanorods > nanocubes at T ≥ 500 °C. Such shape‐dependent activities of these ceria nanocrystals have been correlated to their difference in the local structure distortions and thus in the reducibility. These findings will open up a new strategy for design of advanced catalysts for reduced‐temperature SOFCs by elaborately engineering the shape of nanocrystals and thus selectively exposing the crystal facets.     

Preparation of TiC/Ni3Al Composites by Upward Melt Infiltration

To whom correspondence should be addressedE-mail: yipan@public.hz.zj.cn1. IntroductionThe intermetallic compound Ni3AI is an attractive structural material for high temperature application because of a high modulus, good oxidation resistance and excellent creep resistanced]. One of themajor problems in the application of binary Ni3AIis its poor room-temperature ductility. Single crystal Ni3AI is ductile, but polycrystalline Ni3AI is brittle due to a severe illtergranular breakage at ambi…     

稀土氧化物(La2O3或CeO2)对搅拌摩擦加工制备Ni/Al复合材料组织和性能的影响

采用搅拌摩擦加工（FSP）的方法制备Ni/Al复合材料,并在此基础上添加不同种类稀土氧化物（La₂O₃或CeO₂）,通过SEM、EDS、XRD、电子探针（EPMA）和室温拉伸试验研究稀土氧化物对FSP制备Ni/Al复合材料组织和性能的影响。结果表明：Ni/Al复合材料复合区有较明显的Ni粉团聚物存在,Ni-La₂O₃/Al、Ni-CeO₂/Al复合材料中Ni粉团聚物数量减少,尺寸减小。La₂O₃和CeO₂均对Al-Ni原位反应有较大影响,能够促进Al-Ni原位反应的进行,生成更多增强相。Ni-CeO₂/Al复合材料与Ni-La₂O₃/Al复合材料相比,复合区组织更加均匀,增强颗粒Al₃Ni含量更多。La₂O₃和CeO₂均能显著提高FSP制备Ni/Al原位复合材料的抗拉强度。Ni-La₂O₃/Al复合材料的抗拉强度达到221 MPa,Ni-CeO₂/Al复合材料的抗拉强度达到238 MPa,两者相比于Ni/Al的复合材料抗拉强度（166 MPa）分别提高了33.1%和43.4%。     

Microstructure and Mechanical Behaviour of Proton-and Ion-irradiated Ll_2 Intermetallic Compounds

The results of mechanical testing and transmission electron microscopy on the ordered intermetallic Ll2 compounds1Zr3Al, Ni3Al, Ni3Si and Ni3Ge after irradiation with protons or heavy ions at high or low tem peratu re are presented and discussed. Using a minjaturjzed disk-bend test. it was found that proton irradiation of Zr3Al. Ni3Al and Ni3Si raises their yield strength :a single test of Ni3Ge shows no effect on the fracture stress of this brittle intermetallic The Vickers microhardness of all four alloys is raised by proton irradiation. The irradiations cause all the alloys to disorder. the extent of which is dependent on irradiation temperature Microstructural defects are produced by the irradiations Some exhibit strain-field contrast under dynamic two-beam diffracting conditions. Other distinct defect clusters are imaged only in dark-field using su perlattice reflections, These latter defects are discussed in the context of current arnorphization models. The strength increase of Zr3Al, Ni3Al and Ni3Si is attributed to a combination of disordering and strengthening from defects. The lack of an effect of irradiation on the fracture stress of Ni3Ge. in which voids were observed, requires further experiments     

Environmental Embrittlement in A_3B-type Intermetallic Alloys

Environmental embrittlement in A3B-type intermetallics based on Ni3Al and Fe3Al has been studied in this paper. For the Ni3Al doped with 120 wt ppm B and Ni,(Al,Cr.Zr) doped with 80 wt ppm B,their elongation and ultimate tensile strength decreased in the sequence:of vacuum > air >hydrogen. while for Ni,(Al,Mn) doped with 400 wt ppm B no envifonmental degradation was ob served, although a -Ni3(Al,Mn) alloy without B showed a decrease in ductility when tested in air in stead of oxygen. It is supposed that boron and hydrogen compete for the occupation of interstitial sites near grain boundaries. If boron content is sufficiently low, hydrogen embrittlement occurs ;however, if its content is sufficiently high. boron addition is capable of eliminating envjronmental ef fect in Ni3Al-based alloysi As to the micromechanism of hydrogen embrittlement in Ni3Al+B. S EM in situ observations showed that both grain boundary decohesion and a high stress concentration con tributed to hydrogen-assisted jntergranu lar cracking in this alloy. For the Fe3Al and Fe3 (Al.Cr) alloys.their mechanical properties depended strongly on grain size / grain shape and testing environment. A strain rate effect on ductiIity and fracture strength was also observed in the Fe3Al and Fe,(Al,Cr)+B aIloys. Preoxidation increased the ductility of the Fe,(Al,Cr)+B alloy. All these results can be rationalized from a hypothesis that surface reaction is the controlling process in embrittling Fe3Al-based alloys.     

Uniform Ag Nanocubes Prepared by AgCl Particle–Mediated Heterogeneous Nucleation and Disassembly and Their Mechanism Study by DFT Calculation

Uniform Ag nanocubes are reproducibly synthesized by a AgCl particle‐mediated heterogeneous nucleation and disassembly process in polyol chemistry. By introducing N,N‐dimethylformamide (DMF) in a conventional polyol method with HCl etchant, Ag nanocrystals (NCs) begin to be nucleated on the surface of AgCl‐precipitated particles due to the promoted reduction reaction by DMF. The nucleated Ag NCs on the AgCl particles are grown to Ag nanocubes in shape by consuming Ag sources from the AgCl mother particles. Eventually the grown Ag nanocubes are disassembled from the mother AgCl particles because the AgCl particles are fully digested by the growing Ag nanocubes. Density functional theory calculation confirms that the Ag atoms can be favorably deposited on the (100) facet of AgCl particles and the Ag nuclei on the AgCl particles tend to reveal (100) facet.     

Microstructure,Properties and Wear Behaviors of (Ni_3Al)_p Reinforced Cu Matrix Composites

Pure copper and its composites reinforced with Ni 3 Al particles were produced by powder metallurgy(PM).Ni 3 Al powders were produced by mechanical ball milling from vacuum arc melted compounds.The Ni 3 Al powders were characterized by X-ray diffraction(XRD).The microscopy examinations revealed that the Ni 3 Al particles were distributed uniformly in the matrix.The effects of the particle fraction on the density,electrical conductivity,strength and dry sliding wear resistance of composite were investigated.It was found that the density and electrical conductivity of the composites decrease while the compression yield strength and wear resistance of composites increase with an increase in the particle fraction.The dry sliding wear tests were performed with pin-on-disk geometry.After sliding wear tests,the worn surfaces were examined by scanning electron microscopy(SEM) equipped with an energy dispersive X-ray spectrometer(EDS).Results have shown that the wear mechanism is oxidative and adhesive.     

Nanomechanical properties of a Ni nanodot-patterned surface

Nanomechanical properties of a Ni nanodot-patterned surface (NDPS) on a Si substrate were investigated using nanoindentation. The Ni NDPS was fabricated by thermal evaporation of Ni?through a porous anodized aluminum oxide template onto a Si substrate. Plan-view transmission electron microscopy and nanobeam diffraction were used to characterize the Ni nanodot crystal structure. Scanning electron microscopy and atomic force microscopy were used to characterize the morphology and deformation of the Ni?nanodots before and after nanoindentation. The elastic modulus and hardness of the Ni?nanodots were found to be 159 ± 22 and 7.7 ± 1.0?GPa, respectively. The critical shear stress for initiating plastic deformation in the Ni nanodot was estimated to be 8.3 ± 1.0?GPa, which is close to the theoretical shear strength of 7.6?GPa in dislocation-free single crystal Ni.     

残余热应力对Al2O3/Ni金属陶瓷断裂行为和力学性能的影响

运用残余热应力理论定性地解释也残余热应力对Al2O3/Ni金属陶瓷断裂行为和力学性能的影响，Ni颗粒位于Al2O3晶内或Ni含量低时，在Al2O3-Al2O3晶界产生张应力，易发生沿晶断裂；而其位于Al2O3晶界或Ni含量高时，在Al2O3-Al2O3晶界产生压应力，易产生穿晶断裂。     

Spontaneous Self‐Assembly of Perovskite Nanocrystals into Electronically Coupled Supercrystals: Toward Filling the Green Gap

Self‐assembly of nanoscale building blocks into ordered nanoarchitectures has emerged as a simple and powerful approach for tailoring the nanoscale properties and the opportunities of using these properties for the development of novel optoelectronic nanodevices. Here, the one‐pot synthesis of CsPbBr₃ perovskite supercrystals (SCs) in a colloidal dispersion by ultrasonication is reported. The growth of the SCs occurs through the spontaneous self‐assembly of individual nanocrystals (NCs), which form in highly concentrated solutions of precursor powders. The SCs retain the high photoluminescence (PL) efficiency of their NC subunits, however also exhibit a redshifted emission wavelength compared to that of the individual nanocubes due to interparticle electronic coupling. This redshift makes the SCs pure green emitters with PL maxima at ≈530–535 nm, while the individual nanocubes emit a cyan‐green color (≈512 nm). The SCs can be used as an emissive layer in the fabrication of pure green light‐emitting devices on rigid or flexible substrates. Moreover, the PL emission color is tunable across the visible range by employing a well‐established halide ion exchange reaction on the obtained CsPbBr₃ SCs. These results highlight the promise of perovskite SCs for light emitting applications, while providing insight into their collective optical properties.     

nPEG-TiO₂ nanoparticles: a facile route to elaborate nanostructured surfaces for biological applications

We report the synthesis of diacid-terminated PEG-functionalized cubic TiO(2) nanocrystals by a simple one-step solvothermal method, and their further use to form nanostructured surfaces for protein immobilization. The relevance and major interest of the so-obtained nanocrystals are the presence of terminal carboxylic acid groups at their surface, as confirmed by infrared analyses, in addition to the surrounding PEG chains, essential to avoid non specific interactions. These functional chemical groups were used to (i) immobilize the synthesized nanocubes on a cysteamine-modified Au surface, and to (ii) attach proteins via a presumable covalent link. AFM images show that the shapes and the narrow size distribution of the nanocubes, observed by TEM, were preserved after their immobilization on the modified Au surface. Moreover, the efficiency and specificity of antigen recognition were demonstrated using spectroscopic analyses. Our successful approach provides a versatile and facile way to elaborate specific and sensitive nanostructured surfaces for biosensors.     

Preparation of SiC Fiber Reinforced Nickel Matrix Composite

A method of preparing continuous(Al+Al2O3)-coated SiC fiber reinforced nickel matrix composite was presented,in which the diffusion between SiC fiber and nickel matrix could be prevented.Magnetron sputtering is used to deposit Ni coating on the surface of the(Al+Al2O3)-coated SiC fiber in preparation of the precursor wires.It is shown that the deposited Ni coating combines well with the(Al+Al2O3) coating and has little negative effect on the tensile strength of(Al+Al2O3)-coated SiC fiber.Solid-state diffusion bonding process is employed to prepare the(Al+Al2O3)-coated SiC fiber reinforced nickel matrix with 37% fibers in volume.The solid-state diffusion bonding process is optimized and the optimum parameters are temperature of 870,pressure of 50 MPa and holding time of 2 h.Under this condition,the precursor wires can diffuse well,composite of full density can be formed and the(Al+Al2O3) coating is effective to restrict the reaction between SiC fiber and nickel matrix.     

Ceramics Surface Modification by Excimer Laser Metal Coating

Thin metallic layers (~ 2 μm) of Ni were deposited on polycrystalline Al2O3. ZrO2 and (Ce-TZP)+Al2O3 ceramic substrates. and further irradiated with pulsed excimer (Xeno chloride) laser pulses. The laser energy density was varied from 0.21 to 0.81 J / cm2 to optimize bending strength. For ZrO2 ceramic, it was found that the strength increases from 530 to 753 MPa at 0.51 J / cm2 irradiation. For Al2O3 and (Ce-TZP)+ Al2O3 the fracture strength also increases in varying degree. The causes of strength increment were discussed.     

Up-conversion emissions characteristics of non-aqueous sol-gel derived RE3Al5O12 nanocrystals

The RE3Al5O12 (REAG:Er3Al5O12, Er:Y3Al5O12 and Er:Yb3Al5O12) up-conversion (UC) nanocrystals have been prepared by the non-aqueous sol-gel method. The green and red UC emissions are attributed to the 2H(11/2), 4S(3/2) --> 4I(15/2) and 4F(9/2) --> 4I(15/2) transitions of Er3+, respectively, were obtained for all samples with a 975 nm semiconductor LD excitation. For Er3Al5O12 nanocrystals, the green and red UC emissions have similar intensities. Y and Yb ions have no evident effect on the peak positions, but strongly affected the intensities of the green and red UC emissions of the Er. A much higher intensity of the green relative to red UC emission was observed for Er:Y3Al5O12 nanocrystals, however, the red UC emission became predominant for Er:Yb3Al5O12 nanocrystals. It was suggested that the two-photon process was responsible for the green and red UC emissions mechanism for all the samples.     

High yield synthesis of PbS nanocubes using one-step solid-state reaction in the presence of an anionic surfactant

PbS nanocubes have been synthesized by one-step solid-state reaction between Pb(DS)₂ (DS: dodecylsulfate anion) and Na₂S·9H₂O. The nanocrystals were characterized by X-ray powder diffraction, Transmission electron microscopy, UV–vis absorption spectrum and X-ray photoelectron spectra. The research showed that the functionized surfactant lead dodecyl sulfate (LDS) played an important role in the formation of PbS nanocubes.     

碳纤维增强Al_2O_3-20%Ni金属陶瓷复合材料的制备及组织性能

采用溶胶-凝胶+热压烧结法制备了碳纤维(CF)体积分数分别为0%、5%、10%、15%的CF/Al_2O_3-20%Ni金属陶瓷复合材料,采用XRD、SEM和EDS能谱分析了CF/Al_2O_3-20%Ni复合材料的物相组成、组织形貌及成分分布,并研究了CF含量对CF/Al_2O_3-20%Ni复合材料硬度、抗弯强度和EDS断裂韧性的影响,通过SEM分析了CF/Al_2O_3-20%Ni复合材料的断口形貌并探讨了断裂机制。结果表明:采用溶胶-凝胶法可获得CF分散良好、Ni颗粒分布均匀的CF/Al_2O_3-20%Ni复合材料,并且可在CF表面包覆一层α-Al_2O_3保护膜,从而防止CF在高温烧结过程中的烧损。随着CF体积分数的增加,CF/Al_2O_3-20%Ni复合材料的硬度降低,抗弯强度和断裂韧性都先升高后下降,当CF体积分数为10%时,抗弯强度和断裂韧性均达到峰值,相对不含CF试样分别提高了79%和134%,CF的加入使CF/Al_2O_3-20%Ni复合材料的强度和韧性得以改善。用此方法制备的CF/Al_2O_3-20%Ni复合材料的增韧机制为碳纤维的拔出、桥接及脱粘。     

中间层Ni对TC4/2A14异种金属搅拌摩擦焊接头组织和性能的影响

目的 添加0.05 mm厚的Ni箔作为中间层,对3 mm厚的TC4钛合金和2A14铝合金进行搅拌摩擦焊,分析Ni对接头力学性能的影响。方法 采用扫描电镜、EDS能谱及XRD衍射等微观表征分析方法,对焊接接头的断口形貌、成分进行分析,探究Ni箔对焊接接头力学性能的影响。结果 由于钛合金和铝合金存在较大的物理化学性能差异,Ti/Al异种金属焊接性较差,界面容易产生TiAl3、TiAl、Ti3Al等金属间化合物,其中脆性相TiAl3对接头性能的影响最大,会导致综合力学性能下降。当加入中间层材料Ni后,由于Ni与Al晶体结构均属于面心立方,因此Ni与Al的扩散系数大于Ti与Al的扩散系数,Ni和Al之间优先形成金属间化合物且弥散分布于焊缝中,从而缩短了Ti与Al之间的相互扩散时间,减少了TiAl3相的生成。结论 在未添加中间层材料时,接头平均抗拉强度为237.3 MPa,约为2A14铝合金母材抗拉强度的56.7%;当添加中间层Ni后,对焊缝中金属间化合物的种类和数量进行了调控,减少了对性能影响最大的TiAl3相的生成,接头平均抗拉强度达到285.3 MPa,为2A14铝合金母材抗拉强度的68%。     

Zirconium-Induced Softening in Hyperstoichiometric Ni3Al

The room temperature compressive properties and microhardness of Ni3AI alloys doped with Zr were studied. For the hypostoichiometric Ni3AI alloys, the compressive strength and microhardness increased with an increase in Zr content, while softening behavior induced by doping with a certain amount of Zr was observed in hyperstoichiometric Ni3AI alloy. Possible mechanisms for the softening effect were suggested.