Alloy Shell Research Articles

The influence of metallic shell deformation on the contact mechanics of a ceramic-on-ceramic total hip arthroplasty.

Total hip arthroplasty of ceramic-on-ceramic bearing combinations is increasingly used clinically. The majority of these implants are used with cementless fixation that a metal-backing shell is press-fitted into the pelvic bone. This usually results in the deformation of the metallic shell, which may also influence the ceramic liner deformation and consequently the contact mechanics between the liner and the femoral head under loading. The explicit dynamic finite element method was applied to model the implantation of a cementless ceramic-on-ceramic with a titanium shell and subsequently to investigate the effect of the metallic shell deformation on the contact mechanics. A total of three impacts were found to be necessary to seat the titanium alloy shell into the pelvic bone cavity with a 1 mm diameter interference and a 1.3 kg impactor at 4500 mm s(-1) velocity. The maximum deformation of the metallic shell was found to be 160 µm in the antero-superior and postero-inferior direction and 97 µm in the antero-inferior and postero-superior direction after the press-fit. The corresponding values were slightly reduced to 67 and 45 µm after the ceramic liner was inserted and then modified to 74 and 43 µm under loading, respectively. The maximum deformation and the maximum principal stress of the ceramic liner were 31 µm and 144 MPa (tensile stress), respectively, after it was inserted into the shell and further increased to 52 µm and 245 MPa under loading. This research highlights the importance of the press-fit of the metallic shell on the contact mechanics of the ceramic liner for ceramic-on-ceramic total hip arthroplasties and potential clinical performances.

Determination of Core–Shell Structures in Pd‐Hg Nanoparticles by STEM‐EDX

AbstractThe structural and elemental configuration of a high‐performing Pd‐Hg electrocatalyst for oxygen reduction to hydrogen peroxide has been studied by means of high‐resolution scanning transmission electron microscopy. Pd‐Hg nanoparticles are shown to have a crystalline core–shell structure, with a Pd core and a Pd‐Hg ordered alloy shell. The ordered shell is responsible for the high oxygen reduction selectivity to H2O2.

Magnetic Fe3O4–FeB nanocomposites with promoted Cr(VI) removal performance

In this study, amorphous FeB alloy modified magnetite nanocomposites (Fe3O4–FeB) were facilely synthesized by interfacial reduction of commercial Fe3O4 nanoparticles with NaBH4. TEM, CS-STEM integrated with EDS, Mössbauer spectroscopy analysis confirmed the formation of Fe3O4–FeB, where a shell of amorphous FeB nanoparticles with 2–4nm in size was surrounded on the inner magnetite Fe3O4 part. Fe3O4–FeB displayed a promoted Cr(VI) removal efficiency compared with the bare Fe3O4 counterpart, the interfacial reduced Fe3O4 nanoparticles with hydrogen and/or with hydrazine hydride. XPS analysis evidenced that reduction of Cr(VI) on surface of the Fe3O4–FeB was the major contribution to the Cr(VI) removal. Tafel polarization analysis of the Fe3O4–FeB and aqueous boron species measurement indicated that high Cr(VI) removal efficiency with Fe3O4–FeB was highly depended on amorphous FeB alloy shell, in which boron element containing free electrons could accelerate the electron transfer from Fe to the adsorbed Cr(VI), as well reduce Fe(III) to Fe(II) and thus promote the Fe(III)/Fe(II) cycles. The efficient Cr(VI) removal under a wide range of pH values and its easy magnetic separation make the Fe3O4–FeB be a potential for Cr(VI) contaminated water treatment.

Thermal decomposition synthesis of functionalized PdPt alloy nanodendrites with high selectivity for oxygen reduction reaction

Pt-based bimetallic nanostructures have found intriguing applications in electrocatalysis. However, the pristine Pt-based nanostructures generally lack the selectivity for the target reaction because of their high activity for both oxygen reduction reactions (ORRs) and fuel molecule oxidation reactions. By employing a recently developed chemical functionalization strategy, the functionalized Pt-based nanostructures have achieved their selectivity for the target reaction in fuel cells. In this work, we report a facile thermal decomposition route to synthesize the polyallylamine (PAH)-functionalized Pd–Pt bimetallic core–shell nanodendrites with a Pd-rich PdPt alloy core and a Pt-rich PtPd alloy shell (PdPt@PtPd CSNDs) by using PAH that serves as a complexant, reductant and chemical functionalization molecule. The composition, morphology and structure of PdPt@PtPd CSNDs are characterized in detail. Compared with commercial Pt black electrocatalyst, the PAH-functionalized PdPt@PtPd CSNDs show improved electrocatalytic activity and durability for the ORR, and achieve good selectivity for the ORR in the presence of ethanol molecules. The study shows a promising cathode electrocatalyst for direct alcohol fuel cells (DAFCs). Palladium–platinum core–shell nanodendrites have been made that are promising as a cathode electrocatalyst for direct alcohol fuel cells. Such fuel cells convert the chemical energy of alcohol into electricity and are attractive for powering vehicles and portable electronic devices. To become commercially viable, it is vital to improve the efficiency, activity, alcohol tolerance and durability of platinum electrocatalysts for the oxygen reduction reaction (ORR). Now, researchers in Singapore and China have demonstrated a simple one-step approach involving water-based thermal decomposition for synthesizing polyallylamine-functionalized palladium–platinum nanodendrites that have palladium-rich cores and platinum-rich shells. These bimetallic nanostructures exhibited superior electrocatalytic activity and durability for the ORR than a commercial platinum black electrocatalyst. Importantly, unlike pristine platinum-based nanostructures, they showed good selectivity for the ORR in the presence of ethanol. The polyallylamine functionalization imparted Pd–Pt nanodendrites with extraordinary selectivity for the oxygen reduction reaction because of its steric hindrance effect and ethanol-phobic property.

Fabricating a Homogeneously Alloyed AuAg Shell on Au Nanorods to Achieve Strong, Stable, and Tunable Surface Plasmon Resonances.

Colloidal metal nanocrystals with strong, stable, and tunable localized surface plasmon resonances (SPRs) can be useful in a corrosive environment for many applications including field-enhanced spectroscopies, plasmon-mediated catalysis, etc. Here, a new synthetic strategy is reported that enables the epitaxial growth of a homogeneously alloyed AuAg shell on Au nanorod seeds, circumventing the phase segregation of Au and Ag encountered in conventional synthesis. The resulting core-shell structured bimetallic nanorods (AuNR@AuAg) have well-mixed Au and Ag atoms in their shell without discernible domains. This degree of mixing allows AuNR@AuAg to combine the high stability of Au with the superior plasmonic activity of Ag, thus outperforming seemingly similar nanostructures with monometallic shells (e.g., Ag-coated Au NRs (AuNR@Ag) and Au-coated Au NRs (AuNR@Au)). AuNR@AuAg is comparable to AuNR@Ag in plasmonic activity, but that it is markedly more stable toward oxidative treatment. Specifically, AuNR@AuAg and AuNR@Ag exhibit similarly strong signals in surface-enhanced Raman spectroscopy that are some 30-fold higher than that of AuNR@Au. When incubated with a H(2)O(2) solution (0.5 m), the plasmonic activity of AuNR@Ag immediately and severely decayed, whereas AuNR@AuAg retained its activity intact. Moreover, the longitudinal SPR frequency of AuNR@AuAg can be tuned throughout the red wavelengths (≈620-690 nm) by controlling the thickness of the AuAg alloy shell. The synthetic strategy is versatile to fabricate AuAg alloyed shells on different shaped Au, with prospects for new possibilities in the synthesis and application of plasmonic nanocrystals.

A single-step hot stamping-forging process for aluminum alloy shell parts with nonuniform thickness

In this study, a single-step hot stamping-forging process using a counter punch was proposed to produce pan-shaped shell parts with nonuniform thickness distributions, which are often used in satellites. Through FE simulations, the effects of die temperature, counter punch initial interposition length and counter force on the part thickness were examined. It was found that the material flow is divided at a flow dividing surface (FDS) which moves in the wall during forming. The maximum bottom thickness and nonuniformity were found to be closely related to the counter force and initial interposition length. Base on the simulation results, experiments were carried out using sheet blanks with initial thicknesses of 4mm. After stamping-forging deformation, the part bottom was successfully thickened to 4.3mm while the wall was thinned to 2.5–2.7mm.

Core-shell Au@Pd nanoparticles with enhanced catalytic activity for oxygen reduction reaction via core-shell Au@Ag/Pd constructions.

Core-shell nanoparticles often exhibit improved catalytic properties due to the lattice strain created in these core-shell particles. Herein, we demonstrate the synthesis of core-shell Au@Pd nanoparticles from their core-shell Au@Ag/Pd parents. This strategy begins with the preparation of core-shell Au@Ag nanoparticles in an organic solvent. Then, the pure Ag shells are converted into the shells made of Ag/Pd alloy by galvanic replacement reaction between the Ag shells and Pd2+ precursors. Subsequently, the Ag component is removed from the alloy shell using saturated NaCl solution to form core-shell Au@Pd nanoparticles with an Au core and a Pd shell. In comparison with the core-shell Au@Pd nanoparticles upon directly depositing Pd shell on the Au seeds and commercial Pd/C catalysts, the core-shell Au@Pd nanoparticles via their core-shell Au@Ag/Pd templates display superior activity and durability in catalyzing oxygen reduction reaction, mainly due to the larger lattice tensile effect in Pd shell induced by the Au core and Ag removal.

Heat transfer and stress evolution behaviours of an aluminium alloy low pressure shell casting

Considering the solidification, demoulding and heat treatment processes in low pressure casting, relatively complete processes of an aluminium alloy shell casting are simulated to investigate the heat transfer feature and stress behaviours variation of casting in each multi-processes stage. FDM is used to discrete thermal conduction model when studying the heat transfer process, while FEM is adopted to solve the elastic-plastic model when studying the stress behaviour variation. When matching the two models, we map the finite difference mesh to finite element mesh. Three different temperature conditions, namely 300 °C, 400 °C and 500 °C, are simulated when we research the influence of demoulding temperature on stress behaviour. The simulation results demonstrate that the higher demoulding temperature is, the greater casting deformation and the smaller stress value are. The final casting stress status and the initial heat treatment temperature have a different relationship as for different parts of casting.

One-pot synthesis of small and uniform Au@PtCu core–alloy shell nanoparticles as an efficient electrocatalyst for direct methanol fuel cells

Metal core–shell nanostructures have been extensively studied as one of the most promising electrocatalysts to significantly reduce the loading of the expensive Pt catalyst for fuel cells but it is very challenging to fabricate such a structure to possess proper metal components while making small and uniformly distributed nanoparticles for high catalytic performance. In this work, small and uniformly distributed Au-core/PtCu alloy–shell structured nanoparticles (Au@PtCu NPs) were fabricated by a novel one-pot facile method. The as-prepared Au@PtCu/C has a much larger electrochemical active surface area (ECSA) (64.8m2g−1Pt) than that of AuPtCu/C(38.5m2g−1Pt), PtCu/C (31.02m2g−1Pt) and commercial Pt/C (25.4m2g−1Pt) catalyst. This new catalyst not only greatly reduces Pt loading but also significantly increases the catalytic activity and stability toward methanol oxidation reaction in comparison to the commercial electrocatalyst. This is mainly attributed to a synergistic effect from the small and uniform core–shell nanostructure and the unique chemical compositions of Au and PtCu alloy, thus offering a great potential for a less expensive but highly active catalyst toward direct methanol fuel cells (DMFCs).

Extrusion of the bimetallic aluminum-magnesium rods and tubes

On the basis of theoretical and experimental studies the complex influence of process conditions such as the geometric characteristics of the billet and the tool were investigated regarding the extrusion of bimetallic rods and tubes. As a core material magnesium alloys of the Mg-Al-Zn system and as shell materials aluminum and its alloys of the Al-Mg-Si and Al-Zn-Mg were extruded. An increase in the strength properties of the aluminum alloy shell—compared to the core of a magnesium alloy—increases the inhomogeneity of the speed distribution of the metal flow resulting in defects. A sustainable processing can be established by the extrusion of bimetallic rods which consist of an Mg-Al-Zn-Mn core and an Al-Mg-Si shell.

Octahedral Pd@Pt1.8Ni core-shell nanocrystals with ultrathin PtNi alloy shells as active catalysts for oxygen reduction reaction.

Forming core-shell and alloy structures offers generally two ways to design efficient Pt-based catalysts for oxygen reduction reaction (ORR). Here, we combined these two strategies and invented a versatile aqueous route to synthesize octahedral Pd@Pt1.8Ni core-shell nanocrystals. The Pt/Ni atomic ratios in the resultant shells can be varied from 0.6 to 1.8, simply by changing the amounts of Pt and Ni precursors, with the other conditions unchanged. Experimental studies showed that the mass activities of as-prepared catalysts were 5 times higher than that of the commercial Pt/C. We believe that the ultrathin PtNi shells enclosed by {111} facets made it possible to reduce the Pt content while retaining the catalytic activity toward ORR. This strategy may be extended to the preparation of other multimetallic nanocrystals with shaped and ultrathin alloy shells, which is conducive to design highly active catalysts.

Controlled Surface Segregation Leads to Efficient Coke‐Resistant Nickel/Platinum Bimetallic Catalysts for the Dry Reforming of Methane

AbstractSurface composition and structure are of vital importance for heterogeneous catalysts, especially for bimetallic catalysts, which often vary as a function of reaction conditions (known as surface segregation). The preparation of bimetallic catalysts with controlled metal surface composition and structure is very challenging. In this study, we synthesize a series of Ni/Pt bimetallic catalysts with controlled metal surface composition and structure using a method derived from surface organometallic chemistry. The evolution of the surface composition and structure of the obtained bimetallic catalysts under simulated reaction conditions is investigated by various techniques, which include CO‐probe IR spectroscopy, high‐angle annular dark‐field scanning transmission electron microscopy, energy‐dispersive X‐ray spectroscopy, extended X‐ray absorption fine structure analysis, X‐ray absorption near‐edge structure analysis, XRD, and X‐ray photoelectron spectroscopy. It is demonstrated that the structure of the bimetallic catalyst is evolved from Pt monolayer island‐modified Ni nanoparticles to core–shell bimetallic nanoparticles composed of a Ni‐rich core and a Ni/Pt alloy shell upon thermal treatment. These catalysts are active for the dry reforming of methane, and their catalytic activities, stabilities, and carbon formation vary with their surface composition and structure.

Syntheses of Au@PdAg and Au@PdAg@Ag Core–Shell Nanorods through Distortion-Induced Alloying between Pd Shells and Ag Atoms over Au Nanorods

Noble Au@PdAg and Au@PdAg@Ag core–shell nanorods (NRs) having PdAg alloy shells were synthesized using Au@Pd NRs as seeds. Their crystal structures and growth mechanisms were examined using data from TEM, TEM–EDS, XRD, and UV–Vis–NIR extinction spectroscopy. First, cuboid or dumbbell-type Au@Pd NR seeds were prepared using Au NRs as seeds. In the second step, when Ag+ ions were reduced over these seeds, cuboid and dumbbell-type Au core PdAg alloy shell NRs were formed with maximum Ag content of about 16% and 24%, respectively, after heating at 60 °C. The driving force of alloying between Pd shells and Ag atoms was attributed to the distortion of Pd layers over Au NRs based on peak shifts and broadening of XRD data. The higher Ag content in dumbbell-type Au@PdAg NRs was explained by the greater distortion of Pd shells over Au NRs. When the Ag content exceeds its maximum solubility in Pd shells, the third Ag shells were grown over Au@PdAg NRs. For cuboid Au@PdAg NRs, the crystal growth of Ag shells over cub...

Structural Evolution of AuPt and AuPd Nanoparticles Fabricated by Microwave Assisted Synthesis: A Comparative Study

ABSTRACTBimetallic nanoparticles (NPs), particularly Au/Pd and Au/Pt, have attracted extensive attention due to their wide-spread application in catalysis, optoelectronics and energy recuperation.[1] Here we have attempted the fabrication of Au/Pt and Au/Pd bimetallic NPs by an energy-efficient eco-friendly microwave methodology. The microwave-assisted reactions enable considerably large product yields over conventional colloidal methods due to (a) almost two-fold increased reaction kinetics, (b) localized superheating at reaction sites and rapid rise of initial temperature.[2] Au NPs (sizes 20 ± 3 nm) are fabricated in the first step followed by the reduction of [PdCl2(NH3)2] or [K2PtCl6]in tetraethylene glycol at 180 ºC for 2 min. Controlling and understanding the atomic structure and elemental distributions of these NPs are crucial for their optimized performances. So, we address the fundamental question of the most likely arrangement of Au and Pd or Pt atoms in these bimetallic NPs prepared under similar conditions by complementary characterizations using UV-Vis spectroscopy, X-ray diffraction (XRD) and transmission electron microscopy (TEM). The UV-Vis spectroscopy reveals the formation of an alloy shell. The extent of depression of the plasmon peak of Au and its blue-shift reveals substantial deposition of Pd atoms on an Au core and significant alloying in comparison to Au/Pt NPs. XRD reveals the gradual shift of the diffraction peak from the position of Au to the position of Pd or Pt with change in composition. XRD supports the formation of a thick alloy shell in these NPs. However, the TEM images reveal a very interesting result. With increase in Pt concentration, the size of the dispersed NPs decreases from 20 ± 3 nm to about 16 nm (± 1 nm) and there is evolution of a bimodal particle size distribution with small particles about 1-2 nm diameters. On the contrary, with increasing Pd concentration, the particle size of the dispersed particles increases to about 32 nm (± 1 nm). This discrepancy of particle size evolution for the two systems arises due to the differences in surface energies (Pt > Pd > Au atoms). Pt atoms tend to diffuse towards the core with the formation of Au nano-islands which eventually segregates leading to a reduction in particle size and bimodal distribution. At higher concentration of Pt, Pt and Au atoms tend to nucleate separately also contribute to the bimodal distribution. While for Au/Pd NPs, we have an Au core with an alloyed shell having higher Pd concentration. This is further supported by experimental evidence by selective etching and dissolution of Au by potassium-iodide solution. Furthermore, the Au/Pd bimetallic NPs are found to possess better catalytic activities in the reduction of 4-nitrophenol to 4-aminophenol than Au/Pt and monometallic NPs.

Rational syntheses of core–shell Fe@(PtRu) nanoparticle electrocatalysts for the methanol oxidation reaction with complete suppression of CO-poisoning and highly enhanced activity

We report the syntheses and characterization of ternary nanoparticles of Fex@(PtRu)(1−x)/2(x= 0.0–0.44) with Fe cores and PtRu alloy shells, which exhibit greatly improved electrocatalytic properties for methanol oxidation reaction.

Understanding the effect of ultrathin AuPd alloy shells of irregularly shaped Au@AuPd nanoparticles with high-index facets on enhanced performance of ethanol oxidation.

In this study, irregularly shaped, concave cuboidal Au@AuPd nanoparticles (ISCC-Au@AuPd NPs) with high-index facets were synthesized via Pd overgrowth on pre-formed ISCC-Au NPs with a concentration of Pd precursors as low as 2%. The AuPd alloy nature of the resulting shells was confirmed by X-ray photoelectron spectroscopy, cyclic voltammogram analysis, and energy dispersive X-ray spectroscopy. Among the irregularly shaped NPs obtained, the ISCC-Au97.5@Au0.5Pd2.0 NPs display the largest electrochemically active surface area (up to 92.11 m(2) g(-1)), as their closed-packed agglomeration was prevented, and the best long-term stability with respect to ethanol oxidation (0.50 M) in alkaline media (0.30 KOH) by efficiently removing intermediates. Their mass- and ECSA-normalized current densities (4.15 A mgPd(-1) and 4.51 mA cm(-2)) are about 20.7 times and 6.9 times higher than those of commercial Pd/C catalysts (0.20 A mgPd(-1) and 0.65 mA cm(-2)), respectively.

Die Casting Mold Design for Aluminum Alloy Shell of Instrument

/This paper is about die casting mold design for aluminum alloy shell of instrument. Three-dimensional model of the casting and mold are designed by using Pro/Engineer and AutoCad which can analyze forming quality. Digital design and theoretical calculation can greatly shorten product development cycle and mold design cycle, improve the accuracy of product design and mold design, and reduce the cost of mold design.

Au/Ag nanoalloy shells as near-infrared SERS nanoprobe for the detection of protein

We provide a highly sensitive, uniform and reproducible surface-enhanced Raman scattering (SERS) performance obtained from the randomly aggregated Au/Ag nanoalloy shells substrate. Au/Ag nanoalloy shells consist of SiO2 core and Au/Ag alloy shells layer. The obtained Au/Ag nanoalloy shells with a monodisperse size distribution exhibit different morphology by the analysis of TEM. By changing the ratio of Au and Ag, the plasmonic extinction of Au/Ag nanoshells varied in near-infrared window region. In this experiment, Au/Ag nanoshells with controllable ratio can obtain larger SERS signals, which can be used for ultrasensitive detection of biomolecules. These SERS-active spheres show interesting properties as a novel Raman tag for immunoassays.

Magnetic pulse forming of AZ31 magnesium alloy shell by uniform pressure coil at room temperature

The magnetic pulse forming process of AZ31 magnesium alloy shell using uniform pressure coil at room temperature was investigated. ANSYS FEA software was used to analyze the distribution of magnetic flux density of the uniform pressure coil and magnetic pressure for loading on the AZ31 sheet. The characteristic of forming process of AZ31 shell was revealed, and magnetic pulse forming process of AZ31 shell and effect of Al alloy sheet with different thickness were presented by experiments. Due to impact between sheet and die, the rebound profiles on the bottom of deformed sheets were observed. In order to remove the rebound profile, AA5052 sheets were employed to drive the deformed AZ31 sheets. The section contour of R = 30 mm (R means bottom radius of die) shell deformed by 0.5-mm thickness of driver sheet driving once and R = 15 mm shell deformed by 1-mm thickness of driver sheet driving twice are good agreement with die, not only width direction (AB direction) but also length direction (CD direction). However, there was a big obstacle to deform the AZ31 shell with R = 2 mm, because the die had small bottom radius and sidewall section. Variation of effective strain and velocity with width direction and length direction during magnetic pulse forming without driver sheet and with Al driver sheet were analyzed by simulation.

A numerical investigation of dynamic plastic buckling behaviour of thin-walled cylindrical structures with several geometries

In this study dynamic buckling behaviors of an aluminum alloy cylindrical shell with axial linear variable thickness, discontinuity and conical shaped have been numerically investigated for high velocity impact by means of finite element method. The validation of finite element model was provided by the results of previous studies in literature. Throughout study commerce finite element package program LS-DYNA3D was used and all simulations were fulfilled as explicitly. According to results obtained, the minor changes in the geometry are able to convert the dynamic plastic buckling into dynamic progressive buckling behavior. This study indicates that which of the dynamic buckling or progressive buckling mechanism will be dominant is sensitive to geometrical properties for cylindrical aluminum alloy shells under the high velocity impact.