Bimetallic Rods Research Articles

Oxidative esterification of furfural over Au–Pd/HAP-T and Au–Ag/HAP-T bimetallic catalysts supported on mesoporous hydroxyapatite nanorods

Core–shell (Au–Pd) and alloy (Au–Ag) architectured bimetallic mesoporous hydroxyapatite nano rods in the oxidative esterification of furfural.

Self-consistent nonlocal feedback theory for electrocatalytic swimmers with heterogeneous surface chemical kinetics.

We present a self-consistent nonlocal feedback theory for the phoretic propulsion mechanisms of electrocatalytic micromotors or nanomotors. These swimmers, such as bimetallic platinum and gold rods catalyzing decomposition of hydrogen peroxide in aqueous solution, have received considerable theoretical attention. In contrast, the heterogeneous electrochemical processes with nonlocal feedback that are the actual "engines" of such motors are relatively neglected. We present a flexible approach to these processes using bias potential as a control parameter field and a locally-open-circuit reference state, carried through in detail for a spherical motor. While the phenomenological flavor makes meaningful contact with experiment easier, required inputs can also conceivably come from, e.g., Frumkin-Butler-Volmer kinetics. Previously obtained results are recovered in the weak-heterogeneity limit and improved small-basis approximations tailored to structural heterogeneity are presented. Under the assumption of weak inhomogeneity, a scaling form is deduced for motor speed as a function of fuel concentration and swimmer size. We argue that this form should be robust and demonstrate a good fit to experimental data.

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.

Analysis and finite element simulation of bimetallic backward rod extrusion

In this paper, the process of bimetallic backward rod extrusion through a conical punch, by means of upper bound method and finite element method is investigated. An admissible velocity field is developed and then by calculating the internal, shear and frictional powers, the extrusion force is estimated. The extrusion process is also simulated by using the finite element code, ABAQUS. Analysis and simulations are done for two types of bimetallic rods: aluminium as core, copper as sleeve (Al-Cu) and copper as core, aluminium as sleeve (Cu-Al). The extrusion force from the upper bound method is compared with the finite element results. This comparison shows that the upper bound predictions are in good agreement with the finite element results. The results also show that, the extrusion force in the case of Cu-Al rod is smaller than Al-Cu rod and in both types of bimetallic rods, the aluminium leaves the deformation zone sooner than the copper. Finally the effects of various extrusion parameters, such as the friction factor, reduction in area and semi-punch angle upon the extrusion force are investigated and the optimum semi-punch angle is determined.

A Comparison Between Cold-Welded and Diffusion-Bonded Al/Cu Bimetallic Rods Produced by ECAE Process

In this research, the application of equal channel angular extrusion process to produce both the cold-welded and diffusion-bonded Al/Cu bimetallic rods is assessed. The joints shear strength for both of the methods are measured and compared. The microstructure examinations were also carried out using scanning electron microscope equipped with EDX system and x-ray diffraction analysis. The results exhibit that the strength of the bond in cold-welded specimens is dependent on the amount of stretch and pressure at the materials interface. But in the diffusion-bonded specimens, it is depended on the struggle between the oxidation rate of the mating surfaces accompanied by inter-metallic compounds formation and the aluminum and copper atoms ability to diffuse in the joint interface.

Chemotactic Behavior of Catalytic Motors in Microfluidic Channels

Chemotactic Behavior of Catalytic Motors in Microfluidic Channels

Autonomous Motion of Metallic Microrods Propelled by Ultrasound

Autonomously moving micro-objects, or micromotors, have attracted the attention of the scientific community over the past decade, but the incompatibility of phoretic motors with solutions of high ionic strength and the use of toxic fuels have limited their applications in biologically relevant media. In this letter we demonstrate that ultrasonic standing waves in the MHz frequency range can levitate, propel, rotate, align, and assemble metallic microrods (2 μm long and 330 nm diameter) in water as well as in solutions of high ionic strength. Metallic rods levitated to the midpoint plane of a cylindrical cell when the ultrasonic frequency was tuned to create a vertical standing wave. Fast axial motion of metallic microrods at ~200 μm/s was observed at the resonant frequency using continuous or pulsed ultrasound. Segmented metal rods (AuRu or AuPt) were propelled unidirectionally with one end (Ru or Pt, respectively) consistently forward. A self-acoustophoresis mechanism based on the shape asymmetry of the metallic rods is proposed to explain this axial propulsion. Metallic rods also aligned and self-assembled into long spinning chains, which in the case of bimetallic rods had a head-to-tail alternating structure. These chains formed ring or streak patterns in the levitation plane. The diameter or distance between streaks was roughly half the wavelength of the ultrasonic excitation. The ultrasonically driven movement of metallic rods was insensitive to the addition of salt to the solution, opening the possibility of driving and controlling metallic micromotors in biologically relevant media using ultrasound.

Equal Channel Angular Pressing of Cu-Al Bimetallic Rod

Coextrusion and corolling are the major processes to produce bimetallic rods, tubes and wires, the objective being to perform clad metals, bimetallic joints or seals. The aim of the present work is to produce bimetallic rods showing an ultrafine grained microstructure with enhanced properties. Bimetallic Cu-Al rods were deformed by equal channel angular pressing (ECAP) in order to study their microstructure. ECAP is an interesting process for producing bulk materials with refined microstructure and, consequently, changes in physical, chemical and mechanical properties can be observed. Higher shear strength and dimensional stability are among the advantages of this process. A comparative experimental study of pure commercial copper with cylindrical inner aluminium rods of different diameters processed by one-pass equal channel angular pressing has been carried out. The ECAP die used in this research was a 90º 2-channels intersecting angle. Electron backscattered (EBSD) and X-ray diffraction techniques were used for microstructure characterization (deformation, grain fragmentation and microstrain evaluation) at the interfaces and away from them. It was found that the microstructure in the ECAP deformed Cu-Al bimetallic rods was influenced by the dimensions of the aluminium inner rod. In fact, the microstructure appeared to be much more elongated and refined in the samples containing smaller diameter aluminium rods.

An investigation on diffusion bonding of aluminum to copper using equal channel angular extrusion process

A new method for production of bimetallic rods, utilizing the equal channel angular extrusion (ECAE) process has been introduced before by previous researchers, but no attempt has been made to assess the effect of different temperatures and holding times in order to achieve a diffusional bond between the mating surfaces. In present research copper sheathed aluminum rods have been ECAEed at room temperature and subsequently held at a constant ECAE pressure, at different temperatures and holding times to produce a diffusional bond between the copper sheath and the aluminum core. The bonding quality of the joints was examined by shear strength test and a sound bonding interface was achieved. Based on the results, a bonding temperature of 200°C and holding time of 60–80min yielded the highest shear strength value.

Fabrication of bimetallic rods consist of a Zr-based bulk metallic glass and a crystalline copper by co-extrusion

In this preliminary work, we demonstrated rod-type Zr 44Ti 11Cu 9.8Ni 10.2Be 25 (LM1B) bulk metallic glass/crystalline copper composites fabricated by co-extrusion. The co-extrusion tests were carried out at three different temperature-punch speed combinations within supercooled liquid region of the LM1B bulk metallic glass. The influence of process conditions on the homogeneity of the area fraction between core and sleeve along the extrusion axis, the existence and thickness of the interface layer with or without defect, and overall strength of this bimetallic compound was systematically investigated by various experiments.

A new method for producing bimetallic rods

In this research, a new method for producing bimetallic rods is introduced. The method is a new application of equal channel angular extrusion (ECAE) process. Advantages of using this method can be expressed as; good dimensional control on both the core and clad layer, possibility of performing the process in more than one pass which can result in larger bonding strength, and the possibility of performing the process in different temperatures which is critical for producing most of the bimetallic joints as well as aluminum–copper joint. The shear strength obtained using this method is compared with the same final product produced by general extrusion process. While the shear strength after the first pass of ECAE is almost equal to the sample produced by general extrusion process, using two passes of ECAE result in a 12.5% increase in the shear strength of the joint.

Use of powder metallurgy preforms as alternative to produce bimetallic tubes

Coextrusion is one of the major processes used to produce bimetallic rods, tubes and wires. Previous investigations into the coextrusion of wrought metals have shown that, for the production of a sound coextrusion, the available processing zone is very narrow, with little flexibility in terms of tool and process parameter selection. These limits have many practical implications in the selection of suitable material and process parameter combinations. The present investigation envisages the production of sound bimetallic tubes by controlling the initial materials characteristics through the powder metallurgy (PM) and cold extrusion route. It is shown that the consolidation of PM preforms during extrusion reduces the differential velocity between the core and the sleeve, and high friction at the interface aids sound flow over a wide range of processing conditions. In addition, the non-uniformities of deformation (especially on the hard metal side) are accommodated by the softer preform near the interface, through micromechanical interaction. The present approach implies manufacturing flexibility and reduction of tool/amortisation costs for the production of bimetals.

Theoretical analysis and optimisation of parameters in extrusion process of explosive cladded bimetallic rods

The article discusses the problem of theoretical choice of the optimal shape of extrusion die and extrusion ratio during the extrusion process of aluminium rods copper cladded with the help of the explosive method to join the core and the coat. Mathematical model of extrusion process based on finite elements method was worked out to attaining the objective. The model makes it possible to carry out the analysis of mechanical state (stress and strain) on the boundary of layers for the sake of main parameters of the process. Optimal values of process parameters were obtained basing on the mathematical analysis for bimetallic rod with outer diameter 18 mm and copper layer thickness 2 mm.

Theoretical and experimental analysis of the rolling process of bimetallic rods Cu-steel and Cu-Al

In this study, the authors present the results of their theoretical and experimental analysis of the rolling process of bimetallic rods in stretching passes. The bimetallic rods had different ratios of the yield stress between components. The original rods were round (21.7mm diameter) steel and aluminium rods, covered with 2.8mm copper layer. A numerical model for hot stretching passes rolling was proposed. In the model, the deformation of a bimetallic material was analysed by three-dimensional rigid–plastic finite-element method. The model simulated metal flow during rolling of bimetallic rods in round–oval series. The results of the experiments were compared with the finite-element calculations of the stress distribution and spread of Cu-steel and Cu-Al rods in the deformation zone. The analysis demonstrated that an appropriate selection of shape and size of oval pass allows production of even distribution of the copper layer in the bimetallic roll products. The results of comparison of calculated spread and experimental data confirmed good ability of proposed mathematical model, that is recommended for roll pass design at rolling of bimetallic rods.

Theoretical analysis of bimetallic rods extrusion process in double reduction die

The analysis of strain–stress state in bimetallic rods composed from two different metals was done in this work. The analysis was accomplished for two different extrusion ratios in conical die and in double reduction die. The initial material was composed from copper coat and pure aluminium core by explosive method.During the extrusion process of such composites there can be differences between material properties of components that caused significant non-uniform metal flow in deformation zone and appearing defects like chevron cracking or delamination (for composed rods) especially for significant total elongation. It is proposed to use the double reduction die to decrease the values of tensile stresses and maximal stresses between component layers. The results of approximation of mathematical experiment allowed carrying out an equation helpful to define the maximal stress σxmax on a boundary between layers of bimetal. FORGE2® commercial software based on the FEM was applied to analysis.

Theoretical and experimental analysis of stress and temperature distributions during the process of rolling bimetallic rods

In this study, the authors present the results of their theoretical and experimental analysis of the rolling process of bimetallic bars in stretching passes. For the experimental analysis, a bimetallic bar was manufactured using an explosive technique method. A numerical model for hot stretching passes rolling was proposed. The model simulated metal flow during rolling of bimetallic bars in edge oval–oval series. The original bars were round (21.7 mm diameter) steel rods, covered with 0.85 and 1.8 mm thick copper layer. The finished products were bimetallic bars, 14 mm in diameter. The rolling was performed in a laboratory mill with 320 mm diameter rolls, which rotated at the speed of 30 rpm. The bars were heated in an electric chamber furnace to the temperature of 960 °C. The results of the experiments were compared with the finite-element calculations of stress and temperature distributions of copper–steel rods in the deformation zone.

Fabrication of bimetallic rods by explosive cladding and warm extrusion

Abstract The fabrication of bimetallic aluminium sheathed/copper axisymmetric rods by explosive cladding and subsequent warm extrusion is reported. The effect of the cladding and the extrusion parameters on the macro- and the microscopic features and the soundness of the product at the various stages of the fabrication are indicated using microhardness testing and optical metallography. By employing warm extrusion as a post-welding forming technique, instead of the cold extrusion, the soundness of the components is improved due to advantageous plastic flow of the extruded composite rod at elevated temperatures and the minimization of the characteristic extrusion defects. A theoretical analysis pertaining to the extrusion of axisymmetric bimetallic rods is proposed.

Plastic deformation of porous axisymmetric bimetallic rods in rigid dies

Plastic deformation of porous axisymmetric bimetallic rods in rigid dies

An Immunoelectron-microscopic Study of the Immunoglobulin-synthesizing Cells of the Rheumatoid Synovial Membrane

Bimetallic devices composed of silver and platinum were placed in the periosteum of the right femora of 20 rats. In 40 additional rats silver or platinum rods were placed in the right femora. After six weeks there was an increase in ash weight and 85Sr activity in the femora from the animals with bimetallic rods as compared with those in which pure silver or platinum rods were implanted. After three months no differences were found between the groups.

Induction of partial limb regeneration in Rana pipiens by galvanic stimulation.

AbstractForelimbs of small adult frogs (Rana pipiens) were amputated and the stumps implanted with silver‐platinum bimetallic rods insulated except at the tips. The silver end was at the wound surface in some cases. In others, the platinum end was distally placed. Other animals received separate implants of short pieces of bare silver and platinum wire, with the silver piece placed near the wound surface. Controls consisted of animals with either no implant or implants of partially insulated silver or platinum wire.Only one of the control animals (one with a silver implant) initiated regeneration. Regeneration was minimal with the separate implants (25%), more frequent with the platinum end of a bimetallic couple at the wound surface (70%), and most frequent (83.4%) with the silver end of a bimetallic couple at the wound surface. In three cases in the last named series, lobulated cartilages reminiscent of wrist and hand elements differentiated. The results are ascribed to direct stimulation of the cells, electrophoretic transfer of information‐bearing molecules, or stimulation of nerves.