Bulk Shapes Research Articles

Spark plasma sintering for multi-scale surface engineering of materials

Recently, significant progress has been made in understanding the effect of multi-scale microstructural features, including nano-, micro-, and macro-features, on the properties of materials. Controlling the length scale of micro-structural features provides tremendous opportunities for enhancing the properties of materials, including extraordinary strength and hardness, unprecedented damage from tribological contacts, and improvements in a number of functional properties of the materials. Spark plasma sintering (SPS) process which combines the effects of uniaxial pressure and pulsed direct current is becoming increasingly important for the processing of bulk shapes of amorphous and nanostructured materials. These materials can also be good candidates for high-performance coatings. This article presents a review of our ongoing efforts to use SPS to produce engineered coatings of amorphous and nanostructured materials for various applications, including structural, tribological, and biomedical applications.

In situ phase separation and flow behavior in the glass transition region

The temperature dependence of length change and viscous flow of the Cu 36Zr 48Al 8Ag 8 glassy alloy is examined in both the glass transition and supercooled liquid regions. Moreover, this alloy is found to exhibit phase separation rather by binodal mechanism in the glassy phase prior to crystallization. There is an apparent decrease in viscosity observed upon crystallization that is connected with the densification of the sample, but the intrinsic viscosity does not rise significantly until the initial crystallization process is almost complete. During the process the partly crystallized supercooled liquid still behaves like a fluid until a large fraction of the crystalline phase (∼90%) is formed. This new insight on flow behavior opens up possibilities for innovative processing of precise bulk shapes with high nanocrystal densities.

ナノカーボン系材料のフィラーとしての展望 Ｌｉ‐ｉｏｎ電池用負極材の現在と未来

A variety of carbon materials provide a series of unique properties, reflecting their nano, micro and macro structures. Controlled production of their nano structure, size and shape is a key technology to prepare the optimum material of unique properties. Thus, a variety of carbons and their composites of various bulk structures, shapes, sizes, and surface areas have been produced to apply for the battery application. In this paper, carbons and their composites as effective anode materials for Li-ion battery are reviewed based on the nano-structural analyses. Systematic examinations of carbon materials with unique nano structure can provide promising chances of improving the optimum performance toward particular application, enhancing their excellent performances.

RUBBLE-PILE RESHAPING REPRODUCES OVERALL ASTEROID SHAPES

There have been attempts in the past to fit the observed bulk shapes (axial ratios) of asteroids to theoretical equilibrium figures for fluids, but these attempts have not been successful in many cases, evidently because asteroids are not fluid bodies. So far, however, the observed distribution of asteroid macroscopic shapes has never been attributed to a common cause. Here, we show that a general mechanism exists, capable of producing the observed shape distribution. We base our approach on the idea that aggregates of coherent blocks held together mostly by gravity (gravitational aggregates) can change their shape under the action of external factors, such as minor collisions, that break the interlocking of the constituent blocks, thus allowing them to asymptotically evolve toward fluid equilibrium. We show by numerical simulations that this behavior can produce a shape distribution compatible with the observations. Our results are shown to be consistent with a simple interpretation based on the topology of the potential energy field for rotating bodies. Also, they suggest that most asteroids have an internal structure that is at least partially fragmented, consistent with constraints derived from large asteroids (diameters >100 km) with satellites.

Bulk glass formability for Cu–Hf–Zr–Ag and Cu–Zr–Ag–Si alloys

The effects of the gradual substitution of Zr by Hf on glass formability and thermal stability in the Cu45Zr45−xHfxAg10 alloys and the effects of small additions of Si on glass formability in the Cu45Zr45Ag10 alloy are reported and discussed. The samples were prepared as ribbons of thickness in the range 25–200 μm by melt spinning and as conical bulk shapes, with a length of 50 mm and cone base diameters in the range 2–10 mm, by suction die casting. The alloy Cu45Zr45Ag10 had a critical cylindrical rod diameter for glass formation, dc, of 3.5 mm but substitution of 1.5 and 3.5 at.% Zr by Hf resulted in substantial increases to 5.5 and 4.5 mm, respectively. However, for x in the range 5–40 at.%, dc was reduced to <1 mm. The small addition of Si proved to be beneficial to the glass forming ability (GFA), increasing dc up to 5.5 mm for 0.5 at.% Si. Thus the chemical and atomic size similarities of Hf and Zr do not guarantee that bulk glass formation will be maintained on substituting large proportions of Zr by Hf though small substitutions of Hf and of minor additions of Si were beneficial to the GFA. These effects are discussed in terms of the possible influence of the alloying additions on the liquid structure and on the number density of heterogeneous nucleants.

Investigations into the movement of milled medium in the bowl of a ring-roller mill

This paper presents the results of testing the grind material movement in a ring-roller milling system. The tests were carried out in a 1:4 scale model of an RP-1043x`milling system. The aim of the test was to determine material bulk shapes within a range of parameter changes of a model grinding system i.e. table–roller distancing, pile-up ring height, coal feed and table's rotary speed. Based on the measurements of material layer thickness on the table, its average radial velocity was calculated. The results were then supplemented with tests based on the movement of markers over the surface layer of the coal bulk. These tests enabled the material's average radial and tangential velocities in the surface layer to be determined.

Synthesis and Catalytic Applications of Self‐Assembled Carbon Nanofoams

A new surfactant-templated carbon material, carbon nanofoam (CNF), has been synthesized with a semicrystalline and conductive framework, high surface area and interconnected porous structure, and prepared in a wide variety of bulk shapes and forms. CNF was also successfully applied as a support for palladium in the Heck coupling reaction. Pd/CNF catalyst exhibited negligible Pd cluster growth and agglomeration, and retained high activity even after multiple runs.

Numerical Evaluation of Rotational Speed Degradation in the Superconducting Magnetic Bearing for Various Superconducting Bulk Shapes

In constructing the 100 kWh flywheel energy storage systems, the performance of the Superconducting Magnet Bearing (SMB) needs to be calculated to get better technical and practical results. The SMB system mainly consists of the Superconducting (SC) stator and the Permanent Magnet (PM) rotor. The SMB has the advantage that the rotational dragging force between the PM rotor and the SC stator is greatly smaller compared with the usual bearing systems. However, the magnetic friction becomes large enough to cause significant rotational speed degradation. The rotational speed degradation, which cuts down the stored energy, occurring in the PM rotors is one of the most significant problems for the practical use of the SMBs. It is caused mainly by the Lorentz force due to the inhomogeneous magnetic field of the SC stator and the induced eddy current in the PM rotor. In this study, we tried up various shapes of the SC stator to smooth the magnetic field and decrease the energy loss and then evaluated the levitation force, the magnetic field of the SC stator and the energy loss.

Meso/Macroporous Inorganic Oxide Monoliths from Polymer Foams

Low‐density bimodal inorganic oxide monoliths (see Figure) have been prepared via a two‐step procedure using macroporous polystyrene foams and amphiphilic block copolymer structure‐directing agents. The resulting meso/macroporous inorganic framework structures could be obtained with different 3D bulk shapes and for a range of inorganic oxides, as demonstrated here for silica, zirconia, and titania.

Egg White as an Environmentally Friendly Low‐Cost Binder for Gelcasting of Ceramics

Slurries with different solids loading (34–50 vol%) of alumina were made with egg white (ovalbumin)–water premix. The ovalbumin content in the premix was decreased with increase in solids loading to lower slurry viscosity. The slurries were cast into bulk shapes and heated to 80°C, resulting in denaturation of ovalbumin forming a gel. The gelled samples were dried under controlled humidity and sintered in air to densities 94%–97% of theoretical. Alumina slurries formed with egg white (no water) were used to form tapes as thin as 60 μm in the sintered state.

Basic LOgical Bulk Shapes (BLOBs) for Finite Element Hexahedral Mesh Generation to Support Virtual Prototyping

Manufacturability analysis of product design reduces the downstream problems of manufacturing. Such design approaches are referred to as Virtual Prototyping when performed on the computer. In the present research, Virtual Prototyping is facilitated by the use of an automated method of determining the finite element meshes needed to perform finite element analyses. Finite element analysis requires a finite element mesh of the product model as input. This mesh (an approximation of an object’s geometry and topology, composed in terms of a given individual unit, e.g., a tetrahedron, or a hexahedron), can be generated using a variety of methods. The research presented here offers an approach for automatic mesh generation that addresses some of the limitations in the mesh-generation technologies currently available. This article presents an approach for automatically generating hexahedral meshes from solid models. The mesh generating method presented in this paper involves four major steps. First, objects called Basic LOgical Bulk shapes (BLOBs) are determined from the solid model of a given part. Second, these BLOBs are used to decompose the solid model into its various sub-volumes. Third, a multiple-block structure (MBS), which is a group of hexahedral objects, is constructed to approximate the solid model. Finally, transfinite mapping is employed to project the faces of the MBS onto the surfaces of a model to generate the finite element meshes.

Stability and losses of levitating superconducting disks and cylinders

The authors present a model for calculating the levitation force, magnetic stiffness and damping for a superconductor in the presence of the magnetic field of a permanent magnet. Bulk and thin film shapes are chosen for the superconductor. They compare the results for both and conclude that, in general, the thin film shape enhances the magnitude of the force while maintaining a good stability and without increasing the losses associated with small displacements.

Porous Ca–P–O bio-glassceramics by loose-powder-sintering

Porous resorbable Ca–P–O glassceramic tooth roots based on calcium biphosphate were prepared by loose-powder-sintering then crystallization-annealing. The glass composition is, by weight, CaO/(CaO + P2O5) = 0.33. The sintering behavior of the glass can be described by a conventional viscous flow model. The resultant glassceramic has a pore size of 6 to 36 μm, depending on starting particle size and sintering temperature, while the pore size distribution is independent of sintering time. The flexural strength is 33 to 150 MPa depending mostly on crystallization-annealing treatment. The crystalline phases are β−Ca2P2O7 and CaP2O6. After being implanted into rabbits, these porous implants show remarkable biocompatibility and induce the ingrowth of new bone within 30 days. They are partly resorbed after 90 days and replaced by new bone. In spite of the original small porosity, the ingrowth of blood vessels and bone cells is abundantly seen after 90 days, due to enlarged pores produced by progressive resorption. This glassceramic is a good candidate for resorbable tooth and bone implants. The loose-powder-sintering technique resulting in intricate bulk shapes with controllable pore size distribution and good machinability as well as adjustable mechanical strength hence is a powerful technique for the preparation of porous glassceramics.

Multicomponent sorption kinetics of hydrocarbons in activated carbon: Simultaneous desorption and displacement

Binary desorption and displacement kinetics of ethane and propane in Ajax activated carbon are studied in this paper to further understand the multicomponent adsorption of light hydrocarbons onto activated carbon. The experimental data are collected using a differential adsorption bed over a range of temperatures, bulk concentration combinations, particle sizes and shapes. A macropore, surface and micropore diffusion (MSMD) model recently proposed by Hu and Do (Chem Eng Sci (1993) 48 1317) is used in the analysis of experimental data. This model takes into account the concentration dependency of the surface diffusivity. Both diffusions of free and adsorbed species are allowed for in the theory. The adsorbed species are assumed to diffuse in the particle as well as in the microparticle (grain) coordinates. An imaginary gas-phase concentration concept is used to calculate the local diffusion flux of the adsorbed species inside the microparticle. The local multicomponent adsorption equilibrium at any point within the particle is calculated using the ideal adsorbed solution theory (IAST), with the single-component adsorption equilibrium data described by a Unilan equation.

Radiation damage in Mo 75Re 25 superconducting thin films by He +-particles

The excellent transport properties of superconductors compared to normal conductors make them suitable for a wide range of applications. Low-T c metallic-type superconductors, for example, are utilized in the accelerators environment both in bulk and thin film shapes. One of the requirements these materials must satisfy is their radiation hardness with respect to the particles utilized in the accelerators. This work deals with the study of the radiation hardness of superconducting thin films of Mo 75Re 25, a compound that presents interesting features for its utilization as coating for the accelerating cavities. Two Mo 75Re 25 superconducting thin-films have been investigated together with a Nb one for comparison. The films have been irradiated by means of 2MeV He +-particles, the Mo 75Re 25 films with three successive doses, whereas the Nb one with two. The experimental set-up and some preliminary measurements are described, together with a theoretical extimation of the surface resistance of the materials (the most important parameter to be considered for the application to accelerating cavities). The results obtained show a higher radiation hardness of Mo 75Re 25 films compared to the Nb one for what concerns the degradation of T c and of the residual resistivity; also the calculated values of the surface resistance result less sensible to radiation in Mo 75Re 25 samples than in the Nb one.

Mechanical alloying—a novel synthesis route for amorphous phases

Mechanical alloying (MA) pioneered by Benjamin is a technique for the extension of solid solubility in systems where the equilibrium solid solubility is limited. This technique has, in recent years, emerged as a novel alternate route for rapid solidification processing (RSP) for the production of metastable crystalline, quasicrystalline, amorphous phases and nanocrystalline materials. The glass-forming composition range (GFR), in general, is found to be much wider in case of MA in comparison with RSP. The amorphous powders produced by MA can be compacted to bulk shapes and sizes and can be used as precursors to obtain high strength materials. This paper reports the work done on solid state amorphization by MA in Ti-Ni-Cu and Al-Ti systems where a wide GFR has been obtained. Al-Ti is a classic case where no glass formation has been observed by RSP, while a GFR of 25–90 at.% Ti has been obtained in this system, thus demonstrating the superiority of MA over RSP. The free energy calculations made to explain GFR are also presented.

Rapidly solidified Mg-Al-Zn-Rare earth alloys

Among the light metal alloys, magnesium is the lightest structural material except for beryllium, and yet magnesium alloys have not seen extensive use because of their poor strength and corrosion resistance. Rapid solidification technology offers a possible solution to these problems. A number of Mg-Al-Zn alloys containing rare earth (RE) elements (e.g. Ce, Pr, Y, and Nd) have been investigated using rapid solidification processing for possible structural applications. The processing consists of planar flow or jet casting into ribbons, pulverization of ribbon to powder, and consolidation of powder into bulk shapes. The mechanical properties of some of these alloys show attractive combinations of strength (UTS-513 MPa), ductility (tensile elongation-5%) and corrosion resistance [corrosion rate of 11 milligrams per square decimeter per day (mdd) in 3% NaCl solution]. The microstructures of these alloys are correlated with their mechanical properties. The rapidly solidified Mg-Al-Zn-RE alloys show great potential for applications in automotive and aerospace industries.

Physical vapour deposition processes

Physical vapour deposition (PVD) is the process whereby metals and alloys may be transferred in the vapour state from one source to another. It was known as early as 1857, and since 1912 has been operated in vacuum form, both experimentally and commercially, for applying coatings and fabricating bulk shapes. Over the years the basic PVD process has been modified and used in a number of different ways, and these have been given different names. The development of this sometimes conflicting and confusing nomenclature is reviewed as an introduction to a discussion of the background and present status of the PVD process for depositing overlay protective coatings on gas turbine components, a process which has been in use commercially for over 15 years. The requirements for this application are very different from those for most other uses, and these are discussed in terms of their effects on the adherence, structure, and post–coating processing of the applied coatings. The limitations of the process, such as required compositional ranges, growth defect tolerance, line–of–sight deposition, low–angle coatings, and the ability to deposit elements having widely different vapour pressures, are considered. The latest forms of the PVD process are discussed in terms of how these limitations affect them. The present status of PVD processes is examined in the light of the current economic climate and future technological developments.MST/283

Physical vapour deposition processes

AbstractPhysical vapour deposition (PVD) is the process whereby metals and alloys may be transferred in the vapour state from one source to another. It was known as early as 1857, and since 1912 has been operated in vacuum form, both experimentally and commercially, for applying coatings and fabricating bulk shapes. Over the years the basic PVD process has been modified and used in a number of different ways, and these have been given different names. The development of this sometimes conflicting and confusing nomenclature is reviewed as an introduction to a discussion of the background and present status of the PVD process for depositing overlay protective coatings on gas turbine components, a process which has been in use commercially for over 15 years. The requirements for this application are very different from those for most other uses, and these are discussed in terms of their effects on the adherence, structure, and post–coating processing of the applied coatings. The limitations of the process, s...

Hot Consolidation/Devitrification of Metallic Glasses — Novel Multiphase Crystalline Alloys in Bulk Shapes With Technological Potentials

ABSTRACTIron, nickel and/or cobalt base metallic glasses with low contents of metalloids, predominantly boron, upon heat treatment at temperatures well above crystallization temperature of the glassy phase transform into ultra-finegrained (microcrystalline) alloys containing finely dispersed boride phases.Microcrystalline alloys devitrified from glassy phase are characterised by high strength, excellent thermal stability and superior corrosion/oxidation resistance. Mechanical properties of bulk microcrystalline alloys hot consolidated-devitrified from selected low metalloid metallic glass alloys are reported.