Inter-rod Spacing Research Articles

Hybrid Network Structure and Mechanical Properties of Rodlike Silicate/Cyanate Ester Nanocomposites

Silicate nanorods (attapulgite, ATT) were organically modified and homogeneously dispersed in a cyanate ester (CE) resin. ATT dispersions and networks were characterized by rheological and microscopic measurements. Amine groups grafted onto the particle surface catalyzed the cyclotrimerization of the CE monomers and enabled the CE monomers to enter the inter-rod spacing of loose aggregates easily, resulting in homogenization of the particle size distribution in the nanocomposites. The addition of nanorods decreased the density of organic networks and increased intracyclizations. Covalent bonding at the interface was confirmed by Fourier transform infrared (FTIR) spectroscopy and dynamic mechanical analysis (DMA), which establishes a basis for enhancing/ optimizing mechanical properties of CE resins. Nanocomposite modulus, strength, and toughness increased 40, 42, and 55%, respectively, relative to the neat resin, although high nanorod loadings (e.g., 8 wt %) showed negligible benefit. The interplay between nanorod and resin networks governed the mechanical properties of the nanocomposites. The curing reaction decreased the size of particle aggregates and thus reduced the percolation threshold of particle networks. Particle networks induced the formation of more linear or branching polymer molecular structures, resulting in weaker particle-matrix interactions. These factors reduced the stress transfer efficiency and crack propagation resistance, impairing the extent of reinforcing at high particle loadings.

Fabrication and characterization of Fe 3O 4-based Cu nanostructured electrode for Li-ion battery

Fe 3O 4-based Cu nanostructured electrodes for Li-ion cells are fabricated by a two-step electrochemical process. Cu nanorod arrays acting as current collectors are first prepared on a thin copper disk by alumina template-assisted electrodeposition. The active material of Fe 3O 4 is electrochemically deposited onto the Cu nanorod arrays by potentiostatic deposition. X-ray diffraction identifies textured growth for both the Cu nanorods and Fe 3O 4. Scanning electron microscopic observation further reveals that the active material are deposited between the Cu nanorods, and a 30 s deposition of Fe 3O 4 is sufficient to fill up the inter-rod space under the currently employed condition. Longer electroplating time leads to the coalescence of Fe 3O 4 particles and the formation of bulky Fe 3O 4 islands on the top of the Cu nanorods. Electrochemical properties of the nanostructured electrodes are studied by conventional charge/discharge tests. The results show that the rate capabilities of the nanostructured electrodes are better compared to those of the planar electrodes and the coalescence of Fe 3O 4 particles is detrimental to achieve sustained reversible capacities.

Low temperature synthesis of single crystalline ZnO nanorods by oblique angle deposition

The authors report the growth of single crystalline ZnO nanorods by direct current magnetron sputtering in the oblique angle deposition configuration near room temperature. These isolated nanorods have a diameter of ∼ 40 nm, an inter-rod spacing of ∼ 20 nm, and a height of ∼ 100 nm. The nanorods show a (002) orientation along the rod-axis which is normal to the substrate. The low temperature fabrication of single crystal ZnO nanorods may find potential applications in optoelectronics and energy conversion devices.

Microstructure and properties of Si-TaSi2 eutectic in situ composite for field emission

The Si-TaSi2 eutectic in situ composite for field emission is prepared by electron beam floating zone melting (EBFZM) technique on the basis of Czochralski (CZ) crystal growth technique. The directional solidification microstructure and the field emission properties of the Si-TaSi2 eutectic in situ composite prepared by two kinds of crystal growth techniques have been systematically tested and compared. Researches demonstrated that the solidification microstructure of EBFZM can be fined obviously because of the relatively high solidification rate and very high temperature gradient, i.e. both the diameter and inter-rod spacing of the TaSi2 fibers prepared by EBFZM technique were decreased, and the density and the volume fraction of the TaSi2 fibers prepared by EBFZM technique were increased in comparison with that of the TaSi2 fibers prepared by CZ method. Therefore the field emission property of the Si-TaSi2 eutectic in situ composite prepared by EBFZM can be improved greatly, which exhibits better field emission uniformity and straighter F-N curve.

Microstructure characteristics and interface morphology evolvement of Si-TaSi 2 eutectic in situ composite for field emission

As one of the semiconductor-metal eutectic (SME) composites, Si-TaSi 2 eutectic composite has many characters such as the high melting point of TaSi 2 material, the large density of TaSi 2 fibers incorporated into the Si matrix, three-dimensional array of Schottky junctions grown in the composite spontaneously. So it is an ideal candidate for field emission array cathodes. In this paper, the directionally solidified Si-TaSi 2 eutectic in situ composite for field emission is prepared by means of the electron beam floating zone melting (EBFZM) technique on the basis of Czochralski (CZ) method. The Si-TaSi 2 eutectic in situ composite, which has high-aligned and uniformly distributed TaSi 2 fibers in the Si matrix, can be obtained when the solidification rate changes from 0.3 to 9.0 mm/min. As the solidification rate is increased, both the fibers’ diameter and inter-rod spacing are decreased, while the fibers’ density and the volume fraction are increased. Moreover, the transition from a planar interface to cellular interface and then to planar interface morphologies with increasing velocity is observed with the zero power method.

Effect of high magnetic fields on the microstructure in directionally solidified Bi–Mn eutectic alloy

The eutectic Bi/MnBi alloy has been directionally solidified in the presence of an axial magnetic field to investigate the influence of high magnetic fields on the growth of eutectic Bi/MnBi. The morphology and magnetic properties of the specimens indicate that a high magnetic field promotes the formation of MnBi fiber and makes the directional solidification structure of the eutectic more regular. The MnBi inter-rod spacing and rod diameters gradually increase with the magnetic field intensity. Furthermore, the magnetic field enhances the faceted growth of MnBi phase and the magnetic coercivities of the alloy. This may be attributed to the magnetic anisotropy and the shift of the eutectic point by the magnetic field.

Discontinuous precipitation in {100} planes in a Cu–5.7 wt% Ag alloy single crystal

The formation and growth of disc-shaped aggregates consisting of rod-shaped Ag precipitates and Ag-depleted Cu matrix in the {100} planes in single crystals of a Cu–5.7 wt% Ag alloy have been investigated by transmission electron microscopy. The formation of the aggregates begins on dislocations and their growth progresses through a discontinuous process without existing dislocations. The aggregates grow at a constant velocity in an isothermal condition, maintaining a constant inter-rod spacing. A kinetic analysis of the aggregate growth using the model of Zener has yielded values of the diffusivity of Ag in Cu. The estimated activation energy for diffusion is 185 kJ mol−1.

Joining of NiAl to iron-based alloys by reactive casting

Nickel monoaluminide, NiAl, is exothermically synthesized from elemental liquids of aluminum and nickel and is simultaneously joined to iron-based alloys, such as carbon steels and stainless steels, by the reactive casting method, which is based on the pouring of the elemental liquids onto the base material. The exothermic reaction between the aluminum and nickel liquids produces extremely superheated NiAl liquid. Heat of the NiAl liquid is transferred to the base material, and the contact surface is melted to a depth depending on both the preheating temperature of the base material and the thickness of the NiAl produced. After solification on the base material, NiAl is strongly joined to the base material, showing a joint strength exceeding the inherent strength of NiAl. The high joint strength is attributed to a very fine, rodlike eutectic structure at the joint interface that consists of a mixture of β-NiAl and γ-iron with an interrod spacing of approximately 100 nm.

Eutectic spacing and faults of directionally solidified Al–Al3Ni eutectic

The Al–Al3Ni eutectic was directionally solidified at a thermal gradient of 4.5 K/mm in a vacuum Bridgman–type furnace in order to study eutectic spacing selection criterion.The microstructure was examined in transverse and longitudinal sections and the interrod spacings were measured at different growth velocity. It has been shown that the interrod spacing is not unique and displays a limited range for rodlike Al–Al3Ni eutectic alloy. The initial growth velocities are not responsible for the eutectic spacing range, while such faults as branching, endingand diameter change have a significant influence on the eutectic spacing adjustment.

Modeling of chemical interactions of fuel rod materials at high temperatures II. Investigation of downward relocation of molten materials

In Part II of the modeling of chemical interactions of fuel rod materials at high temperatures, qualitative results on the nature of Zr-rich melt oxidation and interactions with fuel rods allow further interpretation of the post-test examinations of structures (debris) formed in the CORA tests under more complicated conditions, namely during downward relocation of the melt. In this situation, the molten mass extensively oxidizes and simultaneously dissolves UO 2 pellets and ZrO 2 scales of the cladding. The analysis of these simultaneous physico-chemical processes on the basis of the kinetic oxidation/dissolution model developed in Part I of the paper, allows a new interpretation and explanation of the CORA tests results concerning relocation dynamics of the major part of the melt (slow relocation of melt in the form of massive slug rather than quick relocations of droplets and rivulets), formation of local blockages (debris) in the interrod space and accumulation of the melt in the core region in the form of molten pool.

Directional solidification and magnetic properties of MnSb–Sb eutectic composite

The microstructures, solidification behaviour, crystal orientation and magnetic properties of MnSb–Sb eutectic with a high entropy of solution have been studied systematically. The present approach reveals the inherent correlations between them. MnSb–Sb eutectic is characterized by a non-faceted–non-faceted type of growth and well-distributed aligned MnSb rods embedded in a Sb matrix on a micron scale, an ideal composite structure, during directional solidification. The scaling laws of the variation in interrod spacing λ (or rod diameter d) with growth velocity are quantitatively developed. A parallel orientation relation between [001] of MnSb and rod axis is identified through electron diffraction patterns, indicating that the highly anisotropic composite has been fabricated successfully. The hysteresis loops of directionally solidified MnSb–Sb composites are determined along the MnSb rod axis. The saturation magnetization and constant permeability have been evaluated by considering the alignment, size and magnetocrystalline anisotropy.

Evaluation of the rodlike cu 6sn 5 phase in directionally solidified tin — 0.9 wt.% copper eutectic alloys

Sn — 0.9 wt.% Cu alloys were directionally solidified under controlled conditions after which diameters of the aligned and rodlike Cu 6Sn 5 eutectic phase were measured as a function of the imposed growth velocity. A rod diameter ( d) and growth velocity ( V) relation of d 2 V = constant was found, which is analogous to that established for eutectic phase spacings. A discussion is presented for using the fiber diameter, in lieu of or in addition to the interrod spacing, to evaluate the relation between solidification processing parameters and the observed microstructure.

Solidification and Structural Characteristics of α(Al)–Mg<SUB>2</SUB>Si Eutectic

Solidification and structural characteristics of α(Al)-Mg 2 Si eutectic in the Al-Mg-Si system were investigated by thermoanalysis and directional solidification techniques. The two-phase eutectic line of L ⇔ α(Al) + Mg 2 Si, the temperature-change section of a pseudobinary α(Al)-Mg 2 Si system and the eutectic coupled zone within this section have been measured accurately. It was demonstrated that the coupled zone in the pseudobinary α(Al)-Mg 2 Si system could be described as C= 1.35 x 10 3 V + C 0 , where C is the molar percentage of Mg 2 Si, V is the solidification velocity in m/s, C 0 is the molar percentage of Mg 2 Si when the eutectic structure is obtained through a near-equilibrium solidification, and 3.65 mol% < C 0 < 5.0 mol%. In this system, Mg 2 Si is the nucleating and leading phase during eutectic growth, and the primary crystals exhibits a morphology of regular hexahedron with (100) faces. In the eutectic alloy, the morphology of phase Mg 2 Si transforms from lamellae to rods when the solidification velocity is higher than 1.1 x 10 -5 m/s. The relationship between the lamellar or interrod spacing, λ of eutectic Mg 2 Si and the solidification velocity, V, fits the equation λ 1.93 V = 7.1 x 10 -17 G -0.414 where G is the temperature gradient ahead of the solid-liquid interface in the melt, which is in K/m, λ is in m and V is in m/s.

Discontinuous precipitation in a Zn-1.6 wt.% Al alloy

The decomposition processes in a Zn-1.6 wt.% Al alloy, homogenized at 628K and subsequently water quenched, have been studied by scanning electron microscopy during homogenization and isothermal aging at 296K. The presence of the metastable ZnAl phases was verified during homogenization, and their dissolution has given rise to the discontinuous precipitation reaction. The discontinuous precipitation cell structure consisted of the rodlike precipitates interposed in the matrix of Zn-rich solid solution. The interrod spacing coarsened during aging because of the interaction between the discontinuous precipitation cells and the continuous matrix precipitates. From the calculated volume fractions of matrix and precipitated phases during homogenization and aging, probable mechanisms of dissolution of metastable phases and discontinuous precipitation formation have been proposed.

Molecular dynamics simulation of a single-component molecular composite: poly(p-phenylene benzobisthiazole)/meta-poly(aryl ether ketone) block copolymer

Molecular dynamics simulations were performed with a model of a single-component molecular composite in the form of a block copolymer composed of poly( p -phenylene benzobisthiazole) rigid-rod and flexible meta -poly(aryl ether ketone) subunits. The molecular composite concept, applied to improve the compressive strength of rigid-rod polymers and to improve their solubility, relies on a uniform distribution of rods in a coil-like matrix. Pair distribution functions, orientation correlation functions and correlation volumes calculated from equilibrium dynamics trajectories of bulk copolymer, coil homopolymer and rigid-rod homopolymer systems imply that, while inter-rod spacing is only slightly increased in the copolymer, correlation of rod orientation is greatly reduced but to a somewhat lesser extent than previously found for a graft copolymer composed of identical subunits. Conformations of the flexible blocks extend to accommodate the partial rod alignment. The block copolymer topology appears to be a viable alternative to the hairy-rod graft copolymer as a single-component molecular composite.

Electrical microcharacterization of Si-TaSi2 eutectic composites

Semiconductor-metal eutectic composites, formed by directional solidification from the melt, are composed of arrays of continuous metallic fibers contained within a single-crystal semiconductor matrix. Such composites contain rods having diameters of ≈1 μm with inter-rod spacings on the order of 10 μm. These rods form cylindrical Schottky junctions with the Si and can be used as the basis for a variety of electronic and optoelectronic devices, including photodetectors and bulk field effect transistors. Electron beam induced current (EBIC) measurements permit the determination of the depletion zone surrounding the active regions of a semiconductor material. This method has been used to examine the carrier concentration in a Si-TaSi2 eutectic composite.A portion of an oval transistor mounted on a semiconducting wafer consisting of Si-TaSi2 eutectic material with contacted rod elements was studied. The rods were selectively contacted by a deposited CoSi2 film which provided an ohmic contact to the TaSi2 rods yet formed a rectifying Schottky barrier with the Si matrix.

Microstructural effect of elemental additions Zn, Mg, and Pb on Cd–CuCd3eutectic

The microstructure of unidirectionally solidified Cd–CuCd3 eutectic monovariant alloys containing elemental additions of Zn, Mg, and Pb was studied. The addition of either Mg or Pb resulted in changes of eutectic morphology, such as curving and branching of CuCd3 rods, which could be directly attributed to the formation of eutectic cells. The addition of Zn led to microstructural modifications even when the solid/liquid interface was macroscopically flat. Such modifications included an increase of interrod spacing, the stabilisation of a rod morphology at a velocity which produced a mixed blade–rod morphology in the pure eutectic, and the protrusion of CuCd3 phase at the solid/liquid interface. These modifications were attributed to a change of faceting behaviour of the CuCd3 phase by the addition of Zn. It is proposed that the formation of lateral facets on the CuCd3 changed the growth mechanism at the solid/liquid interfaces effecting the modifications described.MST/1009

Si-TaSi2 i n s i t u junction eutectic composite diodes

Nearly ideal diodes have been fabricated using the in situ junctions present in Si-TaSi2 semiconductor-metal eutectic composites. The composites, prepared by directional solidification at the eutectic composition, have a high density of TaSi2 rods in a quasi-single crystalline P-doped, n-type Si matrix. Analysis of the diodes using current-voltage and capacitance-voltage techniques yields a TaSi2/Si Schottky barrier height of 0.62 eV and evidence that the voltage-dependent depletion zones can be made comparable to the interrod spacing to produce a ‘‘pinch-off’’ condition.

Automated analysis of multiple performance characteristics in magnetic resonance imaging systems.

As with other digital imaging systems in heavy medical use, it is desirable with magnetic resonance imaging (MRI) to obtain extensive, rigorous system performance measures from a small set of images of one or two relatively simple test objects. Digital analysis of the parallel square rod (PSR) test object introduces digital image system self-evaluation to MRI and extends automated image evaluation to include rigorous measures throughout the imaging volume rather than just average measures over the image. Precise comparisons with theory and between systems can be performed as well as quality control and corrections for nonuniformities. The PSR test object consists of an 18 X 18 X 36 cm rectangular acrylic container enclosing 60 parallel square acrylic rods running the entire length. The inter-rod space is filled with a liquid or gel that produces strong, tissuelike signals in MRI and high contrast relative to the rods for computed tomography (CT). For profiles of slice thickness and separation, the rods are tilted in the test object to intersect the image plane at a 45 degree angle when the test object sides are parallel and perpendicular to the image plane. The test object itself is rotated 6-12 degrees about its major axis so that the sides of the rods make a small angle to the rows and columns of pixels. This allows digital sampling at finer spacing than the pixels for determination of edge response functions.(ABSTRACT TRUNCATED AT 250 WORDS)

Studies of directionally solidified eutectic Bi/MnBi at low growth velocities

A deviation from the interrod spacing (λ) and growth velocity (V) relation λ2V = constant, anticipated for diffusion-only rod eutectic growth, has been observed at growth velocities ≺5 cm/h (14 µm/s) in directionally solidified eutectic Bi-Mn (Bi/MnBi). At lower growth velocities,V≺ 0.5 cm/h, a breakdown in the aligned rod eutectic, cooperative growth mechanism, has also been noted. The λ2V relation has been experimentally determined over a range of furnace (growth) velocities (0.5 ≤V ≤ 50 cm/h), thermal gradients in the liquid (40 ≤ GL ≤ 120 °C/cm) and solidification orientation with respect to the direction of gravity (parallel, antiparallel, and perpendicular). Naturally induced, convective instabilities are suggested as a possible, lower growth velocity limit for cooperative growth in this system.