Plate-like Inclusions Research Articles

Defect crystal structure of α-Na0.5-xR0.5+xF2+2x (R = Dy-Lu, Y) on X-Ray and electron diffraction data. I. MethoD of Defect structure modelling on the α-Na0.35Dy0.65F2.30 example

For the first time, the crystal α-Na0.35Dy0.65F2.30 was studied using X-ray diffraction at 293 K and 85 K and electron diffraction at 293 K. A unified cluster model of the defective structure of nanostructured crystals with a fluorite-type structure, based on the polymorphism of ordered phases KR3F10 (R = Er, Yb), was expanded with a matrix part model based on the structure of the KYF4 compound. The unified cluster model was applied to construct the defective structure of α-Na0.35Dy0.65F2.30. It was found that the matrix part of the crystal contains Na+ и Dy3+ cations in a 1:1 ratio. Some of the anions in the matrix are displaced to the 32f positions (space group Fm3m). The excess Dy3+ forms octahedral-cubic clusters with Na+ [Na14–nDynF64+n] with cores in the form of distorted and regular cuboctahedrons {F12}. These are composed of interstitial anions in two 32f positions and one 48i position. The cluster component of the α-Na0.35Dy0.65F2.30 crystal contains octahedral-cubic clusters of f-, f–i- and i-types. Electron diffraction showed that α-Na0.35Dy0.65F2.30 is a nanostructured crystal. Its cluster component is in the form of plate-like inclusions about 5 nm thick with superstructural ordering and individual octahedral-cubic clusters. A model of their structure was proposed. Lowering the temperature to 85 K increases the number of interstitial F(32f)1 anions in the matrix component of the crystal.

Stress concentrator at the plate-like inclusion tip as an enhancement factor of diffusion flux

The work aims to evaluate stress-assisted effects in the diffusion growth of plate-like inclusions. We estimate the correction for diffusion flux onto plate-like inclusion tip accounting for the mechanical stress produced by phase transition. Also, the external stress effect on the stress-concentrator and upper-bound flux is evaluated. The stress factor results in the shift of solubility measured as the mean concentration in solution at precipitation. The impact of the stress concentrator was estimated for different thermodynamic systems: θ′-phase (Al2Cu) growth in Al-Cu alloy, zirconium hydrides growth, and perlitic transformation. The stress factor could play a sufficient role in nonstationary conditions and is negligible in steady-state approximation. Stress factor can also have substantial effects on the inclusion orientation if an external stress is present: rigid inclusion lengthening parallel to the external stress, while stacks of inclusions can behave differently depending on nucleation barriers competition for shear and hydrostatic stress components.

Switchable positioning of plate-like inclusions in lipid membranes: Elastically mediated interactions of planar colloids in 2D fluids.

We demonstrate how manipulating curvature in an elastic fluid lamella enables the reversible relative positioning of flat, rigid, plate-like micrometer-scale inclusions, with spacings from about a micrometer to tens of micrometers. In an experimental model comprising giant unilamellar vesicles containing solid domain pairs coexisting in a fluid membrane, we adjusted vesicle inflation to manipulate membrane curvature and mapped the interdomain separation. A two-dimensional model of the pair potential predicts the salient experimental observations and reveals both attractions and repulsions, producing a potential minimum entirely a result of the solid domain rigidity and bending energy in the fluid membrane. The impact of vesicle inflation on domain separation in vesicles containing two solid domains was qualitatively consistent with observations in vesicles containing many domains. The behavior differs qualitatively from the pure repulsions between fluid membrane domains or interactions between nanoscopic inclusions whose repulsive or attractive character is not switchable.

Platinum and platinoids in the Bolotisty gold-placer deposit (Khabarovsky Krai, Russia)

The article shows the results of studies the platinum mineralization (within the framework of studying the complexity of deposits) in the waste of heavy concentrate in the southeastern flank of the Bolotisty gold-placer deposit, which the located in the Khabarovsky Krai (Russia). The deposit is localized in the “erosion window” among the covers of Miocene basalts and Eocene andesites, where Cretaceous sedimentary, tuffaceous-sedimentary rocks of the basement of the volcano structure, broken through by an Eocene intrusive body of intermediate and basic composition, come to the surface. An abbreviated mineralogical analysis for monofraction of precious metals was carried out for a concentrate fraction weighing 1.813 kg with a grain size of -3.0 + 0.1 mm. Gold and platinum were found - 1.38 mg and 1.08 mg. Platinum has an iron impurity up to 3-5 % Fe and Cu, Ir, Rh impurities are variable. There are plate-like inclusions of native osmium with an admixture of ruthenium in 43 % of the studied platinum grains. There are single inclusions of ehrlichmanite. A large amount of high-temperature dipyramidal quartz, along with magnetite, chromite, tourmaline and other minerals is a characteristic feature of the concentrate and platinum grains of this area.

Effective properties of layered auxetic hybrids

In this paper, we study the effective thermo-elastic properties of hybrid materials containing layered auxetic microstructures. We consider three types of arrangements: (1) hybrids with randomly distributed plate-like inclusions possessing the negative Poisson’s ratio and negative thermal expansion coefficient, (2) sandwich structures with auxetic cores and (3) laminates with randomly arranged and ordered auxetic and negative thermal expansion layers. We evaluate the effective characteristics of these hybrids by analysing representative volume elements using the finite element method. We observe that the plate-like auxetic inclusions increase the effective stiffness of the hybrid. This stiffening effect was previously reported for spherical and cubic auxetic inclusions and is further investigated in this study. We demonstrate that the aspect ratio of the plate-like shapes has strong influence on this stiffening effect: the decrease in the aspect ratio reduces stiffening in the direction parallel to the layers and enhances it in the direction perpendicular to them. In the auxetic laminates, the stiffening effect strengths with the increase in the number of auxetic layers. We also show that thinner inclusions provide lower effective linear coefficient of thermal expansion (CTE) in the direction parallel to the layering and higher effective CTE in the direction perpendicular to it.

Application of exchangeable carbon-bonded alumina foam filters in an industrial tundish for the continuous casting of steel

Various melt refining techniques were developed in the past and led to ongoing improvement of casting quality. One of these processes is the so-called metal melt filtration, which became state of the art especially in aluminum foundry operations by using ceramic foam filters. Attempts to adapt the technique for the continuous casting of steel showed numerous difficulties due to the severe thermomechanical conditions and the high quantity of processed melt. Premature blockage or failure of ceramic foam filters implemented in the tundish promoted the application of flow control devices and multi-hole filters as alternatives. In the present study, a new approach for ceramic foam filters in the continuous casting of steel was tested. Thereby, the main disadvantage of limited filter service lifetime was circumvented by the application of an exchangeable filter system without disturbing the underlying continuous casting process. Cylindrical carbon-bonded alumina foam filters were prepared and mounted on alumina-carbon shafts using different adhesives and slag protection measures. The filters were immersed by a crane into the steel melt in an industrial tundish with 80 t capacity. During each test, one batch with approximately 380 t of steel was cast at over 1550 °C before removing the filter. The application of high-alumina mortar as adhesive and a compact filter geometry without macro channels proved to be essential for the successful operation. Samples of the corresponding filter were analyzed by digital light microscopy, X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy and electron backscatter diffraction. The complementary investigations revealed the formation of pronounced clogging layers based on aluminum-rich calcium aluminates, which can be clearly distinguished from the synthetic slag material containing silicon and other trace elements. At the bottom of the filter pronounced clusters of coral-like and plate-like inclusions were observed, which approached the filter surface by buoyancy.

Thermoelastic Characteristics of a Composite with Anisotropic Platelike Inclusions

A mathematical model is constructed describing the thermomechanical action of the elements of a composite structure (platelike inclusion and matrix particles) and isotropic elastic medium with the required thermomechanical characteristics. The model is used at the first stage to obtain the matrix relations by the self-consistent method to find the elastic modulus of the composite. At the second stage, it is used to determine the temperature coefficient of linear expansion. Using the variation approach for the composite considered, the two-way estimates of the volumetric elasticity modulus, shearing modulus, and temperature coefficient of linear expansion are determined. The estimated dependences presented allow forecasting the thermoelastic characteristics of the composite, which is reinforced with the anisotropic platelike inclusions (including in the form of nanostructural elements).

Role of embedded carbon particles on the morphology, microstructure and transport properties of sintered ultra-high molecular weight polyethylene

Selected ultra-high molecular weight polyethylene (UHMWPE) samples extracted from controlled positions along a representative reel from which ski bases are made were analyzed and compared to each other to test their composition and homogeneity. Scanning electron microscopy shows a UHMWPE matrix in which spherical particles are partly agglomerated and homogeneously distributed. Transmission electron microscopy, besides this, reveals the presence of a minority species, namely plate-like inclusions dispersed throughout the matrix. Raman features are traced back to structurally disordered carbonaceous material, with trigonal bond coordination. Surface electrical resistivity is quite low as compared to typical values for UHMWPE, being critically affected by the amount and spatial distribution of carbon particles. The observed homogeneity of distribution of carbon particles in the matrix is likely to be responsible for its ability to dissipate in an effective way the considerable amount of heat generated during ski gliding on hard, packed snow, thus preventing major structural damage of ski bases.

Raman spectra of plate-like inclusions in the EPICA-DML (Antarctica) ice core

A number of scientists have already warned against the risks of interpreting paleoclimate records without an adequate understanding of the diffusion of relevant chemical traces in deep ice cores (Gow, 1971; Ikeda and others, 1999; Bender, 2002; Faria and others, in press, and references therein). Particularly critical is the formation – either prior to drilling or during ice-core storage – of micro-inclusions such as solid inclusions, microscopic bubbles and plate-like inclusions (PLIs).

High‐Density Polyethylene Micro‐ and Nanocomposites: Effect of Particle Shape, Size and Surface Treatment on Polymer Crystallinity and Gas Permeability

AbstractSummary: High‐density polyethylene (HDPE) micro‐ and nanocomposites with spherical and platelike inclusions were prepared and the effect of filler particles on polymer crystallinity and gas permeability was investigated. Platelike inclusions strongly reduce the polymer permeability coefficient, while spherical ones have no influence on it, irrespective of their size. The reduction in gas permeability depends on the average aspect ratio of the inclusions, which in turn depends on the exfoliation of the organo‐montmorillonites (OM) and consequently on its surface treatment.A TEM micrograph of 3 vol.‐% 2C18 · M‐HDPE nanocomposite, showing partial exfoliation of the organo‐montmorillonite.imageA TEM micrograph of 3 vol.‐% 2C18 · M‐HDPE nanocomposite, showing partial exfoliation of the organo‐montmorillonite.

The effect of stacking fault energy on the formation of stress-induced internally faulted martensite plates

Abstract Stress-induced martensitic transformations proceeding by the formation of internally faulted martensite plates are studied. The additional free energy associated with random stacking faults and the distinct elastic anisotropy of parent and product phases are accounted for in the micromechanical analysis of a thin plate-like inclusion of the martensite in the austenite matrix. The microstructure of the martensite plate is obtained as a solution of a constrained minimisation problem for load multiplier. The stress at which the transformation initiates and the predicted microstructure, i.e., plate orientation and the magnitude of shear induced by the stacking faults, depend on the stacking fault energy, loading direction and temperature. As an example, the microstructures are analysed in the 6M (M18R) martensite of a CuZnAl shape memory alloy.

Ultrastructural characterisation of Marteilia species (Paramyxea) from Ostrea edulis, Mytilus edulis and Mytilus galloprovincialis in Europe.

A focused ultrastructural study of Marteilia spp. found in cultured Ostrea edulis, Mytilus edulis and Mytilus galloprovincialis from France and Spain was conducted with emphasis placed on haplosporosomes, striated plate-like inclusions and spore wall morphology. Two types of haplosporosome were identified, sphaeroid and oblate, which were common to the parasite in all 3 host species. A total of 492 haplosporosomes were measured; those from the Marteilia sp. in Mytilus spp. were marginally smaller than those in Ostrea edulis. Spore wall morphology was found to vary depending on the state of maturity of the parasite--the more mature the parasite, the thicker the wall surrounding it. It is suggested that the current criteria used to distinguish M. maurini from M. refringens are invalid and that M. maurini was relegated to a junior synonym of M. refringens.

Plastic zones near the tip of a unilaterally exfoliated rigid inclusion under the conditions of antiplane deformation

We obtained the analytic solutions of the problem of initial stage of the ramified plasticity zone appearing in the vicinity of the tip of a unilaterally exfoliated rigid plate-like inclusion subjected to longitudinal shear. If the zone consists of a single band, it makes an angle of 150° with the nonexfoliated side of the inclusion. The zone of continuous plastic strains is a special case corresponding to the infinite number of plasticity bands. We determined the boundary between the regions of plastic and elastic strains.

The inverse coefficient problem for unions of homogeneous bodies

We propose a model that makes it possible to determine the complex of thermophysical characteristics of a union of homogeneous bodies based on the solution of the nonstationary two-dimensional problem of thermal conductivity for a semibounded body with a foreign platelike inclusion perpendicular to the boundary surface; the body is subject to rapid heating by heat fluxes along thin strips.

Dielectric properties of ice containing acid and salt impurity at microwave and low frequencies

We compare the microwave and low‐frequency (LF) dielectric conductivity of natural and artificial ice as a function of impurity concentration and temperature. We find a linear dependence of conductivity on acid concentration that is independent of the type of acid. There appears to be no evidence of significant dielectric dispersions between LF and 10 GHz in acid‐doped ice. The results are well fitted by a model in which concentrated liquid acid at three‐grain boundaries forms a network, earlier proposed as an explanation for the DC conductivity of polar ice. In contrast, evidence from ice with sea salt impurity shows large discrepancies between the microwave response of low‐salinity sea ice, and both the LF and microwave responses of ice with salinities typical of meteoric ice. These discrepancies may be attributed to sea salt chloride being largely incorporated within the ice lattice in meteoric‐type ice, while in higher‐salinity ice most of the sea salt is contained in platelike inclusions of liquid brine.

Inequalities for electric and elastic polarization tensors with applications to random composites

N ew bounds on the elastic and electric polarization tensors are found for grains of arbitrary shape or connectivity. For a grain shape specified by the characteristic function χ( x), the bounds are given explicitly in terms of the geometric function | \\ ̂ gc( k)| 2. For electric polarizations one of the bounds may be interpreted as the polarization of a homogeneous ellipsoidal inclusion with axes determined by |x( k)|2- The other bound corresponds to a convex sum of polarization tensors for plate-like inclusions. Here the plate normals and weights are specified by | \\ ̂ gc( k)| 2. These bounds are used to predict the range of effective transport properties for hierarchical random suspensions and aggregates that realize the Effective Medium Approximation. The inequalities also provide rigorous bounds for the effective properties of dilute statistically anisotropic random suspensions.

Formation of UHMWPE polymeric transfer films on sliding glass counterfaces: early and steady-state wear studied by transmission electron microscopy

At a temperature of 30°C polymeric transfer films were generated on glass counterfaces during small-amplitude oscillatory sliding contact with an ultra-high molecular weight polyethylene (UHMWPE) pin under a constant load of 6.5 MPa. Early discontinuous and continuous (steady-state) transfer films were studied with vertical platinum-carbon replication and transmission electron microscopy (TEM). Nanometre-scale UHMWPE deposits in these transfer films have been visualized for the first time. Nanometre-scale particles averaging 20.6 ±6.3nm (5–40nm) were deposited on glass in the early stages of UHMWPE film transfer. After formation of a continuous transfer film, UHMWPE particles of slightly smaller dimensions, 13.5±6.1 nm (2–41 nm), were deposited on the transfer film surface. In addition, micrometre-scale particles (0.1–6.4 μm) were found at the ends of the wear track. At high magnification, a fraction of the UHMWPE polymer chains observed in particle surfaces and in the transfer film surface nearby were not oriented in the sliding direction. Some crystal- or plate-like particles of UHMWPE were seen in the transfer film. Plate-like and micrometre-scale spherulitic inclusions were also identified on the mostly amorphous UHMWPE pin surface fractured at liquid nitrogen temperatures. The high frequency of nanometre-scale UHMWPE particles in contrast to the less numerous micrometre-scale deposits near the ends of the wear track suggests that the nanometre-scale deposits contribute significantly to transfer film formation and to the wear characteristics of UHMWPE.

A freeze-etch study of angular marginal-plate-containing peroxisomes in the proximal tubules of bovine kidney

The ultrastructure of peroxisomes in the proximal nephron tubules of bovine kidney cortex was studied using ultrathin-sectioning, diaminobenzidine cytochemistry for the visualization of catalase, and by freeze-fracture. Peroxisomes in this nephron segment are up to 1.5 microns in diameter and exhibit a peculiar angular shape, which is probably related to the occurrence of multiple straight plate-like inclusions (marginal plates) in the matrix of peroxisomes; they lie directly underneath the peroxisomal membranes. The peroxisomal membrane in such regions follows the outline of the marginal plate. The peculiar shape of peroxisomes allows their unequivocal identification in freeze-fracture preparations. Peroxisomal membranes are recognized by their flat, often rectangular appearance. Intramembrane particles are much more numerous on P-fracture faces than on E-fracture faces. A crystalline lattice-structure with a periodicity of approximately 10 nm can be observed on the flat rectangular areas of E-fracture faces. This lattice structure is intensified after prolonged freeze-etching. Intramembranous particles seem to be superimposed over this pattern. The crystalline pattern on the E-fracture faces of peroxisomal membranes is probably not a membrane structure but it reveals the structure of the membrane-associated marginal plates. A cast of the marginal-plate surface may be generated by a collapse of the peroxisomal membrane half onto the immediately underlying matrix inclusion.

Platelike and globelike inclusion bodies associated with rough endoplasmic reticulum in alveolar type 2 cells of the sheep

We studied the ultrastructure of alveolar type 2 cells of sheep. The inclusion bodies of rodlike structures or cisternal bodies derived from the endoplasmic reticulum were found in 13.6 +/- 7.0% (+/- SD) of type 2 cells. The length of the rodlike structure varied, the longest being 2.4 microns; but the width was usually 0.1 micron. Rod-like structures were usually straight and arranged in parallel stacks. An electron-dense line ran longitudinally at the center of the rodlike structures. Serial ultrathin sections revealed that the rodlike structures did not seem to be three-dimensionally rod-shaped structures but were actually plate-disc or cup-shaped, and the piled-up rodlike structures were connected to each other at their ends. This rodlike structure in type 2 cells of sheep seems rather to be a platelike inclusion body. The cisternal body, on the other hand, was circular or oval-shaped cisternae containing aggregated electron-dense materials distributed in an arabesque or speckled pattern. Serial ultrathin section examination revealed the cisternal body to be three-dimensionally a globe. Some plate bodies were arranged near the cisternal body, suggesting the transformation from the latter to the former. The functional significance of these findings has not yet been elucidated.

Laboratory investigation of longitudinal dispersion in anisotropic porous media

In this study, laboratory experiments were used to investigate mechanisms that may cause anisotropy in the dispersion coefficient and to investigate the relation between anisotropy in hydraulic conductivity and anisotropy in longitudinal dispersion. Measurements of sodium chloride concentration (used as a tracer) were made at 105 in situ sampling locations in a new type of sand box designed to allow flow in either of two perpendicular directions. Two types of hydraulic anisotropy were examined. The first consisted of structured zones of increased hydraulic conductivity within a lower‐conductivity medium. The second type involved low‐conductivity platelike inclusions within a homogeneous, isotropic medium. The plates were aligned such that the tortuosity was increased only in one principal direction of permeability. Results using two examples of the first type of media showed that the apparent longitudinal dispersivities for flow parallel to the high‐conductivity direction were greater than those perpendicular to this direction. Two examples of the second type of media produced smaller apparent longitudinal dispersivities for flow parallel to the high‐conductivity direction. The results suggest that the mechanisms causing dispersive anisotropy can be related, conceptually, to the factors causing hydraulic anisotropy.