Layer Spreading Research Articles

Simultaneous Interferometry and Microscopy Reveal Unexpected Nickel Corrosion Dynamics in Confined Geometry

Corrosion of nickel and its alloys in confined areas remains a serious concern for the safety of structural materials. We uniquely combined white light interferometry and microscopy with high spatial and time resolution for a real-time study of the corrosion mechanism of confined nickel surfaces in alkali metal chloride (e.g., NaCl) electrolytes (c = 1 – 100 mM) at pH = 7. A mica surface is used as crevice former in the electrochemical surface forces apparatus to establish 600-1000 µm2 confined dry areas on extended nickel surfaces. NaCl is the wetting medium of the confined zones and the electrolyte layer spreads out along all the surface. The nickel surfaces form interfacial oxides films at the beginning when no electrochemical potential is applied. Subsequent application of an electrochemical potential ramp from -400 mV to +800 mV initiates severe corrosion of the formed crevices. Surprisingly, the corrosion inside the crevices proceeds as preferential and self-catalyzed “pitting” corrosion (inhomogeneous localized dissolution with the formation of pits) within in the confined zone. Moreover, different behavior of the Nickel corrosion is observed depending on the concentration: inside the confined zone at low concentration (<10mM) and outside the crevice at higher chloride concentrations (>10mM). Our data reveal a surprising and detailed view into the initial corrosion mechanism of nickel surfaces in confined zones, and may contribute to a deeper understanding and, ultimately, prevention of localized corrosion of other metallic surfaces. A double-layer theory coupled with diffusion-limited effects provides a plausible explanation for the observed phenomena.

Enhanced bond strength and bioactivity of interconnected 3D TiO2 nanoporous layer on titanium implants

Titanium and its alloys have been extensively used as implant materials due to their excellent mechanical properties, adequate corrosion resistance and good biocompatibility. In this study, an interconnected 3D TiO2 structure on Ti implants is fabricated via anodization method in a fluoride-containing electrolyte with water content larger than 50%. The pore size ranges from 30 to 200 nm with the current density increased from 50 to 100 mA·cm2. Compared with other kinds of porous TiO2 layers, which were fabricated by the same method with different electrolyte composition, the prepared 3D TiO2 structure shows the highest hardness and apparent Young's modulus, which are over 4 times higher than that of the TiO2 nanotube arrays. Moreover, the 3D TiO2 possess the highest adhesion strength as the critical load for the delamination occurred is 0.7 N, while for the nanotube-structured layer and the transition structure, the load are 0.2 and 0.4 N, respectively. Additionally, the 3D TiO2 structure also shows better corrosion resistance than the others. Titanium with 3D oxide layer has also shown good performance in osteogenic cells culturing, since in the cell viability assay, the cells adhered on the 3D oxide layer spread extensively and showed a spindle shape while on the TiO2 nanotube arrays or titanium with transition structure the cells were unfavorable to spread. This work can provide guidelines for improving structural and environmental conditions responsible for modification of Ti surfaces for biomedical applications.

Simultaneous observations of F2 layer stratification and spread F at postmidnight over a northern equatorial anomaly region

AbstractSimultaneous observations of F2 layer stratification and spread F at postmidnight (00:00 LT to 05:00 LT) were carried out on 22, 23, and 28 November 2013, using ionosondes distributed over a northern equatorial anomaly region at three specific locations, i.e., Puer (PUR, 22.7°N, 101.05°E, dip latitude 12.9°N), Chiang Mai (CMU, 18.8°N, 98.9°E, dip latitude 9.04°N), and Chumphon (CPN, 10.7°N, 99.4°E, dip latitude 0.93°N). The results show that both the PUR and CMU stations observed the F2 layer stratification at postmidnight in the Northern Hemisphere, frequently accompanied with gravity waves (the periods~30–100 min). It is reported that F2 layer stratification at postmidnight can be observed in the Northern Hemisphere for the first time. It is suggested that the thermospheric neutral wind triggered by gravity waves strongly contribute to the altitude dependence of the combined vertical plasma velocity, which consequently poses significant impacts on the occurrence of the low‐latitude F2 layer stratification at postmidnight. In addition, the spread F other than F2 layer stratification was observed at the CPN station located at the geomagnetic equator, suggesting that smaller geomagnetic inclination tend to inhibit the postmidnight F2 layer stratification in the equatorial region. Furthermore, on 23 November 2013 a good correlation was identified between the F2 layer stratification at PUR and the spread F at both CMU and CPN, possibly due to that the large‐scale gravity waves originating at middle latitudes contribute to the nighttime spread F observed in the low‐latitude and equatorial regions.

Microstructure modification and bendability improvement of AZ31 magnesium sheet by bending–unbending and annealing process

AZ31 magnesium sheet was processed by room temperature multi-step cyclic bending–unbending (CBU) and subsequent annealing (CBUA) process to modify the microstructure and improve its bendability. The CBU process resulted in a complex stress and strain distribution through the thickness and a multi-layered microstructure after annealing. The grain structure, micro-texture, and micro-hardness of each of the layers were studied by optical microscopy, electron back-scattered diffraction (EBSD) and indentation measurements, respectively. The CBUA process resulted in static recrystallization of grains leading to average grain size of about 2.5μm to a depth of about 40μm from the surface. The grain size, however, significantly coarsened in two intermediate layers through the thickness. The recrystallization was studied by microstructural characterization and micro-hardness measurement after annealing. The through-thickness texture from EBSD experiments indicated texture spreading and weakening in the surface layers. The results are consistent with the mechanics of cyclic bending–unbending (CBU) process, mechanisms of strain induced static recrystallization, texture evolution and its stability with long term annealing. The grain refinement and texture spreading of multi-layered microstructure from CBUA process led to bendability (rmin/t value) improvement in V-bending tests at room temperature.

Eddy Convection in Developing Heated Supersonic Jets

An experimental study of the spatial distribution of integral eddy speeds in heated, supersonic free jets is presented. The physics of such jets are of immediate interest to noise-reduction approaches for tactical aircraft jet noise. In these flows, the noise produced has a strong influence from eddy speeds, particularly for radiation in peak noise directions, due to Mach wave contributions. The measurements obtained using a time-resolved Doppler global velocimetry instrument experimentally indicate a key mechanism of the role of heating in jet noise reduction relative to the classical Lighthill scaling. Measurements are presented in jets issuing from an axisymmetric biconic nozzle at two conditions: total temperatures of 1.6 and 2.0 times that of the ambient and both at approximately diameter Reynolds number and pressure-matched exit conditions. For the higher total temperature case, the scaled streamwise eddy convective velocities within the shear layer were measurably reduced compared to the lower total temperature case, especially as the axial distance from the nozzle exit increased. These findings confirm that core plume heating results in additional shear layer spreading and reduction of scaled eddy convective speeds, making acoustic radiation less efficient with heating. To accompany the eddy convection results, data obtained in the same facility using laser Doppler velocimetry are analyzed for second- and fourth-order moments, indicating the importance of the fourth-order correlation in the region of immediate interface between the potential core and the shear layer.

Effect of technical parameters on porous structure and strength of 3D printed calcium sulfate prototypes

Additive manufacturing methods such as three-dimensional printing (3DP) show a great potential for production of porous structure with complex internal and external structures for bone tissue engineering applications. To optimize the 3DP manufacturing process and to produce 3D printed parts with the requisite architecture and strength, there was a need to fine-tune the printing parameters. The purpose of this study was to develop optimal processing parameters based on a design of the experiments approach to evaluate the ability of 3DP for making calcium sulfate-based scaffold prototypes. The major printing parameters examined in this study were layer thickness, delay time of spreading the next layer, and build orientation of the specimens. Scaffold dimensional accuracy, porosity, and mechanical stiffness were systematically investigated using a design of experiment approach. Resulting macro-porous structures were also studied to evaluate the potential of 3DP technology for meeting the small-scale geometric requirements of bone scaffolds. Signal-to-noise ratio and analysis of variance (ANOVA) were employed to identify the important factors that influence optimal 3D printed part characteristics. The results showed that samples built using the minimum layer thickness (89?m) and x-direction of build bed with 300ms delay time between spreading each layer yielded the highest quality scaffold prototypes; thus, these parameters are suggested for fabrication of an engineered bone tissue scaffold. Furthermore, this study identified orientation and new layer spreading delay time as the most important factors influencing the dimensional accuracy, compressive strength, and porosity of the samples. Display Omitted Cylindrical calcium sulfate-based prototypes were designed, printed, and characterized.3DP process was optimized by a design of experiment approach and statistical analysis.Dimensional accuracy, porosity, and mechanical stiffness were evaluated.x-direction built samples with 89 ?m layer thickness and 300 ms delay time were optimal prototypes.Orientation and delay time were the most important factors influencing the quality of the samples.

An approximate Riemann solver for shallow water equations and heat advection in horizontal centrifugal casting

An approximate Riemann solver was developed for solving modified shallow water equations (SWE) and energy transport describing the average flow dynamics of a single layer spreading inside a horizontally rotating cylinder. The numerical model was particularly developed for simulating the horizontal centrifugal casting (HSC) of the outer shell of a work roll. The SWE were derived in the rotating frame of reference; therefore, fictitious forces (the centrifugal force and the Coriolis force) were considered. In addition, other forces such as the bed shear force, the force of gravity, the wind shear force and forces arising from the variable liquid/solid interface were taken into account. The Jacobian matrix of the nonlinear hyperbolic system of PDEs was decomposed into a set of eigenvalues and corresponding eigenvectors using standard and corrected Roe averages. A Harten–Hyman entropy fix was used to prevent expansion shocks (entropy violating solutions) typically occurring during transonic rarefactions. Source terms were applied as a stationary discontinuity and were physically bounded and well-balanced for steady states (producing non-oscillatory solutions). Each wave was upwinded using the explicit Godunov’s method. The high resolution corrections with flux limiters were used to achieve second order of accuracy and dispersion free solutions at discontinuities. In addition to the Riemann solver, a central scheme FV model was used to solve the heat diffusion inside the cylinder (mold) and partially solidified liquid layer, coupled with the solidification model. Several simulations were performed, results were analyzed and discussed.

Photoacoustic Signals of Depletion Layer Spread Beneath Metal Electrode in Metal/Semiconductor Structure

SUMMARYThe photoacoustic (PA) signal from the depletion layer beneath the metal electrode in a metal/semiconductor (M/S) structure was detected using the PA method. To measure the reverse‐bias voltage dependence of distribution of the PA signal from the depletion layer, the surface of the electrode was illuminated and scanned by an intensity‐modulated optical beam. It was found that the PA signal phase differences between depletion layer formation and the absence of a depletion layer were dependent on depletion layer spreading. One‐dimensional scanning of the electrode also revealed that spreading of the depletion layer extends from the edges of the electrode.

Volcanic spreading forcing and feedback in geothermal reservoir development, Amiata Volcano, Italia

We made a stratigraphic, structural and morphologic study of the Amiata Volcano in Italy. We find that the edifice is dissected by intersecting grabens that accommodate the collapse of the higher sectors of the volcano. In turn, a number of compressive structures and diapirs exist around the margin of the volcano. These structures create an angular drainage pattern, with stream damming and captures, and a set of lakes within and around the volcano. We interpret these structures as the result of volcanic spreading of Amiata on its weak substratum, formed by the late Triassic evaporites (Burano Anhydrites) and the Middle-Jurassic to Early-Cretaceous clayey chaotic complexes (Ligurian Complex). Regional doming created a slope in the basement facilitating the outward flow and spreading of the ductile layers forced by the volcanic load.We model the dynamics of spreading with a scaled lubrication approximation of the Navier Stokes equations, and numerically study a set of solutions. In the model we include simple functions for volcanic deposition and surface erosion that change the topography over time. Scaling indicates that spreading at Amiata could still be active. The numerical solution shows that, as the central part of the edifice sinks into the weak basement, diapiric structures of the underlying formations form around the base of the volcano. Deposition of volcanic rocks within the volcano and surface erosion away from it both enhance spreading. In addition, a sloping basement may constitute a trigger for spreading and formation of trains of adjacent diapirs. As a feedback, the hot hydrothermal fluids decrease the shear strength of the anhydrites facilitating the spreading process.Finally, we observe that volcanic spreading has created ideal heat traps that constitute todays' exploited geothermal fields at Amiata. Normal faults generated by volcanic spreading, volcanic conduits, and direct contact between volcanic rocks (which host an extensive fresh-water aquifer) and the rocks of the geothermal field, constitute ideal pathways for water recharge during vapour extraction for geothermal energy production. We think that volcanic spreading could maintain faults in a critically stressed state, facilitating the occurrence of induced and triggered seismicity.

2D quasicrystals from perovskites

Perovskite oxides represent a versatile class of materials with a simple cubic or pseudo-cubic crystal structure. The family of perovskite oxides contains insulators, metals, semiconductors, and superconductors with nearly identical lattice parameters. This structural equivalence additionally allows to combine perovskites with different properties in multilayer systems to produce functional materials with unique properties. We report here on the formation of a quasicrystal (QC) thin film on a threefold Pt(111) surface. This QC film is derived from the classical perovskite oxide BaTiO3 which is the most intensely studied ferroelectric perovskite oxide. An easily accessible ferroelectric to paraelectric phase transition at 400 K makes the material so interesting for basic and applied research. Due to matching lattice conditions BaTiO3 can be grown epitaxially on selected metal substrates. Periodic thin films of either BaTiO3(100) or BaTiO3(111) have been grown depending on substrate orientation and preparation conditions on Pt(001) and on Pt(111) [1, 2]. As we demonstrate here, astonishingly also a two-dimensional dodecagonal quasicrystalline structure can be formed by annealing an initially 1.4 nm thick BaTiO3 film on Pt(111) [3]. It develops at a temperature of 1250 K from a wetting layer spreading between a few thicker BaTiO3(111) islands. Surface sensitive electron diffraction (LEED) shows a bright and sharp pattern with dodecagonal symmetry. High-resolution scanning tunneling microscopy (STM) images reveal an arrangement of quadratic, triangular, and rhombic elements which compares well to a Gähler tiling. The development of higher-order self-similar structures is widely suppressed by a linear phason strain. This is supported by the fine structure of the diffraction data.

터널 화재시 연기확산 방지를 위한 국소제연설비의 성능 평가 연구

장대화되고 대심도화 되는 현대 터널은 반밀폐적인 구조로 인하여 화재발생시 효과적인 배연에 많은 어려움이 있으며, 고온의 온도상승과 함께 유독성 연기로 인한 피난과 소화활동에 많은 어려움을 주고 있다. 본 연구에서는 화재시 발생되는 연기를 인접구역으로 확산되지 않도록 구획하여 피난자의 대피로를 확보하고 대피시간을 연장 시킬 수 있는 국부제연설비인 에어커튼을 적용한 성능평가 실험을 수행하였다. 실험결과 에어커튼에 의하여 형성된 연기차단막은 터널 내부의 차량 화재로 인한 고온 연기층의 확산 방지 효과를 확인할 수 있었다. 또한 에어커튼에 의한 차단막 내외부의 일산화탄소 측정결과에서도 40배 이상 차이를 보임으로써 에어커튼을 적용한 터널 화재시 연기확산방지 효과를 기대할 수 있을 것으로 평가 되었다. The modern tunnel tends to be long and deep and therefore has a lot of difficulties for effective smoke ventilation on fire due to the semi-hermetic structure. Also, it has difficulty on evacuation and fire fighting by toxic gases together with high increase rate of temperature. The smoke occurring on fire is to avoid spreading over adjacent area and secure a escape road for prolonging the escape time. Accordingly, test on performance evaluation has been carried out applying air curtain, local smoke extraction facilities, in this study. As a result of the test, it can be seen that the smoke barrier formed by the air curtain has an effect on prevention of the smoke layer spreading. In addition, in the result of the measurement on the carbon monoxide inside and outside the barrier by the air curtain, there was difference of 40-time carbon monoxide inside and outside. Therefore, it has been shown that the effect to prevent the smoke from spreading is expected on fire of the tunnel applying the air curtain.

Water and acrylamide monomer transfer rates from a settling basin to groundwaters.

The aim of this paper was to estimate the potential leakage of acrylamide monomer, used for flocculation in a settling basin, towards the groundwaters. Surface-groundwater interactions were conceptualized with a groundwater transport model, using a transfer rate to describe the clogged properties of the interface. The change in the transfer rate as a function of the spreading of the clogged layer in the settling basin was characterized with respect to time. It is shown that the water and the Acrylamide transfer rate are not controlled by the spreading of the clogged layer until this layer fully covers the interface. When the clogged layer spreads out, the transfer rate remains in the same order of magnitude until the area covered reaches 80 %. The main flux takes place through bank seepage. In these early stage conditions of a working settling basin, the acrylamide flux towards groundwaters remains constant, at close to 10 g/year (±5).

Charge Loss Characteristics of Different Al Contents in a HfAlO Trapping Layer Investigated by Variable Temperature Kelvin Probe Force Microscopy

Kelvin probe force microscopy (KFM) technology is applied to investigate the charge storage and loss characteristics of the HfAlO charge trapping layer with various Al contents. The experimental results demonstrate that with the increase of Al contents in the HfAlO trapping layer, trap density significantly increases. Improvement of data retention characteristic is also observed. Comparing the vertical charge loss and lateral charge spreading of the HfAlO trapping layers, the former plays a major role in the charge loss mechanism. Variable temperature KFM measurement results show that the extracted effective electron trap energy level increases with increasing Al contents in HfAlO trapping layer, which is in accordance with the charge loss characteristics.

Asymmetrically interacting spreading dynamics on complex layered networks.

The spread of disease through a physical-contact network and the spread of information about the disease on a communication network are two intimately related dynamical processes. We investigate the asymmetrical interplay between the two types of spreading dynamics, each occurring on its own layer, by focusing on the two fundamental quantities underlying any spreading process: epidemic threshold and the final infection ratio. We find that an epidemic outbreak on the contact layer can induce an outbreak on the communication layer, and information spreading can effectively raise the epidemic threshold. When structural correlation exists between the two layers, the information threshold remains unchanged but the epidemic threshold can be enhanced, making the contact layer more resilient to epidemic outbreak. We develop a physical theory to understand the intricate interplay between the two types of spreading dynamics.

Controlled synthesis of different morphologies of TiB2 microcrystals by aluminum melt reaction method

TiB2 microcrystals with different morphologies, including hexagonal plate-like, tower-like and dendritic, were fabricated by aluminum melt reaction method in this study. The growth mechanisms of these microcrystals are also discussed based on the fundamental crystal growth theories. It is found that the growth of TiB2 is controlled by two-dimensional nucleation in aluminum melt. If the atomic concentration, reaction rate and atomic diffusion rate in the melt are high, TiB2 microcrystals exhibit hierarchical tower-like and dendritic morphologies. Otherwise, the single crystal of hexagonal plate-like morphology is obtained. The growth of the hierarchical TiB2 microcrystals is controlled by two steps, intermittent two-dimensional nucleation and continuous lateral spreading of layers on the growth faces.

Connecting Turbulence and Meandering Parameterization to Describe Passive Scalars Dispersion in Low Wind Speed Conditions

The following study deals with meandering of the horizontal mean wind. The main motivation for such investigation came from the difficulty in describing contaminant dispersion in meandering conditions. Observational field measurements point out that the autocorrelation function of the horizontal wind components, obtained for the meandering cases, displays an oscillating behavior with the presence of large negative lobes. Such negative lobes are described by an equation containing functions that represent patterns of movement associated to meandering and turbulence. As a consequence, this mathematical formulation connects the turbulence and meandering phenomenon establishing the employment of hybrid parameters in models that describe the meandering dispersion. Therefore, considering this dualistic aspect between meandering and turbulence manifestations, a new set of relations for the turbulence parameterization joined with the meandering of the wind have been developed and are available. This new turbulence parameterization for a stable shear forcing planetary boundary layer, united with a meandering mean time scale is able to describe contaminant meandering enhanced spread in a low wind speed stable planetary boundary layer.

Photoacoustic Signals of Depletion Layer Spread beneath Metal Electrode in Metal/Semiconductor Structure

The photoacoustic PA signal from the depletion layer beneath the metal electrode in a metal/semiconductor M/S structure was detected using the PA method. To measure the reverse-bias voltage dependence of distribution of the PA signal from the depletion layer, the surface of the electrode was illuminated and scanned by an intensity-modulated optical beam. It was found that the PA signal phase differences between depletion layer formation and the absence of a depletion layer were dependent on depletion layer spreading. One-dimensional scanning of the electrode also revealed that spreading of the depletion layer extends from the edges of the electrode.

Synthesis and Crystal Structure of the Cesium Silver ­Permanganate Cs3Ag[MnO4]4

AbstractAfter successful syntheses and structural refinements of the already known permanganates of cesium (Cs[MnO4]) and silver (Ag[MnO4]) we started to blend aqueous solutions of both components in various molar ratios. From crystallization experiments of these mixtures only three species of crystals with different chemical compositions were obtained: tricesium monosilver tetrakispermanganate (Cs3Ag[MnO4]4) and, depending upon the respective ratio, either additional silver permanganate or surplus cesium permanganate, namely. The new title compound crystallizes in the orthorhombic space group Pnnm (no. 58) with two formula units per unit cell and cell dimensions of a = 764.53(4), b = 1883.57(9) and c = 584.34(3) pm. The crystal structure of Cs3Ag[MnO4]4 consists of two crystallographically distinguishable cesium cations. (Cs1)+ is surrounded by fourteen oxygen atoms constructing a slightly distorted bicapped hexagonal prism. These polyhedra are connected through edge‐sharing with two other polyhedra of this kind to form chains along [001]. The chains are linked to each other via sixfold coordinated Ag+ cations (d(Ag–O) = 238–246 pm), arranged in such a manner that they link three oxygen atoms of two cesium polyhedra, leading to a two‐dimensional layer spreading out parallel to the (001) plane. Together with the two crystallographically different tetrahedral oxomanganate(VII) anions [MnO4]– (d(Mn–O) = 161–162 pm) the other kind of cesium cations ((Cs2)+ with CN = 13) finally connect these layers three‐dimensionally.

Dynamics of a viscous layer flowing radially over an inviscid ocean

AbstractWe present a theoretical and experimental study of a viscous fluid layer spreading over a deep layer of denser, inviscid fluid. Specifically, we study an axisymmetric flow produced by a vertical line source. Close to the source, the flow is controlled viscously, with a balance between radial compressive stresses and hoop stresses. Further out, the flow is driven by gradients in the buoyancy force and is resisted by viscous extensional and hoop stresses. An understanding of these different fluid-mechanical relationships is developed by asymptotic analyses for early times and for the near and far fields at late times. Confirmation of the late-time, far-field behaviour is obtained from a series of laboratory experiments in which golden syrup was injected into denser solutions of potassium carbonate. We use our mathematical solutions to discuss a physical mechanism by which horizontal viscous stresses in a spreading ice shelf, such as those in West Antarctica, can buttress the grounded ice sheet that supplies it.

Mesoporous titanosilicate/reduced graphene oxide composites: layered structure, high surface-to-volume ratio, doping effect and application in dye removal from water

In this study, a new system of integrated photocatalytic adsorbents (IPCAs), three-dimensional wormhole-like mesoporous titanosilicate/reduced graphene oxide layered composites, were prepared with various Ti/Si ratios. The reduced graphene oxide (RGO) nanosheets played the role of giant two-dimensional (2D) platforms for the deposition, spreading and growth of mesostructured layers, leading to a significant enhancement in mesoporosity. The substitution of titanium species into the mesoporous silica/RGO significantly changed the textural, physicochemical and optical properties. Gradually increasing the Ti doping content dramatically promoted the adsorptivity and UV-photocatalytic degradation of the dye contaminant; however, an excess dosage (20 mol%) inhibited the UV activity. This could be attributed to the changes in the coordination geometry and electronic states of Ti species in the composites. The IPCAs that dominantly contained highly dispersed and isolated Ti-oxide species in tetrahedral coordination within a mesostructured framework exhibited much higher photoactivity than those composed of aggregated and octahedrally coordinated Ti species due to the formation of efficient charge-transfer excited states.