Porous Layer Thickness Research Articles

Electrospinning of nanofibrous layers of As-S chalcogenide glass

AbstractWe report on electrospinning of As3S7 chalcogenide glass from propylamine solution. The prepared glass layers consist of nanofibers with a typical diameter of ~100 nm. The deposited layers are highly porous from the nature of the electrospinning process. The calculated effective-refractive index value of the layers is n ~1·165, at λ = 1550 nm; assuming 87 vol.% of the air and the bulk glass index n = 2·27 at the same wavelength. In contrast to the continuous 2-micron thick spin-coated layer, which had the absorption edge near 420 nm, the 10-micron thick porous nanofibrous layer had no significant absorption edge at all. The relative stiffness of electrospun glass nanofibers was found to be 98% of the value measured for the bulk glass of the same composition. So far, electrospinning is the only solution-based technique, which directly deposits solvent-free chalcogenide glass layers with no need for any post-deposition annealing.

Experimental and numerical study of optimum thickness of porous silica transition layer in aeronautic laminated glass

The application of a porous silica (PS) transition layer in an inorganic-organic aeronautic laminated glass can effectively solve the material failure caused by the performance difference of the inorganic-organic materials. The effect of porous silica transition layer thickness on the mechanical and optical properties of laminated glass was investigated. The microstructure of the porous silica transition layer was analyzed by scanning electron microscopy. The film thickness was verified using a step profiler. The failure strength of laminated glass with the porous silica transition layer was tested by a universal testing machine. Finite element modeling of laminated glass with the porous silica transition layer was performed by ANSYS software. Tensile stress between the porous silica and the polyurethane was simulated for different porous silica film thicknesses. Experimental and theoretical results indicated that with the increasing the thickness of the transition film, the failure stress of the laminated glass increased. Improvements in the mechanical properties of the laminated glass are saturation at a PS thickness of approximately 3.8μm.

Amorphous Molybdenum Sulfide Deposited Graphene Liquid Crystalline Fiber for Hydrogen Evolution Reaction Catalysis

Amorphous Molybdenum Sulfide Deposited Graphene Liquid Crystalline Fiber for Hydrogen Evolution Reaction Catalysis

Horizontal and vertical motion at surface of a gassy ocean sediment layer induced by obliquely incident SV waves

Free gas is ubiquitous at shallow sediment depths of the continental margins of the worldwide oceans. However, theoretical study of the dynamic behavior of gassy seafloor under the action of earthquake has been rare. In this paper, a theoretical model for the analysis of the horizontal and vertical motion at the surface of a gassy ocean sediment layer induced by SV waves is developed based on the multiphase poroelasticity theory. The marine sediment layer with finite thickness is assumed to between seawater and underlying elastic solid seabed. The pores of sediment are filled by two compressible and viscous fluids (i.e., liquid and gas). The theoretical formulation is derived for the computation of horizontal and vertical motion in forms of displacement amplitudes, displacement ratios and amplification coefficients, which are defined as a function of incident angle, wave frequency, thickness of porous layer and saturation degree of sediment. Numerical results show that even a slight decrease of full saturation of the porous sediment may lead to significant influence on sediment's displacement amplitudes, displacement ratios as well as the amplification coefficients. Apart from saturation degree, this influence also depends on the incident angle, wave frequency and thickness of sediment layer.

Natural convection of water in a partially porous enclosure with a heat-generating element

Paper presents the numeral results of transient natural convection in a partially porous enclosure with a heat-conducting and heat-generating element. The horizontal walls of the cavity are adiabatic, while the vertical ones are isothermal and have low temperature. A mathematical model formulated in dimensionless variables such as vorticity, stream function and temperature have been solved by means of the finite difference method. The governing parameters are the porous layer thickness and dimensionless time. The effects of these parameters are shown using streamlines, isotherms and average temperature of the heat-conducting element. The results demonstrate an opportunity to intensify the passive cooling system using the porous layer.

Расчетная модель упорного подшипника с пористым покрытием на поверхности направляющей

Introduction. The development of the design model of a thrust sliding bearing with a two-layer porous coating on the way surface running on an electrically conductive lubricant is described. The work objectives are the development and computational justification of the possible increase in oil consumption, growth of the bearing capacity, and reduction of the frictional force, due to their design models refinement. This is based on the formation of the computed hydrodynamic models of thrust bearings taking into account the dependence of the porous layers permeability on the way surface under the steady flow of the electroconductive liquid lubricant. Materials and Methods. New mathematical models that describe a steady flow of the electrically conductive lubricant in the working gap between an inclined slider and a guide with a bilayered porous coating are proposed. The given numerical analysis of the essential performance features has shown that bearings with a two-layer porous coating on the way surface significantly increase the damping characteristics of the supports and bearing capacity of the bearing, and reduce the frictional force. Research Results. A design model of the thrust sliding bearing is formed taking into account the porous coating permeability on the way surface. That is based on the equations of the steady flow of the electrically conductive incompressible liquid lubricant for a “thin layer” in the working gap, continuity and Darcy in the presence of an electromagnetic field. The authors have found the exact self-similar solution to a thrust bearing with a two-layer porous coating on the way surface for the field of velocities and pressures in the lubricating layer and porous coating. Besides, multiparameter expressions for the essential bearing performance with the account for the availability of electromagnetic fields, the permeability of porous layers, and the ratio of the thicknesses of porous layers, are specified. Discussion and Conclusions. The received updated calculation models have made it possible to determine the effect of a number of additional factors, as well as to perform a comparative analysis of the newly obtained results and those already available which confirms the close approximation of the new model to the actual practice. The theoretical models provide the necessary engineering design calculations in a sufficiently wide range of speeds and loads for the application in engineering, aircraft building, instrument making, etc.

AC Impedance Studies on Metal/Nanoporous Silicon/p-Silicon Structures

Alternating current (AC) impedance measurements have been performed on 10- to 15-μm thick porous silicon layers on a (100) p-type silicon (p(+)Si) substrate with the aluminium (Al) top electrode in a sandwich configuration in the range of 20 Hz–1 MHz and in the temperature ranging between 152 K and 292 K. The ac conductivity σac was found to increase with frequency f according to the universal power law: sigma_{text{ac}} , = ,,Af^{s} where the exponent s is a frequency and temperature-dependent quantity. A hopping process is found to be dominant at low temperatures and high frequencies, while a thermally activated free band process is responsible for conduction at higher temperatures. Capacitance is found to decrease with frequency but increase with temperature. Frequency dependence of the loss tangent is observed with a temperature-dependent minimum value.

Numerical study of evaporation of falling liquid film on one of two vertical plates covered with a thin porous layer by free convection

The numerical study of coupled heat and mass transfer during the evaporation of flowing liquid film has been analysed. The film falls down on one plate of a vertical channel under free convection. The wetted plate is covered with a thin porous layer and externally subjected to a uniform heated flux while the second one is dry and isothermal. The liquid consists of pure water film while the gas mixture has two components: dry air and water vapour. The results concern the influence of porosity and porous layer thickness of the porous media on the coupled heat and mass transfer performance and on the film evaporation. The results show that, in the free convection, the presence of the porous layer enhances the heat and mass transfer performance at the liquid-gas interface during the liquid film evaporation.

A detailed study of AlN and GaN grown on silicon-on-porous silicon substrate

In this study, we investigate the growth of AlN and GaN epilayers on silicon-on-porous silicon (SOP) as a compliant substrate. The porous silicon layers is obtained by electrochemical etching of silicon wafers in HF based solutions. Different porosities (10–30%) and porous layer thicknesses (3–30 μm) have been investigated. In order to obtain a single orientation GaN, a Si cap layer is grown on porous silicon by chemical vapour deposition leading to a smooth epi-ready surface. Then, the subsequent growth of AlN by molecular beam epitaxy and GaN by metal-organic chemical vapour deposition is investigated by atomic force microscopy and X-ray diffraction. The epilayers grown on SOP show similar surface morphology and structural quality to state of the art GaN layers grown on bare silicon. In addition, strain in the GaN layers grown on SOP and Si has been investigated. Interestingly, the results indicate that a slight compliant effect is achieved on SOP substrate with the thicker porous layer.

Sulfide stress corrosion study of a super martensitic stainless steel in H2S sour environments: Metallic sulfides formation and hydrogen embrittlement

Thanks to their high corrosion resistance, super martensitic stainless steels are commonly used in the oil and gas industry, particularly in sour environments. Some grades are however susceptible to undergo hydrogen and mechanically-assisted corrosion processes in the presence of H2S, depending on the pH. The martensitic stainless steel EN 1.4418 grade exhibits a clear protective passive behavior with no sulfide stress corrosion cracking when exposed to sour environments of pH≥4, but undergoes a steep decrease in its corrosion resistance at lower pH conditions. The present paper investigated this abrupt loss of corrosion resistance with electrochemical measurements as well as different physicochemical characterization techniques. Results indicated that below pH 4.0 the metal surface is covered by a thick (ca 40μm) porous and defect-full sulfide-rich corrosion products layer shown to be straightforwardly related to the onset of hydrogen and sulfide mechanically-assisted corrosion phenomena.

Very High Efficiency Porous Silica Layer Open-Tubular Capillary Columns Produced via in-Column Sol-Gel Processing.

It is demonstrated that 5 μm i.d. capillaries can be coated with mesoporous silica layers up to 550 nm thickness. All the columns produced using in-column sol-gel synthesis with tetramethoxysilane provide plate height curves that closely follow the Golay-Aris theory. In 60 cm long columns, efficiencies as high as N = 150 000 and N = 120 000 were obtained, respectively, for a 300 and 550 nm thick porous layer. An excellent retention and plate height reproducibility was obtained when the recipes were subsequently applied to produce very long (1.9 and 2.5 m) capillaries. These columns produced efficiencies up to N = 600 000 plates for a retained and around N = 1 000 000 plates for an unretained component. Given the good reproducibility on the long capillaries, and considering that mesoporous silica is still the preferred support for LC, it is believed the present study could spur a renewed interest in open-tubular LC.

Analysis of Thermal Flow in a Rotating Porous U-Turn Duct Using Lattice Boltzmann Method

The lattice Boltzmann method is carried out to investigate the heat transfer enhancement in a U-turn duct which is partially filled with a porous media. The porous layer is inserted at the core of the duct and is modeled using the Brinkman–Forchheimer assumptions. In order to validate the results, first a channel flow problem without any porous layer is compared with available data. Second, the porous Couette flow and partially porous channel flow are successfully compared with the studies of other researchers. Then, fluid flow in a clear U-turn duct is studied looking carefully at the velocity, curvature and rotation effects. Finally, the effects of porous layer thickness on the rate of heat transfer and pressure drop are investigated. Parametric studies are conducted to evaluate the effects of various parameters (i.e., Reynolds number, Darcy number, rotation number), highlighting their influences on the thermo-hydrodynamics behavior of the flow. The optimum values of porous layer thickness are presented for specific flow parameters.

Preparation and evaluation of 3 m open tubular capillary columns with a zwitterionic polymeric porous layer for liquid chromatography.

A 3 m zwitterionic polymeric porous layer open tubular column (3 m × 25 μm id × 375 μm od) with a polymeric porous layer thickness of 4 μm was fabricated by the copolymerization of [2-(methacryloyloxy)ethyl] dimethyl-(3-sulfopropyl) ammonium hydroxide and N,N'-methylenebis(acrylamide). The effects of the diameter of the capillary, reaction temperature, and polymerization time on the preparation of the open tubular column were investigated. Characterized by scanning electron microscopy, the zwitterionic layer was observed to be rough and throughout the fused-silica capillary homogenously, which increased the phase ratio. The separation of neutral, basic, and acidic compounds demonstrates the strong hydrophilicity of the poly[2-(methacryloyloxy)ethyl] dimethyl-(3-sulfopropyl) ammonium hydroxide coating. In addition, the poly[2-(methacryloyloxy) ethyl] dimethyl-(3-sulfopropyl) ammonium hydroxide porous layer open tubular column was applied for the analysis of flavonoids from the rootstalk of licorice, revealing the potential in separating complex samples. The relative standard deviation of retention time for run-to-run (n = 5), day-to-day (n = 3), and column-to-column (n = 3) of toluene, N,N-dimethylformamide, formamide, and thiourea were below 1.2%, exhibiting good repeatability.

(Invited) Thin Porous Silicon Produced By Metal-Assisted Etching

Metal-assisted etching of silicon can produce porous silicon and silicon nanowires by simply immersing metal-modified silicon in a hydrofluoric acid solution without electrical bias (1). Such etching proceeds by a local galvanic cell mechanism consisting of local anodic dissolution of silicon and local cathodic reduction of an oxidizing agent on metal. The structure of porous silicon is widely controlled from nm to sub-mm scale in pore size and from straight to an ants’ nest like in pore morphology by changing etching conditions (1-3). We have been studying the metal-assisted etching of silicon to produce porous structures for antireflection of solar cells (2), and for autocatalytic electroless formation of metal-nanorods and metal films on Si surfaces (4). In this paper, we present size-controlled thin porous silicon layers consisting of straight pores and those applications. Noble metal nanoparticles were deposited on crystalline silicon wafers by electroless displacement deposition immersing the wafers into a metal salt solution containing hydrofluoric acid. The metal-particle-deposited silicon wafers were immersed in a hydrofluoric acid solution including hydrogen peroxide as an oxidizing agent. Under suitable etching conditions, uniform porous silicon thin layers consisting of straight pores were formed on silicon wafers. The diameter of pores was consistent with the size of metal nanoparticles remained at the bottom of each pore. Thus, the diameter of pores, that is, the porosity of porous layers is easily controlled in the nm scale with the deposition time of nanoparticles. The thickness of porous layers, that is, the length of the straight pores is also easily controlled by the etching time. Optical properties of the porous layers thinner than 1 μm depends on those porosity and thickness (5). This is applicable for antireflection of solar cells. The strength of metal nanorods, which were produced by electrolessly filling the pores, increased with the diameter of pores from 10 to 25 nm. These nanorods work as nanoanchors of metal films on silicon wafers. Acknowledgements The present work was partly supported by JSPS KAKENHI (26289276). References 1) Z. Huang, N. Geyer, P. Werner, J. de Boor, U. Gösele, Adv. Mater., 23, 285 (2011). 2) S. Yae, H. Tanaka, T. Kobayashi, N. Fukumuro, H. Matsuda, Phys. Stat. Sol. (c), 2(9), 3476 (2005). 3) S. Yae, M. Tashiro, M. Abe, N. Fukumuro, H. Matsuda, J. Electrochem. Soc., 157, D90 (2010). 4) S. Yae, K. Sakabe, N. Fukumuro, S. Sakamoto, and H. Matsuda, J. Electrochem. Soc., 158, D573 (2011). 5) K. Yamakawa, S. Sakamoto, N. Fukumuro, S. Yae, ECS Trans., 69(2), 185 (2015).

Electrochemical Pore Formation in InP: Understanding and Controlling Pore Morphology

Research on semiconductor nanostructures is motivated by two key considerations. The first is the continuing call for smaller and more efficient versions of existing semiconductor devices. The second is the characterisation and exploitation of the unique characteristics that are often exhibited by structures at the nano-scale. While a wide variety of semiconductor nanostructures can be produced without difficulty (e.g. by self-assembly or preferential etching), precise control over the morphology of these structures is often much harder to achieve. The electrochemical formation of nano-scale porosity in semiconductors has been studied extensively1-5 and has found some application due to its bulk characteristics e.g. the use of porous silicon as a passivation layer6. However, the exploitation of the nano-scale properties of these structures is unlikely until a comprehensive understanding of the factors affecting pore morphology has been obtained. We have previously demonstrated7-9 the formation of nano-scale porosity in n-type InP anodised in KOH. Pores emerge form pits in the electrode surface10 and grow and branch along the <111>A crystallographic directions9 forming tetrahedral porous domains8. Under certain conditions, current-line oriented pores can also be obtained.11 In order to understand the factors effecting pore morphology, porous InP was formed under a range of different temperatures, electrolyte concentrations, carrier concentrations and current densities. The morphology of the resulting porous layers was analysed in detail. In particular, the pore width, layer thickness and porosity of the layers were all measured. We show that at low current densities, the pore width is dominated by the magnitude of the current density. At higher current densities, we show that both the pore width and the porosity are inversely related to the kinetics of the electrochemical reaction: the pore width being lowest at high temperatures and intermediate KOH concentrations. The pore width decreases with increasing carrier concentration, which is likely due to the associated decrease in the space charge layer thickness. Porosity varies in a similar manner to pore width and the maximum porous layer thickness is correlated to the pore width in all cases. These results support a model9of pore formation based on competition in kinetics between hole supply at the pore tip and the electrochemical reaction at the semiconductor electrolyte interface. It will be shown that this model makes the correct qualitative predictions for the variation of pore morphology with temperature, electrolyte concentration, carrier concentration and current density. Such an understanding of the factors affecting the morphology of these porous layers is an essential step in achieving the process control necessary for them to be integrated into standard semiconductor fabrication techniques.

Active through-mask electrochemical machining with its interelectrode gap filled with flexible porous material

It has been one of issues that conventional through-mask electrochemical machining is very hard to fabricate surface texture efficiently on the non-planar workpiece. To solve this problem, a modified active through-mask electrochemical machining process (active TM-ECM) with its interelectrode gap filled with flexible porous material was proposed on the basis of development of a special tool cathode. The newly developed tool cathode allows for inlet and distributing of electrolyte as well as discharging of solution. The flow field within the interelectrode was analyzed and optimized numerically, and the effects of key process parameters including mask thickness, flexible porous layer thickness, clamping force and pulsed current parameter on the geometric profiles and their distributing characteristics of the machined microdimple were investigated experimentally. The arrays of microdimples with a fairly good distribution of geometric dimensions were successfully machined on both the stainless steel planar substrate and cylindrical workpiece by using the optimal process conditions. It is showed that the modified active TM-EMM process exhibits favorable machinability and applicability to produce microdimples on the planar and non-planar surfaces.

Accelerated cell-surface interlocking on plasma polymer-modified porous ceramics

Excellent osseointegration of permanent implants is crucial for the long lasting success of the implantation. To improve the osseointegrative potential, bio-inert titanium alloy surfaces (Ti6Al4V) are modified by plasma chemical oxidation (PCO®) of the titanium-oxide layer to a non-stoichiometric, amorphous calcium phosphate layer. The native titanium-oxide film measuring only a few nanometers is converted by PCO® to a thick porous calcium phosphate layer of about 10μm. In a second step the PCO surface is combined with a cell adhesive plasma-polymerized allylamine (PPAAm) nano film (5 and 50nm). Independent of the PPAAm coating homogeneity, the human osteoblast-like MG-63 cells show a remarkable increase in cell size and well-developed filopodia. Analyses of the actin cytoskeleton reveal that the cells mold to the pore shape of the PPAAm-covered PCO, thereby establishing a strong attachment to the surface. Interestingly, we could demonstrate that even though our untreated PCO shows excellent hydrophilicity, this alone is not sufficient to facilitate fast cell spreading, but the positive surface charges mediated by PPAAm.This multilayer composite material guarantees enhanced interlocking of the cells with the porous surface.

Critical heat flux maxima resulting from the controlled morphology of nanoporous hydrophilic surface layers

Porous hydrophilic surfaces have been shown to enhance the critical heat flux (CHF) in boiling heat transfer. In this work, the separate effects of pore size and porous layer thickness on the CHF of saturated water at atmospheric pressure were experimentally investigated using carefully engineered surfaces. It was shown that, for a fixed pore diameter (∼20 nm), there is an optimum layer thickness (∼2 μm), for which the CHF value is maximum, corresponding to ∼115% enhancement over the value for uncoated surfaces. Similarly, a maximum CHF value (∼100% above the uncoated surface CHF) was observed while changing the pore size at a constant layer thickness (∼1 μm). To explain these CHF maxima, we propose a mechanistic model that can capture the effect of pore size and pore thickness on CHF. The good agreement found between the model and experimental data supports the hypothesis that CHF is governed by the competition between capillary wicking, viscous pressure drop and evaporation, as well as conduction heat transfer within the porous layer. The model can be used to guide the development of engineered surfaces with superior boiling performance.

Optimal performance of an annular heat exchanger with a porous insert for a turbulent flow

The use of porous materials as a passive technique to intensify heat transfer has been well established. Yet, this is always accompanied by a non-desirable and costly effect that is a higher pressure drop. Adopting such a technique requires a compromise between hydrodynamics and thermal performances in order to use efficiently the available energy. In this study, we analyze the performance of an annular heat exchanger with a porous insert by means of the assessment of entropy generation rate due to fluid friction and heat transfer for a turbulent flow. The porous substrate is attached over the inner pipe. A modified κ-ε model is used to account for turbulence in the porous medium. Effects of several parameters such as the porous layer thickness, its permeability, its thermal conductivity and the inlet temperature difference are investigated and documented. It is highlighted that the porous insert with an optimal thickness allows a significant reduction of total entropy generation when it has a high effective thermal conductivity. Hence, this heat transfer enhancement technique has a great merit for thin porous inserts not exceeding about 40% of the annular gap.

Performance variation with SDC buffer layer thickness

The performance of anode-supported solid oxide fuel cells was investigated as the SDC buffer layer thickness was varied between ∼0.4 μm and ∼2.3 μm. The thickness of the buffer layer has a significant effect with the peak performance varying in magnitude by a factor of almost three. A peak power density of 1106 mW cm−2 was achieved at 800 °C and an optimal SDC buffer layer thickness of ∼1.5 μm. The performance variation was complex due to a balance between ohmic and polarization losses, triple phase boundary area, pin holes and interfacial reactions between the BSCF + SDC cathode, SDC buffer layer, and YSZ electrolyte. Understanding this variation is essential in order to compare two fuel cells having a different porous buffer layer thickness.