Structural and hydraulic characteristics of porous metals from bound gauzes

Characteristic pore-opening size O95 or O90 has been widely used in the filter design of woven geotextiles. These manufactured products have different pore size proportions of large pore diameters, medium pore diameters, and small pore diameters, respectively. Therefore, uncertainties still exist regarding the prediction of geotextile pore diameter variations under the uniaxial tensile strain. This paper investigates the variations in five characteristic pore-opening sizes O95, O80, O50, O30, and O10, with uniaxial tensile strain by using the image analysis method. The large pore diameters, medium pore diameters, and small pore diameters show different variation behaviors as the uniaxial tensile strain increases. Fifteen specific pores are selected and then their pore diameter variations are monitored under each tensile strain of 1%. The colorful pore size distribution diagram is a visual way to identify the variation of pores arranged in the tension direction (warp direction) and the direction perpendicular to tensile loads (weft direction). The various pore diameters are proved to agree well with the bell-shaped Gaussian distribution. The results exhibit an accurate prediction of the variation in large pore sizes, medium pore sizes, and small pore sizes, respectively, for all tested woven geotextiles with uniaxial tensile strain.

In this study, laminated composite materials were hybridized with E-glass fiber and Nitinol (Nickel-Titanium) wires. Hand lay-up technique was used to prepare the samples, epoxy resin type (Sikadur 52 N) was used as matrix reinforced by one fiber from E-glass fiber woven roving with embedded nitinol wires with a diameter 0.5 mm for samples and number of wires such as 0, 1, 3, 5 and 9 to find the effect of the number of wires on the natural frequency. The samples were fixed as a cantilever beam. The effects of increasing the number of nitinol wires, the diameter of nitinol wires, the length of the cantilever beam and the thickness of beam on the natural frequencies of the beam were studied. Also, the effects of the tapered in width side and thickness side on the natural frequencies of cantilever beam were studied. The results showed that the increasing in the number of nitinol wires and the diameter of nitinol wires lead to decrease the natural frequency in martensite phase and increase the natural frequency in austenite phase. Also, the increasing in thickness of beam and width ratio of the beam lead to increase the natural frequency. As well as, the increasing in the thickness ratio leads to increase the first natural frequency and decrease the second and third ones. In addition, the increasing in the length of the beam decreases the natural frequency.

Powder metallurgy has been developed to fabricate metal foams from various materials including magnesium. One particular challenge on powder metallurgy is fabrication of highly-ordered and interconnected porous products. Pores interconnectivity is important in application of porous magnesium alloy for biodegradable orthopedic implants. Meanwhile, 3D polymeric printing technology offers capability to build precise and rapid lattice wireframe products in a simple and low-cost manner. Here, we design and validate the capability of 3D polymeric lattice as template in powder metallurgy for fabrication of magnesium-based biodegradable implants. Lattice structures were made of ABS, PLA, and PVA filaments. Lattice structures were cubical-shaped with uniform dimension and variations in pore size are included in the study. Both computational and experimental tests are performed to determine the compressive strength of the lattice structures. Uniaxial stress with uniform magnitude is applied to test the lattice structures. The resulting stress, strain, and deformation of the 3D polymeric lattice are observed. Variations in materials and pore size affect the stress, strain and deformation of the 3D polymeric lattice. Parameters can be further optimized to meet the requirement of the design and fabrication process in consideration of the tolerable stress, strain and deformation.

Hollow core-shell silica nanoparticles (HCSNs) with desirable interior space have attracted intensive interest in the field of controlled drug delivery. In the present research work facile two-step method was employed to synthesize HCSNs by using sacrificial polystyrene (PS) template. Monodispersed spherical polystyrene nanoparticles with size range 200-250 nm were synthesized by emulsion polymerization method. Silica was coated on PS template using TEOS as precursor and cetyltrimethyl ammonium bromide (CTAB) as the shell structure directing agent. Complete removal of the template particles was achieved by calcination at 550 °C confirmed by fourier transform infrared spectroscopy (FTIR). Variation in pore size was attained by altering ethanol/water volume ratio and visualized in scanning electron microscope (SEM). Average specific surface area of HCSNs verified by Brunauer Emmett Teller (BET) method observed to be 842.57 m2/g. Drug release behavior was investigated using doxorubicin as model drug by varying pore size of HCSNs, displayed a pore size dependent release. HCSNs with reduced pore size (2.2 nm) showed maximum delay in the doxorubicin release, demonstrated the potential application of HCSNs in targeted drug delivery.Hollow core-shell silica nanoparticles (HCSNs) with desirable interior space have attracted intensive interest in the field of controlled drug delivery. In the present research work facile two-step method was employed to synthesize HCSNs by using sacrificial polystyrene (PS) template. Monodispersed spherical polystyrene nanoparticles with size range 200-250 nm were synthesized by emulsion polymerization method. Silica was coated on PS template using TEOS as precursor and cetyltrimethyl ammonium bromide (CTAB) as the shell structure directing agent. Complete removal of the template particles was achieved by calcination at 550 °C confirmed by fourier transform infrared spectroscopy (FTIR). Variation in pore size was attained by altering ethanol/water volume ratio and visualized in scanning electron microscope (SEM). Average specific surface area of HCSNs verified by Brunauer Emmett Teller (BET) method observed to be 842.57 m2/g. Drug release behavior was investigated using doxorubicin as model drug by varyi...

Porous tungsten gradient materials with ordered gradient variations in pore size have significant application value in the field of vacuum electronic devices. This work combines tape casting and dealloying methods to achieve the integrated preparation of porous tungsten gradient materials with a wide range of controllable porosity. The study focused on the phase composition and microstructure evolution during the preparation of porous tungsten gradient materials. The results show that the tape casting process allows for the precise and controllable thickness of each layer of the porous tungsten materials and uniform composition structure, while the stepwise dealloying of Fe and Ti enables a wide range of controllable porosity for the porous tungsten gradient materials. PVB, after thermal decomposition, provides a carbon source for the in situ reaction to form W-Fe-C compounds, and the surface diffusion behavior of W-Fe-C compounds at high temperatures improves the stratification of the porous tungsten gradient materials. This work provides a design concept for the integrated preparation of porous metal gradient materials.

Network-based membrane filters: Influence of network and pore size variability on filtration performance

An interconnect electrode called conductive belt was applied to modules instead of interconnection ribbons. The conductive belt has multiple wires and can achieve a multibusbar structure by forming ohmic contacts with the cell electrodes. The following problems were studied with innovative approaches to optimize the multibusbar modules: the shading rate and the contact resistance of the conductive belts, the relationship between the finger series resistance and the wire number, and the influence of the series resistance variation on the maximum power output. Furthermore, the wire number and diameter were optimized according to the following conditions: the cell sizes were full, half, and one-third, and the finger wet weights of a full cell were 80 mg, 40 mg, and 20 mg. The result showed that multibusbar and half-cell structures could achieve the maximum power output, the wire number was 16 and the wire diameter was 200 μm, and the finger wet weight was reduced to 20 mg. Finally, the reliability of the modules made with conductive belts was tested and was qualified according to International Electrotechnical Commission standards.

Results on fabrication and DC-characterisation of vertical InAs nanowire wrap-gate field-effect transistor arrays with a gate length of 50 nm are presented. Each nanowire array was processed into a transistor with a systematic variation in a number of wires and wire diameter over the sample. Extensive studies have been performed on the influence of wire number and diameter on the transistor characteristics due to a high device yield (84%). In particular it is shown that the threshold voltage depends on the wire diameter, with a change in the order of 5 mV/nm. These results show the possibility of changing the transistor characteristics on the sample by altering the wire dimensions, still using only one patterning and growth sequence.

The effect of variation in pore size on the rate of radiolytic corrosion of graphite by carbon dioxide

Research on flow diverter (FD) has progressed over the past decades; however, the relationships between parameters such as stent diameter, porosity, and number of wires and the properties of FDs, such as partial compressive force and push resistance, are not well understood. In this study, the partial compressive force and push resistance of braided FDs with varying porosity (61%-75%), diameter (2.5-5.0 mm), and number of wires (48 or 64) were evaluated using finite element analysis (FEA) and bench tests. At a small compression ratio, the 48-wire stents exhibited a larger partial compressive force than 64-wire stents of the same diameter. But when the compression ratio was 50%, the 64-wire stents had better resistance to pressure. The partial compressive force decreased as the stent diameter increased when all other parameters were equal. However, the influence of the diameter decreased as the stent porosity increased. The push resistance decreased as the porosity and diameter increased, and increased with the number of wires. These results provide useful information for FD design. Decreasing the number of wires can reduce the push resistance, while the push resistance is mainly influenced by the porosity and number of wires, and almost has no relationship with the partial compressive force. The FEA model proved very reliable, and corresponded well to the bench test results, which indicates that this model can be utilized to guide the design of FDs.

Silicon wafers are crucial for determining the price of solar cell modules. To reduce the manufacturing cost of photovoltaic devices, the thicknesses of wafers are reduced. However, the conventional module manufacturing method using the tabbing process has a disadvantage in that the cell is damaged because of the high temperature and pressure of the soldering process, which is complicated, thus increasing the process cost. Consequently, when the wafer is thinned, the breakage rate increases during the module process, resulting in a lower yield; further, the module performance decreases owing to cracks and thermal stress. To solve this problem, a module manufacturing method is proposed in which cells and wires are bonded through the lamination process. This method minimizes the thermal damage and mechanical stress applied to solar cells during the tabbing process, thereby manufacturing high-power modules. When adopting this method, the front electrode should be customized because it requires busbarless solar cells different from the existing busbar solar cells. Accordingly, the front electrode was designed using various simulation programs such as Griddler 2.5 and MathCAD, and the effect of the diameter and number of wires in contact with the front finger line of the solar cell on the module characteristics was analyzed. Consequently, the efficiency of the module manufactured with 12 wires and a wire diameter of 0.36 mm exhibited the highest efficiency at 20.28%. This is because even if the optical loss increases with the diameter of the wire, the series resistance considerably decreases rather than the loss of the short-circuit current, thereby improving the fill factor. The characteristics of the wire-embedded ethylene vinyl acetate (EVA) sheet module were confirmed to be better than those of the five busbar tabbing modules manufactured by the tabbing process; further, a high-power module that sufficiently compensated for the disadvantages of the tabbing module was manufactured.

Molecular dynamics simulations were performed to investigate structural, dynamical and electrical properties of ionic liquids (ILs) confined inside different nanoporous materials. These systems have potential uses in environmental and energy applications. The main goal is to understand how these IL properties are affected by a) characteristics of nanoporous materials such as chemical nature of the pore walls (e.g., carbon, titania), pore size and pore morphology, and b) characteristics of electrolyte, such as amount of IL inside the pores (pore loading) and concentration of organic solvent, in the case of mixtures of ILs with organic solvents. The results obtained in this work indicate that the properties of the nanoporous materials have a profound effect on the structure and dynamics of ILs. Formation of layers of ILs near the interface is observed in all systems studied, however density and thickness of these layers depends on variations in pore size, amount of IL inside the nanopores, density of electrical charges in the porous walls, pore morphology, the material of the pore walls, and concentration of solvent (in the case of mixtures of ILs with organic solvents). Our results indicate that variation in pore size, pore loading and pore morphology induce only slight changes in the local structure of liquid, but other variables such as variations in surface charge density and changing the material in the porous walls has a significant effect on the structure of the confined ions. In all systems the structure of ions far away from the pore walls closely resembles that of the bulk IL. We observed that the cations have faster dynamics than the anions in each system studied, except in very small slit graphitic pores. Dynamics of ions near the pore walls are slower as compared to those of the ions in the center regions of the pores. Varying pore loading of ions have pronounced effects on the dynamics of the ions in the center of the pore, with slight effect on the ions close to the pore surfaces. We observed that increases the density of electrical charges in the pore walls lead to an important reduction in the mobility of the ions, especially in the direction perpendicular to the pore walls. The slow dynamics of ILs can be enhanced by increasing pore sizes, or by adding organic solvents such as acetonitrile.

Multi-objective design optimization of bioresorbable braided stents

Selection of metals for the optimal performance of metamaterial based hollow core fibers for terahertz applications

We applied a recently developed method, laser metrology, to characterize the influence of collector rotation on porosity gradients of electrospun polycaprolactone (PCL) widely investigated for use in tissue engineering. The prior- and post-sintering dimensions of PCL scaffolds were compared to derive quantitative, spatially-resolved porosity 'maps' from net shrinkage. Deposited on a rotating mandrel (200 RPM), the central region of deposition reaches the highest porosity, ~92%, surrounded by approximately symmetrical decreases to ~89% at the edges. At 1100 RPM, a uniform porosity of ~88-89% is observed. At 2000 RPM, the lowest porosity, ~87%, is found in the middle of the deposition, rebounding to ~89% at the edges. Using a statistical model of random fiber network, we demonstrated that these relatively small changes in porosity values produce disproportionately large variations in pore size. The model predicts an exponential dependence of pore size on porosity when the scaffold is highly porous (e.g., >80%) and, accordingly, the observed porosity variation is associated with dramatic changes in pore size and ability to accommodate cell infiltration. Within the thickest regions most likely to 'bottleneck' cell infiltration, pore size decreases from ~37 to 23 μm (38%) when rotational speeds increased from 200 to 2000 RPM. This trend is corroborated by electron microscopy. While faster rotational speeds ultimately overcome axial alignment induced by cylindrical electric fields associated with the collector geometry, it does so at the cost of eliminating larger pores favoring cell infiltration. This puts the bio-mechanical advantages associated with collector rotation-induced alignment at odds with biological goals. A more significant decrease in pore size from ~54 to ~19 μm (65%), well below the minimum associated with cellular infiltration, is observed from enhanced collector biases. Finally, similar predictions show that sacrificial fiber approaches are inefficient in achieving cell-permissive pore sizes.