Kinds Of Porous Structures Research Articles

Fabrication and experimental investigation of a porous zinc alloy structure

A porous structure has been designed and fabricated to generate very regular shaped pores. The porous structure has 20% porosity with a relative density of 0.8. Radiographic examinations conducted on the samples confirmed regular shaped porous structure throughout. Compression testings were carried out on the samples at three different strain rates viz. 7.93 × 10e-5/ sec, 7.93 × 10e-4/ sec and 3.96 × 10e-2/ sec respectively and the nominal stress-nominal strain graphs were plotted with 0.2% proof strength taken as the onset of yield in the structure, the testing revealed an approximately elasto-plastic strain rate sensitive response behaviour in the yield strength as well as plateau region of the porous samples. Energy absorption analysis was carried out up to ≅0.25 strain. The method described in this paper can be used to generate and study different kinds of porous structures.

Development and Evaluation of Zeolites and Metal–Organic Frameworks for Carbon Dioxide Separation and Capture

AbstractWith increasing carbon dioxide (CO2) emissions from the combustion of fossil‐based fuels, the concentration of CO2 in the atmosphere is growing at 407.54 parts per million, as released in May 2016. Accordingly, the reduction of CO2 emissions is an essential issue for global climate changes. Tremendous efforts have been directed towards the goal of CO2 separation and capture. These have led to the development of novel classes of porous materials that possess unique potential applications in the capture and sequestration of CO2. Hence, this comprehensive review focuses on studying and analyzing newly developed methods to reduce greenhouse gas emissions and to sequester CO2 released from anthropogenic activities. It compares and analyzes, in terms of storage capacity and adsorption selectivity, the innovative technologies that capture CO2. Also described are the key advancements in CO2 capture from chemical absorption post‐ and precombustion industrial units and its subsequent physical adsorption by using various zeolites and metal–organic framework (MOF) materials for CO2 adsorption, storage, and separation. Current progress in MOF materials for CO2 capture is considered, and the potentials and limitations of new discoveries in the area are addressed, as it is a rapidly growing area. Furthermore, trends in the design of various kinds of porous structures with tailored macro‐ and microstructures and target surface properties are examined.

Molecular dynamics simulation of thermal conductivity of mesoporous α-Al2O3

In this paper, molecular dynamics simulation was performed to predict the thermal conductivities of ordered mesoporous α-Al2O3. A kind of porous structure was proposed to guarantee the electrical neutrality. Based on the Matsui potential, the nonequilibrium molecular dynamics method adapted by Mller-Plathe was used to calculate the lattice thermal conductivity of mesoporous alumina along the axial direction of pore at various temperatures. Effects of pore size and porosity were also investigated. It turns out that with increasing temperature the thermal conductivity of mesoporous α-Al2O3 rises first until the temperature reaches 200–400 K, then decreases almost linearly. In addition, as the pore size gets larger, the specific surface area decreases, and the thermal conductivity increases because the boundary scattering has been weakened. On the other hand, the number of phonons in the pore wall decreases greatly with increasing porosity, thus dramatically reducing the thermal conductivity of the mesoporous material. Range analysis shows that the porosity is more influential than the pore size on the thermal conductivity of mesoporous materials.

A Technological Method to Improve the Filtration Efficiency of Fiber Materials

Fiber is a new and efficient water treatment and environmental protection material. The key to improve the filtration efficiency of fiber materials is that water pass through the fiber bed, the porous structures of fiber in-depth bed is controlled by the internal construction, fiber arrangement, and fiber zigzag degree. This study presented a method to improve the removal capacity of fiber filtration materials. There are three kinds of porous structures discovered here: Tubular water passage hole (T-pass), Curvilinear water passage hole (C-pass), Labyrinth water passage hole (L-pass). The T-pass let water more easily go through but less sediment and rush strongly off suspensions deposit on the surface of filter materials. The L-pass has resistance to flow and suspension intend to deposit at backside area of filter materials, where not advantage to rush but sediment easily. The function of C-pass is between that of T-pass and L-pass. The experiment shows that C-pass filter bed is the idea structure which can be increased the efficiency of 5-10 times than others.

Formation of Porous Structure with Subspot Size under the Irradiation of Picosecond Laser Pulses

A study was presented in this paper on porous structure with microsize holes significantly smaller than laser spot on the stainless steel 304 target surface induced by a picosecond Nd:van regenerative amplified laser, operating at 1064 nm. The target surface variations were studied in air ambience. The estimated surface damage threshold was 0.15 J/cm2. The target specific surface changes and phenomena observed supported a complementary study on the formation and growth of the subspot size pit holes on metal surface with dependence of laser pulse number of 50–1000 and fluences of 0.8 and 1.6 J/cm2. Two kinds of porous structures were presented: periodic holes are formed from Coulomb Explosion during locally spatial modulated ablation, and random holes are formed from the burst of bubbles in overheated liquid during phase explosion. It can be concluded that it is effective to fabricate a large metal surface area of porous structure by laser scanning regime. Generally, it is also difficult for ultrashort laser to fabricate the microporous structures compared with traditional methods. These porous structures potentially have a number of important applications in nanotechnology, industry, nuclear complex, and so forth.

Comparison study of liquid replenishing impacts on critical heat flux and heat transfer coefficient of nucleate pool boiling on multiscale modulated porous structures

The critical heat flux (CHF) and heat transfer coefficient of de-ionized (DI) water pool boiling have been experimentally studied on a plain surface, one uniform thick porous structure, two modulated porous structures and two hybrid modulated porous structures. The modulated porous structure design has a porous base of 0.55 mm thick with four 3 mm diameter porous pillars of 3.6 mm high on the top of the base. The microparticle size combinations of porous base and porous pillars are uniform 250 μm, uniform 400 μm, 250 μm for base and 400 μm for pillars, and 400 μm for base and 250 μm for pillars. Both the CHF and heat transfer coefficient are significantly improved by the modulated porous. The boiling curves for different kinds of porous structures and a plain surface are compared and analyzed. Hydrodynamic instability for the two-phase change heat transfer has been delayed by the porous pillars which dramatically enhances the CHF. The highest pool boiling heat flux occurring on the modulated porous structures has a value of 450 W/cm 2, over three times of the CHF on a plain surface. Additionally, the highest heat transfer coefficient also reaches a value of 20 W/cm 2 K, three times of that on a plain copper surface. The study also demonstrates that the horizontal liquid replenishing is equally important as the vertical liquid replenishing for the enhancement of heat transfer coefficient and CHF improvement in nucleate pool boiling.

Heat Transfer Enhancement by Using Four Kinds of Porous Structures in a Heat Exchanger

Four kinds of porous structures, copper wire mesh, metal foam, copper fiber sintered felts and cross-connected micro-channel plates were applied in a heat exchanger. Heat transfer coefficient per unit volume, pressure drop and comprehensive heat transfer effect of the heat exchanger were studied. The results show that: four kinds of porous structures can enhance the heat transfer performance obviously. The heat exchanger with copper metal foam has the largest comprehensive heat transfer coefficient which can reach 821.5W•m-3•K-1•Pa-1. And it increased about 2.5 times than that of the heat exchanger without porous structures. The comprehensive heat transfer coefficient increases with the flow rate in small case and decreases with the flow rate in large case. The coefficient reaches the largest value at the flow rate range of 6L/h-8L/h. The heat transfer coefficient per unit volume of the heat exchanger with four kinds of structures increases with the flow rate, and the increasing trend tends slowly. Metal foam of brass has the largest heat transfer coefficient per unit volume of 1266.8 W•m-3•K-1. Pressure drop increases with the flow rate, and the increasing trend tends rapidly. The 200 mesh copper wire mesh has the least pressure drop of 968.8Pa.

Morphological study on the reactivity of styrene‐divinylbenzene copolymers in a chloromethylation reaction

AbstractStyrene‐divinylbenzene (S‐DVB) copolymers with different kinds of porous structures were synthesized by aqueous suspension polymerization using n‐heptane as the pore forming agent. The amount of this solvent (monomer dilution degree) and the DVB content in the organic phase were varied. The combination of three different dilution degree values and three DVB contents yielded three series of copolymers with a variety of porous structures. The three series were composed by copolymers with pore diameters (D) in the following ranges: D < 500 Å, 500 < D < 1000 Å, and D > 1000 Å, respectively. The effect of synthesis conditions on the pore size distribution and on the copolymer matrix rigidity was evaluated. These copolymers were submitted to a chloromethylation reaction with a paraformaldehyde/gaseous HCl mixture in the presence of zinc chloride as a Lewis acid catalyst and 1,2‐dichloroethane as solvent. The effect of the copolymer porosity on the chloromethylation reaction extension was evaluated. It was possible to observe that a gel copolymer with a high swelling capacity in the reaction medium achieved the same chloromethylation yield observed for a high porous copolymer. This result thus indicates that, in the case of the chloromethylation reaction studied here, the high swelling capacity of the gel copolymer can counterbalance its limited surface area, turning this type of polymer structure as reactive as a macroporous one. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Influence of the matrix porosity on the synthesis and adsorption behavior of dithiocarbamate styrenic resins toward zinc(II) and cadmium(II) ions

AbstractThe dependence of the adsorption behavior toward Zn2+ and Cd2+ on the synthesis conditions of dithiocarbamate styrenic resins was investigated. We synthesized styrene–divinylbenzene copolymers with different kinds of porous structures by varying the divinylbenzene (DVB)‐to‐styrene ratio and the dilution degree of the monomers with n‐heptane. The porous structure of these materials was characterized. The introduction of the dithiocarbamate moiety on the copolymers followed a synthetic pathway based on the nitration reaction, reduction of the nitro group to the amino one, and finally, the addition of the amino group to CS2. All of the synthesis steps were monitored by Fourier transform infrared spectroscopy. Only the addition reaction to CS2 was greatly influenced by the copolymer porosity. The effect of the dilution degree on the reaction extension was more pronounced than the effect of the DVB content. The more porous materials with higher dithiocarbamate contents adsorbed a higher amount of ions in a faster way, with Zn2+ being preferable over Cd2+ ions. The difference between the Zn2+ and Cd2+ adsorption rates was enhanced with the copolymer porosity, and also enhanced was the difference between the amounts of ions adsorbed by the copolymer; this suggested that the selectivity toward these ions could be controlled by the copolymer porous structure. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Deformation behavior and mechanism of porous PLLA under compression

scaffolds. The PLLA dioxane solutions in test tubes were cooled from the bottom surfaces at a constant rate by using liquid nitrogen to induce solid–liquid phase separation. The phase-separated samples were then dried under vacuum at -5 C for about 6 days to remove the solvent completely. Cylindrical samples were obtained and then trimmed to be a cylinder with 8-mm diameter and 12-mm length. Porosity (volume fraction of pores) of a scaffold was estimated from the densities of PLLA solid and the scaffold. Compression tests were then performed using a conventional mechanical testing machine at a loading rate of 1 mm/min. A fieldemission scanning electron microscope (FE-SEM) was also used to observe the microstructures of the porous samples and the deformation behavior of the porous samples at the critical point. FE-SEM micrographs of the cross-sections in the transverse direction are shown in Fig. 1. Homogeneous distribution of pores is observed, and the size of the pores tends to decrease with increase in the concentration of the solution. The porosities of these porous samples were estimated as 94.7, 90.0, and 88.5% for the concentrations of 3, 5, and 7 wt.%, respectively. FE-SEM micrograph of a crosssection in the vertical direction is shown in Fig. 2. For all the samples, this kind of porous structure was observed. These structures shown in Figs. 1 and 2 suggest that the crystals of the solvent grow in the vertical and transverse directions at a constant speed by the freezing process. Typical stress–strain curves under compression are shown in Fig. 3. The stress– strain relation of this porous structure of PLLA can be characterized by four different regions as shown in Fig. 4. The region A is the initial linear portion corresponding to linear elastic deformation of the porous structure. The end of the region A and the transition point to the region B is recognized as a critical point where localized failures of the wall structures of the pores take place. In the region B, stress

Analyses of structures for a synthetic leather made of polyurethane and microfiber

AbstractA gradient extraction method was developed and used for a synthetic leather made of polyurethane (PU) and microfiber polycaprolactam (PA‐6), by which the two components were separated using DMF and formic acid as solvents, respectively. Their chemical structure was confirmed by FTIR spectra, and the result showed that the PU is a kind of polyester polyurethane with phenylene rings in the molecule. The condensed phase structure was analyzed using X‐ray diffraction (XRD). The crystallinity of the PA‐6 is about 65.6%, and for the PU, there was not distinct crystalline character shown in the XRD pattern but a phase separation structure of hard block‐soft block with the hard domains content about 58.7%. SEM images showed that the PA‐6 microfibers transfixing the PU matrix form a net bundle structure, and there are two kinds of porous structures in the synthetic leather, with one type of pore sized 5–80 μm between the components of PU and PA‐6, and the other in PU matrix with a size of 0.1–2 μm. The multipores run through the synthetic leather as three‐dimensional channels, benefit for transportation of air, water, dyes, and so on. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 903–908, 2007