Maximum Pore Size Research Articles

Raw Juice Concentration by Osmotic Membrane Distillation Process with Hydrophobic Polymeric Membranes

Hydrophobic polymeric membranes (PP, PTFE, and PVDF) were efficiently applied in juice concentration by osmotic membrane distillation process at room temperature. The properties of applied membranes were characterized by the value of static contact angle, hysteresis of contact angle, surface free energy, roughness, mean flow pore size, maximum pore size or bubble point, and the pore size distribution before and after their utilization in osmotic membrane distillation (OMD). Furthermore, the mechanical strength of the membranes was evaluated using the Mullen burst technique and characterization of fouling behavior was done. The impact of stripping solutions, characterized by different water activities (NaCl and CaCl2), type of membrane materials, and membrane morphology, on the transport properties in a dehydration process was evaluated. Apple and beet juices with a high level of antioxidants were chosen. The quality of juices has been assessed by determination of total polyphenols and antioxidant activity. In the dehydration process, the most efficient were 0.45-μm PTFE and 0.45-μm PVDF membranes (24 % improvement). No loss of polyphenol content or reduction of antioxidant activity was observed after the juice dehydration.

Oxidation behaviors of porous Haynes 214 alloy at high temperatures

The oxidation behaviors of porous Haynes 214 alloy at temperatures from 850 to 1000°C were investigated. The porous alloys before and after the oxidation were examined by optical microscopy, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) analyses, and X-ray photoelectron spectroscopy (XPS). The oxidation kinetics of the porous alloy approximately follows a parabolic rate law and exhibits two stages controlled by different oxidation courses. Complex oxide scales composed of Cr2O3, NiCr2O4 and Al2O3 are formed on the oxidized porous alloys, and the formation of Cr2O3 on its outer layer is promoted with the oxidation proceeding. The rough surface as well as the micropores in the microstructures of the porous alloy caused by the manufacturing process provides fast diffusion paths for oxygen so as to affect the formation of the oxide layers. Both the maximum pore size and the permeability of the porous alloys decrease with the increase of oxidation temperature and exposure time, which may limit its applications.

Factors affecting the property of porous Ti3SiC2 metal ceramic fabricated through pressureless sintering

In this paper, micrometer-sized porous Ti3SiC2 metal ceramic was fabricated through a reactive synthesis method using titanium hydride, silicon and graphite elemental powders. The factors including raw powders, pressing pressure, sintering procedure affecting the purity and the pore property of porous Ti3SiC2 were systematically studied. The results indicate that the purity, pore property including maximum pore size and porosity can be effectively controlled by adjusting the synthesis parameters.

Preparation of a hydrophobically enhanced antifouling isotactic polypropylene/silicone dioxide flat‐sheet membrane via thermally induced phase separation for vacuum membrane distillation

ABSTRACTIsotactic polypropylene (iPP) hydrophobic flat‐sheet membranes were fabricated for use in vacuum membrane distillation (VMD) through a thermally induced phase‐separation process with dispersing hydrophobically modified SiO2 nanoparticles in the casting solution to achieve a higher hydrophobicity and to sustain a stable flux in VMD. The contact angle (CA) measurements indicated that the incorporation of nano‐SiO2 into a casting solution mixture containing 20 wt % iPP had a 20.9% higher CA relative to that of SiO2‐free membranes. The addition of nano‐SiO2 also induced morphological changes in the membrane structure, including changes in the pore size distribution, porosity, and suppression of macrovoids. The pore size distribution of the iPP–SiO2 membranes became narrower compared with that of the SiO2‐free membranes, and the porosity also improved from 35.45 to 59.75% with SiO2 addition. The average pore size and maximum pore size of the iPP–SiO2 membranes both decreased. The ability of the membranes to concentrate an astragalus aqueous solution (a type of traditional Chinese medicine) with VMD was investigated. The surface hydrophobicity and antifouling performance of the iPP–SiO2 membranes improved with nano‐SiO2 addition to the membrane casting solution. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42615.

High-performance nanofibrous membrane for removal of Cr(VI) from contaminated water

A simple and effective approach for the preparation of electrospun nanofibrous microfiltration membrane having positive surface charges, capable of removing Cr(VI) from contaminated water, was demonstrated. In this membrane, polyacrylonitrile was electrospun into a nanofibrous scaffold with an average fiber diameter of about 200 nm. Polyvinylamine, a positively charged polymer was grafted onto the nanofibrous scaffold through cross-linking reaction by glutaraldehyde. The microfiltration characteristics of the original and modified membranes, such as the maximum and mean pore size, particle rejection ratio, pure water flux and mechanical strength, were investigated. The effects of the pH value (1.0 to 13.0) and initial Cr(VI) concentration (5 mg/L to 100 mg/L) on the static adsorption rate of the membrane were also studied. Both experimental and theoretical results showed that the optimal pH range for Cr(VI) adsorption was from 3.0 to 5.0. Due to the high surface charge density, the polyvinylamine -grafted nanofibrous membrane exhibited a saturation adsorption capacity of 57.1 mg Cr(VI) per gram of the membrane, based on the Langmuir model analysis, and also a high Cr(VI) adsorption capacity in the dynamic adsorption test. In addition, this membrane could be regenerated from the desorption of Cr(VI) using a 0.1 mol/L of NaOH aqueous solution.

Characterization and application of porous Ti3SiC2 ceramic prepared through reactive synthesis

Abstract Porous ternary compound Ti 3 SiC 2 with purity of higher than 99.0 wt.% was fabricated through a reactive synthesis method using titanium hydride, silicon and graphite elemental powders. The parameters of pore structure including the maximum pore size, open porosity and air permeability, obey the Hagen–Poiseuille formula with the constant G = 0.226 m −1 Pa −1 s −1 for the reactively synthesized porous Ti 3 SiC 2 . The porous Ti 3 SiC 2 shows excellent corrosion resistance in concentrated acids. Further, a typical filter application in zinc metallurgy has been reported. The excellent overall performance predicts the porous Ti 3 SiC 2 material has a broad application in industry.

Effect of pressure on pore structure of porous FeAl intermetallics

A series of porous FeAl intermetallics with nominal composition of Fe–25wt.% Al was fabricated under pressure ranging from 60MPa to 360MPa by Fe and Al elemental powder reactive synthesis. The effect of pressure on the pore structure of the resultant porous FeAl intermetallics was systematically studied. Results show that open porosity, maximum pore size and permeability can be manipulated by varying the pressure. Permeability decreases with increasing pressure. Permeability (K), open porosity (θ) and maximum pore size (dm) were verified to meet the Hagen–Poiseuille equation. A universal equation of K=Adm2θ, with A=0.2379, was established to reflect the relationship between the permeability and pore structure parameters for porous FeAl intermetallics fabricated under different pressure.

Fabrication and properties of microporous metakaolin-based geopolymer bodies with polylactic acid (PLA) fibers as pore generators

This paper reports the synthesis and characterization of a microporous geopolymer body based on metakaolin. Two kaolinites were used as the starting materials in conjunction with sodium silicate and sodium hydroxide and three sizes of polylactic acid (PLA) fibers (12, 20 and 29µm diameter) were used as the pore-forming media. The microporous bodies were formed from geopolymer pastes of optimized composition by extrusion, which yielded bodies with reasonably well-aligned pore-forming fibers which were decomposed by the alkaline conditions during curing and drying of the bodies. XRD, FTIR, 27Al MAS NMR, and SEM were used to characterize the chemistry and microstructure of the porous products and their compressive strengths were also measured. The molar composition SiO2/Al2O3=4 was found to give the best geopolymer characteristics, while the optimal ratio Na2O/Al2O3 which affected the leachability of the PLA fibers and thus the size of the resulting pores, was optimized in the range 1.5–1.75 depending on the kaolinite. Water permeability measurements indicate that the use of PLA fibers as pore-formers significantly increases the permeability of the samples, while the maximum pore size of the porous bodies, determined by bubble point measurements, is related to the size of the particulate matter that could be retained, and indicates that their performance could be tailored for particular filtering applications by adjusting their synthesis parameters.

Effect of process parameters on fouling and stability of MF/UF TiO2 membranes in a photocatalytic membrane reactor

The investigations on the influence of TiO2 photocatalyst (Aeroxide® TiO2 P25) loading, feed cross-flow velocity (vF) and transmembrane pressure (TMP) on the fouling and stability of ceramic membranes in a photocatalytic membrane reactor are presented. Two ultrafiltration membranes with molecular weight cut-off of 5kDa (Filtanium 5) and 100kDa (Filtanium 100), and one microfiltration membrane (Filtanium 0.2) with maximum pore size of 0.2μm were used. Regardless of the applied vF (3–6m/s), TMP (1–3bar) and TiO2 P25 loading (0.5–1.5g/dm3) no permeate flux decline was observed when the UF membranes were used. On the opposite, an increase of the flux for 5–10% compared to pure water flux due to abrasion of the membranes separation layer by TiO2 P25 particles was found. In case of MF membrane a significant influence of vF and TMP on permeate flux was observed. Application of vF=3m/s led to a significant membrane fouling while at vF=6m/s the permeate flux exceeded pure water flux in the whole range of TMP. The fine UF Filtanium 5 membrane lost its separation properties due to abrasion by TiO2 P25 particles, whereas the performance of the ordinary UF Filtanium 100 membrane did not change during 100h of operation in the PMR. Additionally, the influence of a commercial TiO2 ST01 (Ishihara Sangyo, Japan) and laboratory made A700 (anatase) and A800 (rutile) on the permeate flux through Filtanium 100 membrane were assessed. The difference between the lowest and the highest values of the permeate fluxes measured for various TiO2 materials did not exceed 12%.

Technological processes of obtaining of replicated aluminium foam

A comparison of technological processes of replicated aluminium foam obtaining by two impregnation techniques (impregnation under high gas pressure of sintered NaCl powder and vacuum impregnation of loose NaCl powder) is performed. The typical ranges of porosity, minimum and maximum pore size, permeability characteristics obtained by alternative technologies are shown.

Preparation and characterization of braided tube reinforced polyacrylonitrile hollow fiber membranes

ABSTRACTPolyacrylonitrile (PAN) and polyester (PET) braided hollow tube that used as a special reinforcement are braided from their filaments via two‐dimensional weaving techniques. PAN braided tube reinforced homogeneous PAN hollow fiber membranes and PET braided tube reinforced heterogeneous PAN hollow fiber membranes are prepared by concentric circles squeezed‐coated spinning method. As for PAN hollow fiber membrane, the effects of PAN concentration on the performance of the prepared hollow fiber membranes are investigated in terms of pure water flux, protein rejection, mechanical strength, and morphology observations by a scanning electron microscope (SEM). The interfacial bonding state of the braided tube reinforced PAN hollow fiber membranes is studied by constant speed stretching method. Results show that the breaking strength of two‐dimensional braided tube reinforced PAN hollow fiber membranes is higher than 80 MPa. The structure of separation surface is similar to the structure of an asymmetric membrane. With the increase of polymer concentration, the membrane flux decreases while the retention rate of BSA increase. The membrane porosity and maximum pore size have the same decreasing tendency as the increase of PAN concentration. The results also show that the interfacial bonding state of the PAN two‐dimensional braided tube reinforced homogeneous PAN hollow fiber membranes is better than that of the PET two‐dimensional braided tube reinforced heterogeneous PAN hollow fiber membranes. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41795.

Doped tricalcium phosphate scaffolds by thermal decomposition of naphthalene: Mechanical properties and in vivo osteogenesis in a rabbit femur model.

Tricalcium phosphate (TCP) is a bioceramic that is widely used in orthopedic and dental applications. TCP structures show excellent biocompatibility as well as biodegradability. In this study, porous β-TCP scaffolds were prepared by thermal decomposition of naphthalene. Scaffolds with 57.64% ± 3.54% density and a maximum pore size around 100 μm were fabricated via removing 30% naphthalene at 1150°C. The compressive strength for these scaffolds was 32.85 ± 1.41 MPa. Furthermore, by mixing 1 wt % SrO and 0.5 wt % SiO2 , pore interconnectivity improved, but the compressive strength decreased to 22.40 ± 2.70 MPa. However, after addition of polycaprolactone coating layers, the compressive strength of doped scaffolds increased to 29.57 ± 3.77 MPa. Porous scaffolds were implanted in rabbit femur defects to evaluate their biological property. The addition of dopants triggered osteoinduction by enhancing osteoid formation, osteocalcin expression, and bone regeneration, especially at the interface of the scaffold and host bone. This study showed processing flexibility to make interconnected porous scaffolds with different pore size and volume fraction porosity, while maintaining high compressive mechanical strength and excellent bioactivity. Results show that SrO/SiO2 -doped porous TCP scaffolds have excellent potential to be used in bone tissue engineering applications.

Controllable synthesis of ordered mesoporous NiFe₂O₄ with tunable pore structure as a bifunctional catalyst for Li-O₂ batteries.

Three-dimensional ordered mesoporous (3DOM) NiFe2O4 materials with tunable pore size ranging from 5.0 to 25.1 nm have been synthesized via a hard template and used as bifunctional electrocatalysts for rechargeable Li-O2 batteries. Characterization of the catalysts by X-ray diffraction and transmission electron microscopy confirms the formation of a single-phase 3DOM NiFe2O4 structure. Linear scanning voltammetry measurements reveal that Ketjen black (KB) carbon-supported 3DOM NiFe2O4 exhibits a decreased overpotential for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) than commonly used KB. A reduction in both the ORR and OER overpotentials increases with the mean pore size of 3DOM NiFe2O4 materials. Importantly, Li-O2 batteries with 3DOM NiFe2O4 materials as the cathode catalysts exhibit a significant enhancement in the discharge capacity, rate capability, and cyclability, and these performances increases with the mean pore size of 3DOM NiFe2O4 materials. For a Li-O2 battery equipped with a 3DOM NiFe2O4 catalyst with a maximum mean pore size of 25.1 nm, a long cycling life of up to 100 cycles under the limiting capacity of 1000 mAh gC(-1) is achieved, strongly indicating that the mesoporous size of the bifunctional catalysts plays a crucial role in enhancing the performance of Li-O2 batteries. The combined use of 3DOM NiFe2O4 with a maximal pore size of 25.1 nm and a poly(vinylidene difluoride hexafluoropropylene) separator with a tuned pore structure further improves the Li-O2 battery performance, highlighting the importance of the pore structure in the development of bifunctional catalysts and separators.

Cold rolling for controllable narrowing of pore size and pore size distribution of commercial fluoroplastic microfiltration membrane

A cold-rolling method for modifying MFFK commercial microfiltration membranes based on the fluoroplastic F-42L has been developed and investigated. The method is based on the cold flow property of fluoropolymers and make it possible to alter the physical properties of a membrane without affecting its chemical structure. Scanning electron microscopy and capillary flow porometry studies have shown that this method also makes it possible to controllably narrow the through-pore diameter distribution, reduce the maximum pore size, and vary permeability depending on the applied force. In addition, rolling is a simple fluoroplastic-membrane modification process that is appropriate in engineering design and is easy to integrate into the membrane manufacturing cycle. According to available published data, this is a pioneering attempt to use the method for controllable reducing the pore diameter and narrowing the pore size distribution of fluoroplastic microfiltration membranes.

Soil water availability strongly alters the community composition of soil protists

Abstract Drought and heavy rainfall are contrasting conditions expected to result from increasingly extreme weather during climate change; and both scenarios will strongly affect the functioning of soil systems. However, little is known about the specific responses of soil microorganisms, whose functioning is intimately tied to the magnitude of the water-filled pore space in soil. Soil heterotrophic protists, being important aquatic soil organisms are considered as key-regulators of microbial nutrient turnover. We investigated the responses of distinct protist taxa to changes in soil water availability (SWA) using a modified enumeration technique that enabled quantification of protist taxa up to genus level. Our study revealed a non-linear shift of protist abundance with decreasing SWA and this became apparent at a maximum water-filled pore size of ≤40 μm. Generally, taxa containing large specimen were more severely affected by drought, but responses to either drought or rewetting of soils were not uniform among taxa. Changes in water availability may thus affect the functioning of key taxa and soil ecosystems long before aboveground “drought” effects become apparent.

Pore-size tuning and optical performances of nanoporous gold films

Through pulse electrochemical dealloying (PED) and chemical dealloying (CD), a variety of nanoporous gold (NPG) films of 100nm thickness with a wide range of pore size (4–140nm) were prepared. The coarsening mechanism of pore and the effect of residual Ag on optical performances were investigated. The pore size was tuned by controlling the dissolution rate of active Ag atoms and surface diffusion rate of noble Au atoms along the alloy/solution interfaces. The maximum pore size of 140nm was obtained by surfactant-assisted chemical dealloying (SA-CD) and the minimum pore size of 4nm was achieved by PED. It is found that the surface diffusivity of gold in PED is about 0.4–2×10−20m2s−1, four orders of magnitude smaller than that in SA-CD (2.4×10−16m2s−1). Finally, optical performances of the NPG films were investigated by UV–vis and surface-enhanced Raman scattering (SERS) spectra. The results reveal that the NPG film with a pore size of 8nm fabricated by PED exhibits higher surface-plasmon absorption and the strongest SERS effect.

The influence of manufacturing parameters and adding support layer on the properties of Zirfon® separators

The composite separator comprising of polysulfone and zirconia was prepared by phase inversion precipitation technique. The influence of manufacturing parameters on its properties was investigated, and the results show that the manufacturing parameters affect the ionic resistance and maximum pore size significantly. A modified composite separator with a support layer was prepared to enhance the tensile strength of separator. By adding support layer, the tensile strength of the separator increases from 1.85MPa to 13.66 MPa. In order to evaluate the practical applicability of the composite separator, a small-scale industrial electrolytic experiment was conducted to investigate the changes of cell voltage, gas purity and separator stability. The results show that the modified composite separator has a smaller cell voltage and a higher H2 purity than the asbestos separator, and are promising material for industrial hydrogen production.

Perspectives of suspension plasma spraying of palladium nanoparticles for preparation of thin palladium composite membranes

Suspension plasma spraying (SPS) of Pd nanoparticles was evaluated as a new method for coating of dense Pd films for H2 separation on porous substrates. The substrates were prepared by coating porous sinter metal disks with a porous yttria stabilized zirconia (YSZ) layer acting as a barrier against intermetallic diffusion between the sinter metal and the Pd membrane (diffusion barrier layer, DBL). Before applying the Pd coating, the sinter metal substrates were characterized by N2 permeance measurements. The maximum pore sizes before and after coating of the DBL were determined. For SPS of Pd, particles with diameters in the range between 250nm and 550nm were suspended in ethyl cellulose containing diethylene glycol monobutyl ether solution. A wide process parameter field was tested in the SPS. After Pd coating, the membrane morphology was characterized with scanning electron microscopy (SEM) and electron probe microanalysis (EPMA), and the membrane performance was evaluated with N2 and H2 permeation measurements. The thickest Pd layer (9.5µm) showed an ideal H2/N2 permselectivity of 60 at 350°C and a H2 permeability of 1.2×10−7exp(−1392/T) molm−1s−1Pa−0.5. Yet rather thick Pd layers of around 10µm were required to close the pores of the rough YSZ layers, but with further optimizations, SPS appears to be a promising new way for the fabrication of robust Pd coatings on porous substrates. A particular advantage is seen in the very quick deposition.

The bubble point of supported ionic liquid membranes using flat sheet supports

Supported ionic liquid membranes were tested to determine the maximum pressure drop that can be withstood before expulsion of the liquid from the membrane pores, also known as the bubble point. Bubble point was measured using two ionic liquids, 1-hexyl-3-methylimidazolium bis(trifluoromethyl-sulfonyl)imide ([hmim][Tf2N]) and 1-ethyl-3-methylimidazolium ethyl sulfate ([emim][EtSO4]), and four porous flat sheet supports, including anodic alumina, track etched polyester, nylon, and polysulfone. These supports represented a variety of pore morphologies that ranged from straight and cylindrical to highly tortuous, interconnected and irregularly shaped. An effective maximum pore size and pore size distribution were determined for each porous support using gas–liquid displacement porometry with isopropanol as a wetting fluid. From this it was possible to accurately predict the bubble point for ionic liquids using the Laplace–Young equation, but only if a contact angle of zero was assumed for all combinations of liquids and supports. Also, the effects of surface tension, pore size, and temperature on the bubble point were evaluated. It was found that a judicious combination of support structures and ionic liquids can lead to a very stable system which can satisfy many membrane applications.

Bone Tissue Response in a Metallic Bone Architecture Microstructure

Porous metallic structures have been developed to mimic the natural bone architecture, having interconnected porosity, disposing enough room to cell migration, anchoring, vascularization, nourishing and proliferation of new bone tissue. Research involving porous titanium has been done with purpose to achieve desirable porosity and increasing of bone-implant bond strength interface. Samples of titanium were prepared by powder metallurgy (PM) with addition of different natural polymers (cornstarch, rice starch, potato starch and gelatin) at proportion of 16wt%. In aqueous solution the hydrogenated metallic powder (TiH2) and the polymer were mixed, homogenized and frozen in molds near net shape. The water was removed in kiln and the polymer by thermal treatment in air- (350°C/1h) before sintering in high-vacuum (1300°C/1h). The biological evaluation was performed byin vivotest in rabbits. Histological analysis was performed by scanning electron microscopy (SEM), energy dispersive spectroscopy (SEM-EDS) and fluorescence microscopy (FM). The processing methodologies using natural low cost additives propitiate the production of porous metallic implants in a simplified manner, with different porosities, proper porosity degree (40%), distribution, and maximum pore size of 80 μm to 220 μm depending of natural polymer used. The samples added with rice starch, presented the most similar structure organization when compared to the bone tissue microstructure organization of the trabecular bone. All implants osseointegrated, the pore microarchitecture and its interconnected network allowed bone ingrowth in all pore sizes, but the continuous bone maturation occurred in pores bigger than 80 μm.