Maximum Pore Size Research Articles

Novel synthesis of high-surface-area ordered mesoporous TiO 2 with anatase framework for photocatalytic applications

Ordered mesoporous TiO 2 materials with an anatase frameworks have been synthesized by using a cationic surfactant cetyltrimethylammonium bromide (C 16TMABr) as a structure-directing agent and soluble peroxytitanates as Ti precursor through a self-assembly between the positive charged surfactant S + and the negatively charged inorganic framework I − (S +I − type). The low-angle X-ray diffraction (XRD) pattern of the as-prepared mesoporous TiO 2 materials indicates a hexagonal mesostructure. XRD and transmission electron microscopy results and nitrogen adsorption–desorption isotherms measurements indicate that the calcined mesoporous TiO 2 possesses an anatase crystalline framework having a maximum pore size of 6.9 nm and a maximum Brunauer–Emmett–Teller specific surface area of 284 m 2 g −1. This ordered mesoporous anatase TiO 2 also demonstrates a high photocatalytic activity for degradation of methylene blue under ultraviolet irradiation.

Development of a new graded-porosity FeAl alloy by elemental reactive synthesis

A new graded-porosity FeAl alloy can be fabricated through Fe and Al elemental reactive synthesis. FeAl alloy with large connecting open pores and permeability were used as porous supports. The coating was obtained by spraying slurries consisting of mixtures of Fe powder and Al powder with 3–5 μm diameter onto porous FeAl support and then sintered at 1100 °C. The performances of the coating were compared in terms of thickness, pore diameter and permeability. With an increase in the coating thickness up to 200 μm, the changes of maximum pore size decreased from 23.6 μm to 5.9 μm and the permeability decreased from 184.2 m 3 m − 2 kPa − 1 h − 1 to 76.2 m 3 m − 2 kPa − 1 h − 1 , respectively, for a sintering temperature equal to 1100 °C. The composite membranes have potential application for excellent filters in severe environments.

Development, characterization, and in vitro bioactivity studies of sol–gel bioactive glass/poly( l-lactide) nanocomposite scaffolds

Developing materials combining the advantages of synthetic polymers and bioactive glass nanoparticles can provide an efficient bone engineering scaffold. In this study, sol–gel bioactive glass (SG) nanoparticles were synthesized by quick alkali-mediation; sol–gel derived bioactive glass/poly( l-lactide) nanocomposite scaffolds were then developed. The influence of the glass content on the porosity of nanocomposite scaffolds was evaluated by SEM. The results showed that the neat polymer scaffold (PLA) has a highly interconnected porous structure with a maximum pore size of about 250 μm. For the composite scaffold containing 25 wt.% glass (SGP25), the decrease in the maximum pore size, (to about 200 μm) was not significant while for the SGP50 composite scaffold containing 50 wt.% glass it was a significant decrease (to about 100 μm). The apparent porosity of the scaffolds was 56.56% ± 7.15, 54.14% ± 3.84, and 53.11% ± 3.99 for PLA, SGP25, and, SGP50 respectively. FT-IR, TGA, and XRD results revealed some interaction of the glass filler with the polymeric matrix in the scaffolds. The degradation study showed that, by increasing the glass content in the scaffolds, the water absorption decreased, the weight loss increased, and the cumulative ion concentrations released from them also increased. This indicates the possibility of modulating the degradation rate by varying the glass/polymer ratio. At the end of the incubation period, the weight losses were around 5.44% ± 0.96, 32.50% ± 2.73, and 41.47% ± 3.02 for the PLA, SGP25, and SGP50, respectively. Moreover, the water uptake reached 119.65% ± 18.88 and 93.39% ± 13.01 for SGP25 and SGP50, respectively. The addition of the SG to the scaffolds was found to enhance their in vitro bioactivity. Therefore, these nanocomposite scaffolds have a potential to be applied in bone engineering. All data are expressed as mean ± standard deviation ( n = 3).

Foam Tests for Lubricating Oils: Limitations of Reliability and Reproducibility

Abstract The ASTM D892 foam test is a simple yet important method for evaluating the foaming tendency and stability of lubricating oils. Numerous interlaboratory studies have clearly shown the poor repeatability and reproducibility of this test. Often the quality of diffusers used in the test is questionable, yet many laboratories do not verify the diffuser quality. Perhaps using only the metal diffusers will improve the situation since these are machine made and can be fabricated to the required maximum pore size and permeability specifications. A review of the critical factors involved in conducting the ASTM D892 foam test is presented. Changes are proposed to the materials and procedures that will improve the precision of this important test method.

Preparation of polyvinylidene fluoride membrane via a thermally induced phase separation using a mixed diluent

AbstractPolyvinylidene fluoride (PVDF) membranes were prepared via a thermally induced phase separation method with a mixed diluent (dibutylphthalate/dioctyl phthalate). The effects of PVDF concentration and cooling bath temperature (CBT) on the structure and properties of the membranes were investigated. Scanning electron microscopy photos showed that the cross‐section of all the membranes, regardless of PVDF concentration and CBT, presented a bi‐continuous structure with the spherulitic pattern; moreover, the spherulitic patterns became clear gradually from the top surface to the bottom surface, and the top surface was denser than the bottom surface. As a result, all the membranes exhibited an asymmetric structure. The membrane property measurement indicated that, as PVDF concentration increased from 25 to 35 wt %, the pure water flux (PWF) decreased from 342 to 80 L m−2 h−1, and the porosity decreased slightly, whereas the minimum bubble point pressure (BPP) increased, which indicates maximum pore size decreased. In addition, with the increase in CBT, the PWF increased, but, the minimum BPP and porosity decreased. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Preparation and Application of Porous Stainless Steel Cone/Tube in Coal Gasification Engineering

Abstract In the Shell Coal Gasification Process (SCGP), porous stainless steel cone is used as a gas-distributor to make pulverized coal entering fluidization which can insure the continuous transportation of coal powder and improve the combustion efficiency. In the service conditions the porous cone must have not only high and uniform permeability, but also a proper strength. This study focuses on the preparation of porous stainless steel cone and tube with high performances such as permeability and strength etc. for applications. The porous cone/tube with 32%-35% in porosity, 20 micron in maximum pore size was prepared by CIP. After welding and sealing, the breaking pressures of cone/tube are larger than 2.5 MPa which meet the requirements for fluidization transportation of coal powder in SCGP.

Formation of porous Ni–Al intermetallics through pressureless reaction synthesis

Pressureless reaction synthesis method was used to produce porous NiAl and Ni 3Al intermetallics using elemental Ni and Al powder mixture in this investigation. The sintering behavior of Ni and Al mixed powder compacts was investigated by applying XRD, SEM and EDS in the temperature range of 510–1000 °C. It has been found that the formation of porous Ni 3Al and NiAl was accompanied by the volume expansion due to the formation of intermediates and pores during the reaction synthesis procedure. The intensive reaction and phase transformation procedures were similar in the Ni–14 wt% Al and Ni–30 wt% Al. However, the maximum pore size, expansion ratio and porosity have been found to be varied with the sintering temperature and Al content in the compacts. The Al content in the green compacts could effectively influence the volume expansion and pores of the products: the volume expansion and maximum pore size of NiAl are much higher than that of Ni 3Al under the same sintering procedure.

Lipid nanopores can form a stable, ion channel-like conduction pathway in cell membrane

Cell permeabilization by electric pulses (EPs), or electroporation, has been well established as a tool to indiscriminately increase membrane flows of water solutes down the concentration and voltage gradients. However, we found that EPs of nanosecond duration (nsEPs) trigger formation of voltage-sensitive and inward-rectifying membrane pores. NsEP-treated cells remain mostly impermeable to propidium, suggesting that the maximum pore size is ∼1 nm. The ion-channel-like properties of nsEP-opened nanopores vanish if they break into larger, propidium-permeable “conventional” pores. However, nanopores can be stable for many minutes and significantly impact cell electrolyte and water balance. Multiple nsEPs cause fast cell swelling and blebbing, whereas opening of larger pores with digitonin abolishes swelling and causes blebs to implode. The lipid nature of nsEP-opened nanopores is confirmed by fast externalization of phosphatidylserine residues. Nanopores constitute a previously unexplored ion transport pathway that supplements classic ion channels but is distinctly different from them.

Preparation and characterization of alumina hollow fiber membranes

With the rapid development of membrane technology in water treatment, there is a growing demand for membrane products with high performance. The inorganic hollow fiber membranes are of great interest due to their high resistance to abrasion, chemical/thermal degradation, and higher surface area/volume ratio therefore they can be utilized in the fields of water treatment. In this study, the alumina (Al2O3) hollow fiber membranes were prepared by a combined phase-inversion and sintering method. The organic binder solution (dope) containing suspended Al2O3 powders was spun to a hollow fiber precursor, which was then sintered at elevated temperatures in order to obtain the Al2O3 hollow fiber membrane. The dope solution consisted of polyethersulfone (PES), Nmethyl-2-pyrrolidone (NMP) and polyvinylpyrrolidone (PVP), which were used as polymer binder, solvent and additive, respectively. The prepared Al2O3 hollow fiber membranes were characterized by a scanning electron microscope (SEM) and thermal gravimetric analysis (TG). The effects of the sintering temperature and Al2O3/PES ratios on the morphological structure, pure water flux, pore size and porosity of the membranes were also investigated extensively. The results showed that the pure water flux, maximum pore size and porosity of the prepared membranes decreased with the increase in Al2O3/PES ratios and sintering temperature. When the Al2O3/PES ratio reached 9, the pure water flux and maximum pore size were at 2547 L/m2·h and 1.4 μm, respectively. Under 1600dgC of sintering temperature, the pure water flux and maximum pore size reached 2398 L/(m2·h) and 2.3 μm, respectively. The results showed that the alumina hollow fiber membranes we prepared were suitable for the microfiltration process. The morphology investigation also revealed that the prepared Al2O3 hollow fiber membrane retained its’asymmetric structure even after the sintering process.

Silk fibroin/polyacrylamide semi-interpenetrating network hydrogels for controlled drug release

The present study describes a semi-interpenetrating network hydrogel fabricated using silk fibroin/polyacrylamide for controlled drug delivery applications. Hydrogels were synthesized using varied ratios of silk fibroin/acrylamide mixtures crosslinked by N, N′-Methylenebisacrylamide. Fourier-Transform Infrared analysis was performed suggesting β sheet transition of silk fibroin with hydrogels. Scanning electron microscopy revealed microporous surface with maximum pore size of 50 ± 11 μm. Rheological properties along with swellability, degradation, sol fraction estimation, equilibrium water content and swelling kinetics were evaluated. Compressive strength of 241.9 ± 5.5 kPa was observed suggesting mechanically stronger gels. MTT assay showed biocompatibility and absence of deleterious effects of hydrogel on cell viability and functionality. In vitro release studies using two model compounds i.e. trypan blue dye and FITC-inulin reveal their sustained release from the fabricated hydrogel constructs.

Estimate of maximum pore size in keyhole laser welding of carbon steel

Porosity is easily formed in welded joints during high power laser welding due to keyhole instability. Large pores have detrimental effects on the fatigue resistance of a component and cause many failures in welded parts. This paper is aimed at predicting the maximum pore dimension in long laser welded joints, starting from the sampling of large pores in shorter joints. Two sampling strategies and, consequently, two estimating techniques, both belonging to the statistics of extremes, were explored. The first approach, extreme value type, is used to estimate the size of the maximum pore in each of a series of steel samples. In each sample, the larger single pore or two large pores which are very close are the measured maximum pore. The second approach, threshold value type, is used to estimate the size of pores larger than a critical threshold in a single sample of steel. Both approaches lead to good estimates of the largest pore distribution in short laser welded joints. However, the first one is more adequate to describe the largest pore distribution, because it allows the synergetic effect of two adjacent pores to be considered. In particular, the Gumbel distribution adequately fits the experimental data even in the case of welded joints 10 times longer than the investigated bead length.

Research on TiAl Alloy Porous Metal Flow Restrictors

For the restriction application, the uniformity of pore size and connectivity of pore channels are much more important for TiAl restrictor. TiAl porous materials have expansion phenomenon during reaction sintering for the Kirkendall Effect, and the pores were generated by its partial diffusion. In this paper, elemental powders blending and reaction sintering methods were adopted to prepare TiAl porous flow restrictor materials. The influence of particle size, the fraction of Ti and Al powder, pressing pressure, sintering temperature on the pore character of TiAl porous flow restrictor was studied. The results show that the maximum pore size and expansion coefficient increased with the increase of Al powder particle size, the porosity and permeability increased only when the Al powder particle size is larger than 400/+600 mesh. With the decrease of larger particle Al powder fraction, the porosity and permeability decreased, but the maximum pore size shows little change. With the increase of fraction of fine Al powder, the porosity and permeability increased to a certain value then decreased. With the increase of pressing pressure, maximum pore size, porosity and permeability decreased. When the sintering temperature is lower than 800C, the porosity and permeability increased with the increase of sintering temperature. At above 800C, the porosity and permeability decreased with the increase of sintering temperature. [doi:10.2320/matertrans.M2009120] (Received April 6, 2009; Accepted July 23, 2009; Published September 25, 2009)

ULTRAFILTRATION MEMBRANE FORMATION OF PES-C, PES AND PPESK POLYMERS WITH DIFFERENT SOLVENTS

Ultrafiltration membranes were prepared using phenolphthalein polyarylethersulfone (PES-C), polyethersulfone (PES) and poly(phthalazinone ether sulfone ketone) (PPESK) as polymers and NMP, DMAc, DMF and DMSO as solvents by immersion precipitation via phase inversion. Experimental data of thermodynamic properties of the polymer solutions and kinetic process of membrane formation were reported. For polymer solutions with good solvents, the sequence of the viscous flow activation energy (Eη) was coincident with that of the viscosity (η), without depending on the dissolving power of the solvents (characterized by intrinsic viscosity ([η])). The cloud point of the dilute polymer solutions was related to [η] of the polymer and gave a strong influence on the gelation rate in membrane formation process. The pure water flux (J) and the bovine serum albumin (BSA) rejection (R) of PES-C, PES and PPESK membranes were measured, the pure water flux (J) of membranes significantly depended on the gelation rate. The open porosity (OP) and the maximum pore size of membrane surface were calculated, and the relationship between membrane performance and membrane pore structure was discussed.

Effect of the porous structure of thermal-barrier coatings on their heat conductivity

A phenomenological model is proposed to show the dependence of the heat conductivity of a porous coating on the pore size using experimental data on ZrO2 + 7% Y2O3 coatings. To obtain plasmasprayed coatings with different structures, powders with different properties are used. The concept of critical pore size at a given porosity is proposed. It is the maximum pore size at which the heat conductivity depends not only on the total porosity but also on the pore size, which is especially important for materials with submicron and nanosized structural components. Since the free path of phonons scattered by pores depends on the distance between them, the concept of critical distance between pores is introduced. It is the maximum distance beyond which the heat conductivity depends on the integral porosity alone.

Multilayer Assembly of Hyaluronic Acid/Poly(allylamine): Control of the Buildup for the Production of Hollow Capsules

The objective of this work was to investigate the formation of hollow microcapsules composed of hyaluronic acid (HA) and poly(allylamine) (PAH) by layer-by-layer adsorption on CaCO 3 microparticles and subsequent core removal by addition of chelating agents for calcium ions. We found that the molecular weight of HA as well as the HA solution concentration used during deposition are crucial parameters influencing the multilayer structure. Whereas the effect of molecular weight of HA was mainly attributed to the porous structure of the template which allows penetration of polyelectrolytes when their size is below the maximum pore size of the template ( approximately 60 nm), that of the concentration of the HA solution was related to the intrinsic properties of the polysaccharide. Indeed, as shown by quartz crystal microbalance with dissipation monitoring as well as electron microscopy techniques, the latter leads to dense structures for concentrations from five to ten times the critical overlap concentration during adsorption. Such conditions were found to be favorable for the formation of hollow shells. Regarding conditions for core dissolution, we demonstrated the possibility to use either ethylenediaminetetraacetic acid (EDTA) or citric acid as chelating agents. However, in some cases, it was necessary to chemically cross-link the shell to maintain its integrity.

Effect of heating rate on pore structure of porous FeAl material

The sintering behaviour of elemental powders of Fe and Al was investigated at various heating rates (0˙5–10°C min–1). It was found that the formation of porous FeAl material was accompanied by the volume expansion during the formation of the intermediate phase Fe2Al5. The final pore structure of porous FeAl material depends strongly on the heating rate; the higher the heating rate, the higher the volume expansion and the larger the porosity and the maximum pore size. It has been found that the pore structures produced with different heating rates experienced different formation routes.

A study of lubrication mechanisms using two-phase fluids with porous bearing materials

A potential, novel lubrication mechanism involving two-phase fluids and porous bearing materials is examined in this study both theoretically and experimentally. Lubricating oils with a secondary particulate phase have been considered operating in oil-saturated porous media with the elements of the particulate phase acting as one-way valves on the pores, blocking and unblocking them, depending on the direction of contact load. The goal is to enhance the lubrication, mainly in starved contacts and in some ‘difficult’ applications, as for example in big end bearings for marine engines. The theoretical part of this work deals with the mathematical analysis of an oil-saturated, porous slab, in contact with a solid sphere and lubricated with a two-phase oil containing thin and soft platelets. The problem is analysed using Biot's theory of consolidation in porous media. A subsequent study deals with the effects of the maximum contact load, size, and number of pores of the porous medium, elastic modulus of the medium, and the viscosity of the oil used to carry the particulate phase, on the lubrication performance of the system. Furthermore, a rig was built to study the concept on a macroscale and the results are reported in the paper. Both the theoretical and the experimental work gave good indications that the concept works, at least in some cases. Potential problems with application of this lubrication mechanism have also been identified and are briefly discussed in the paper.

Effect of porosity on PVdF- co-HFP–PMMA-based electrolyte

A novel MPPBEM based on PVdF- co-HFP–PMMA was prepared with a preferential polymer dissolution process. The N 2 gas adsorption/desorption and SEM analysis were used to reveal the porous structure of the polymer matrix and attain the maximum pore size in the range of 251 nm. AC-impedance spectroscopy measurement was carried out to investigate the ionic conductivity of MPPBEMs and achieved a maximum ionic conductivity of 10.23 × 10 −3 S cm −1 at room temperature. The lithium transference numbers of MPPBEMs were measured using the DC-polarization method coupled with AC-impedance spectra are found to be above 0.639. Finally, the electrode/electrolyte interfacial resistance was evaluated by monitoring the impedance response at different time intervals.

Fatigue strength and fracture mechanism of different post-fused thermal spray-coated steels with a Co-based self-fluxing alloy coating

The characteristics and adhesive strength of thermal-sprayed coatings at the interface between the coating and substrate are affected by the post-fusing treatment process. We investigated the effect of the adhesive strength on the fatigue strength and fracture mechanism of post-fused specimens. Rotating bending fatigue tests were conducted on specimens with a Co-based self-fluxing alloy coating on a medium carbon steel substrate. The post-fusing treatment was performed using a vacuum furnace, an electric furnace, or an induction heating system. A diffusion layer formed at the interface of the specimens treated in either furnace at 1100 °C for 4 h. These conditions produced a strong adhesive strength; the fatigue strength of these specimens also increased remarkably compared to the substrate-only specimens. However, the specimens treated with an induction heating system at 1100 °C for 120 s had a much lower adhesive strength since a diffusion layer was not formed, leading to delamination of the entire coating from the substrate during the first stage of the fracture process. The fatigue strength of these specimens was almost equal to that of the substrate-only specimens. Thus, thermal-sprayed coatings treated in vacuum and electric furnaces were more effective due to the formation of a diffusion layer, which contributed to improving the fatigue strength of the steel specimens. The expected maximum pore size of the coatings treated in vacuum and electric furnaces were estimated using statistics of extreme value.

Effect of the flowing gases of steam and CO 2 on the texture and catalytic activity for methane combustion of MgO powders

In this work, the MgO powders was prepared by the precipitation method with carbonate following calcination at 1200 °C, and then the obtained MgO powders was treated under the flowing gaseous mixture of steam and CO 2. The variations of textural properties and activity for methane combustion of the MgO sample were investigated. The sample was characterized by N 2 adsorption isotherm, TEM, XRD, and TG-DTA. The results showed that the treatment temperature and the CO concentration have a significant influence on the textural properties of the MgO sample. After run at 700 °C for 24 h under the flowing gaseous mixture of steam/CO 2/N 2 (CO 2/N 2 = 15/85 volume ratio), the maximum pore sizes varied and the pore volumes increased obviously; and remarkably, the surface area of the MgO sample increased from 37.9 to 80.1 m 2 g −1. It was proposed that during the process, the disaggregation and rearrangement of the particles have occurred, leading to the obvious variations of the textural properties of the sample. As a result, the treated MgO sample showed a higher activity for methane combustion than the original one.