Decrease Of Mean Pore Size Research Articles

Hierarchical micro/nanofibrous filter for effective fine-particle capture

Hierarchical micro/nanofibrous filters are fabricated by blending electrospun polyurethane (PU) nanofiber with polyethylene terephthalate (PET) microfibers followed by spunlace reinforcement. PET microfibers mainly act as a skeletal framework and PU nanofiber is employed for capturing fine particles. The incorporation of PU nanofiber optimizes inner structures and improves filtration properties of hybrid filters. The mean pore size decreases and pore size distribution shifts to smaller pore sizes with the increased content of PU nanofiber. When the PU nanofiber accounts for 1.87%, the composite filter exhibits a high filtration efficiency (76.63%) for PM0.26 and low pressure drop (17.3 Pa) under an airflow velocity of 5.3 cm/s. This composite filter exhibits a high quality factor of 0.084 Pa−1. Furthermore, the removal efficiency for PM2.5 reaches to 99.93% with a low terminal pressure drop of 26.3 Pa. The composite filters with excellent filtration performances prepared can be applied to industrial production and commercial applications.

Study on dynamic characteristic of closed-cell aluminum foam

Closed-cell aluminum foam has been widely used in aerospace, rail transit and mechanical for its outstanding performance. But for a long time, the research on its vibration damping performance is only limited to the material damping test, there are relatively few studies on its dynamic characteristics. In this paper, we studied the relationship between dynamic characteristic and feature parameters. Modal assurance criterion and Finite element method were used to verify the accuracy of experimental model. It turned out that the average pore diameter of closed-cell aluminum foam conforms to Gaussian distribution. The modal analysis method can be used in the research of dynamic characteristic of closed-cell aluminum foam. Its damping ratio showed increasing trend with the increase of porosity, natural frequency and the decrease of mean pore size. Each order natural frequency increases along with the increase of porosity.

Correlation of pore structure and alkali vapor attack resistance of bauxite–SiC composite refractories

Alkali attack resistance of cement kiln refractories has become one of the key factors affecting their performance life. In this paper, the correlation between mean pore size, pore size distribution of bauxite–SiC composite refractories and their alkali attack resistance was investigated by means of mercury intrusion porosimetry, X-ray diffraction (XRD), and scanning electron microscopy (SEM). Also, the percolation theory, as well as modeling prediction, was applied associated with thermodynamic calculations. The results showed that quartz phase was generated from the oxidation process of silicon filling in part of pores, which resulted in a significant decrease in both the mean pore size and permeability of the samples. The proposed alkali attack mechanism indicated that K2CO3 was firstly reduced to K vapor and then infiltrated into the sample through the open pores. Consequently, the KAlSiO4 phase was formed in the edge part of the samples. When the K vapor permeated into the center of the sample, the KAlSi2O6 phase was first generated. Afterwards, the decomposition of KAlSi2O6 in the K-rich atmosphere gave rise to the formation of quartz and KAlSiO4. The decrease of mean pore size and apparent porosity, especially the reduction of the proportion of large pores, helped to prevent the alkali vapor from infiltrating into the samples, bringing about a superior vapor attack resistance at high temperature.

Effect of copolymer concentration on the structure and permeability of temperature-sensitive poly(vinylidene fluoride) hollow fiber membrane

Temperature-sensitive poly(vinylidene fluoride)-grafted-poly( N-isopropylacrylamide) (PVDF- g-PNIPAAm) copolymer hollow fiber membrane was fabricated by dry–wet spinning technique using N,N-dimethyl formamide as solvent and poly(ethylene glycol) as pore-making agent, respectively. The effect of PVDF- g-PNIPAAm copolymer concentration in the spinning solution on the structure and performance of resultant fiber membranes were investigated by field-emission scanning electronic microscopy, pore size measurements, mechanical tests, and filtration experiments. It was found that the microvoid in the inner cross-section of hollow fiber membrane changed to a finger-like structure with the increase of copolymer concentration from 16 to 20%. The increasing copolymer concentration also led to the increase of the inner diameter, outer diameter, and wall thickness and the decrease of mean pore size and porosity. When the permeation temperature was increased from 20 to 45°C, a remarkable reduction of pure water flux and a drastic increase of the retention of bovine serum albumin were observed around 32°C, indicating an obvious temperature-sensitive permeability.

The fabric of consolidation in Gulf of Mexico mudstones

How the micro-scale fabric of clay-rich mudstone evolves during consolidation in early burial is critical to how they are interpreted in the deeper portions of sedimentary basins. Core samples from the Integrated Ocean Drilling Program Expedition 308, Ursa Basin, Gulf of Mexico, covering seafloor to 600 meters below sea floor (mbsf) are ideal for studying the micro-scale fabric of mudstones. Mudstones of consistent composition and grain size decrease in porosity from 80% at the seafloor to 37% at 600 mbsf .Argon-ion milling produces flat surfaces to image this pore evolution over a vertical effective stress range of 0.25 (71 mbsf) to 4.05MPa (597 mbsf). With increasing burial, pores become elongated, mean pore size decreases, and there is preferential loss of the largest pores. There is a small increase in clay mineral preferred orientation as recorded by high resolution X-ray goniometry with burial.

Capillary effects on hydrate stability in marine sediments

[1] We study the three-phase (Liquid + Gas + Hydrate) stability of the methane hydrate system in marine sediments by considering the capillary effects on both hydrate and free gas phases. The capillary pressure, a measure of the pressure difference across a curved phase interface, exerts a key control on the methane solubility in Liquid + Hydrate (L + H) and Liquid + Gas (L + G) systems. By calculating the L + H and L + G solubilities as a function of water depth (pressure) and pore size (interface curvature), we show how the solubility requirements for forming both gas hydrate and free gas can be met in a three-phase zone. The top of the three-phase zone shifts upward in sediments as the water depth increases and the mean pore size decreases. The thickness of the three-phase zone increases as the distribution of pore sizes widens. The top of the three-phase zone can overlie or underlie the bulk three-phase equilibrium depth. At Blake Ridge, we predict that the three-phase zone is 27.7 m thick and that the top of the three-phase zone lies 13 m above the predicted bulk equilibrium depth. This reconciles the observation of the bottom-simulating reflector (BSR) at Blake Ridge that is shallower than the predicted bulk equilibrium depth. In contrast, at Hydrate Ridge where water depth is shallower, we predict that the three-phase zone is 20.4 m thick and that the top of the three-phase zone lies 0.7 m below the predicted bulk equilibrium depth. Our model, which predicts an upward shift in the top of free gas occurrence with increasing water depth (pressure), is compatible with worldwide observations that the BSR is systematically shifted upward relative to the bulk equilibrium depth as water depth (pressure) is increased.

Preparation of Symmetric Network PVDF Membranes for Protein Adsorption via Vapor-Induced Phase Separation

Symmetric network poly(vinylidene fluoride) (PVDF) membranes without a dense skin layer were prepared by vapor-induced phase separation from a PVDF/N,N-dimethylacetamide (DMAc)/water system. The effects of evaporation atmosphere, temperature, and humidity during the preparation of the membranes on their morphologies were investigated by scanning electron microscope (SEM). With low temperature and high humidity, the polymer crystallization mechanism dominated the membrane formation process, and the casting solution formed membranes with symmetric morphologies in the vapor phase containing 0.79% DMAc. The effect of additives on the membrane structure and performance was also investigated. The results of adsorption experiments showed that the binding capacity of bovine serum albumin (BSA) increased with the appearance of a circular network morphology and the decrease of mean pore size of the membrane. With the addition of LiCl to the casting solution, the obtained membrane can adsorb BSA up to 150 μg/cm2. Proteins on sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis gels were successfully electro-blotted onto these PVDF membranes. Compared with commercial membranes, the PVDF membranes prepared in this work were more suitable for protein blotting.

Preparation, Morphology, Performance, and Hydrophilicity Studies of Poly(amide-imide) Incorporated Cellulose Acetate Ultrafiltration Membranes

Fouling-resistant cellulose acetate (CA) membranes were prepared by the phase inversion technique using hydrophilic poly(amide-imide) (PAI) as the modification agent. The prepared membranes were characterized using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), pure water flux, water content, porosity, and contact angle technique to investigate the influence of PAI on the final properties of the membranes. Intermolecular interactions between the components in blend membranes were established by ATR-FTIR, and semicrystalline nature was confirmed by XRD. SEM analysis showed that blend CA membranes have a thinner top layer and higher porosity in the sublayer. AFM surface roughness analysis data substantiate the enhanced surface porosity with an increase in PAI content, while the mean pore size decreases. The contact angle measurements indicated that the hydrophilicity of the CA membranes was improved by the addition of PAI due to the preferential orientation of functional groups towards the surface. Moreover, the surface free energy parameters of the membrane such as surface free energy, interfacial free energy, work of adhesion, and spreading coefficient were calculated. From the results, it was revealed that low interfacial free energy membranes prepared by the incorporation of PAI may be valuable in fouling-resistant industrial separations.

Mechanism for viscoelastic polymer solution percolating through porous media

The pore throat of porous media is modeled as a constricted channel or expanded channel. The flow of viscoelastic polymer solution in pore throat model is studied by numerical method. Relationship between pressure drop and flow rate is developed, viscoelasticity and throat size are found to be two main factors in high flow resistance. According to pore throat model, 2-D stochastic channel bundle is put forward to model porous media, which is composed of pore throat models in series - parallel connection with size and length accord to Haring - Greenkorn stochastic distribution. Percolation model of viscoelastic fluid is developed on the basis of Darcy equation and pressure drop vs. flow rate relation in 2-D stochastic channel bundle. Results indicate that the seepage ability of viscoelastic polymer solution decreases with the increase of viscoelasticity, injection rate, and heterogeneity as well as the decrease of mean pore size of porous media. The high pressure drop of viscoelastic fluid at the connection of pore to throat plays a great role in its anomalous high flow resistance through porous media.

Superficial performance and pore structure of palygorskite treated by hydrochloric acid

In order to amend the superficial performance of palygorskite and improve its application, the natural palygorskite(NP) was treated in the dipping and ionic exchanging experiments using 6 mol/L hydrochloric acid treatment. The performance and pore structure of the treated palygorskite(TP) were investigated by means of microscope analyses, FT-IR, XRF, BET-SSA and full hole distribution analytical techniques. The results show that the hydrochloric acid treatment can make the gracile and aggregating compact crystal bundles inside palygorskite clay broken and dispersed, the roughness of microcrystalline surface increases, which not only can dissolve or remove dolomite but vary the superficial performance of palygorskite to some degree. The specific surface area and pore volume increase a lot, while the mean pore size decreases. The pore structure of TP changes remarkably compared with that of NP after 6 mol/L hydrochloric acid treatment, and the relevant physicochemical performance can be improved.

Studies on Porous and Morphological Structures of Expanded PTFE Membrane through Biaxial Stretching Technique

A porous expanded polytetrafluoroethylene (ePTFE) membrane was prepared from emulsion polymerized PTFE fine powders by a series of mechanical operations, which included extrusion, rolling, stretching and heat setting. Very small holes in the PTFE sheet were observed by SEM analyses after extrusion and rolling, and which were elongated and enlarged by longitudinal stretching. Fibrils between the slits are observed by SEM analyses. The second stretching operation, transverse stretching, provided a lattice-like porous structure. After heat setting, an island-like structure was formed, which is composed of billions of tiny inter-connected continuous fibrils and nodes. The porous structure was studied through SEM and the COULTER POROMETER tester. Results show that the mean pore size and porosity increase with an increase in longitudinal stretching ratio, transverse stretching ratio, and heat setting temperature. The mean pore size decreases and the porosity increases with an increase in transverse stretching rate. Remarkably, increasing transverse stretching rate increases porosity while the mean pore size decreases slightly, resulting in a membrane with a more uniform cell and denser cell structure. DSC, WAXD analysis and mechanical testing show that mechanical processing and heat setting decrease both the crystallinity and crystallite size.