Cylinder Pores Research Articles

The latent heat of confined fluids calculated from the Clausius-Clapeyron equation

Monte Carlo simulations of simple Lennard Jones fluids confined in different geometries, sphere, cylinder and slit-like pores are conducted to study the vapour-liquid transition. Phase diagrams, in the temperature-density (T-ρ) and pressure-temperature (P-T) are obtained. For each geometry the coexistence lines are plotted from the clapeyron equation of each systems and a P −T equation is proposed in terms of the critical temperature which works for all the systems. Additionally, the transition latent heat is also evaluated, from the enthalpy calculation obtained directly from the simulation data, and the fluid structure from density profiles.

Resource recovery from RO concentrate using nanofiltration: Impact of active layer thickness on performance

Modelling the removal of monovalent and divalent ions from seawater via nanofiltration is crucial for pre-treatment in seawater reverse osmosis systems. Effective separation of divalent ions through nanofiltration and allowing the permeate containing only monovalent ions to pass through the reverse osmosis system produces pure NaCl salt from the concentrate. However, the Donnan steric pore model and dielectric exclusion assume a uniformly distributed cylinder pore morphology, which is not representative of the actual membrane structure. This study analyzed the impact of membrane thickness on neutral solute removal and investigated the effect of two different methods for calculating the Peclet number on rejection rates of monovalent and divalent salts. Results show that membrane thickness has a significant effect on rejection rates, particularly for uncharged solutes in the range of 0.5–0.7 solute radius to membrane pore size ratio. Operating pressures above 10 bar favour the use of effective active layer thickness over the membrane pore size to calculate the Peclet number. At low pressures, using the effective active layer can lead to overestimation of monovalent salt rejection and underestimation of divalent salt rejection. This study highlights the importance of appropriate Peclet number calculation methods based on applied pressure when modelling membrane separation performance.

Impedance Analysis on Initiation and Growth of Ant-Nest Corrosion of Copper

The branched pitting corrosion often occurs on copper tubes used in heat-exchanger units in air-conditioners and leads to leakage of heat-exchanger fluid for several months. Figure 1 shows a photograph of this unique localized corrosion formed by galvanostatic polarization in the laboratory. The morphology is characterized by the fractal structure in which pits of several ten micro-m diameter are formed at copper surface and smaller pores are developed on the pit walls randomly. This localized corrosion has been reported with some names: ant-nest corrosion, formicary corrosion, unusual corrosion, branched pits and pinhole corrosion [1]. It’s well known that the occurrence of this localized corrosion is related to trace phosphorus in copper and presence of low molecular weight carboxylic acid such as formic acid. However, the origin to form branched structure has not been clarified. We reported an impedance method to analyze the branched (fractal) pore electrode with transmission line model (TLM) [2, 3]. Impedance spectrum of simple cylinder pore electrode on Nyquist plane normally describes straight-line of 45 degree slope in the high frequency range. In the case of electrode with fractal pores, the slope of straight-line decreases depending on the fractal dimension [3]. In this study, we employed this impedance analysis to investigate the initiation and growth of branched pores in ant-nest corrosion of copper.

Study of the Influence of Biodegradation on Coal Micro-Nano Pore Structure Using Low-Temperature N₂ Adsorption.

An experimental study of biodegradation of Shenmu coal was carried out by using Ochrobactrum cytisi, Novospingobium naphthalenivorans, Alcaligenes faecalis and Pseudomonas fluorescens. The micro-nano pore structure of coal samples before and after biodegradation was studied by low-temperature N₂ adsorption. For biodegraded coal, the results showed that micropores and mesopores are primarily open pores with good connectivity, including parallel plate pores and cylinder pores with two open ends; the specific surface area of biodegraded coal decreased from 2.2174 m²/g to 1.6255˜2.0537 m²/g, and the pore size of the coal biodegraded by the four bacteria decreased following biodegradation from 250 nm to 170˜200 nm, which may be due to collapse of the coal structure due to the bacterial degradation. Coal biodegradation by the dominant bacterium P. fluorescens led to a diminished mesopore size and an increased number of smaller mesopores, with the smaller mesopores gradually taking on dominant roles.

A Stable Zn-Based Metal–Organic Framework as an Efficient Catalyst for Carbon Dioxide Cycloaddition and Alcoholysis at Mild Conditions

Developing highly efficient heterogeneous catalysts for cycloaddition of CO2 and epoxides to produce cyclic carbonates is promising but challenging. In this work, a novel three-dimensional metal organic framework (MOF) with cylinder pore systems and unsaturated Zn sites has been demonstrated as potent candidate in CO2 fixation at mild and solvent-free conditions. The Zn(atz)(bdc)0.5, where atz = aminotriazole and H2bdc = terephthalic, exhibits microporous nature that can regulate the catalytic interaction of active centers and substrates. The structure stability has been systematically investigated and proven to be sufficient for practical application. Furthermore, the cooperative effects of porosity, CO2 binding affinity, activation centers, and synergism with co-catalyst have been deeply investigated. Moreover, high propylene epoxide conversion (97%) and selectivity (> 99%) have been achieved at mild conditions (60 °C and 1 MPa) with excellent cycle stability. Owing to the well-defined pore system, an obvious substrates selectivity has been clearly observed. A possible catalytic mechanism has been proposed and verified by DFT calculations. Furthermore, the prepared Zn-MOF can also be used as an efficient heterogeneous catalyst for the reaction of epoxides with alcohols to produce β-alkoxy alcohol.

Effect of pore structure on CO2 gasification reactivity of biomass chars under high-temperature pyrolysis

The CO2 gasification reactivity of pine sawdust chars (PS char) obtained from the different high-temperature pyrolysis is studied based on non-isothermal thermogravimetric method. Results show that the order of gasification reactivity is PS char-1073 > PS char-1273 > PS char-1473. Under the effect of high-temperature pyrolysis, the surface structure of biomass char is gradually destroyed and the pore structure parameters of specific surface area, total pore volume and average pore diameter increase. By means of the N2 adsorption-desorption isotherms, it is seen that biomass char has more micro- and mesoporous at higher pyrolysis temperature. Besides, the PS char-1073 mostly has rich closed cylinder pores and parallel plate pores, and the PS char-1273 and PS char-1473 have plentiful open cylinder pores and parallel plate pores. An increase of pyrolysis temperature contributes to the development of porosity and improves diffusion path, which promotes the gasification reactivity. But, its effect on the decline of active site hinders the gasification reactivity. What's more, the kinetic model of distributed activation energy model (DAEM) is applied to calculate activation energy and pre-exponential factor with the integral and differential methods. The calculation results of integral method is more accurate and precise because the differential method is more sensitive than integral method for experimental noise. There is a compensation effect in the CO2 gasification process.

Phase Behavior in Shale Organic/Inorganic Nanopores From Molecular Simulation

Summary Production from shale reservoirs is receiving more attention from the petroleum industry. However, there are many complexities associated with optimal production of shale reservoirs. One complexity is the unclear fluid-phase behavior in shale nanopores. In the shale nanopores, the interaction between the pore wall and fluid molecules can significantly change the fluid-phase behavior from the bulk (unconfined) condition. Therefore, the type of pore material can influence the fluid-phase behavior. There have been several recent efforts to model the confined fluid-phase behavior in shale reservoirs. However, the effect of pore material on fluid-phase behavior in shale reservoirs has not been addressed in the previous studies. In this paper, to have a better understanding of phase diagrams in different shale environments, we perform molecular simulations with three materials (two inorganic minerals and one kerogen) and two types of nanopores (slit and cylinder) to model the confined-phase behavior of pure fluids (methane and propane) and one ternary fluid (C1/C3/nC5). From the pure-fluid simulations in the pores of three diameters (4, 7, and 10 nm), confined liquid densities are decreased, whereas vapor densities are increased in the slit and cylinder pores. When pore diameters are increased, critical points are shifted to low densities and high temperatures. Critical temperature and density under confinement can deviate as high as 15 and 60%, respectively, from the original values in bulk. Molecular simulations are conducted for the ternary fluid in the slit and cylinder pores at 160°F. Under confinement, there is a large shift in the nC5 composition of the vapor phase in the ternary diagrams, whereas only small changes have been observed in the ternary diagrams of liquid phase. The density difference between two phases is reduced. Additional tests are performed at one typical shale temperature (290°F) for this ternary fluid in both nanopore types. Phase separation is observed in the slit-pore tests, although only one phase is formed in the tests of the cylinder pores. Because the cylinder pore has more adsorption surface area compared with the slit pore, a stronger adsorption effect is introduced in all tests of the cylinder pores. Based on the comparison of all results (pure fluids and ternary fluid) from the three materials, the calcite pores provide a stronger confinement effect on fluids, and the other two materials have a similar confinement effect on the phase diagrams.

Microstructural investigation of gas shale in Longmaxi Formation, Lower Silurian, NE Sichuan Basin, China

The purpose of this paper is to probe into the nature and variability in vertical microstructure within Longmaxi gas shales of well WX2, Lower Silurian, located in the NE Sichuan Basin of China. To understand the pore system of these rocks, the total porosity, pore size distribution (PSD), surface area, organic geochemistry, and mineralogy, some image analyses by electron microscopy are performed. The obtained results indicated the following. (1) Gas shales have a complex pore structure. Total porosity from helium pycnometry ranges between 0.75% and 4.62%. Total organic content ranges between 3.4 wt.% and 11 wt.%, and vitrinite reflectance measured between 2.5% and 3.1%. The gas shales are quartz and clay rich. (2) Focused ion beam milling and field emission scanning electron microscopy provide high-resolution images of pores distribution and types. Three primary types of pores, organic matter (OM)-hosted pores, mineral-hosted pores, and micro-fractures, and 11 subgroups have been recognized. (3) The N2 isotherm curves are grouped into two types, II b as well as IV a, with the hysteresis loop belonging to Type B, reflecting the morphology of slits pores, and Type A, presenting cylinder pores. Combination of N2 and CO2 isotherm curve shows bimodal in two diameter sections, 0.3–1 nm and 2–5 nm, revealing meso-pores play important role in pore volume, whereas the micro-pores have great influence on pore specific surface area. (4) Total organic carbon (TOC) is considered to be the dominant contributor to total porosity and pore types, with the proportion of OM-hosted pores following the upward decreasing tendency of TOC. In plane, pore types are controlled by sedimentary facies. The OM-hosted pores are more prevalent in deep shelf facies within lower part of shale other than upper formation, instead of shallow shelf facies.

Evaluation of the Pore Structure of Reservoirs Based on NMR T 2 Spectrum Decomposition

Nuclear magnetic resonance (NMR) T 2 distributions can be employed to understand the geometry of pores, but they are not sensitive enough to determine pore connectivity. In this paper, the pore space in reservoirs is regarded as a series of different sizes of the combination of spherical pores and cylinder pores based on the pore network model and Sphere–Cylinder model. In terms of the optimized T 2 inversion method, T 2 spectral distribution is decomposed into two groups, sphere pore distribution and cylinder pore distribution. It is assumed that cylinder pore controls the connectivity and permeability of the reservoir and the sphere pore is the main place of fluid storage. The more cylinder pores that exist, the better the connectivity and permeability are. The data of eight core plugs are analyzed using this method, and the results are in accordance with those of core analysis, which proves the practicability of our research and provides a basis for the direct evaluation of reservoir pore structure using NMR T 2 distribution.

Evaluation Shale Pore Size Spectrum Using Mercury Porosimetry and Nitrogen Adsorption Experiment: A Case Study from the Longtan Formation Shale, Southeastern Hunan, China

Gas shales have a complex pore structure. Using mercury porosimetry and nitrogen adsorption experiment on shale of Longtan Formation in southeastern of Hunan, the pore structure characteristics were contrast analyzed, influencing factors and its impact on reservoir-forming were discussed. Longtan Formation shale is composed of nanopores, include the cylinder pores with two ends open and parallel-plate pores with four sides open. The efficiency of mercury ejection ranges 31.45%~63.82%, 51.94% on average, pores uniformity is well. The size of nanopores is 5~30nm, taking up 94.74% of the total volume and 98.08% of specific surface area. Brittle minerals content is high, as an important parameter influencing pore development. The nanopores have a strong ability to absorb gas, methane molecule exist in a structured way.

熱力学的モデルに基づくC<sub>3</sub>Sの水和反応に及ぼす相対湿度の影響の解析

耐久的なコンクリート構造物を製造するためには環境要因がセメントの水和反応に及ぼす影響について詳細な実験を行い半実験式を構築するか、物理・化学の基礎原理に基づく水和反応モデルを構築し、製造時に予測した環境変化に対する長期的な水和反応の進行を予見する必要がある。本研究ではセメントの主要鉱物であるC3Sを対象として相対湿度が変化した際の反応率の変化を吸着試験、脱着試験に分けて実験的に明らかにするとともに、各相対湿度とC3Sの水和反応について熱力学的アプローチにより予測を行った。脱着過程において予測と実測値に乖離が生じ、低相対湿度においてスリット状細孔の水が水和に使われていることが示唆された。

Alumina with Various Pore Structures Prepared by Spray Pyrolysis of Inorganic Aluminum Precursors

The microstructure of alumina plays a critical role in the catalytic performance of catalysts based on alumina; thus, the preparation of alumina with various pore structures has been the focus of great attention. In this study, alumina products with different microstructures were obtained from alumisol, AlCl3·6H2O, and Al(NO3)3·9H2O by the spray pyrolysis method. The pore structures of the alumina products were found to be closely related to the morphologies of aluminum precursors. The rod-shaped colloidal particles in the alumisol cross-linked with each other to form a mesoporous framework with cylinder pores. The lamellar-shaped AlCl3 flakes overlapped during atomization and evaporation and subsequently led to the formation of lamellar pores. Al(NO3)3 underwent melting and decomposition during the spray pyrolysis process, resulting in the generation of solid particles. The present study also provides a flexible and economical opportunity for the industrial production of alumina with various microstructures.

Fabrication of a Helical Tubular Pore in YSZ Ceramics by the Superplastically Foaming Method

We have already proposed and demonstrated novel ceramic foams named foamed utilizing the superplastic deformation. Since almost all the processes are carried out in solid phase, figure and the location of the foaming agent can be controllable, leading to desired patterning of closed pore in a fully densified ceramics. We have already demonstrated two-dimensional (2D) pore patterning through the superplastically foaming method. In the present study, we aim to fabricate helical tubular pore in zirconia based ceramics as a typical 3D patterned pore. As a foaming agent, SiC powders were used with a form of thin sheet based on methylcellulose aqueous solution followed by drying. A core cylindrical matrix compact was first fabricated using φ 10 steel die and the liner foaming agent was attached to make helical pattern. The patterned core matrix was placed in φ 14 or φ 15 steel die and pressed together with the filled matrix powder. The resultant powder compact was heat treated at 1600°C for 8h for sintering followed by foaming to give a ceramics with 3D tubular pore. Continuous upheaval reflecting the tubular pore was clearly observed on the side wall of the cylinder and helical tubular pore with different pitch can be fabricated.

Size-selective separations of biological macromolecules on mesocylinder silica arrays

In order to control the design functionality of mesocylinder filters for molecular sieving of proteins, we fabricated tight mesocylinder silica nanotube (NT) arrays as promising filter candidates for size-exclusion separation of high-concentration macromolecules, such as insulin (INS), α-amylase (AMY), β-lactoglobulin (β-LG), and myosin (MYO) proteins. In this study, hexagonal mesocylinder structures were fabricated successfully inside anodic alumina membrane (AAM) nanochannels using a variety of cationic and nonionic surfactants as templates. The systematic design of the nanofilters was based on densely patterned polar silane coupling agents (“linkers”) onto the AAM nanochannels, leading to the fabrication of mesocylinder silica arrays with vertical alignment and open surfaces of top-bottom ends inside AAM. Further surface coating of silica NTs hybrid AAM with hydrophobic agents facilitated the production of extremely robust constructed sequences of membranes without the formation of air gaps among NT arrays. The fabricated membranes with impermeable coated layers, robust surfaces, and uniformly multidirectional cylinder pores in nanoscale sizes rapidly separate large quantities of proteins within seconds. Meanwhile, comprehensive factors that affect the performance of the molecular transport, diffusivity, and filtration rate through nanofilter membranes were discussed. The mesocylinder filters of macromolecules show promise for the efficient separation and molecular transport of large molecular weight and size as well as concentrations of proteins.

Development of Micromechanics Models and Innovative Sensor Technologies to Evaluate Internal Frost Damage of Concrete

Internal frost damage is a major problem affecting the durability of concrete in cold regions. Micromechanics models and innovative sensor technologies were used to study the mechanisms of frost damage in concrete. Crystallization pressure resulting from ice nucleation within capillary pores is the primary cause of internal frost damage of concrete. Crystallization pressure of a cylinder pore was formulated with interface energy balance with thermodynamics analysis. Crystallization pressure on the pore wall was input for fracture simulation with the extended finite element model on a homogeneous beam sample with a vertical cylinder pore; this simulation led to a straight line. An image sample was obtained with imaging process and ellipse fitting techniques to capture microstructure of a tested specimen. Crack simulation of this image sample with the same cylinder pore under crystallization pressure matched fracture patterns of the single-edge-notched bending specimen. Extended finite element model simulation results were verified by open-mode fracture behavior in middle-notched single-edge-notched bending and freezing tests. An innovative time-domain reflectometry sensor was developed to nondestructively monitor the freezing process. Data show that sensor signals from time-domain reflectometry can detect the freezing degree, an important input parameter. Studies indicate that the micromechanics models and time-domain reflectometry sensor techniques can help practitioners evaluate internal frost damage of concrete. Future work will incorporate sensor measurements into micromechanics models to predict, in real time, internal frost damage process in concrete specimens. The goal of this study was to provide practical nondestructive testing and computational tools for designing concrete that is resistant to freezing damage.

Pore geometry influence on the deactivation behavior of Ni-based catalysts for simultaneous production of hydrogen and nanocarbon

Pore geometry of Ni-containing Mg–Al–O mixed oxide catalysts could be controlled by varying the Ni content in the synthesis. Low Ni content may lead to the catalysts having mesopores with shape cylinder and narrow pore size distribution; high Ni content results in the catalyst having pores with shape ink-bottle and a wide pore size distribution. In methane decomposition to produce hydrogen and nanocarbon, the 50 wt.% Ni/Mg–Al–O catalyst was rapidly deactivated after 2 h of reaction; however, the catalysts with 15 and 25 wt.% of Ni showed much longer lifetime, which can be explained by assuming a new modal related to pore geometry of the catalysts.

Sol–gel derived La 0.6Sr 0.4CoO 3 nanoparticles, nanotubes, nanowires and thin films

This work has demonstrated how to tailor the structure and form of the sol–gel derived La 0.6Sr 0.4CoO 3 perovskite material from zero-dimension (nanoparticles) to one-dimension (nanotubes and nanowires) and two-dimension (thin films). The nanoparticles with a diameter of 50–100 nm are obtained by calcination of the pulverized gel powder. The nanotubes with a diameter of 100 nm and the nanowires with a diameter of 40–60 nm are formed by shaping the sol with the cylinder pores in an anodic aluminum oxide (AAO) template. The 150 nm thick thin film with the grain size of around 40 nm is prepared by spin coating the sol on a silicon substrate. The effects of the sol recipe on the formation of final product have been studied. A relatively high pH value of the sol and the addition of appropriate amount of chelating agent are critical to ensure the formation of the monolithic La 0.6Sr 0.4CoO 3 perovskite structure. When preparing a thin film, ethylene glycol is an essential component for enhancing the affinity between the sol and the silicon substrate.

Experimental studies on the influence of porosity on membrane absorption process

Eight kinds of flat membranes with different micro-structures were chosen to carry out the membrane absorption experiments with CO2 and de-ionized water or 0.1 mol·L−1 NaOH solution as the experimental system. According to experimental results, the membrane pores shape (stretched pore and cylinder pore) and membrane thickness do not affect the membrane absorption process, and the membrane porosity has only little influence on membrane absorption process for slow mass transfer system. However, the influence of porosity on the membrane absorption process became visible for fast mass transfer system. Moreover, the mass transfer behavior near the membrane surface on liquid side was studied. The results show that the influence of membrane porosity on mass transfer relates to flow condition, absorption system and distance between micro-pores, etc.

Certification of Reference Material with Special Emphasis on Porous Solids

AbstractCertified reference materials (CRMs) are very important for the reliability of the results of chemical analyses and, at the same time, constitute the basis of comparability of analytical data. The development of a new type of CRMs is demonstrated using the example of porous and finely dispersed solids having specific surface area, specific pore volume, pore volume distribution, and mean pore radius as their characteristic values.Many of the properties of reference materials to be certified, such as their elemental content, are established by means of measurement procedures relying on different and independent principles of measurement. With porous or finely dispersed solids, however, the characteristic values referring to pores strongly depend on the size of the probe molecules used, a fact which is due to the fractal character of these substrates. This is particularly true for the specific surface area or the pore volume. As a result, when applying the method of gas adsorption, the certified values refer to a specific probe gas, e.g. to nitrogen. The use of other gases yields different numerical values for the characteristic values to be certified.Generally, the pore system of a solid contains pores of irregular shape. Therefore, depending on the presence of e.g. cylinder or slit pores, different evaluation models must be applied. For the verification of model calculation of microporous solids, zeolites with their crystallographically defined voids are particularly well suited. They can serve as a reference point for the correctness of the model used.

Molecular-dynamics studies of adsorption and transport in micropores of different geometries

We report molecular-dynamics simulation results on adsorption and self-diffusion of Lennard-Jones fluids confined in cylindrical and ‘‘sphere–cylindrical’’ pore geometries. The results include local-density profiles for a wide range of temperatures and densities for both models, dependence of the self-diffusion coefficient parallel to the pore walls D*∥ on temperature, density, and in the case of the sphere–cylinder pore geometry on the ratio of the radius of the sphere to the radius of the cylinder Rs/Rc.