Maximum Pore Diameter Research Articles

Bio-fabrication of multifunctional nano-ceria mediated from Pouteria campechiana for biomedical and sensing applications

The present study focuses on the synthesis of size-controlled nano-ceria (CePC NPs) from aqueous extract of Pouteria campechiana via self-propagating solution combustion synthesis. The extract volume is varied to know the influence of extract on the physical, optical and surface properties of CePC NPs. The p-XRD study revealed the size-controlled synthesis of CePC NPs from 11.46 to 15.59 nm. The nano-regime size is having a definite effect on the biomedical and sensing applications of the NPs. The specific surface area of 34.04 m2g−1, with a maximum pore diameter of 24.33 nm was observed for CePC NPs with a size 11.46 nm. The antioxidant behaviour was maximum with 71.73% of DPPH inhibition at concentration 500 μg/mL. In vitro A546 cancer suppressive activity of CePC NPs reveals that phytochemicals functionalized by highest volume during synthesis showed a low IC50 value of 118.92 μg/mL despite the large size. The bio-derived NPs shows RBC membrane protection above ∼93%, owing to its non-toxic behaviour. The CePC NPs exhibits suitable antibacterial applications against Bacillus subtilis, Staphylococcus aureus, Pseudomonas syringae and Pseudomonas aeruginosa. The bio-fabricated samples exhibited the best hydrogen diffusion value of 1.035 × 10−5. The Rct values of the CePC NPs are comparable with each other (∼73.03–90.39 Ω) with high capacitance, and hence the bio electrodes have superlative efficiency in sensing the Paracetamol drug.

Porosity-based representative elementary volume for geomaterials and its fractal theory-based approximate criterion

<p indent=0mm>The representative volume element (RVE) and/or the representative elementary volume (REV) and their existence and determination are a basic scientific issue in the research field of size effect. The similarities and differences between the RVE and REV are analyzed from the fields of composite micromechanics and geotechnical engineering. A three-level classification of the REV research on geomaterials is then proposed based on these fields, especially REV research in geotechnical engineering. The pore size distribution and the corresponding fractal dimension are introduced and selected as the constrained parameters for describing the complex pore structure of geomaterials. Accordingly, an approximate criterion is first presented via theoretical deduction and comparison with previous research results, through which the size of a P-REV of mesoscale porous geomaterials can be determined using their pore size distributions (i.e., the edge length of the cubic P-REV is approximately equal to five times of the maximum pore diameter). Finally, some statistical methods, such as low-order probability functions, are utilized to validate the performance of the proposed criterion. The verification results using two types of geomaterials, namely, sandstone and foamed concrete, reveal that both are in a reasonable agreement, indicating that the P-REV determined according to this approximate criterion can provide representative statistical results and find a balance between characterization accuracy and calculation efficiency.

Effects of slurry viscosity and particle additive size on filter cake formation in highly permeable sand

Filter cake is critical to maintaining the stability of the excavation face of an underwater shield tunnel in a high-permeability stratum. In a high-permeability formation, generating an effective filter cake on the excavation face is difficult with a pure bentonite slurry, which penetrates the ground and may not achieve the required suspension pressure. Determining how to efficiently and quickly form a thin and low-permeability filter cake on the tunnel working face has become a key engineering problem in the construction of slurry shield tunnels in high-permeability strata. In this study, the relationship between slurry viscosity and the slurry pressure gradient of pure bentonite was established by performing slurry permeability experiments. The influence of slurry viscosity on the formation of the filter cake in a high-permeability formation was studied under different pressure gradients. In addition, the effect of additive particle size on the slurry filter cake formation was analyzed by introducing additives with different particle sizes to pure bentonite slurries with different viscosities. The test results indicate that (1) for the pure bentonite slurry, the critical initial pressure gradient can be used as a rough indicator of the formation of the filter cake, and the relationship between the critical maximum pore diameter and the average pore diameter of the formation can be compared to establish and analyze the formation law of the slurry filter cake; (2) adding particles to the slurry can enhance the effect of the pure bentonite slurry; and (3) adding coarse-grained materials can effectively improve the film-forming effect. The slurry is more compact when the particle size is close to the average pore size of the formation.

A FRACTAL MODEL FOR PREDICTING THE EFFECTIVE THERMAL CONDUCTIVITY OF ROUGHENED POROUS MEDIA WITH MICROSCALE EFFECT

The effective thermal conductivity (ETC) of roughened porous media (RPM) is of interest in a number of applications of heat transfer. In this work, a fractal analytical model for the ETC of RPM with microscale effect is proposed. The proposed fractal model is expressed in terms of relative roughness, the molecular mean free path, porosity, fractal dimensions (pore area fractal dimension and tortuosity fractal dimension), maximum pore diameter, capillary straight length, and the thermal conductivity of the solid matrix and gas. It is observed that the dimensionless ETC of RPM decreases with increasing relative roughness, pore area fractal dimension and tortuosity fractal dimension. Besides, it is found that the dimensionless ETC of RPM increases with thermal conductivity ratio of gas phase over solid phase. In addition, it is found that the dimensionless ETC of RPM is slightly dependent on the relative roughness and tortuosity fractal dimension when [Formula: see text]. The determined dimensionless ETC of RPM is in good agreement with experimental data and existing models reported in the literature. With the proposed fractal model, the physical mechanisms of heat transport through RPM with microscale effect are better elucidated. Every parameter in the fractal analytical model has clear physical meaning, with no empirical constant.

Utilization of magnesium resources in salt lake brine and catalytic degradation of dye wastewater by doping cobalt and nickel

• The process of treating dye wastewater with different products of purification, chlorination, electrolysis doping and calcination of Mg in salt lake brine was designed. • MgCo 2 O 4 nanoparticles have the maximum surface area of 151.5 m 2 /g, and Mg/Co(OH) 2 has a maximum average pore diameter of 51.5 nm. • After irradiation for 20 min, the degradation rate of H 2 O 2 was only 31.95%, while adding Mg/Co(OH) 2 (98.94%), Mg/Ni(OH) 2 (71.29%), MgCo 2 O 4 (98.18%) and MgNiO 2 (77.05%) increased by at least 2 times. • Mg/Co(OH) 2 (99.62% after 2 h) and MgCo 2 O 4 (99.59% after 4 h) could effectively catalyze H 2 O 2 degradation of MB under shading which could be left standing in a beaker without any operation. In this paper, a wet recovery and reuse process from salt lake brine is designed. Nano Mg/Co(OH) 2 and Mg/Ni(OH) 2 composite materials are prepared by acid leaching and electrolytic doping from magnesite which is evaporated and crystallized from salt lake brine. Oxides MgCo 2 O 4 and MgNiO 2 are calcined using the electrolytic products as precursors. The structure of the products is characterized by XRD, FTIR, N 2 -adsorption desorption, XPS, DSC-TGA, SEM, TEM testing methods, etc. The results show that the obtained samples are Mg/Co(OH) 2 , Mg/Ni(OH) 2 , MgCo 2 O 4 and MgNiO 2 with good crystallinity; The synthesized composites material have the macroporous structure, and MgCo 2 O 4 has a maximum specific surface area of 151.5 m 2 /g, Mg/Co(OH) 2 has a maximum average pore size of 51 nm; The product is composed of a large number of flaky crystals with diameters ranging from tens to hundreds of nanometers. Then, the catalytic ability of the composite material on the degradation of methylene blue simulated wastewater in organic wastewater with H 2 O 2 is investigated. The results show that all products can efficiently catalyze the degradation of methylene blue simulated wastewater by H 2 O 2 ; Mg/Co(OH) 2 has the best activity under dark condition, the reaction time is 120 min, the decolorization rate reaches 99.62%, without any operation and any energy, just wait for the end. If the time factor is taken into account, the Mg/Co(OH) 2 activity is the best under UV light irradiation, and the decolorization rate reaches 99.59% after 40 min of reaction. The high activity of Mg/Co(OH) 2 is related to the abundant hydroxyl groups on its surface and its macroporous structure. The catalytic degradation of methylene blue in sewage by composite materials can be described by the first-order reaction kinetic equation.

Mortar pore pressure prediction during the first hours of cement hydration

During cement hydration, solid, fluid, and total volumes vary as water is consumed by chemical reactions. Those volume variations lead to pore water pressure decrease during the first hours of hydration. The deformations induced by early hydration are quantified in order to understand their consequences on the internal stress state within the hardening material.This paper aims to link pore water pressure with autogenous and chemical shrinkage during the first hours of hydration in the bulk of early setting cement mortar. It is demonstrated that specific volume variations are compensated by an increase of air-entrained volume. The variation of the volume of air is used to predict the air pressure. Using the size of a maximum capillary pore diameter filled with water, the capillary pressure is estimated using the Young-Laplace equation. In order to validate the approach, the pore water pressure is measured and compared to the thermodynamic prediction and air content.

A STUDY ON GAS DRAINAGE CONSIDERING COUPLING PROCESS OF FRACTURE-PORE MICROSTRUCTURE AND COAL DEFORMATION

Coal seam contains a large number of fractures, whose shape and structure of fissures are complicated, and they are the main channels for gas migration. Therefore, the quantitative analysis of the internal relationship between the microstructure and the macroscopic permeability is the key issue to increase the drainage volume. Some investigators discussed the permeability of coal seams based on the fractal theory, but the mechanisms of gas migration under the influence of fissure microstructures and coal deformation are still unclear. Moreover, most of the multi-process coupling analysis in the stage of Coal Bed Methane (CBM) mining was not taken into account. In this paper, the effects of fissure structures on the coal gas drainage rate in multi-field coupling are studied. Aiming at the mechanisms of gas drainage under the joint action of fracture structure, in-situ stress and adsorption deformation, we propose a two-scale multi-field coupling model, which takes into account the influences of micro fracture and pore structure. On this basis, we obtained the pressure evolution rule of coal seam pore system and fissure system and the distribution rule of coal seam displacement with drilling positions. Meanwhile, the effects of coal seam maximum fracture length, maximum pore diameter, the fractal dimension for fractures and fractal dimension for pores on coal seam extraction are discussed.

A Leakage Model of Contact Mechanical Seals Based on the Fractal Theory of Porous Medium

A theoretical model for calculating the leakage rate of contact mechanical seals based on the fractal theory of the porous media, which can consider the real seal contact interface and objectively reflect the flow of the interfacial fluid from a microscopic perspective, is established. In order to obtain the microstructural parameters of the porous media included in the leakage model, such as the fractal dimension and the maximum pore diameter, the real seal contact interface obtained from experiments is reconstructed, a contact model between the dynamic and static rings is proposed, and then the calculation methods for the interface characteristic parameters are provided. Numerical simulation results show that as the contact pressure increases from 0.05 to 0.5 MPa, the interface porosity and the maximum pore diameter decreases gradually. Furthermore, the fractal dimension of the pore area increases and the leakage rate of the interface decreases from 0.48 to 0.33 mL/h. The proposed method provides a novel way of calculating the leakage rate of contact mechanical seals.

Prediction of electrospun web maximum pore diameter reliability

Porosity of electrospun web could be evaluated by the diameter of the maximum pore and the reliability of this value. The distributions of the maximum pore diameter usually differ from Gausian normal distribution, and due to that the standard reliability cannot be used for maximum pore size prediction. The method of electrospun web porosity evaluation by the maximum pore size in the Web is presented in this paper. The main investigations were done with polyamide 6 electrospun nanofibrous web. It was stated that in order to estimate the maximum pore size with a confidence level of 99.5%, it is not possible to use the standard 3S (3 standard deviations) rule in all cases. For reliability prediction, it is possible to use skewness coefficient A or a relative distance between the maximum pore diameter and average value Δd. When skewness coefficient A is up to 1.5 or Δd up to 120% the 4S rule needs to be used instead 3S rule for the same 99.5% reliability prediction.

On the characterization of the shrinkage behavior and soil-water retention curves of four soils using centrifugation and their relation to the soil structure

In this study, a consistent centrifuge procedure was applied to four soils. The height shrinkage, bulk density increase, soil shrinkage curve (SSC), and soil-water retention curve (SWRC) of the soils were analyzed. Scanning electron microscopy (SEM) tests and image processing techniques were adopted to qualitatively and quantitatively investigate the microstructure of the soils with different bulk densities. The results showed that under a matric suction ranging from 0 to 2000 kPa, the bulk density increased from an initial value of 1.30 g/cm3 to 1.60, 1.72, 1.61, and 1.57 g/cm3 for the soils retrieved from Chanhe, Qingyang, Yan’an, and Lvliang, respectively, resulting in corrected SWRCs considering soil shrinkage that was higher than the uncorrected SWRCs, consistent with previously published work. However, this difference was effectively reduced by retesting the soil samples. A reduction in water volume resulted in the same reduction in the bulk soil volume in the normal shrinkage state, while a shrinkage rate higher than one was found with increasing soil drying. More hydraulically active and connected macropores were detected in the low-density soil. The maximum pore diameter, total pore area ratio (PAR), pore size, and number distribution considerably changed with increasing density. The captured microstructural information is beneficial for the interpretation of the shrinkage behavior and hydraulic properties of soil.

FRACTAL ANALYSIS OF SURFACE ROUGHNESS EFFECTS ON GAS DIFFUSION IN POROUS NANOFIBERS

Fractal model of gas diffusion in porous nanofibers with rough surfaces is derived, in which the porous structure is assumed to be composed of a bundle of tortuous capillaries whose pore size distribution and surface roughness follow the fractal scaling laws. The analytical expression for gas relative diffusion coefficient is a function of the relative roughness and the other microstructural parameters (porosity, the fractal dimension for pore size distribution and tortuosity, the maximum and minimum pore diameter and the characteristic length). The proposed fractal model is validated by comparison with available experimental data and correlations. At the same time, the effect of microstructural parameters of porous fibrous materials on gas diffusion has been studied in detail. It is believed that the current model may be extended to porous materials other than fibrous materials.

Multiple-flow-regime models for real gas transport in fractal porous media at high pressure

A Mathematical model for total mass flow rate per unit area and total permeability of real gas flow in fractal porous media was proposed on the basis of fractal theory. Proposed models in this paper paid attention to the influence of real gas effect on gas, taking transition regime as the coupling of slip regime and Knudsen diffusion, considering multi-flow-regime coexist, multi-flow-regime is continuum flow regime, slip flow regime, transition flow regime and Knudsen diffusion regime., pore which pore diameter is λ mass flow rate per unit area multiply corresponding pore number dN obtain mass flow rate(dq). Integrate dq within corresponding diameter range and divide fractal porous media work out corresponding flow regime the mass flow rate per unit area. The total mass flow rate per unit area was then calculated through integrating over the mass flow rate deduced, where different flow regimes have been engaged, including continuum regime, slip regime, transition regime and Knudsen diffusion. Based on the Darcy theory, the total permeability was then calculated. In order to verify correctness of model, compare proposed model to Wang's model and Fan's model. Calculate correlation coefficient of proposed model and Wang's model, R2=0.9912; Calculate correlation coefficient of proposed model and Wang's model, R2=0.9997. Indicate that proposed model can fit well with Wang's model and Fan's model, proposed model can correctly predict total permeability. And calculate correlation coefficient of D.B.Bennion experiment data and three model.In the last part, the paper analyzed the influence factor of total mass flow rate per unit area and total permeabilities and mass flow rate per unit area and permeability of different flow regimes. The concludes as follow: (1) total mass flow rate per unit area, total permeability and each flow regime mass flow rate per unit area and permeability increase with fractal dimension(Dp) increasing and tortuous fractal dimension(Dt) decreasing. Variation of Dp and Dt has different influence on each flow regime. Dp and Dt has most influence on Knudsen diffusion flow regime, least influence on continuum flow regime. (2) Real gas effect affects the mass flow rate per unit area and permeability in different flow regime by affecting the mean free path of gas molecule. Whether consider real gas effect would cause great difference, maximum difference is 232.35%. (3) Flow regime that have the lowest Knudsen number play leading role in variation of total mass flow rate and total permeability. (4) The more maximum pore diameter of fractal porous media, the more significant influence of total mass flow rate per unit area and total permeability. Maximum pore diameter has different influence on each flow regime, has most influence on Knudsen diffusion flow regime, least influence on continuum flow regime.

Maximum Sizes of Fluid-Occupied Pores within Hydrate-Bearing Porous Media Composed of Different Host Particles

Hydraulic properties of hydrate-bearing sediments are largely affected by the maximum size of pores occupied by fluids. However, effects of host particle properties on the maximum size of fluid-occupied pores within hydrate-bearing sediments remain elusive, and differences in the maximum equivalent, incircle, and hydraulic diameters of fluid-occupied pores evolving with hydrate saturation have not been well understood. In this study, numerical simulations of grain-coating and pore-filling hydrate nucleation and growth within different artificial porous media are performed to quantify the maximum equivalent, incircle, and hydraulic diameters of fluid-occupied pores during hydrate formation, and how maximum diameters of fluid-occupied pores change with hydrate saturation is analyzed. Then, theoretical models of geometry factors for incircle and hydraulic diameters are proposed based on fractal theory, and variations of fluid-occupied pore shapes during hydrate formation are discussed. Results show that host particle properties have obvious effects on the intrinsic maximum diameters of fluid-occupied pores and introduce discrepancies in evolutions of the maximum pore diameters during hydrate formation. Pore-filling hydrates reduce the maximum incircle and hydraulic diameters of fluid-occupied pores much more significantly than grain-coating hydrates; however, hydrate pore habits have minor effects on the maximum equivalent diameter reduction. Shapes of fluid-occupied pores change little due to the presence of grain-coating hydrates, but pore-filling hydrates lead to much fibrous shapes of fluid-occupied pores.

Surface activity correlations of mesoporous 3-D hierarchical ZnS nanostructures for enhanced photo and electro catalytic performance

Owing to larger surface area and high porosity of 3-D hierarchical nanostructures, it developed the intensive research interests of material scientists. Mesoporous 3-D hierarchical ZnS nanostructures have been synthesised using Hydro/solvothermal route. Using different precursors and chemical compositions different morphologies (Raspberry-like, Nanoballs, Nanoflowers) with different defect states are obtained. It has been seen that cationic and anionic vacancies can be controlled and confirmed by EDX and XPS study. Based on the various surface characteristics studies, it is proved that the solvent assisted 3-D ZnS hierarchical nanostructures have good photocatalytic and electrochemical performance. All samples possess best photocatalytic efficiency for the degradation of Eosin Y (EY) dye i.e., more than 94%. Among three samples Raspberry-like (ZA1) and Nanoflowers (ZA3) exhibit highest photodegradation efficiency due to larger specific surface area than sample Ball-like (ZA2). High specific capacitance value of 494.80, 725.40 and 625.54F/g (from the CV curves) at scan rates of 5 mV/s and 362.40, 442.40 and 408.00F/g (from charge-discharge curves) at current density 2 mA/cm2 for ZA1, ZA2 and ZA3 respectively were obtained. Sample ZA2 and ZA3 possess best supercapacitor characteristics i.e. highest specific capacitance as it has smallest crystallite size, maximum pore diameter and high diffusion coefficient among present samples.

A Molecular Dynamics Study of Primary Production from Shale Organic Pores

Summary We created a model of mature kerogen saturated with a black oil. Our fluid model spans light, intermediate, and long alkane chains; and aromatics, asphaltenes, and resins. The maximum pore diameter of our kerogen model is 2.5 nm. The insertion of a microfracture in the system allows us to study fluid transport from kerogen to the microfracture, which is the rate-limiting step in hydrocarbon production from shales. Our results indicate that the composition of the produced fluids changes with time, transitioning from a dry/wet gas to a gas condensate, becoming heavier with time. However, at any given time, the produced fluid is significantly lighter than the in-situ fluid. The species with the greatest mobility is methane, which is expected because it is the lightest molecule in the fluid and its ability to migrate is greater than that of all other fluid molecules. A sensitivity analysis shows that the produced fluid composition strongly depends on the initial composition of the fluids in organic pores.

Effect of gamma irradiation on the critical heat flux of nano-coated surfaces

An anodic electrophoretic deposition (EPD) technique is used to create a uniform TiO2 thin film coating on boiling thin steel plates (1.1 mm by 90 mm). All of the effective parameters except time of the EPD method are kept constant. To investigate the effect of gamma irradiation on the critical heat flux (CHF), the test specimens were irradiated in a gamma cell to different doses ranging from 100 to 300 kGy, and then SEM and BET analysis were performed. For each coated specimen, the contact angle and capillary length were measured. The specimens were then tested in a boiling pool for CHF and boiling heat transfer coefficient. It was observed that irradiation significantly decreases the maximum pore diameter while it increases the porosity, pore surface area and pore volume. These surface modifications due to gamma irradiation increased the CHF of the nano-coated surfaces compared to that of the unirradiated surfaces. The heat transfer coefficient (HTC) of the nano-coated surfaces irradiated at 300 kGy increased from 83 to 160 kW/(m2 K) at 885 kW/m2 wall heat flux by 100%. The CHF of the irradiated (300 kGy) and unirradiated surfaces are 2035 kW/m2 and 1583 kW/m2, respectively, an increase of nearly 31%.

Fractal characterization of permeability prediction model in hydrate-bearing porous media

Studies have shown that the permeability plays an extremely important role in NGHs decomposition flow and production analysis. However, several existing permeability calculation models are very divergent and usually contain some empirical parameters with unclear physical meaning. The accurate determination of these empirical parameters is often very difficult and needs to be improved urgently. In this work, a novel fractal permeability prediction model for water flowing through hydrate-bearing porous media is established based on the fractal theory. The fractal permeability model is expressed as a function of the pore area fractal dimension, tortuous dimension, porosity, hydrate saturation, and maximum pore diameter. In this expression, each parameters has specific physical meaning. The reliability of the deduced model is validated by comparing predictive results of the model with the available open experimental data. A good agreement is found between them and the accuracy of model prediction is always within ±10% error range.

The effects of surfactants on properties of lightweight concrete foam

Lightweight concrete foam is mainly used as a filling for sandwich panels for insulation of buildings. Surfactants are chemical admixtures that play an important role in stabilising the air pores in fresh concrete foam before stiffening. This study investigates the effects of surfactants on the microstructure and pore characteristics of concrete foam analysed by X-ray microtomography. The formation of larger pores due to poor stability of bubbles in the concrete foam is directly related to a substantial reduction of compressive strength. Anionic (negatively charged) surfactants produce a stable aqueous foam. However, in the presence of cement particles, the majority of anionic surfactants adsorb on positively charged sites of cement particles. As the result of considerable migration of surfactants from the air–liquid interface of bubbles, the concrete foam is destabilised. Therefore, a surfactant that can generate a stable foam (with water only) may not be able to generate a stable concrete foam. A combination of an anionic and a non-ionic (neutral) surfactant reduced the maximum pore diameter from 1·84 mm to 1·49 mm and increased strength by 25% compared to the concrete foam stabilised by anionic surfactants alone.

Fractal analysis of shape factor for matrix-fracture transfer function in fractured reservoirs

As the core function of dual-porosity model in fluids flow simulation of fractured reservoirs, matrix-fracture transfer function is affected by several key parameters, such as shape factor. However, modeling the shape factor based on Euclidean geometry theory is hard to characterize the complexity of pore structures. Microscopic pore structures could be well characterized by fractal geometry theory. In this study, the separation variable method and Bessel function are applied to solve the single-phase fractal pressure diffusion equation, and then the obtained analytical solution is used to deduce one-dimensional, two-dimensional and three-dimensional fractal shape factors. The proposed fractal shape factor can be used to explain the influence of microstructure of matrix on the fluid exchange rate between matrix and fracture, and is verified by numerical simulation. Results of sensitivity analysis indicate that shape factor decreases with tortuosity fractal dimension and characteristic length of matrix, increases with maximum pore diameter of matrix. Furthermore, the proposed fractal shape factor is effective in the condition that tortuosity fractal dimension of matrix is roughly between 1 and 1.25. This study shows that microscopic pore structures have an important effect on fluid transfer between matrix and fracture, which further improves the study on flow characteristics in fractured systems.

Ionic Liquids under Confinement: From Systematic Variations of the Ion and Pore Sizes toward an Understanding of the Structure and Dynamics in Complex Porous Carbons.

We use molecular simulations of an ionic liquid in contact with a range of nanoporous carbons to investigate correlations between the ion size, pore size, pore topology, and properties of the adsorbed ions. We show that diffusion coefficients increase with the anion size and, surprisingly, with the quantity of adsorbed ions. Both findings are interpreted in terms of confinement: when the in-pore population increases, additional ions are located in less-confined sites and diffuse faster. Simulations in which the pores are enlarged while keeping the topology constant support these observations. The interpretation of properties across structures is more challenging. An interesting point is that smaller pores do not necessarily lead to a larger confinement. In this work, the highest degrees of confinement are observed for intermediate pore sizes. We also show a correlation between the quantity of adsorbed ions and the ratio between the maximum pore diameter and the pore limiting diameter.