Increase In Average Pore Diameter Research Articles

A lattice Boltzmann simulation on the gas flow in fractal organic matter of shale gas reservoirs

The gas flow in the organic matter with multiple flow regimes is critical to the shale gas production from shale gas reservoirs, but simultaneously simulating the full flow regimes of shale gas in the nanopores of the fractal shale organic matter is still unavailable. This paper presents a modified lattice Boltzmann model with effective relaxation time to simulate the shale gas micro-flow behaviors in fractal organic matter for permeability prediction. Firstly, some fractal shale organic matters are reconstructed by the quartet structure generation set (QSGS) algorithm, and the structural parameters such as fractal dimension, lacunarity and average pore diameter are calculated to characterize the complexity of the fractal shale organic matter. Secondly, effective viscosity and Knudsen layer are introduced into the effective relaxation time to formulate a modified lattice Boltzmann model. Thirdly, this modified lattice Boltzmann model is verified by comparing with the theoretical permeability models for the gas flow in the body centered cubic (BCC) arrays. Finally, a series of gas flow simulations in reconstructed fractal shale organic matter are conducted to explore the effects of structure parameters on permeability. Numerical simulations show that the modified lattice Boltzmann model can simulate the full gas flow regimes and predict the permeability of the fractal shale organic matter. The logarithm of permeability is negatively linearly correlated with fractal dimension and positively linearly correlated with lacunarity of the shale organic matter. This permeability exponentially increases with the increase of average pore diameter and a power law is observed between the fractal dimension and average pore diameter of these fractal shale organic matters. The anisotropic structures have great impacts on the directional permeability of shale organic matter. The permeability kx in the horizontal direction increases first and then decreases with the increase of anisotropic ratio (AR) and reaches the peak when AR is about 20. The permeability ky in the vertical direction monotonically decreases with the increase of AR.

Effects of Thermal Treatment on Mineral Composition and Pore Structure of Coal

With the increasing depth of coalbed methane (CBM) exploitation, temperature becomes the main factor affecting the efficiency of CBM exploitation. The change of temperature has significant influence on the mineral composition and pore structure of coal. To study the effects of thermal treatment on mineral composition and pore structure of coal, X-ray diffraction (XRD) test, scanning electron microscopy (SEM) test, and mercury intrusion test were carried out for three groups of coal. The mineral composition and pore structure of coal specimens after thermal treatment (25, 50, 75, and 100°C) were analyzed. The results show that the main mineral compositions of three groups of coal specimens after different temperatures are basically unchanged, and the maximum diffracted intensity after different temperature treatments decreases first and then increases with the increasing temperature. The count of fissures decreases first and then increases with temperature, and the count of pores increases first and then decreases with the increasing temperature. The velocity of mercury injection in high pressure (100~400 MPa) of coal specimens increases first and then decreases with temperature. The porosity, pore area, median pore diameter, and average pore diameter increase with the increasing temperatures. The volume of microfracture decreases, then increases, and finally decreases. The volume of macropore and mesopore increases slowly, and that of transition pore decreases slowly with the increasing temperature. Meanwhile, the volume of micropore increases first and then decreases during the process of thermal treatment. The fractal dimension of pore size ranges from 2.6 to 2.9 and increases linearly with the increasing temperature.

Modification of Activated Carbon from Elaeis Guineensis Jacq Shell with Magnetite (Fe3O4) Particles and Study Adsorption-Desorption on Ni(II) Ions in Solution

Activated carbon coated with magnetite (ACA-Fe3O4) was synthesized in this study. Activated carbon was synthesized using an Elaeis Guineensis Jacq (EGJ) as a raw material followed by physical and chemical activation. Physical activation is carried out by heating at a temperature of 700°C and followed by a reaction with H3PO4 solution as chemical activation. Furthermore, the activated carbon was reacted with a mixture of FeCl3 and FeSO4 solution then followed by the addition of NaOH solution up to a pH of 10. Characterization with X-Ray Diffraction (XRD) and Scanning Electron Microscopy - Energy Dispersive X-Ray (SEM-EDX) on ACA-Fe3O4 was done to confirm that magnetite has succeeded to coating on ACA. Brunauer-Emmett-Teller Surface Area Method (SBET) confirmed that pore volume and average pore diameter increase with the presence of magnetite. Optimum conditions for Ni(II) ion adsorption with ACA-Fe3O4 was under conditions of 0.5 grams adsorbent, 25 mL of Ni(II) ion solution 100 ppm, and contact time of 1 hour with the acquisition of 99.11%. Adsorption process more suitable with pseudo-second-order and Langmuir adsorption isotherm pattern. Desorption of Ni(II) ion of 70.84% using HCl.

Isothermal Drying Process and its Effect on Compressive Strength of Concrete in Multiscale

Drying could change the microstructure of cement-based materials and inevitably affect their mechanical properties. The isothermal drying process of concrete at three scales and its effect on compressive behavior and microstructure were investigated. The deformations of cement paste, mortar, and concrete in the drying process all exhibit the characteristics of expansion first and then shrinkage. The porosity and average pore diameter increase after drying, which is mainly attributed to the increase of pores less than 100 nm diameter for paste and to the pores within 100~1000 nm for mortar. Drying makes paste denser, while the bonding between paste and aggregate is weakened. Microstructural studies indicate that the increase in compressive strength of concrete caused by isothermal drying is the competition result between the strengthening effect and the weakening effect, and is related to the paste content.

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.

Cu/SSZ-13 zeolites prepared by in situ hydrothermal synthesis method as NH3-SCR catalysts: Influence of the Si/Al ratio on the activity and hydrothermal properties

This study focuses on investigating the influence of Si/Al ratio on the performance of hydrothermally aged Cu/SSZ-13 catalysts prepared by in situ hydrothermal synthesis method. It was found that NH3-SCR performance and hydrothermal stability of Cu/SSZ-13 decreased with increasing Si/Al ratio. Fresh and hydrothermally aged Cu/SSZ-13 with Si/Al ratio of 6.5 showed the best SCR activity and N2 selectivity in a broad temperature of 200–500 °C, in which more than 90% NOx was reduced with superior N2 selectivity above 95%. The effect of Si/Al ratio on the properties of the physicochemical structure, the change of acidity intensity, and Cu species migration or transformation of the fresh and aged Cu/SSZ-13 catalysts were comprehensively characterized by NH3-TPO, NH3-TPD, H2-TPR, N2 physisorption, XRD, ICP-AES, and XPS. The increase of the surface CuO species, the decrease of the amount of Cu2+ in active sites, the chemisorption NH3 species, the specific surface area, the total pore volume, and the increase of average pore diameter, may be the main reasons for performance deterioration over high-Si/Al-ratio catalysts after hydrothermal aging. Furthermore, in situ DRIFTS indicate that, with the increasing Si/Al ratio, the zeolitic structure was easy to collapse, and that the surface acid sites, the active copper species, as well as the adsorbed surface nitrate, decreased after hydrothermally aged. After hydrothermal aging, the amount of isolated Cu2+ decreased, and more CuO species were aggregated, mainly coming from the conversion of the unstable isolated Cu2+ species in D6R or CHA cages. The decrease of isolated Cu2+ and CuO species aggregation were significant in Cu/SSZ-13 with high Si/Al ratios. The CuO leaded to the instability of the SSZ-13 skeleton structure and NH3 oxidation promotion, resulting in catalysts deactivation.

Effect of Fly Ash Content on the Carbonization Resistance of Cement Paste

Carbonation test was carried out on the cement paste specimens with fly ash content of 0% to70%. The change rules of pore structure of cement paste with different fly ash (FA) content before and after carbonation were studied by means of microscopic test, which included mercury intrusion porosimetry (MIP) test and Brurauer Emmerr Teller (BET) test. It is found that total porosity, harmful holes’ prosity (pore diameter>50nm), as well as most probable pore diameter and average pore diameter increase obviously when the content is above 40%, and a certain two order function relationship between the CO2 gas composite diffusion coefficient and the content of FA is presented.

Evaluation of activated carbons based on olive stones as catalysts during hydrogen production by thermocatalytic decomposition of methane

Catalytic decomposition of methane over carbon materials has been intensively studied as an environmental approach for CO2-free hydrogen production without further by-products except hydrogen and valuable carbon. In this work, we will investigate the catalytic activity of activated carbons based on olive stones prepared by two different processes. Additionally, the effect of three major operational parameters: temperature, weight of catalyst and flow rate of methane, was determined. Therefore, a series of experiments were conducted in a horizontal-flow fixed bed reactor. The outflow gases were analysed using a mass spectrometer. The textural, structural and surface chemistry properties of both fresh and used activated carbons were determined respectively by N2 gas adsorption, X-Ray Diffraction and Raman and Temperature Programmed Desorption. The results reveal that methane decomposition rate increases with temperature and methane flow however it decreases with catalyst weight. The two carbon samples exhibit a high initial activity followed by a rapid decay. Textural characterization of the deactivated carbon presents a dramatic drop of surface area, pore and micropore volumes against an increase of average pore diameter confirming that methane decomposition occurs mainly in micropores. XRD characterization shows a turbostratic structure of fresh samples with more graphitization in deposed carbon explaining the lowest activity at the end of reaction. Raman spectra reveal the domination of the two bands G and D which varying intensities affirm that the different carbons tend to organise in aromatic rings. Finally the surface chemistry qualitatively changes greatly after methane dissociation for CAGOC unlike CAGOP but quantitatively a small difference is observed which indicates that these functionalities may have a role in this heterogeneous reaction but cannot be totally responsible. Among the two catalysts tested, CAGOC has the highest initial methane decomposition rate but CAGOP is the most stable one.

Ammonia nitrogen removal from aqueous solution using zeolite modified by microwave-sodium acetate

The characteristics of the zeolite modified by microwave and sodium acetate and its sorption of ammonia-nitrogen from simulated water sample were investigated. The results show that the modified zeolite by microwave-sodium acetate (SMMZ) has a high sorption efficiency and removal performance. The ammonia-nitrogen removal rate of SMMZ reaches 92.90%. The surface of SMMZ becomes loose and some pores appear, the specific surface area, total pore volume and average pore diameter increase after modification. Compared to the natural zeolite, SMMZ has a more concentrated pore size distribution in the range of 0-10 nm. The cation exchange capacity (CEC) of SMMZ is higher than that of the natural zeolite. And the ammonia nitrogen removal rate is consistent with the change of CEC. The SMMZ possesses rapid sorption and slow balance characteristics and ammonia-nitrogen sorption is consistent with both Langmuir adsorption isotherm model and Freundlich adsorption isotherm model. The adsorption kinetics of ammonia-nitrogen follows the pseudo-second order kinetic model.

A Micro-Fracture Model and its Application in Hardened Cement Paste

A micro-fracture model is presented to investigate mechanics properties of porous media such as cement paste on basis of micromechanics theory and fracture theory. Relationships between mechanics properties of porous media and the parameters of pores such as shape, size, and porosity are analysed by this model. Calculation results show that, to a hypothetic porous media with same porosity, the ultimate strength and elastic properties are reduced with an increase of average pore diameter. Nano-scale pores have little effect on the ultimate strength of this porous media while the micron-scale pores have great effect on it. The stress-strain relationship of this porous media with the micron-scaled pores is nonlinear obviously. The results also show that the ultimate strength and elastic properties of the porous media are reduced with an increase of the porosity and shape parameter. Mechanics properties of a cement paste with water cement ratio of 0.5 are tested. The calculation results from the model are in agreement with the experimental results.

Structural, optical and electrical characterization of nanostructured porous silicon: Effect of current density

In this work, an attempt has been made to fabricate porous silicon (PS) from p-type crystalline silicon (c-Si) wafers by using the electrochemical etching process at six different current densities (40, 60, 75, 100, 125 and 150mA/cm2) with constant time (30min). The influence of varying current density on morphological, structural, optical and electrical properties of PS samples were analyzed by using SEM, AFM, XRD, FT-IR, PL and electrical (I–V) techniques, respectively. Microstructural images clearly showed that the average pore diameter and thickness increase with increase current densities up to 100mA/cm2 and decrease for 125mA/cm2. It could be related to breaking of pore walls and exposing to the next layer of c-Si. Further increase the current density about 150mA/cm2, the average pore diameter increase as in the case of first layer (40–100mA/cm2) of c-Si wafer. The result is reflected in PL emission band (at 708nm) and the intensity of the emission band shifted towards red region. The X-ray diffraction pattern confirm the formation of porous silicon as appeared as a broad peak at 2θ=69.3° belongs to (400) reflection. The FTIR study supports the X-ray diffraction analysis that shows the vibrational bands of S–H2 and Si–O–Si at 2109cm−1, 915cm−1 and 615cm−1 and 1107cm−1, respectively. The I–V characteristic of PS exhibited rectifying behavior with different values of ideality factor (η) and barrier height (ϕb). It is concluded from the experimental results that the formed pores developed up to 100mA/cm2 in the top layer of c-Si and the formed pores exposed to the next layer of c-Si when increase the high electrochemical etching process (above 100mA/cm2).

Rheological, physical, and sensory attributes of gluten-free rice cakes containing resistant starch.

In this study the effect of resistant starch (RS) addition on gluten-free cakes from rice flour and tapioca starch physical and sensorial properties was investigated. Increase in RS concentration made cake batters less elastic (drop of G'(ω), G''(ω) values) and thinner (viscosity decreased). Cakes specific volume increased with an increase in RS level and was maximized for 15 g/100 g RS, although porosity values were significantly unaffected by RS content. Crumb grain analysis exhibited a decrease in surface porosity, number of pores and an increase in average pore diameter as RS concentration increased. During storage, cake crumb remained softer in formulations with increasing amounts of RS. Sensory evaluation of cakes demonstrated the acceptance of all formulations, with cake containing 20 g/100 g RS mostly preferred. Gluten-free cakes with improved quality characteristics and high nutritional value can be manufactured by the incorporation of RS.

Incorporation of zinc for fabrication of low-cost spinel-based composite ceramic membrane support to achieve its stabilization

In order to reduce environment risk of zinc, a spinel-based porous membrane support was prepared by the high-temperature reaction of zinc and bauxite mineral. The phase evolution process, shrinkage, porosity, mechanical property, pore size distribution, gas permeation flux and microstructure were systematically studied. The XRD results, based on a Zn/Al stoichiometric composition of 1/2, show a formation of ZnAl2O4 structure starting from 1000°C and then accomplished at 1300°C. For spinel-based composite membrane, shrinkage and porosity are mainly influenced by a combination of an expansion induced by ZnAl2O4 formation and a general densification due to amorphous liquid SiO2. The highest porosity, as high as 44%, is observed in ZnAl4 membrane support among all the investigated compositions. Compared with pure bauxite (Al), ZnAl4 composite membrane support is reinforced by ZnAl2O4 phase and inter-locked mullite crystals, which is proved by the empirical strength–porosity relationships. Also, an increase in average pore diameter and gas flux can be observed in ZnAl4. A prolonged leaching experiment reveals the zinc can be successfully incorporated into ceramic membrane support via formation of ZnAl2O4, which has substantially better resistance toward acidic attack.

Effect of pore size distribution on tetracycline adsorption using magnetic hypercrosslinked resins

Pore structures are very important factors that influence the adsorption and fouling-resistance properties of adsorbents. This study prepared three magnetic porous resins using different amounts of porogen. The pore volume, average pore size, and specific surface area of the resin improved with increased usage of the solvating porogen toluene. Q100-3, which was obtained at a porogen ratio of 3:1, showed the largest surface area (1322m2/g) and pore volume (2.8cm3/g). The increase in average pore diameter improved the adsorption equilibrium of the resins, and the increase in total pore volume and specific surface area enhanced the number of adsorption sites of the adsorbents. Q100-3 showed a larger adsorption capacity for tetracycline (TC) than Q100-1 and Q100-2. Two model compounds of natural organic matter, humic acid (HA) and tannic acid (TA), were chosen to evaluate the fouling-resistance of the resins during TC removal. The resins adsorbed very low amounts of HA (3–13mg/g); thus, competition between HA and TC was weak. HA molecules, because of their large size, were prevented from transportation into the pores by size exclusion effects, leading to negligible pore blocking. By contrast, because of its small molecular size, TA could be well adsorbed by all three resins. The competitive adsorption experiment demonstrated that the presence of TA had a very important effect on both Q100-1 and Q100-2 in terms of TC adsorption. In particular, the amount of TC adsorbed onto Q100-1 with 200mg/L TA dropped to only 7.88% of the adsorbed amount of TC on Q100-1 without TA because of serious pore blockage. Adsorbed TA could not cause pore blockage in the magnetic resin Q100-3, which featured an unobstructed internal pore structure. Thus, the decrease in adsorbed amount of TC was controlled to within 3% in this resin.

Fabrication of Lotus-Type Porous Al-Si Alloys Using the Continuous Casting Technique

Lotus-type porous Al-Si (4, 8, 12, 14, and 18 wt pct) alloys were fabricated using the continuous casting technique under a hydrogen gas pressure of 0.1 MPa at various transference velocities, and the effects of the silicon content level and transference velocity on the pore morphology and porosity were investigated. Both the porosity and the average pore diameter increase as the silicon content level increases and decrease as the transference velocity increases. In particular, the velocity dependence is obviously exhibited at a silicon content level higher than 12 wt pct. The pore shape is changed from irregular in the higher-dendrite fraction to nearly circular in the lower-dendrite fraction. The porosity and the pore morphology are influenced by the silicon content level and transference velocity. In the model, these results can be understood with the explanation that the pores, which contribute to the increase in porosity, are generated at the eutectic fronts. This indicated that the porosity and the pore size in lotus-type porous Al-Si alloys can be well controlled by varying the silicon content level and the transference velocity.

Semi-Degradable Scaffold for Articular Cartilage Replacement

Existing technologies have not met the challenge of designing a construct for the repair of focal cartilage defects such that it mimics the mechanical properties of and can integrate with native cartilage. Herein we describe a novel construct consisting of a non-degradable poly-vinyl alcohol (PVA) scaffold to provide long-term mechanical stability, interconnected pores to allow for the infiltration of chondrocytes, and poly-lactic glycolic acid (PLGA) microspheres for the incorporation of growth factors to enhance cellular migration. The objective of this study was to characterize the morphological features and mechanical properties of our porous PVA-PLGA construct as a function of PLGA content. Varying the PLGA content was found to have a significant effect on the morphological features of the construct. As PLGA content increased from 10% to 75%, samples exhibited a 6-fold increase in average percentage porosity, an increase in average microsphere diameter from 8 to 34 microm and an increase in average pore diameter from 29 to 111 microm. The effect of PLGA content on aggregate modulus and permeability was less profound. Our findings suggest that that morphology of the construct can be tailored to optimize cellular infiltration and the dynamic mechanical response. The experiments herein presented were conducted at the Hospital for Special Surgery.

Mesoporous Nickel−Yttria−Zirconia Fuel Cell Materials

A novel synthesis method for mesoporous nickel−yttria−zirconia (meso-Ni−YZ) has been developed using a surfactant-templated co-assembly strategy, involving yttrium(III)−zirconium(IV) glycometalate and nickel(II) precursors. Nickel loading has been investigated over the range 0−45 Ni at. % and found to control the average pore size of the oxidized meso-NiO1+x−YZ and reduced meso-Ni−YZ products. Under the synthesis conditions utilized, the cationic surfactant glycometalate co-assembly is proposed to involve nickel in the form of Ni4(OH)44+, which subsequently transforms to a co-assembly containing nanoscale Ni(OH)2. Upon thermal posttreatment in air, the nickel hydroxide species is converted to the nanocrystalline p-type nickel oxide, NiO1+x, located in the pores of meso-NiO1+x−YZ. The channel walls of meso-NiO1+x−YZ are composed of nanocrystalline yttria−zirconia, and the gas adsorption isotherm appears as type I. Thermal reduction of the NiO1+x component of the mesostructure in hydrogen creates nickel nanocrystals. A concomitant dramatic increase in average pore diameter is observed with concurrent evolution of an adsorption isotherm of type IV. This behavior is attributed to a structural transformation of meso-NiO1+x−YZ to meso-Ni−YZ involving a reduction in NiO1+x nanocrystal size on conversion to Ni with accompanying migration and aggregation of Ni nanocrystals. The outcome of these combined effects widens the pores within meso-Ni−YZ relative to meso-NiO1+x−YZ. Preliminary ac impedance spectroscopy of meso-Ni−YZ at a loading of less than 40 at. % Ni depicts an electrical response dominated by oxygen ion conductive nanocrystalline YZ channel walls of the meso-Ni−YZ mesostructure. By contrast, higher nickel loaded meso-Ni−YZ samples give a metallic response most likely due to a better connectivity of Ni nanocrystals within the mesostructure.

Effect of supercritical drying temperature on the properties of zirconia, niobia and titania-silica aerogels

Aerogels of zirconia, niobia and titania-silica were prepared by supercritical drying of the corresponding alcogels with carbon dioxide at 343 and 473 K. The higher drying temperature of 473 K increased the pore volume of all three oxides (by 30–70% relative to samples dried at 343 K) after calcination at 773 K but affected their pore size distributions differently. There was an increase in average pore diameter for zirconia and titania-silica but not for niobia. There was also a significant effect on crystallization behavior. A higher drying temperature facilitated crystallization of tetragonal zirconia and anatase titania, but a lower drying temperature facilitated the anatase-to-rutile transformation of titania and crystallization of a low-temperature modification of niobia, the TT phase. The structural evolution of niobia and titania-silica altered their acidic properties as shown by kinetic results of 1-butene isomerization.