Microporous Zones Research Articles

Mechanical and Microstructural Characterization of Rammed Earth Stabilized with Five Biopolymers.

This study aims to check the compatibility of a selection of waste and recycled biopolymers for rammed earth applications in order to replace the more common cement-based stabilization. Five formulations of stabilized rammed earth were prepared with different biopolymers: lignin sulfonate, tannin, sheep wool fibers, citrus pomace and grape-seed flour. The microstructure of the different formulations was characterized by investigating the interactions between earth and stabilizers through mercury intrusion porosimetry (MIP), nitrogen soprtion isotherm, powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). The unconfined compressive strength (UCS) was also evaluated for all stabilized specimens. Three out of five biopolymers were considered suitable as rammed earth stabilizers. The use of wool increased the UCS by 6%, probably thanks to the combined effect of the length of the fibers and the roughness of their surfaces, which gives a contribution in binding clay particles higher than citrus and grape-seed flour. Lignin sulfonate and tannin increased the UCS by 38% and 13%, respectively, suggesting the additives’ ability to fill pores, coat soil grains and form aggregates; this capability is confirmed by the reduction in the specific surface area and the pore volume in the nano- and micropore zones.

Pore-scale investigation on ion transport and transfer resistance in charged porous media with micro-macro structure

Capacitive deionization is an electrochemical desalination technology, in which ions are removed from aqueous solution using porous carbon electrodes. Poisson-Nernst-Planck equations are fully solved by the lattice Boltzmann method to investigate the dynamic ion transport and adsorption processes from macropores between carbon particles into micropores inside carbon particles. Effects of potential, ion concentration and thickness of the microporous zone on the dynamic ion transport processes are investigated. Pore-scale results show that the ion transport first occurs at the micropore/macropore interface and then extends to the inner part of the microporous zone. Adsorption of Na+ ion consumes more time to reach the equilibrium state compared with expulsion of Cl− ion, and the ion concentrations of microporous zones in the steady state predicted by simulations agree well with the results obtained by the Donnan model. The kinetic rate parameters of the finite-rate ion transport model are obtained using data fitting based on the individual ion transfer fluxes into micropores calculated by the pore-scale simulation. It is found that identified kinetic rate parameters are constant showing the validity of the model, and the thickness of the microporous zone has a great influence on the values.

Relationship between mechanical properties and microstructure of yttria stabilized zirconia ceramics densified by spark plasma sintering

Porous ceramics are widely used for many applications such as filters, insulators, electrodes for SOFC, membranes or bone scaffolds, with porosity in the typically range of 20–50%vol. The functionality of those materials comes at the expense of the degradation of their mechanical properties which are highly impacted by the rate, distribution, shape and size of the porosity. Among them tetragonal stabilized zirconia (TSZ) is one of the most industrially used; it is sometime called: “the ceramic steel” since in its dense state it exhibits the highest toughness for ceramics. It is known that the porosity has a huge impact on the thermo-mechanical properties of refractory ceramics as Yittria Stabilized Zirconia (YSZ). This study aims to capitalize the mechanical properties as a function of porosity to provide future applications and ensure the behavior in service of thermal barrier coating.In the present paper, the correlation between the microstructure and the mechanical properties such as Young modulus, hardness and strength of YSZ ceramics obtained by Spark Plasma Sintering (SPS) was investigated. Two types of YSZ powder, a nanometric one from Tosoh and a micrometric one obtained by sol-gel route were studied to prepare homogeneous mesoporous or oriented macroporous microstructure by partial sintering. SPS parameters have been determined and optimized to manage the porosity rate. Furthermore, a bimodal microstructure can be obtained, by mixing both powders, allowing the formation of linking bridges between the microporous zone and the nanopowder during sintering. The macroporous ceramics have lower Young modulus, hardness and strength than mesoporous ones. These characteristics are discussed in the paper taking into account the differences between microstructure and contacts between particles with various form factors. Thus, it is clearly evidenced that the morphology of raw powders and the level of porosity are key parameters to optimize the mechanical properties of such porous material.

The rock physics and geochemistry of carbonates exposed to reactive brines

AbstractWhen carbonate‐rich rocks are brought into contact with an acidic brine their mechanical and acoustic responses depend on many factors including pH, porosity, permeability, effective stress, and time. These complexities hinder the understanding of processes such as hydrothermal fluid circulation, seismicity, and deep burial diagenesis. The present study addresses how different lithofacies exposed to the same reactive brine undergo varying degrees of transformation and whether it is possible to remotely detect these phenomena in the Earth. Results are presented from fluid injections carried out on a large and varied set of calcareous rocks under hydrostatic stress. The output brine was analyzed for dissolved mineral concentrations and the rock porosity, permeability, axial strain, ultrasonic velocity, and images from electron microscopy were contrasted before and after injection. Microbialites were found to be the lithofacies most vulnerable to changes in their transport properties. However, all samples irreversibly compacted with the greatest strain in the most porous and permeable cores. The most extreme structural changes discovered through imaging were the welding of microporous zones, grain sliding, and the fracturing of various phases. Observations are consistent with a chemically enhanced weakening of the rock frame that generated compliant pores. The associated decrease in velocity of the dry rock can be approximated with linear relations that depend on both porosity and effective stress.

Numerical Study on Drag Reduction by Micro-Blowing/Suction Compounding Flow Control on Supercritical Airfoil

Micro-Suction technique(MST) is proposed by the development of micro-blowing technique(MBT). Current experiments and numerical studies are mostly focusing on MBT, micro-suction flow control in turbulent boundary layer remains unstudied. Thus, based on 2D-RAE2822 supercritical airfoil, numerical research on MST and MB/ST compounding flow control have been carried out. And Micro-Porous Wall Model(MPWM) is used to represent the real effects that the blowing and suction of the micro-porous wall has on the surface flow.The numerical results of micro-suction indicate that micro-suction control is capable of inducing a lower pressure zone in front of the micro-porous zone, and a higher pressure zone in the rear end. Given that micro-porous zone is placed on the particular section of airfoil, where the pressure drag direction is backward parallel to free-stream direction, the reduction of the pressure induced by micro-suction control can result in the decrease of pressure drag. Finally, combining the previous study on the MBT, a compounding configuration of micro-blowing/suction flow control on RAE2822 airfoil is proposed. The compounding configuration can take the advantage of both micro-blowing and micro-suction, over 20% increase of the lift and up to 15% decrease of the drag can be realized. Therefore, the compounding flowing control of micro-blowing/suction shows a great potential for the flow control on aircraft.

Effect of the porous structure of activated carbon on the adsorption kinetics of gold(I) cyanide complex

The effect the porous structure of activated carbons obtained from furfural and coconut shells has on the kinetics of [Au(CN)2]− ion adsorption is studied. Effective diffusion coefficients for [Au(CN)2]− anions in transport and adsorbing pores and mass transfer coefficients in a transport system of the pores and in microporous zones are calculated using the statistical moments of the kinetic curve.

Therapeutic management of dental fluorosis: A critical review of literature

Dental fluorosis is a specific condition due to chronic ingestion of excessive fluoride during enamel formation. The cleavage and removal of enamel proteins are disturbed. Retention of the proteins and water results in varying degrees of subsurface porosities related to the severity of fluorosis. The porosities may attract extrinsic stains, causing enamel discoloration. Posteruptively, occlusal trauma may cause detachment of surface enamel weakened by the subsurface porosities. The therapeutic management options include bleaching, microabrasion, veneering and crowning. The bleaching agents break down the chromogens into smaller molecules, resulting in teeth with lighter and brighter shades. The microabrasion is aimed at removing the superficial microporous zone together with the entrapped extrinsic stains, while laminate veneers and crowns provide esthetic masking of the discolored fluorosed enamel. It is suggested that mild-to-moderate fluorosis be treated by microabrasion and bleaching, while severe fluorosis, with loss of some surface enamel, is managed by veneering and crowning, depending on the extent of surface enamel loss. Long-term clinical trials are needed to evaluate the appropriateness of the various management options for fluorosis of varying severity.

Comparison of Microscopic and Macroscopic Modeling Approaches for Subsurface Contaminant Transport

The practice of contaminant transport and remediation has shown significant progress in recent years. However, despite the significant progress made, remediation efforts are often delayed by extremely long breakthrough curve tails that render efforts to bring the level of contaminants below the regulatory standards inefficient. One hypothesis is that these long tails are due to the reservoir-like slow diffusive processes in soil micropore zones. This study compares the effects of micropores at macroscopic and microscopic levels and establishes a link between these approaches for validation and calibration purposes. The link between macroscopic and microscopic levels is established through comparisons and testing of the two models while incorporating appropriate scale and boundary effects. Despite the differences in conceptual approaches and simulation time, the two approaches rendered meaningful results. The link helps forecast the effects of micropore zone transport processes in the subsurface efficiently and thus allows development of numerical tools that could contribute towards more efficient remediation design.

Modeling Contaminant Transport at the Pore-Micropore Interface

Understanding and ultimately simulating the contaminant transport processes occurring in, or around, micropore zones is a topic that will help further the advancement of efficient design and implementation of future remediation techniques. This paper proposes a method to forecast effects of micropores on contaminant transport using a new conceptual method that is based on a model that comprises three zones, namely mobile, immobile, and micropore zones and has two different porosity zones. The model is successfully tested against other established methods (van Genuchten and Wierenga, 1976) and experimental data (Brusseau, 1993).

Weathering of marbles and granites in marine environment: petrophysical properties and special role of atmospheric salts

The aim of this paper was to study the weathering mechanism of marbles and granites exposed to the marine environment at the Delos archaeological site. Alterations, as granular disintegration, contour scaling and alveolus formations, can be observed either at the base of blocks and columns, or at the median-high zones of monuments. A white marble, which originated from Naxos Island, had a weak porosity (0.2%). Its porous network was organized into two subnetworks of rectilinear and sinuous cracks, which limited capillary transfer to ∼10 cm. The granite, which originated from Delos Island, had a relatively high porosity (2.15%), and had a well-connected system of cracks and microporous zones of weathered minerals. This homogeneous network allowed good capillary transfer for long distances (1–2 m). For the marble, as for the granite, evaporation occurred mainly at depth in the stone, and encouraged its deterioration. This damage depends on the dissolution and crystallization of salts, which occur in cycles. First, by the capillary transfer of water and salt from the ground, when the stones are located near the sea. This processes can explain the deterioration of the marble and the granite bases, and the decay of granite on all its surfaces. Second, by fixation of water vapor by sea salt deposited on the stone by wind. This phenomenon can explain the degradations observed on the median-high parts of monuments in marble and granite, even though, for the granite, the first mechanism was more active.

Prediction of the micropore structure parameters and adsorption properties of activated carbons

A regularity govering variations of volume and linear size of micropores in carbon adsorbents during their vapor-gas activation was found. A parameter was proposed that characterizes the degree of development of the micropore system in activating carbons and an initial carbonized material. The parameter is defined as the number (or surface area) of micropores in the volume unit of the micropore zones. This parameter allows one to rationalize the choice of carbonized materials for the preparation of activated carbons with specified adsorption properties and to establish the range of activation beyond which the structure of the micropores loses stability. Furthermore, the parameter serves to predict how activation affects micropore structure parameters and adsorption properties of carbons. This in turn indicates the optimal degrees of microporosity of carbons needed to attain required adsorption properties.

Increase in the amount of adsorption on modified activated carbon by using neutron flux irradiation

Neutron flux irradiation was used to modify the surface properties of activated carbon as a means to increase the amount of moisture adsorption on the modified activated carbon samples. The activated carbon was first dropped into the saturated boric acid solution to make the boron-doped activated carbon. The dried boron-doped activated carbon sample was further irradiated by neutrons to produce the alpha particles ( 4 2He). The alpha particles bombarded the activated carbon randomly to enhance the microscopic damages and/or to increase the micropore zones. As a result, the effective surface area on the activated carbon was increased and the amount of adsorption per unit volume of absorbent was increased also. An equipment to measure the breakthrough curves of water vapor adsorption on the activated carbon samples was built in this study. A computer real-time control for data logger was also designed successfully for recording the data points in the breakthrough curves. The BET sorptometer was used to measure the surface properties of the adsorbents in this study. Under the operating conditions, the amount of moisture adsorption by the modified activated carbon increased by more than 18.8% of that of the original activated carbon sample.

Increase in the amount of adsorption on modified silica gel by using neutron flux irradiation

Boron-doped silica gel was formulated successfully in this study. The silica gel was doped with boron-10 to enhance microscopic damage and/or to increase micropore zones within the solid during neutron irradiation. As a result, the adsorbed amount per unit volume of silica gel in the adsorption–dehumidification systems was increased and the quantity of regeneration heat needed was decreased. A novel equipment for measuring breakthrough curves was built and utilized in the investigation. A computer real-time data acquisition system was designed for monitoring and recording the experimental data. A detailed description of the technique and its utilization will be given in this study. The surface properties of the modified adsorbents were measured by a BET sorptometer. Under operating conditions of this study, the amount of moisture adsorption by the modified adsorbent was increased by more than 23% of that of the commercial silica gel.

Model for the sulfidation of calcined limestone and its use in reactor models

AbstractA mathematical model describing the sulfidation of a single calcined limestone particle was developed and experimentally verified. This model, which includes no fitting parameters, assumes a calcined limestone particle to consist of spherical grains of various sizes that react with H2S according to the classic shrinking‐core model. The initial size distribution of the grains is derived from mercuiy porosimetiy. The transport of H2S through the bidisperse limestone particle is calculated based on the randompore model of Wakao and Smith, which distinguishes macropore and micropore zones. Knudsen diffusivity inside the micropore zones is calculated according to the dusty‐gas approach. The single‐particle model delivers the value of a new defined utilization factor, which includes effects of external mass‐transfer limitation, pore‐diffusion limitation, and grain‐size distribution on particle reactivity. A correlation derived for a single batch of calcined limestone explicitly expresses this utilization factor as a function of conversion and relevant process parameters. This correlatiori can be easily incorporated into reactor models, as shown for an existing model describing the capture of H2S by a fluidized bed of calcined limestone particles.

Transient modelling of a packed tower: Mass and heat transfer with reaction

A packed tower is modelled transiently for fluid-solid reactions. Heat and mass transfer are considered, with allowance for structural changes. The Knudsen, molecular and bulk flow terms are accounted for in the packed tower and within the pellets of the packing. Homogeneous, heterogeneous and catalytic reactions are handled. Conduction, convection and radiation model of heat transfer are considered. The thermophysical, structural and transport properties are included as variables. Three levels of space are used in the system: packed tower, macroporous pellets, and microporous zone (grain). The solution in these spaces includes the distributions of concentrations, temperature, pressure and solids conversion as well as all other parameters at any given time. The three zones are linked together via boundary values.

Development of Microporosity in Clinochlore Upon Heating

AbstractThe “modified chlorite structure” forms by the dehydroxylation of the interlayer octahedral sheet of magnesian chlorite at around 500°C and results in a structure with a basal spacing near 27 Â (Brindley and Chang 1974). This process involves drastic textural modifications as indicated by gas adsorption experiments which reveal the formation of structural micropores. Infrared spectroscopy as well as thermogravimetry and mass spectrometric analysis show that these micropores are filled with molecular atmospheric water, carbon dioxide, nitrogen, argon and hydrocarbons which condense once the samples cool down. A high temperature treatment is needed in order to release the different phases. A heterogeneous dehydroxylation mechanism is proposed in which micropores are formed in donor regions and magnesium and oxygen are concentrated in acceptor regions. This leads to a 27 Å structure with micropore zones and enriched interlayer oxide zones alternating along the z-axis of the mineral.

Integration of DST Flow Results with Sedimentary and Diagenetic Studies, Cooper Basin, Australia

Petroleum reserves in the Permian-Triassic Cooper basin of central Australia are reservoired in fluvial channel and crevasse splay sandstones, as well as distributary delta mouthbar/shoreline deposits. The reservoir intervals are buried to depths between 1.8 and 3.6 km, and contain about 6 tcf of sales gas. Gas flow rates determined from drill-stem tests are highly variable, ranging from rates too small to measure of 13 MMCFD. Diagenetic investigation of over 800 core and ditch samples shows that remnant primary porosity is the key control in determining these flow rates. However, microporosity associated chiefly with kaolin stores much of the gas and contributes to long-term production in many petroleum fields. Microporosity is the dominant porosity type in the cooper basin where almost 75% of reservoir rocks have permeabilities of 5 md or less. Preservation of primary porosity was made possible by a lack of detrital clay in the lower to midpoint bar sections where early reservoir silicification helped to resist the effects of compaction. Primary porosity is also prominent in delta mouthbar/shoreline deposits of proximal nature where extensive winnowing resulted in high-textural and compositional sediment maturity. With increasing depth, the overall proportion of Cooper basin rocks dominated by microporosity increases. Advancedmore » reservoir cementation, mechanical and chemical compaction, clay authigenesis, and broad downbasin facies changes from fluviatile to [open quotes]lake[close quotes] environments all combine to decrease average core porosity and permeability. Locally, however, high-permeability intervals interfinger with microporous zones to depths approaching 3 km. Two of the largest gas fields in the Cooper basin, Moomba and Big Lake, produce from reservoir zones, where much of the total porosity is microporosity. These findings underscore the importance of deep-basin gas exploration.« less

Adsorption and mobility of water molecules and organic substances in carbon adsorbents 5. Self-diffusion of adsorbed molecules and fractal properties of carbon adsorbents

The self-diffusion coefficients of molecules of C6H6 and C6H14 adsorbed in two active carbons (AC) are not a function of the observation time in the time range from 1 to 600 msec. These AC have extensive microporous zones, and the AC studied do not exhibit fractal properties in the range of movements of 2–40 μm for one and 1–100 μm for the other.

Dynamics of physical adsorption for porous grains with a complex internal structure

The dynamics of physical adsorption for a porous medium consisting of porous grains having a complex internal structure is analysed. The analysis is based on a combined theoretical model describing the mass transfer of an adsorbate inside a porous adsorbent grain with a complex internal structure. The model takes into account the effect of the dead-end transport channels (pores) inside the porous adsorbent grain on the nature of the mass transfer of a substance. For frontal adsorption dynamics with convex isotherms equations have been developed for calculating the width of the zone corresponding to intensive mass exchange in the adsorber (the width of the stationary front). Equations were also obtained for calculating the times of relaxations due to different mechanisms of interphase mass transfer inside a porous grain with a complex internal structure and to mass transfer in the intergrain space of the porous medium. It is shown that a strong interaction can take place between the mass transfer within the zones of a porous grain and the dead-end transport channels. When this occurs the width of the stationary front and the relaxation times characteristic of mass transfer inside the porous grain are in quasilinear dependence on the geometrical dimension of the porous grain and the geometrical dimension of the microporous zone inside the porous grain. These dimensions are: radius R0 in the case of a porous grain of an adsorbent having a spherical form and radius R0 in the case of a microporous spherical zone. An analysis of the frontal dynamic curves and the measurement of the coefficients of diffusion inside the microporous zone by other physical methods (e.g., n.m.r. measurements) show a lack of coincidence of the values of the diffusion coefficients. The possible cause of this non-coincidence is indicated.

Kinetic properties of biporous adsorbents with concave microporous zones

1. Kinetic properties were examined for biporous adsorbents with concave microporous zones. 2. Expressions were obtained for the first statistical moments of the kinetic curves for desorption from such zones. 3. A study of the dependence of the logarithm of the first moment on the ratio of the characteristic dimensions of the microporous zones shows that there it is possible to decelerate mass transfer in the study of rapid diffusion processes.