Effect Of Pore Characteristics Research Articles

Effective Stress Coefficient for Seismic Velocities in Carbonate Rocks: Effects of Pore Characteristics and Fluid Types

The concept of effective stress is key for understanding the dependence of rock elastic and compaction behaviors on stress and pore-fluid pressure. Previous studies on the concept largely used data acquired on siliciclastic rocks. Carbonate rocks, however, display elastic and compaction behaviors that can be very different than those of siliciclastic rocks. For example, applying most velocity-to-pore-pressure transforms in the context of carbonate reservoirs can be quite challenging. Our study used an experimental approach (a disequilibrium compaction scenario) to assess effective stress coefficient (n) for velocities in three carbonate samples displaying comparable porosities but different dominant pore types (in terms of shape and compliance). Different saturating fluids (nitrogen and distilled water) were used, one at a time, which allowed us to compare both pore and fluid type effects on the coefficient n between these rocks. We found that n is generally bounded by unity. The exception is with nVs (n derived from shear wave velocities) obtained under nitrogen-saturated conditions; nVs is higher than 1 on the three studied samples. Under nitrogen-saturated conditions, the less compliant the main pore types in a given rock are, the higher the value of nVs is. Higher-than-unity values of nVs indicate a deviation from the behavior predicted by existing theories. This could stem from (i) the fact that theoretical analyses assume a pore fluid whose properties are not comparable to those of nitrogen and/or (ii) the way the bulk volumetric strain (a main factor in elastic wave propagation) is incorporated into those theories.

Effects of aggregate microstructure on slag resistance of lightweight Al2O3-MgO castable

Corundum-spinel castables using lightweight aggregate have drawn much attention due to their energy-saving potential, in particular when they are applied in high-temperature areas, such as the work lining of refining ladle. One of the main issues which hinder their application is their relatively poor slag corrosion performance. In this study, one type of dense tabular corundum and three types of lightweight corundum were chosen as aggregates to prepare four different model corundum-spinel castables. Their slag resistance was evaluated by an induction furnace corrosion test method. As well as SEM, EDS, and XRD characterizations, thermodynamic and kinetic analyses were carried out to assist understanding the corrosion mechanism. Results indicated that size and shape of crystalline grain in aggregate were important for the slag corrosion (dissolution) resistance of lightweight corundum-spinel castables under dynamic condition (enforced convection), whereas the effects of pore characteristics were not significant. Use of aggregates having large average crystal size and flake-shaped crystals led to a thicker diffusion boundary layer and lowered dissolution rate, i.e., good corrosion resistance, whereas use of aggregates with small and spherical crystals and larger pores led to poor slag resistance.

Development of Electrocatalysts for PEFC By Encapsulating Pt Particles into Carbon Mesopores

Electrocatalysts for PEFC are generally composed by Pt dispersed on carbon supports and have an important role to determine the performance of PEFC. Decrease in Pt active sites during the long-time use becomes a serious problem for practical use of PEFC. Pt particles have tendency to agglomerate, or dissolve and re-precipitate under the potential cycles, resulting in the growth of particles. In this study, suppressing such Pt particle growth has been focused on. So far, increasing the durability of electrocatalysts by encapsulating Pt into the nanochannnels of mesoporous carbon (MC) has been reported in our group.1 The basic idea comes from reducing Pt mobility on the curved carbon surface, which has also been supported by theoretical study.2 In this particular report, the effect of pore characteristics, such as pore diameter and pore volume, on PEFC performance are evaluated. MCs were made from the self-organization formaldehyde/resorcinol and Pluronic F127,3 but the procedure was slightly modified for each kind of MCs. Then, electrocatalysts were synthesized from platinum(II) acetylacetonate as a precursor by depositing ca. 30 wt% Pt on MCs. These MC based materials were used for the cathode, and a standard Pt/Ketjen black catalyst (TEC10E50E, TKK Corp.) was used for the anode, in order to prepare membrane electrode assemblies (MEAs). Current-voltage (IV) characteristics of MEAs were measured in this study. Then, ohmic loss, concentration loss, and overvoltage were further analyzed separately after ohmic resistance was found by impedance measurements. When three electrocatalyts, a standard Pt/MC, Pt/air-treated MC, and Pt/high pore volume-MC, are compared, the concentration overvoltage resulted in high with the order of a standard Pt/MC > Pt/high pore volume-MC > Pt/air-treated MC. Regarding to the activation overvoltage, it is reduced with the order of Pt/air-treated MC < a standard Pt/MC < Pt/high pore volume-MC. The correlation between the pore structure and the PEFC performance will be discussed.

Effect of pore characteristics on coalbed methane adsorption in middle-high rank coals

Gas hazards are still one of the most severe disasters restricting mine safety, and the occurrence of them is heavily dependent on the storage and transportation of methane in coal seams. In order to investigate the influence of pore structure characteristics of middle-high rank coals (V daf < 25 %) on coalbed methane adsorption, six coal samples of different metamorphism were studied with regard to their surface chemical structure and pore morphological features using Fourier transform infrared (FTIR) spectroscopy, low-pressure nitrogen gas adsorption (LP-N2GA) and scanning electron microscopy (SEM), and their coalbed methane adsorption capacities were also tested. Based on the Langmuir equation, the Langmuir volume and Langmuir pressure were obtained to characterize the adsorption capacity, and the impact of structural parameters of coal samples on coalbed methane adsorption was analyzed. The results indicate that the pore shape varies a lot between coal samples, suggesting the significant heterogeneity on coal surface. The micropores (<10 nm) in coal samples are well-developed, and the pore size distributions from adsorption analysis are multi-modal. Pore characteristics in coal samples is affected by coalification to a large extent. The adsorption volume of gas mainly concentrates in micropores, and the adsorption capacities of different coal samples display remarkable difference. The Langmuir volume (V L) is closely related to micropores, but shows little relationship with mesopores, while the Langmuir pressure (P L) is remarkably affected by both micropores and mesopores. The research results are of great importance for the coalbed methane storage and the accurate prediction of gas emission.

Superelastic behaviors of biomedical porous NiTi alloy with high porosity and large pore size prepared by spark plasma sintering

A process of combing use of one-step spark plasma sintering (SPS) method and space holder technique was developed to have successfully fabricated the porous NiTi alloy. To optimize porous NiTi for bone implant applications, the effects of pore characteristics and microstructures on mechanical properties and superelastic behaviors of the porous NiTi alloys were investigated by varying sintering temperatures (800–1050°C) and ammonium hydrogen carbonate (NH4HCO3) contents (0–20wt.%). The results showed that porous NiTi alloys with 18–61% porosity and 21–415μm average pore size all consisted of nearly single NiTi phase with few undesired phases Ti2Ni and Ni3Ti. The superelastic recovery strain ratio of the porous NiTi alloy could be improved up to 90% through training, but with further increasing of training cycles, the curves showed an obvious ladder shaped stress plateau, which indicated the collapse of the pores. This enhanced superelasticity will greatly degrade the mechanical mismatch between bones and porous NiTi. Furthermore, with increasing the porosity and pore size, elastic modulus and compressive strength of the porous NiTi alloys decreased. However, the compressive strength was higher or close to those of human bone and the elastic modulus was close to those of human bone. The unique combination of inter-connected pore characteristics, pure phase composition, low elastic modulus, high strength and large superelastic recovery strain made this material a good candidate for ideal long-term load-bearing hard tissue implants.

Evaluation of soil aggregate microstructure and stability under wetting and drying cycles in two Ultisols using synchrotron-based X-ray micro-computed tomography

Soil structure and the soil pore system are important for many soil environmental processes. However, little is known about the influence of intra-aggregate microstructure on aggregate stability. The objective of this study was to evaluate the effect of soil pore characteristics on wet aggregate stability and aggregate tensile strength (TS) using synchrotron-based X-ray micro-computed tomography (SR-μCT) under wetting and drying cycles. Undisturbed topsoils (200cm3) derived from shale (S) and Quaternary red clay (Q) were submitted to three wetting and drying treatments under controlled laboratory conditions. 3–5mm aggregates were collected from different treatments and scanned at 3.7μm voxel-resolution for the reconstruction of 3D micro tomography images. The wet aggregate stability and TS were measured after each treatment. The relationships among pore characteristics, wet aggregate stability, and TS were analyzed using partial least squares regression (PLSR). The results indicated that porosity (P), percentage of pores >100μm (Pd>100), and fraction of elongated pores (FEP) all significantly increased with an increasing number of wetting and drying cycles, while the opposite trends were observed for the total number of pores (TNP), the percentage of pores with a diameter of 75–100, 30–75, and <30μm. Decrease in wet aggregate stability and TS of both soils was mainly due to higher P, a more extensive and complex pore network, which caused increased air pressure, increased rate of water entry, and high probability of crack propagation and interaction. The TNP, Pd75–100, P, and Pd>100, were identified as the primary factors controlling the wet aggregate stability and TS according to PLSR. The pore characteristics and soil clay content accounted for as much as 99% of the variation in wet aggregate stability and TS. This study provides insights for improved understanding of the change in topsoil microstructure; however, the effect of pore characteristics on the aggregate breakdown mechanism requires further investigation.

Effect of pore characteristics on permeability of sintered diatomite filter for microfiltration

Diatomite, because it is inherently porous and irregular, presents an interesting opportunity to investigate how the processing conditions of green bodies and the incorporation of spherical pores affect the final properties of a sintered ceramic filter. The water flux of a diatomite filter sintered at 1200°C was 6·3×104 L m−2 h−1 bar−1, which is higher than the water fluxes of typical ceramic filters such as spherical fly ash (1·6×104 L m−2 h−1 bar−1), γ-alumina (∼1·0×103 L m−2 h−1 bar−1) and zirconia (1·6×103 L m−2 h−1 bar−1) filters. The results obtained in this study show that the pressure applied during the processing of green bodies and the incorporation of spherical pores directly affect pore characteristics and accordingly determine the permeability of the sintered diatomite filters.

Effect of Pore Characteristics on Mechanical Properties and Annulus Fibrosus Cell Seeding and Proliferation in Designed PTMC Tissue Engineering Scaffolds

SummaryDegeneration of the intervertebral disk is the main cause of chronic back pain. Disk degeneration often leads to tearing of the annulus fibrosus (AF) and extrusion of the nucleus pulposus. As the current surgical strategies are suboptimal, reconstruction of the AF tissue by a tissue engineering strategy has emerged as an alternative. However, regeneration of the AF is challenging due to its complex and non‐homogeneous structure. Since there is a lack of knowledge regarding the effects of scaffold pore sizes on the behavior of human AF cells (hAFCs), scaffolds with a well‐defined and controlled pore architecture with pore sizes ranging from 230–420 µm were prepared by stereolithography. The scaffolds were prepared from the crosslinked biodegradable elastomer poly(trimethylene carbonate) (PTMC). The compression modulus of the scaffolds was inversely related to the pore size and ranged from 0.31–0.21 MPa. These values are similar to those reported for native AF tissue. Seeded hAFCs adhered to the PTMC network and proliferated well in all scaffolds during a culture period of 14 days. However, cell distribution was less homogeneous in the scaffold with 230 µm pore size. In view of its relatively high stifness, the latter scaffold is most suitable for AF tissue engineering, provided that the cell seeding procedure in this scaffold is optimized.

Effect of pore characteristics on electrochemical capacitance of activated carbons

Activated carbons (ACs) for electric double layer capacitors (EDLCs) were fabricated from waste tea leaves, activated with the pore-forming substances ZnCl2 then, carbonized at high-temperature in N2 atmosphere. The surface texture and porosity of the ACs were determined using transmission electron micros-copy and N2 adsorption/desorption studies. The surface area of the 20 wt % ZnCl2 treated sample was found to be 1029 m2g−1 and had a distribution of micropores and mesopores. The electrochemical properties of the ACs were evaluated by using cyclic voltammetry and galvanostatic charge-discharge studies. ACs from waste tea leaves exhibited excellent specific capacitance as high as 196 F g−1 in the 0.1 M Na2SO4 neutral electrolyte, with rectangular-like cyclic voltammetry curves at a cell potential of 1.5 V and good cyclability with a capacitance retention of 95% at a high current density of 100 mA g−1 for 2000 cycles. The results show that the pore texture properties and specific surface area of ACs are dominated by changing carbonization temperature and the amount of activating agent ZnCl2. The electrochemical performance is influenced mainly by surface area, but the pore size distribution becomes a dominating factor for specific capacitance of a carbon electrode material when the pore structure is in range of micropores/mesopores.

Effect of Pore Characteristics in Slip Cast Alumina on Glass Infiltration and Mechanical Properties of the Composites

Development of alumina/glass composites with minimal residual porosity and superior mechanical properties requires systematic studies on glass infiltration into porous alumina. This work has examined the effect of alumina particle size and the resulting pore size distribution on glass infiltration. Samples were prepared by slip‐casting a coarser alumina powder and blends of the coarse (d50 ~ 3.4 μm) and a finer (d50 ~ 0.7 μm) alumina powder. After presintering (1200°C) and following a single cycle of infiltration (1100°C), the sample with 50:50 (wt%) coarse and fine alumina showed highest flexural strength. Improvement in flexural strength could be imputed to the better glass infiltration.

Effect of Pore Characteristics in Slip Cast Alumina on Glass Infiltration and Mechanical Properties of the Composites

Effect of Pore Characteristics in Slip Cast Alumina on Glass Infiltration and Mechanical Properties of the Composites

The effect of pore characteristics on Ni suppression of porous NiTi shape memory alloys modified by surface treatment

The surfaces of porous NiTi shape memory alloys (SMAs) with different pore characteristics were modified by combined treatment of passivation and oxygen plasma immersion ion implantation methods. It has been found that the pore characteristics play an important role in improving Ni suppression performance. It is helpful to have large pore size and high pore interconnectivity for enhancing the Ni suppression performance of modified porous NiTi SMAs.

Effect of pore characteristics of AlO(OH) nano gel on crystal growth of α-Al2O3 platelets by molten salt precipitation

Effect of pore characteristics of AlO(OH) nano gel on crystal growth of α-Al2O3 platelets by molten salt precipitation

Small angle neutron scattering investigation and the low frequency dielectric response of sinteredZrO2–8 mol%Y2O3 ceramic compacts: the effect of pore characteristics

The effect of the pore structure on the low frequency (0.01–100 kHz) dielectric response of sinteredZrO2–8 mol% Y2O3 ceramic compacts has been investigated. Pore characteristics such as the pore sizedistribution, specific surface area and pore morphology have been estimated by means ofsmall angle neutron scattering (SANS). It has been observed that both the real and theimaginary parts of the complex dielectric permittivity for the specimens depend not onlyon the porosity but also on the pore characteristics, significantly. Unlike in the normalDebye relaxation process, the imaginary part of the dielectric constant increases in thelower frequency region. The variation in the dielectric response is explained by apore structure dependent interfacial polarization, ion hopping and conduction.

Effect of pore characteristics on the dynamics of cyclohexane molecules confined in ZSM-5 and MCM-41 molecular sieves: FTIR and QENS study

Fourier-transform infrared and quasi-elastic neutron scattering investigations have revealed that the cyclohexane molecules undergo phase transformation on adsorption at room temperature in HZSM-5 and MCM-41 molecular sieves. A comparison with similar studies on polycrystalline silica and zeolite-Y confirmed that the physical state of occluded molecules depended upon the size and the structure of the pores in host material. The confinement in HZSM-5 resulted in the development of non-equilibrium and highly condensed phase of cyclohexane, which remained trapped in the zeolitic pores even after partial desorption. This compression of cyclohexane as a result of adsorption in HZSM-5 is in agreement with the reported phenomena of super-cooling on physical confinement of fluids inside the narrow pores. On the other hand, relatively smaller amounts of cyclohexane were held in the pores of MCM-41 during the adsorption under identical conditions; and for all the loadings below 5 mmol g−1 the guest molecules acquired a transition state the density of which lay between that of the vapor and the liquid phases of cyclohexane. The results of this study are consistent with our recent findings on the formation of a clustered state of benzene during its adsorption into microporous materials (A. Sahasrabudhe, V. S. Kamble, A. K. Tripathi and N. M. Gupta, J. Phys. Chem. B, 2001, 105, 4374; A. K. Tripathi, A. Sahasrabudhe, S. Mitra, R. Mukhopadhyay, N. M. Gupta and V. B. Kartha, Phys. Chem. Chem. Phys., 2001, 3, 4449), and are also in line with the current theories on capillary condensation of fluids in narrow pores.

Effect of pore characteristics on carrier-facilitated transport of Am(III) across track-etched membranes

Track-etched membranes (TEMs) with well-defined pore characteristics were prepared by bombarding polycarbonate plastics with 161 Dy ions of 13.0 MeV per nucleon energy and by bombarding polycarbonate plastics with fission fragments from a 252 Cf source. In order to optimise the properties of TEMs for their applications as model supports in supported liquid membrane (SLM) studies, the transport of Am(III) across the SLM with TRUEX extractants (0.2 M n-octylphenyl ( N, N-diisobutyl carbamoyl methyl) phosphine oxide (CMPO)+1.2 M tributyl phosphate (TBP) in dodecane) as carrier has been examined. The latent tracks formed by heavy-ions in the plastics were enlarged into well-defined pores by chemical etching. The geometry of the pores formed in the plastics was obtained by the track-etched model, based on the dynamics of pore etching. The TEMs were converted as supports for SLM studies by impregnating them with the carrier (0.2 M CMPO+1.2 M TBP in dodecane). The SLMs with different supports were used for studying the facilitated transport of Am(III). The permeation across the SLM formed by using TEM with 17% porosity was found to be comparable to those SLMs formed by using commercial membranes with much higher porosities. The comparison of permeability coefficients ( P) obtained by using TEMs with 29–30 μm and 10 μm thickness indicated that P decreases linearly with thickness and hence transport of Am(III) is diffusion controlled, and reaction kinetics of extraction and stripping steps are fast. The variation of P as a function of porosity of the TEM support indicated that P decreased with increase in porosity upto 10% and thereafter it remained constant. The data on variation of P as a function of porosity were used to obtain the thickness of the aqueous diffusion layer and the membrane diffusion coefficient of the SLM system studied in the present work. The TEMs with very small pore size (0.07 μm) and very large pore size (3 μm) were found to deviate from the expected trend and gave anomalously low P values. Such low P values were also reported elsewhere with membranes of small pore size. The low P values with small pore size support may be due to hindered diffusion due to aggregation of the permeant (Am–CMPO complex in this case), but no satisfactory explanation was found for low P values in the case of supports with large pore size.

Effect of pore characteristics on elastic constants of sintered iron: M.Yuasa et al. (Science University of Tokyo, Tokyo, Japan.) J. Jpn Soc. Powder Powder Metal., vol 45, no 10, 1998, 920–925. (In Japanese.)

Effect of pore characteristics on elastic constants of sintered iron: M.Yuasa et al. (Science University of Tokyo, Tokyo, Japan.) J. Jpn Soc. Powder Powder Metal., vol 45, no 10, 1998, 920–925. (In Japanese.)