Microporosity Fraction Research Articles

Determination of the Volume Fraction of Microporosity in Single Crystals of Nickel-Based Superalloys

Determination of the Volume Fraction of Microporosity in Single Crystals of Nickel-Based Superalloys

Estimating permeability in a limestone geothermal reservoir from NMR laboratory experiments

A wireline NMR (Nuclear Magnetic Resonance) logging tool has recently been deployed in the Dogger geothermal aquifer of the Paris Basin to provide a continuous permeability estimation throughout the reservoir. The complex pore structure of heterogeneous carbonate systems means that careful consideration must be given to standard permeability prediction. A laboratory study was performed on cores from a geothermal well at Bobigny, north of Paris. Petrographic and petrophysical analyses of thin sections, water permeability and laboratory NMR relaxation time T2 were conducted on 72 samples. A classification was established using four main facies and the impact of microporosity and micritization on flow properties was investigated. The range of permeability is wide [0.05–1000 mD] and the evaluation addresses different relationships between permeability and a combination of porosity and T2 distributions. Since the latter distributions can provide an estimation of the pore size distributions and in particular the fraction of microporosity within the total porosity, several possibilities arise for better constraining the permeability relationship. For one facies, permeability is nearly independent of porosity over a porosity range of [0.12–0.22], illustrating the well-known difficulty of predicting permeability in carbonate lithologies. The best permeability prediction is obtained when considering only macroporosity instead of total porosity in a classical power law.

Qualitative assessment of improved oil recovery and wettability alteration by low salinity water injection for heterogeneous carbonates

This study aims to evaluate the qualitative potential for low salinity water injection (LSWI) to alter the wettability and increase oil production in heterogeneous oil-wet coquina cores (one of the facies of Pre-Salt reservoirs) in relevant conditions of brine salinity, temperature, and initial wettability. We also aimed to verify the impact of micro-porosity fraction on oil recovery. Finally, we verified whether the presence of micro-dispersion in the oil phase upon contact with low salinity would have a positive correlation with improved oil recovery due to low salinity water injection.To achieve these objectives, we performed zeta-potential experiments to evaluate the charges at the oil-brine and brine-rock interfaces that affect rock wetting state and contact tests to test for the presence of micro-dispersions in the oil phase and potential for LSWI. A series of spontaneous imbibition and coreflood experiments were performed to calculate the Amott index and evaluate wettability of coquinas in core-scale as a function of brine salinity. Tertiary and secondary low salinity waterfloods were carried out to investigate whether a diluted desulfated seawater would increase oil production in coquina cores. The effect of predominance of macro-, meso-, and micro-porosity on secondary low salinity waterflood was also evaluated. Our results have shown that heterogeneity had a greater impact on recovery factor compared to brine salinity. Oil recovery for low salinity brine for a core with predominance of macro-pores was smaller than for cores with higher fraction of micro-pores flooded with FW and DSW. Low-salinity oil recovery was also smaller than high-salinity was for core with microporosity but with presence of dead-end pores. Secondary injection of low-salinity using the same core with large fraction of micro-porosity showed that it accelerated oil production compared to high-salinity brine. We have also observed that LSWI resulted in increased oil recovery in coquinas both in tertiary mode (average 10%) compared to FW/DSW and secondary mode using the same core (18% compared to FW) due to wettability alteration. This result was supported by spontaneous imbibition as well as zeta-potential results. The contact test between crude oil and low salinity brine resulted in a micro-dispersion ratio of 11.7, showing that a positive oil is likely to result in improved oil recovery due to low salinity injection. Despite the increased oil recovery seen during the tests, the results showed that oil production in tertiary mode was significantly delayed (after 4 PV), likely due to adverse oil/water viscosity ratio and water dispersion due to mixing between low- and high-salinity brines. We observed that for the shorter more oil-wet core significant oil production was measured during bump flow with both high-salinity and low-salinity brines, due to capillary end effects. This could mean that residual oil saturation was not achieved during high-salinity water injection and an overestimation of recovery factor due to low-salinity was seen.

An explicit stabilised finite element method for Navier-Stokes-Brinkman equations

We present an explicit stabilised finite element method for solving Navier-Stokes-Brinkman equations. The proposed algorithm has several advantages. First, the lower equal-order finite element space for velocity and pressure is ideal for presenting the pixel images. Stabilised finite element allows the continuity of both tangential and normal velocities at the interface between regions of different micro-permeability or at the interface free/porous domain. Second, the algorithm is fully explicit and versatile for describing complex boundary conditions. Third, the fully explicit matrix–free finite element implementation is ideal for parallelism on high-performance computers. In the last, the implicit treatment of Darcy term allowed larger time stepping and a stable computation, even if the velocity varies for several orders of magnitude in the micro-porous regions (Darcy regime).The stabilisation parameter, that may affect the velocity field, has been discussed and an optimal parameter was chosen based on the numerical examples. Velocity stability at interface between different micro-permeability has been also studied with mesh refinement. We analysed the influence of the micro-permeability field on the regime of the flow (Stokes flow, Darcy flow or a transitional regime). These benchmark tests provide guidelines for choosing the resolution of the grayscale image and its segmentation. We applied the method on real Berea Sandstone micro-CT images, and proceeded the three-phases segmentation. We studied the influence of the micro-porosity field, using the well-known Kozeny-Carman relation to derive the micro-permeability field from the micro-porosity field, on the effective permeability computed. Our analysis shows that a small fraction of micro-porosity in the rock has a significant influence on the effective permeability computed.

Nanoparticle additions promote outstanding fracture toughness and fatigue strength in a cast Al–Cu alloy

Fatigue resistance and fracture toughness are essential to the reliability of castings during service. Reducing microporosity in cast alloys is a crucial issue for improving their fatigue strength and fracture toughness. Here we report a significant reduction in microporosity of a cast aluminum-copper alloy developed using in situ TiC nanoparticle additions coupled with a stir-casting method. The addition of TiC nanoparticles is found to improve the interdendritic feedability of liquid metal and as a result reduces the volume fraction of microporosity by two orders of magnitude compared to a conventionally cast Al–Cu alloy. This method, which is mechanistically associated with a pore-dominated process, acts to significantly improve the fatigue strength, fracture toughness and uniform elongation of the cast Al–Cu alloy to values which, to the best of our knowledge, represent the highest ever achieved for a cast aluminum alloy.

Zeolite Beta Precursors as Building Units toward Enhancing the Microporosity Fraction of Mesoporous Aluminosilicates

Our group has reported the synthesis of hydrothermally stable mesoporous aluminosilicates (MAs) by self-assembly of triblock copolymers and zeolite Y precursors. However, degradation of zeolite Y precursors in the acidic synthesis system will inevitably lead to low microporosity fraction of final products. Development of a facile route to obtain MAs simultaneously with high hydrothermal stability and microporosity fraction is still a great challenge. Herein, we employ zeolite Beta precursors as building units to solve this problem. In this strategy, zeolite Beta precursors were more stable than zeolite Y precursors in the acidic synthesis system due to the presence of organic directing agent TEAOH, which would result in more microporosity implanted into the framework of MAs. By fine-tuning the assembly time, the microporosity fraction could be adjusted in a range of 38.7%–52.9%. In addition, the synthesized MAs maintain well-resolved crystal patterns, high surface area, and pore volume even after a severe...

Metal incorporated biochar as a potential adsorbent for high capacity CO2 capture at ambient condition

This work investigates the development of metal incorporated biochar as a low-cost and robust adsorbent for high capacity CO2 capture at ambient condition. For this purpose, biochars were prepared through single-step pyrolysis of walnut shell (WS) at different temperatures (500, 700 and 900 °C). The biochar with larger specific surface area and higher microporosity fraction (WS900) was then subjected to metal impregnation followed by N2 heat treatment. The incorporation of basic metal sites into the biochar skeleton enhanced the adsorption of acidic CO2 gas onto the metalized-biochar in the sequence of Mg > Al > Fe > Ni > Ca > raw-biochar > Na. The enhanced CO2 uptake of Mg-loaded biochar (82.0 mg/g) compared to the pristine biochar (72.6 mg/g) at 25 °C and 1 atm, could be explained by the synergistic effects of physical and chemical interactions, yet kinetic studies showed that physisorption was the main governing mechanism controlling the adsorption of CO2 onto the metalized-biochar. Cyclic CO2 capture studies indicated the great stability of Mg-loaded biochar upon several cycles of adsorption-desorption, with no loss in its CO2 capture capacity. It also showed easy regeneration and fast desorption kinetic which makes it a promising inexpensive candidate for real-world CO2 capture systems. Moreover, the adsorbent showed a superior capture performance towards CO2 over N2, O2 and CH4.

Effect of Solidification Behavior on Microstructures and Mechanical Properties of Ni-Cr-Fe Superalloy Investment Casting.

The effect of solidification behavior on the microstructures and mechanical properties of Ni-Cr-Fe superalloy investment casting is given. Metallographic and image analysis have been used to quantitatively examine the microstructures’ evolution. For the parts with the thickness of 3 mm and 24 mm, the volume fraction and maximum equivalent radius of the Laves phase increases from 0.3% to 1.2%, from 11.7 μm to 23.4 μm, respectively. Meanwhile, the volume fraction and maximum equivalent radius of carbides increase from 0.3% to 0.5%, from 8.1 μm to 9.9 μm, respectively. In addition, the volume fraction of microporosity increases from 0.3% to 2.7%. As a result, the ultimate tensile strength is reduced from 1125.5 MPa to 820.9 MPa, the elongation from 13.3% to 7.7%, and the quality index from 1294.2 MPa to 954.0 MPa, respectively. A typical brittle fracture is observed on the tensile fracture. As the cooling rate decreases, the microstructures become coarser.

Pore volume compressibilities of sandstones and carbonates from Helium porosimetry measurements

For decades, several efforts have been put in place to understand the interaction between rock and fluids, and on the physical laws that describe the fluid behavior in a porous media. Petrophysical modeling is used in drilling, completion, compaction evaluation of the reservoir rocks and wellbore production to avoid unexpected interventions and optimize the hydrocarbon production throughout the life of the well. Pore volume compressibility is one of the main parameters to characterize the behavior of the reservoir rock as it quantifies the incremental pore volume variations due to external or internal pressures. This parameter is needed for reserve estimation, production forecasting, wellbore stability evaluation and seismic monitoring issues. In this work, uniaxial compression tests were carried out using helium gas porosimetry, which measured the variation of the pore volume for each applied load. The pore volume compressibility calculation was possible through a power-law fitting between pore volumes and confining pressure. That procedure was applied to six sandstone, six limestone and one dolomite samples at nine different confining pressures ranging from 400–2000 psi. Porosity was calculated for each pressure stage and the interdependency of the pore compressibility and porosity was evaluated, assuming that grain volume remains unaltered and using the pore volume measurements. Optical microscopy and Mercury Intrusion Porosimetry (MIP) aided to understand the pore space of some of the rocks and to quantify microporosity fraction, which impacts on a dual porosity system. This work also shows that the amount of microporosity influences how the pore volume changes as the external pressure increases. For rocks with small microporosity, the power-law behavior is likely to describe the relationship between the pore volume and the confining pressure practically perfect (R2~1), but as microporosity increases, the accuracy of this relationship decreases.

Significance of microporosity on the interaction of phenol with porous graphitic carbon

Many researches have produced porous activated carbons from various precursors for phenol removal from wastewater. A number of literature focus on the optimization of activation conditions to obtain adsorbents with higher specific surface areas as a result of the general misconception that higher surface areas result in higher adsorption capacities, disregarding the effect of the pore geometry. The aim of this study is to demonstrate the significance of micropore surface area, rather than total surface area, in the adsorption of phenol. It has been confirmed that for activated carbons with similar surface areas, the one with higher fraction of microporosity leads to higher phenol uptake. This has been attributed to the π–π London dispersion forces between the graphitic carbon basal planes and the phenol aromatic ring. Thus, it is hypothesized that hydrogen bonding does not occur between the phenol molecules and the functional groups on the carbon surface.

Preparation and characterization of chemically activated carbons derived from Mediterranean Posidonia oceanica (L.) fibres

In the present work, the preparation of several chemically activated carbons (CACs) from marine Posidonia oceanica fibrous biomass was performed using various activating agents. The chemical activation was carried out using phosphoric acid (H3PO4), potassium hydroxide (KOH), zinc chloride (ZnCl2) and hydrogen peroxide (H2O2). The effects of those impregnating agents were investigated for all produced CACs via several chemical and structural analyses.The results showed that H3PO4 seems to induce the deepest impact on the P. oceanica fibres by providing the lowest conversion yield (16.9%). Besides, the pore analysis showed that two types of porosity were developed: (i) CACs characterized by an inner structure combining significant fraction of both mesopores and micropores (i.e. CAC-H3PO4, CAC-KOH and CAC-ZnCl2) and (ii) CAC-H2O2 with a large mesoporous structure and a small fraction of microporosity. Dealing with the RAMAN and XPS analysis, it was showed that the main carbon fraction is structurally organized (i.e. graphite), especially for the CAC-ZnCl2 sample. As for the isotherm and kinetic investigation, the experimental and modelling results revealed that CAC-H3PO4 was the best performing activated carbon by removing the highest methylene blue dye amount (137mg/g) in the shortest time (1.3h to reach the half reaction point).

니켈계 초내열합금 CM247LC의 일방향응고 시 미세조직 형성거동 분석

The Ni-base superalloy CM247LC was directionally solidified (DS) using the Bridgman-type furnace to understand the effect of the chill plate on the microstructural evolution, such as dendrite arm spacing, microporosity, and MC-type carbide. The DS process was also modeled by the PROCAST to predict the solidification rate, thermal gradient, and resultant cooling rate in the entire length of the DS specimen. Due to the quenching effects of chill plate, four distinct areas were found to form in the specimen, in which the solidification rate was changed, during DS at a given withdrawal rate of 0.083 mm/s. Among the microstructural features investigated, the dendrite arm spacings and average size of the MC-type carbide near the chill plate were found to be influenced by the quenching effect of the chill plate. However, no significant influence was found on the size and volume fraction of microporosity, and the volume fraction of the MC-type carbide. The relationship between the microstructural features and the solidification variables was also analyzed and discussed on the basis of a combination of experimental and modeling results.

Influence of Microporosity Morphology on Hot Compression Behavior of 6063 Alloy

The influences of microporosity morphology on the flow stress behavior of 6063 alloy were investigated by isothermal compression test at 300°C-500°C and strain rate of 0.01-10s-1. After 60% compression, the area fraction of microporosity of sample having lage microporosity decreases obviously. The flow stress increases with increasing strain rate and decreasing temperature. The flow stress stress behavior of 6063 alloy during hot compression can be described by a Zener-Hollomon parameter including Arrhenius item. The increasing of area fraction of microporosity decreases the deformation activiation energy Q.

Influence of Chemical and Physical Properties of Activated Carbon Powders on Oxygen Reduction and Microbial Fuel Cell Performance

Commercially available activated carbon (AC) powders made from different precursor materials (coal, peat, coconut shell, hardwood, and phenolic resin) were electrochemically evaluated as oxygen reduction catalysts and tested as cathode catalysts in microbial fuel cells (MFCs). AC powders were characterized in terms of surface chemistry and porosity, and their kinetic activities were compared to carbon black and platinum catalysts in rotating disk electrode (RDE) tests. Cathodes using the coal-derived AC had the highest power densities in MFCs (1620 ± 10 mW m(-2)). Peat-based AC performed similarly in MFC tests (1610 ± 100 mW m(-2)) and had the best catalyst performance, with an onset potential of E(onset) = 0.17 V, and n = 3.6 electrons used for oxygen reduction. Hardwood based AC had the highest number of acidic surface functional groups and the poorest performance in MFC and catalysis tests (630 ± 10 mW m(-2), E(onset) = -0.01 V, n = 2.1). There was an inverse relationship between onset potential and quantity of strong acid (pKa < 8) functional groups, and a larger fraction of microporosity was negatively correlated with power production in MFCs. Surface area alone was a poor predictor of catalyst performance, and a high quantity of acidic surface functional groups was determined to be detrimental to oxygen reduction and cathode performance.

Microstructural changes by heat treatment for single crystal superalloy exposed at high temperature

The effects of heat treatment for recovering microstructure of Ni-based single crystal superalloy with added C and Hf after thermal exposure have been evaluated. The optimum heat treatment conditions were drawn from the microstructure analysis, after thermal exposure at 982°C for 3000h and rejuvenation treatment. The solvus and solidus temperatures of this alloy were 1305 and 1315°C respectively, and most of Ta and Ti-rich carbide dissolved after performing γ′ solid solution treatment at 1305–1310°C. The fraction of microporosity and eutectic phase showed a tendency of increase at solvus temperature. Also, an uphill diffusion of Al, Cr, Ta and Re was observed in eutectic phase at the solvus temperature, and the change of the composition of Ta was relatively higher than other elements. The gradient of heating curves in DSC analysis showed its sharp change after γ′ solid solution treatment at the temperature below solvus temperature of 1305°C because of the existence of un-dissolved coarse γ′ in the interdendritic region.

Effect of local volume fraction of microporosity on tensile properties in Al–Si–Mg cast alloy

Porosity in Al–Si–Mg cast alloys utilised in automotive parts affects directly products quality, i.e. mechanical properties. In this study, the effect of micropores on mechanical properties has been investigated by X-ray tomography from the viewpoint of clustering micropores. The local volume fraction (LVF) of porosity was introduced to analyse the effect of clustering micropores. The statistical Weibull method was also used in order to explain strength of the alloy tested. The fracture strain decreased drastically from 17 to 3% on an inverse parabolic relationship with increasing porosity. In the case of the specimens that contain the largest pore higher than 100 m m, the ultimate tensile strength decreases monotonically. It is found that the fracture surface passes through high LVF regions. The fracture strain obviously depends on the ratio of LVF higher than 10%. It is confirmed that the LVF, which represents unevenly distribution of micropores cluster, is one of important dominant factor for managing the mechanical properties in the Al–Si–Mg cast alloy.

Adsorption characteristics of phenol on novel corn grain-based activated carbons

The adsorption of phenol on highly porous novel corn grain-based activated carbons (CG-ACs) (>2000 m 2/g) were assessed in a batch mode. The optimum conditions for the adsorption of phenol on R-series (R-1/2, R-1/3, and R-1/4) CG-ACs were determined by analyzing the various adsorption conditions such as the adsorption temperature (293.15–313.15 K), initial solution concentrations (25–150 mg/L), and initial pH (3–12) of the solution. In addition, effects of CG-AC properties such as physical properties, energetic heterogeneity nature and surface chemistries on phenol adsorption were also investigated. In overall, it was found that the influences of physical properties and energetic heterogeneity nature of CG-ACs on phenol adsorption are considerably high compared to their surface chemistry. More specially, the increase in phenol adsorption capacity with increasing fraction of microporosity ranging from 3 to 11 Å, is likely due to the micropore filling, was noted. The Langmuir model well fitted with the experimental results compared to the Freundlich. Besides, the pseudo second-order equation was successfully used to represent the results of kinetic studies.

Optimization of microporous palm shell activated carbon production for flue gas desulphurization: Experimental and statistical studies

Optimizing the production of microporous activated carbon from waste palm shell was done by applying experimental design methodology. The product, palm shell activated carbon was tested for removal of SO 2 gas from flue gas. The activated carbon production was mathematically described as a function of parameters such as flow rate, activation time and activation temperature of carbonization. These parameters were modeled using response surface methodology. The experiments were carried out as a central composite design consisting of 32 experiments. Quadratic models were developed for surface area, total pore volume, and microporosity in term of micropore fraction. The models were used to obtain the optimum process condition for the production of microporous palm shell activated carbon useful for SO 2 removal. The optimized palm shell activated carbon with surface area of 973 m 2/g, total pore volume of 0.78 cc/g and micropore fraction of 70.5% showed an excellent agreement with the amount predicted by the statistical analysis. Palm shell activated carbon with higher surface area and microporosity fraction showed good adsorption affinity for SO 2 removal.

Microporosity Simulation in Aluminum Castings Using an Integrated Pore Growth and Interdendritic Flow Model

A new computational model for predicting microporosity in aluminum alloys is described. The model was calibrated against literature data for binary Al-7 pct Si alloys, and subsequently applied to a chill plate test casting in A356 alloy and to an engine block in 319 alloy. The new model allows spherical micropores to nucleate and grow by hydrogen diffusion from a material volume surrounding the pores. This differs from a conventional interdendritic flow computational model for calculating porosity that assumes spherical pores have a diameter proportional to the secondary dendrite arm spacing (SDAS). The new integrated pore growth and interdendritic flow model predicts larger pore diameters and a volume fraction of microporosity that is in better agreement with experimental observations than the interdendritic flow model.

Microporosity enhances bioactivity of synthetic bone graft substitutes

This paper describes an investigation into the influence of microporosity on early osseointegration and final bone volume within porous hydroxyapatite (HA) bone graft substitutes (BGS). Four paired grades of BGS were studied, two (HA70-1 and HA70-2) with a nominal total porosity of 70% and two (HA80-1 and HA80-2) with a total-porosity of 80%. Within each of the total-porosity paired grades the nominal volume fraction of microporosity within the HA struts was varied such that the strut porosity of HA70-1 and HA80-1 was 10% while the strut-porosity of HA70-2 and HA80-2 was 20%. Cylindrical specimens, 4.5 mm diameter x 6.5 mm length, were implanted in the femoral condyle of 6 month New Zealand White rabbits and retrieved for histological, histomorphometric, and mechanical analysis at 1, 3, 12 and 24 weeks. Histological observations demonstrated variation in the degree of capillary penetration at 1 week and bone morphology within scaffolds 3-24 weeks. Moreover, histomorphometry demonstrated a significant increase in bone volume within 20% strut-porosity scaffolds at 3 weeks and that the mineral apposition rate within these scaffolds over the 1-2 week period was significantly higher. However, an elevated level of bone volume was only maintained at 24 weeks in HA80-2 and there was no significant difference in bone volume at either 12 or 24 weeks for 70% total-porosity scaffolds. The results of mechanical testing suggested that this disparity in behaviour between 70 and 80% total-porosity scaffolds may have reflected variations in scaffold mechanics and the degree of reinforcement conferred to the bone-BGS composite once fully integrated. Together these results indicate that manipulation of the levels of microporosity within a BGS can be used to accelerate osseointegration and elevate the equilibrium volume of bone.