Limited Porosity Research Articles

The role of stratabound fractures for fluid migration pathways and storage in well- bedded carbonates

Fracture analysis, carried out on two reservoir analogues cropping out at Faito and Chianello Mts. (southern Italy) allowed us to unravel the role of stratabound joint networks for oil migration and storage within well-bedded carbonate successions. The fracture regression analysis pointed out that stratabound fracture aperture increases as a function of bed thickness according to a linear law, independently by the lithological characteristics of the analyzed rock. Furthermore, statistical results suggest that fracture aperture and spacing exhibit, for each bed thickness value, a lognormal probability distribution. The estimation of the stratabound fracture porosity allowed us to identify, in well-bedded sedimentary successions, three classes of multilayer packages: ( i ) thin beds, characterized by a dual role of permeable pathways and oil storage systems; ( ii ) medium sized beds, showing limited permeability and porosity values and ( iii ) thick beds, acting as highly permeable pathways and showing a negligible storage capacity. Our results permit a full characterization and modeling of stratabound fracture networks. In particular, they provide a powerful tool for predicting preferential fluid pathways and major oil storage systems based on bed thickness data, within the framework of an analysis that may be further enhanced by the integration of petrophysics data.

Adsorptive capacity and evolution of the pore structure of alumina on reaction with gaseous hydrogen fluoride.

Brunauer-Emmet-Teller (BET) specific surface areas are generally used to gauge the propensity of uptake on adsorbents, with less attention paid to kinetic considerations. We explore the importance of such parameters by modeling the pore size distributions of smelter grade aluminas following HF adsorption, an industrially important process in gas cleaning at aluminum smelters. The pore size distributions of industrially fluorinated aluminas, and those contacted with HF in controlled laboratory trials, are reconstructed from the pore structure of the untreated materials when filtered through different models of adsorption. These studies demonstrate the presence of three distinct families of pores: those with uninhibited HF uptake, kinetically limited porosity, and pores that are surface blocked after negligible scrubbing. The surface areas of the inaccessible and blocked pores will overinflate estimates of the adsorption capacity of the adsorbate. We also demonstrate, contrary to conventional understanding, that porosity changes are attributed not to monolayer uptake but more reasonably to pore length attenuation. The model assumes nothing specific regarding the Al2O3-HF system and is therefore likely general to adsorbate/adsorbent phenomena.

Carbonyl-Iron Electrodes for Rechargeable-Iron Batteries

AbstractNickel-iron and iron-air batteries are attractive for large-scale-electrical-energy storage because iron is abundant, low-cost and non-toxic. However, these batteries suffer from poor charge acceptance due to hydrogen evolution during charging. In this study, we have demonstrated iron electrodes prepared from carbonyl iron powder (CIP) that are capable of delivering a specific discharge capacity of about 400 mAh g−1 at a current density of 100 mA g−1 with a faradaic efficiency of about 80%. The specific capacity of the electrodes increases gradually during formation cycles and reaches a maximum in the 180th cycle. The slow increase in the specific capacity is attributed to the low surface area and limited porosity of the pristine CIP. Evolution of charge potential profiles is investigated to understand the extent of charge acceptance during formation cycles. In situ XRD pattern for the electrodes subsequent to 300 charge/discharge cycles confirms the presence of Fe with Fe(OH)2 as dominant phase.

Combustion and pyrolysis of activated carbon fibre from oil palm empty fruit bunch fibre assisted through chemical activation with acid treatment

Thermochemical reactions viz. combustion and pyrolysis are important processes in the conversion of biomass from agricultural wastes into functional materials activated carbon fibre (ACF). Acid treatment during combustion and pyrolysis leaves a major impact which affects quality and properties of the resulting ACF such as pore size control and surface area enlargement. In this study, carbonisation and activation of empty fruit bunch (EFB) fibre into ACF was carried out using acid treatment assisted combustion and pyrolysis followed by CO2 gas flow. The effects of acid treatment on the physicochemical properties and pore characteristics was studied by applying sulphuric acid and switching the sequence of acid treatment before and after combustion and pyrolysis. Intercalation of sulphuric acid and exfoliation reactions on the acid-treated EFB fibre resulted in a higher thermal degradation rate compared to raw EFB fibre without acid treatment. Higher BET surface area and total pore volume were obtained for ACF samples treated with acid. The higher pore volume is due to the intercalated sulphuric compound which facilitated the removal of volatile matter and generated more pores for adsorption. However, severe acid oxidation could also lead to pore blocking with excess oxygen complexes and creation of limited porosity. The results show that properties of the ACF can be affected by the sequence of the acid treatment depending on the thermochemical process applied.

Analysis of Cortical Bone Structures in Perimenopausal Female Patients With Recent Fragility Fractures

Aims: The aim of this study was to investigate trabecular and cortical bone microstructure in perimenopausal patients with atraumatic peripheral or vertebral fractures. We hypothesize that in perimenopausal women cortical bone is more affected by osteoporosis than trabecular bone. Methods: We consecutively investigated 26 perimenopausal treatment naive female patients (mean age: 47.8 yrs) with peripheral fractures (PG) and compared them to ageand sex-matched healthy controls (CG; n538; mean age 42.7 yrs). Patients had an average of two atraumatic fractures, but were otherwise healthy. The distal radius and the ultradistal tibia of all patients were scanned on an HRpQCT scanner (XtremeCT, SCANCO Medical, Br€uttisellen, Switzerland). Trabecular bone volume fraction (BV/TV) from the volumetric BMD of the trabecular compartment (Tb.BMD), the peripheral region adjacent to the cortex (pTb.BMD) and the central trabecular region (mTb.BMD) were analyzed. From the binary trabecular ridge image, trabecular number (Tb.N) was measured using the direct 3D distance transform approach. Based on the densitometric BV/TV and direct Tb.N, trabecular thickness (Tb.Th) and trabecular separation (Tb.Sp) were derived using traditional plate model assumptions, as has been described previously (Boutroy et al., JCEM 2005). To assess cortical bone microarchitecture, the trabecular and cortical compartment were segmented by automated algorithm (Burghardt et al., JBMR 2009). We analyzed cortical BMD (Ct.BMD), cortical porosity (Ct.Po), cortical pore volume (Ct.Po.V), cortical pore diameter (Ct.Po.Dm) and cortical pore diameter distribution (Ct.Po.Dm.SD). Results: Structural analysis by HR-pQCT showed significant differences between patients and healthy controls regarding cortical but not trabecular parameters at both sites. At the radius patients had increased cortical pore volume (7.74 4.97mm vs. 5.29 3.78; p!0.01), increased cortical pore diameter (0.17 0.03mm vs. 0.15 0.02mm; p! 0.001) and an increased distribution of cortical pore diameters (7 3% vs. 4 3%; p!0.01) compared to controls. In addition, at the tibia cortical pore volume (61.15 30.66mm; p!0.01) and also cortical porosity (7 4% vs. 4 3%; p!0.01) were significantly increased. Strong correlations of cortical parameters were found between the tibia and radius. In addition, most cortical structure parameters were correlated with age in patients and controls. Conclusion: Our results suggest that bone fragility and fracture susceptibility in perimenopausal females are likely to contribute to poor cortical bone strength and increased cortical porosity. However, HR-pQCT resolution is limited and cortical porosity, analyzed by different algorithm, was reported to be much higher. Disclosure of Interest: None Declared

Microstructural evolution of 7075 Al gas atomized powder and high-pressure cold sprayed deposition

This study investigates the microstructure evolution of as-atomized 7075 aluminum powder during high pressure cold spray deposition. The as-received powder and the deposition were characterized via scanning electron microscopy, electron backscatter diffraction, and transmission electron microscopy. The as-received powder was composed of two different particle types, differentiated by their grain boundary structure and solute element distribution. Significant solute element segregation was observed at grain boundaries for both particle types. The powder also contained nanoscale subgrain and dislocation structures. High pressure cold spray resulted in the formation of a high quality deposition with limited porosity and inter-particle voids. The deposition was characterized by two distinct regions: particle/particle boundaries and particle interiors. Particle/particle boundaries showed a high degree of deformation resulting in the formation of an ultra-fine grain structure and a low density of low angle grain boundaries. The formation of the ultra-fine grain structure is attributed to dynamic recrystallization and recovery processes. Particle interiors were characterized by larger grains containing a high density of low angle grain boundaries and dislocation structure. Large grains in the deposition contained precipitates distributed both within the grain interior and at grain boundaries. Precipitates in small grains were distributed primarily at grain boundaries. The effect of these precipitates on the microstructure evolution was also discussed.

Fabrication of surface-treated SiC/epoxy composites through a wetting method for enhanced thermal and mechanical properties

• SiC/epoxy composites is prepared by the wetting method. • The surface treatment of SiC particles results in an enhanced wettability of epoxy. • The measured thermal conductivity is correlated with theoretical models. • Storage modulus reveals that the wetting process results in enhanced mechanical properties. Silicon carbide (SiC)/epoxy composites were prepared by a wetting method. To increase the dispersion of dropped epoxy resin on top of the SiC cake, a surface oxidation treatment was applied to the SiC particles. The surface treatment of the SiC particles was applied for an enhanced wettability of the epoxy resin due to a secondary interaction between SiC and epoxy. The thermal transport properties of the composites were maximized at 70 wt.% of SiC during the wetting process because of the limited porosity of the SiC cake. The measured thermal conductivity as a function of the filler concentration correlated with Agari’s model. The results, based on the coefficient obtained by Agari’s model, indicated that the wetting method for the production of the composites combined with a surface treatment of SiC particles facilitates the formation of conducting paths. Storage modulus results also revealed that the wetting process results in enhanced mechanical properties of the composites.

Novel and High-Performance Magnetic Carbon Composite Prepared from Waste Hydrochar for Dye Removal

In recent years, more and more attention has been paid to the hydrothermal liquefaction (HTL) of waste biomass for the production of bio-oil and hydrochar (a solid residue from HTL process). However, hydrochar possesses limited porosity and surface area, hindering its environmental application. In the present work, to promote the development of a sustainable application of waste biomass, waste hydrochar was activated and modified to a novel magnetic carbon composite, which exhibited high performance for dye removal from aqueous solutions. The composite possessed a saturation magnetization of 38.5 emu g–1 at room temperature and could be facilely attracted from an aqueous solution by an external magnet. The as-prepared composite exhibited a superior malachite green (MG) adsorption capacity (476 mg g–1), which was much higher than the known magnetic adsorbents. Our results suggested that the waste hydrochar could be efficiently transformed to a high-performance sustainable material for dye removal.

ChemInform Abstract: New Modelling Approach to Liquid‐Solid Reaction Kinetics: From Ideal Particles to Real Particles

AbstractReview: 41 refs.

New modelling approach to liquid–solid reaction kinetics: From ideal particles to real particles

Typical features of liquid–solid reactions were reviewed: reaction kinetics, mass transfer effects and particle morphology. It was concluded that classical liquid–solid models based on ideal, non-porous geometries (sphere, infinite cylinder, slab) cannot satisfactorily describe real reactive solid particles with various surface defects, such as cracks, craters and limited porosity. Typically a too low reaction order for the reactive solid is predicted by the classical models. The surface morphology can be revealed by electron microscopy, which gives inspiration to develop new mathematical models for reactive solids.Generalized product layer and shrinking particle models were developed for arbitrary geometries deviating dramatically from ideal geometries. The approach is based on the use of a shape factor (a), which can obtain high values for particles with surface defects. The modelling approach was illustrated with numerical simulations and an experimental case, leaching of zinc sulphide with ferric ions. A general methodology for investigation of fluid–solid reactions was proposed.

The mechanism of hydrogen sulfide adsorption on fine rubber particle media (FRPM)

A commercial rubber waste product, fine rubber particle media (FRPM), was found to adsorb hydrogen sulfide (H2S) at 0.12mg H2S/g FRPM of adsorption capacity. Since FRPM seems to be an attractive alternative to treat H2S owing to its economic advantages as well as its physicochemical characteristics, several analyses were conducted to investigate fundamental information, surface properties, and breakthrough characteristics of FRPM as adsorbent. The physical properties of FRPM including composition and surface chemistry were investigated to compare its performance with commonly available commercial H2S adsorbents such as activated carbon and assess the possible adsorption mechanism. The specific surface area of FRPM was less than 1% of activated carbon. FRPM does not have enough surface area supporting a pure physical adsorption of H2S because it is particulate in nature with limited porosity. The adsorption of FRPM to remove H2S was complex mechanism and involved a combination of zinc compounds and carbon black.

Resistance to oxidation and ablation of SiC coating on graphite prepared by chemical vapor reaction

A thick SiC coating was prepared on graphite by chemical vapor reaction. The coating reveals a typical crystalline structure with limited porosity and combines well with the substrate. Oxidation tests demonstrate that the coating has a weak self-healing ability at 1100K and good self-healing ability at temperatures from 1623 to 1823K. An oxyacetylene torch test verifies that the prepared coating can effectively protect graphite from ablation for 50s. After the ablation test, the silica microspheres and other interesting silica structures such as microwires, microparticles, microflowers, nanowires and nanoparticles are formed at the ablation center and its surroundings.

A simplistic model for the tortuosity in two-phase close-celled porous media

We present an analytical model capable of demonstrating the dependence of tortuosity of two-phase porous media upon two topological parameters: porosity and pore shape. Based on a generalized effective thermal conductivity model and a particular solution to the Laplace heat conduction equation for two-phase porous media having randomly distributed non-conducting circular pores, an analytical model of tortuosity is derived. For non-circular pores such as idealized polygonal pores, the circularity-based concept of pore shape factor is incorporated into the model, which is capable of analytically unifying existing models which are valid only for limited porosity ranges and circular pore shapes.

Controlled release of small molecules from silica xerogel with limited nanoporosity

Conventional sol-gel processing requires several distinct steps involving hydrolysis, condensation and drying to obtain a highly porous, glassy solid material. With the goal of achieving controlled release of small molecules, herein we focus on the acceleration of the condensation and drying steps by casting the hydrolyzed sol on a large open surface to achieve a denser 100 % silica xerogel structure. Thus, cast xerogel with a more limited porosity was prepared. The effect of synthesis parameters during sol-gel synthesis on the release kinetics of bupivacaine, vancomycin and cephalexin was investigated. The release kinetics fitted well with the Higuchi model, suggesting a diffusional release mechanism. Combining the release and nanostructure data, the formation mechanism of cast xerogel is described. Without introducing additional precursors or additives into sol-gel systems, sol-gel casting is an easy technique that further expands the applicability of sol-gel materials as excellent carriers for the controlled release of a variety of drugs.

Creating 3D Angiogenic Growth Factor Gradients in Fibrous Constructs to Guide Fast Angiogenesis

Fast angiogenesis in 3D fibrous constructs that mimic the morphology of the extracellular matrix remains challenging due to limited porosity in the densely packed constructs. We investigated whether mimicking the in vivo chemotaxis microenvironment for native blood vessel formation would stimulate angiogenesis in the fibrous constructs. The chemotaxis microenvironment was created by introducing 3D angiogenic growth factor gradients into the constructs. We have developed a technique that can quickly fabricate (∼40 min) such 3D gradients by simultaneously electrospinning polycaprolactone (PCL) fibers, encapsulating gradient amount of bFGF (stabilized by heparin) into poly(lactide-co-glycolide) (PLGA) microspheres, and electrospraying the microspheres into PCL fibers. Gradient formation was confirmed by fluorescence microscopy. Gradients with different steepnesses were obtained by modulating the initial concentration of the bFGF solution. All of the constructs were able to sustainedly release bioactive bFGF over a 28 day period. The release kinetics was dependent on the bFGF loading and steepness of the gradient. In vitro cell migration study demonstrated that bFGF gradients significantly increased the depth of cell migration. To assess the efficacy of bFGF gradients in inducing angiogenesis, we implanted constructs subcutaneously using mouse model. bFGF gradients significantly promoted cell penetration into the constructs. After 10 days of implantation, a high density of mature blood vessels (positive to both CD31 and α-SMA) were formed in the constructs. Vessel density was increased with the increase in steepness of the bFGF gradient. These gradient constructs may have potential to engineer vascularized tissues for various applications.

Influence of different mixing ratios on in-vessel co-composting of sewage sludge with horse stable straw bedding waste: maturity and process evaluation

Composting sewage sludge alone would reduce the decomposition efficiency due to free limited porosity in sludge. To alleviate this, the use of horse stable straw bedding waste (HSB) was evaluated as a co-composting material with sewage sludge in a 10 tonnes day(-1) in-vessel composter for a period of 7 days before curing in a static aeration pile. Sludge was mixed with HSB at 1 : 1.5 (HSL) and 1 : 2.9 (LSL) on a fresh weight basis. After a composting period of 56 days, both mixing ratios demonstrated to be feasible with LSL having a better organic decomposition and a shorter time to reach maturity. The overall decomposition rates were 52.0 and 58.9% (dry weight basis) for HSL and LSL, respectively. In both treatments, temperature in the in-vessel composters could reach 65°C, which was sufficient to remove the pathogens. Although both products were free of pathogens, HSL exhibited a higher ammoniacal nitrogen contents but a lower seed germination index than that of LSL indicating a higher phytotoxicity and a longer curing period would be required. It can be concluded that HSB provided a better composting conditions at a mixing ratio of 1 : 2.9.

Process control and optimized preparation of porous alumina ceramics by starch consolidation casting

This work concerns details of porosity and pore size control in starch consolidation casting of alumina ceramics using corn starch. In particular, the influence of the solids loading (68–78 wt.% alumina in suspensions with nominal starch contents of 20–50 vol.%) on the porosity, bulk density and shrinkage of alumina ceramics is studied. The results indicate a linear decrease of the linear shrinkage and the bulk density (and a corresponding increase in porosity) as the alumina concentration increases, with slopes that are independent of the starch content. The pore size is characterized via microscopic image analysis, the pore throat size via mercury porosimetry. Relations between the volumetric shrinkage, porosity and the volume fractions of starch and water in the suspensions are discussed, and a new concept, called “affine limit porosity” is proposed to explain the apparently paradoxical finding that the porosity increases with increasing alumina content in the suspension.

Mechanical properties of multilayered chitosan/CNT nanocomposite films

A multi-performance MWCNT-reinforced chitosan nanocomposite was fabricated by two methods: a freeze-drying process associated with the sublimation and compression (SAC) method; and the casting-evaporation (CE) method. We obtained ordered and multilayered structures with limited porosity, and well-dispersed MWCNT structures of the chitosan nanocomposite, especially with the SAC method. In the case of the nanocomposite films prepared by the CE method, the mechanical strength and elongation were significantly increased by up to about 40% compared with the pure chitosan films. On the other hand, the ordered and porous multilayered pure chitosan films prepared by the SAC method showed significantly lower tensile strength and elongation compared to the pure solid chitosan films. However, the relative enhancement of the mechanical properties of multilayered MWCNT/chitosan nanocomposites with porosity was higher, especially in terms of the elongation, which showed a twofold improvement in strain. The relaxed bond, which could be a relatively strong hydrogen bond, between the functional groups in the chitosan chains and the functionalized surface of the MWCNTs might be stretched under stress, thereby improving the ductility of the multilayered nanocomposite films. In addition, the viscoplastic behavior of the films by the CE method could become more active with increasing strain rate. Interestingly, ordered and porous pure chitosan films did not reveal the viscoplastic behavior; it rather presented strain softening and viscoelastic characteristics. However, the interaction between the chitosan chains and the surface-modified MWCNTs could regenerate viscoplasticity of the chitosan films.

Gradients with Depth in Electrospun Fibrous Scaffolds for Directed Cell Behavior

A major obstacle in creating viable tissue-engineered constructs using electrospinning is the lack of complete cellularization and vascularization due to the limited porosity in these densely packed fibrous scaffolds. One potential approach to circumvent this issue is the use of various gradients of chemical and biophysical cues to drive the infiltration of cells into these structures. Toward this goal, this study focused on creating durotactic (mechanical) and haptotactic (adhesive) gradients through the thickness of electrospun hyaluronic acid (HA) scaffolds using a unique, yet simple, modification of common electrospinning protocols. Specifically, both mechanical (via cross-linking: ranging from 27-100% modified methacrylated HA, MeHA) and adhesive (via inclusion of the adhesive peptide RGD: 0-3 mM RGD) gradients were each fabricated by mixing two solutions (one ramping up, one ramping down) prior to electrospinning and fiber collection. Gradient formation was verified by fluorescence microscopy, FTIR, atomic force microscopy, and cellular morphology assessment of scaffolds at different points of collection (i.e., with scaffold thickness). To test further the functionality of gradient scaffolds, chick aortic arch explants were cultured on adhesive gradient scaffolds for 7 days, and low RGD-high RGD gradient scaffolds showed significantly greater cell infiltration compared with high RGD-low RGD gradients and uniform high RGD or uniform low RGD control scaffolds. In addition to enhanced infiltration, this approach could be used to fabricate graded tissue structures, such as those that occur at interfaces.

Utilising Metal Melts of Low‐Melting Metals as a Novel Approach for MOF Synthesis: The 3D‐Imidazolate 3∞[Ga2(Im)6ImH] from Gallium and Imidazole

AbstractMetals with low melting points like gallium (mp. 30 °C) prove a new approach for the synthesis of MOFs. As the melting point of gallium is even lower than of the linker ligand imidazole, formation of the MOF ${}^3_\infty[\textrm{Ga}_2(\textrm{Im})_6\textrm{ImH}]$, Im– = imidazolate anion, ImH = imidazole, can be achieved by reaction of a melt of the referring metal with a melt of the ligand. Gallium is oxidised in the reaction, and hydrogen gas and the imidazolate amide as colourless single crystalline product are formed. At the melting point of imidazole (mp. 88–90 °C) two liquid phases are observed. Phase separation lasts until the reaction, starting at 120 °C, consumes the liquid reagents. We consider this a reaction on the phase border between the liquid phases as no mixing is observed. ${}^3_\infty[\textrm{Ga}_2(\textrm{Im})_6\textrm{ImH}]$ constitutes of a three‐dimensional framework structure with a 3,6 topology that is built of two Kagome nets sharing common connectivity points. Each Ga3+ ion is octahedrally coordinated by six nitrogen atoms of imidazolate and imidazole ligands. The framework exhibits a limited porosity of 8.5 % of accessible space and a diameter of 376–509 pm for the pore windows.