Porosity Network Research Articles

Temporal and spatial variations in the discharge and dissolved organic carbon of drip waters in Beijing Shihua Cave, China

AbstractTo detect the causal relationship between cave drip waters and stalagmite laminae, which have been used as a climate change proxy, three drip sites in Beijing Shihua Cave were monitored for discharge and dissolved organic carbon (DOC). Drip discharges and DOC were determined at 0 to 14‐day intervals over the period 2004–2006. Drip discharges show two types of response to surface precipitation variations: (1) a rapid response; and (2) a time‐lagged response. Intra‐annual variability in drip discharge is significantly higher than inter‐annual variability. The content of DOC in all drip waters varies inter‐ and intra‐annually and has good correlation with drip water discharge at the rapid response sites. High DOC was observed in July and August in the three years observed. The flushing of soil organic matter is dependent upon the intensity of rain events. The DOC content of drip water increases sharply above a threshold rainfall intensity (>50 mm d−1) and shows several pulses corresponding with intense rain events (>25 mm d−1). The DOC content was lower and less variable during the dry period than during the rainy period. The shape of DOC peak also varies from year to year as it is influenced by the intensity and frequency of rainfall. The different drip sites show marked differences in DOC response, which are dominated by hydrological behaviour linked to the recharge of the soil and karst micro‐fissure/porosity network. The results explain why not all stalagmite laminae are consistent with climate changes and suggest that the structure of the rainy season events could be preserved in speleothems. Copyright © 2008 John Wiley & Sons, Ltd.

Assessment of cell wall porosity in Arabidopsis thaliana by NMR spectroscopy

The impact of homogalacturonans deficiency on the cell wall porosity of Arabidopsis thaliana QUA1 mutant was investigated using NMR measurements of protons mobility interpreted in terms of pore size variations at nanometer and micrometer scales. Isolation and purification of wild type and mutant stems and calli cell walls permitted to exacerbate the putative impact of the mutation on cellulose–hemicelluloses assembly in highly and poorly organised cell walls, respectively. NMR relaxation measurements of water and exchangeable biopolymer protons and self-diffusion processes of polyethylene glycol in walls informed about the porosity network density and heterogeneity. The role of pectins and proteins as well as the growth status of the cells on the wall porosity regulation are discussed.

Oxygen isotope evidence for short-lived high-temperature fluid flow in the lower oceanic crust at fast-spreading ridges

Millimeter-scale amphibole veins in the lower oceanic crust record fracture-controlled fluid flow at high-temperatures but the importance of this fluid flow for the thermal and chemical evolution of the lower oceanic crust is unclear. In the section of lower oceanic crust recovered at Hess Deep from ODP Hole 894G, which formed at the fast-spreading East Pacific Rise, these veins are randomly distributed with an average spacing of ∼ 1 m. We unravel the history of fluid flow through one of these veins by combining in situ O-isotope analyses of wall-rock plagioclase with major element analyses, geothermometry and diffusion modeling. Thermometry indicates vein sealing by amphibole at ∼ 720 °C over a narrow temperature interval (± 20 °C). In situ O-isotope analyses by ion microprobe, with a precision of < 0.5‰, reveal zoning of O-isotopes in plagioclase adjacent to the vein. The zoning profiles can be reproduced using a diffusion model if the duration of O-isotope exchange was ≤ 100 yr. A similar interval of fluid–rock exchange is suggested by modeling potassium depletion in plagioclase adjacent to the vein. If representative of fracture controlled fluid flow in the lower oceanic crust the limited duration of fluid flow, and its occurrence over a narrow temperature interval, suggest that high-temperature fluid flow in this porosity network does not transport significant heat.

Dual-Porosity Carbon Templated from Monosize Mesoporous Silica Nanoparticles

A mesoporous carbon structure was template-synthesized from small nanoparticles of silica with internal M41S type mesopores. The silica template was synthesized according to Suzuki et al. using an ionic surfactant to create the internal mesopores 1.8−3.5 nm diameter and a nonionic surfactant to limit the overall size of the particle. Larger mesopores in the silica are needed for carbonization to a better structure. This was achieved by the use of a swelling agent, trimethylbenzene (TMB). Characterization by transmission electron microscopy (TEM), X-ray diffraction (XRD), and nitrogen sorption analysis showed a mesocellular foamlike carbon structure composed of porous cells with internal hexagonally arranged channels. In addition to the 3 nm internal channels, there were larger mesopores connecting the cellular domains. These larger mesopores were formed in the interparticle voids created during carbonization. The dual porosity network structure had a high surface area (>1000 m2/g) and large pore volume (>1.2 mL/g). When loaded with Pt−Ru nanoparticles, the PtRu/carbon became a good electrocatalyst and gave the highest activity for methanol oxidation among several PtRu electrocatalysts including commercial electrocatalysts.

Permeation of hydrogen through MPG-8 graphite

Hydrogen gas driven permeation through fine-grain graphite MPG-8 has been investigated in the range of thickness from 0.55 to 4.38mm and pressures from 10−2 to 1Pa. The permeation rate is proportional to the gas pressure and inversely proportional to the thickness. It has been concluded that GDP through fine-grain graphite is due to gas flow through the internal porosity network in the molecular regime. The specific bulk conductivity of the graphite is measured to be of about (5–7.3)×1015moleculess−1m−1Pa−1. Surface treatment influences the permeation through membranes thinner than 1mm. Surface polishing, washing in the ultrasonic bath, hydrogen and argon plasma irradiation, methane plasma treatment, argon ion irradiation, and annealing at 1000K have 0–10% influence on the permeation rate.

Dynamically tessellating algorithm for analysis of pore size distribution in particle agglomerates

We describe a novel physical application of the OctTree data structure [P. Meagher, Comput. Graphics Image Process 19(2) (1982) 129–147] in a dynamically tessellating algorithm, in conjunction with an object-oriented, constructive solid geometry library (DOC), to efficiently determine pore size distributions in large multi-particle systems. We apply the DOC library to investigate the evolving dynamics of pore formation in multi-particle systems, such as a mixture of smooth hard cubes and spheres and a collection of frictional soft spheres. We demonstrate that the algorithm is able to provide insight into the effect of structural changes on the porosity network; for example, during the uniaxial compaction of soft spheres, we find the number density of pores increases while the mean volume of the pores decreases. This trend is responsible for a shift in the distribution of the pore volumes to favour smaller volumes. We anticipate that the DOC method will have wider applications in the area of granular materials for studying the changes in pore structure in both experimental and numerical systems as a complement to the analysis of particle packing.

Using physical properties to understand the porosity network geometry evolution in gradually altered granites in damage zones

Abstract This study, based on petrophysics, is linked to the geothermal project developed at Soultz-sous-Forêts, in northeastern France. In such a context, understanding and modelling the thermo-hydro-mechanical and chemical processes implies a good knowledge of the porosity network geometry and its evolution during alteration. Various physical properties (permeability, specific surface and porosity) were measured on samples from the protolith and damage zones of fault zones in the geothermal reservoir exploited at Soultz-sous-Forêts. Measured porosity values vary from 0.2 to 10%, and using structural parameters (threshold values, specific surface and porosity distribution), three groups are identified. Each of them shows a specific pore shape distribution and the porosity increase within a given group is assumed to be associated with an increase of pore number rather than an enlargement or shape modification.

Microstructure-based multistage fatigue modeling of a cast AE44 magnesium alloy

The multistage fatigue model developed by McDowell et al. was modified to study the fatigue life of a magnesium alloy AE44 for automobile applications. The fractographic examination indicated three distinct stages of fatigue damage in the high cycle fatigue loading regime: crack incubation, microstructurally small crack growth, and long crack growth. Cracks incubated almost exclusively at the cast pores that were near the free surface, located near sharp geometry changes of the test specimen, or at extremely large pores inside the specimens. Microstructurally small cracks grew in the eutectic region along the weak boundaries of the grains and dendrites or at very closely packed microstructural discontinuities. Long cracks were observed to grow in a transgranular fashion. Specimens fabricated from as-cast bars and extracted from a cast engine cradle were tested at room temperature and an elevated temperature typically required for automotive powertrain applications. A large variation of fatigue life in the high cycle fatigue region was observed in specimens from both conditions due to the sensitivity from microstructural discontinuities. The microstructure-based multistage fatigue model was generalized for the AE44 magnesium alloy to capture the network of porosity and temperature dependence. The modified multistage fatigue model was also used to estimate the upper and lower bounds of the strain-life curves based on the extreme microstructural discontinuities.

Fault zone geometry of a mature active normal fault: A potential high permeability channel (Pirgaki fault, Corinth rift, Greece)

We present results from petrophysical analysis of a normal fault zone with the aim of defining the flow pathways and their behavior during seismic and interseismic periods. Data are obtained on porosity geometry, strain structure and mineralogy of different domains of a normal fault zone in the Corinth rift. Data point out a close relationship between mineralogy of the clayey minerals, porosity network and strain structures and allow definition of a macroscopic anisotropy of the flow parameters with a strong control by microscopic ultracataclasite structures. The Pirgaki fault zone, developed within pelagic limestone, has a sharp asymmetric porosity profile, with a high porosity volume in the fault core and in the damage zone of the hanging wall. From porosity volumes and threshold measurements, a matrix permeability variation of 6 orders of magnitude could be expected between the protolith and the fault core. Modifications of this pathway during seismic and interseismic phases are depicted. Healing of cracks formed during seismic slip events occurred in the fault core zone and the porous network in the damage zone is sealed in a second step. The lens geometry of the fault core zone is associated with dissolution surfaces and open conduits where dissolved matter could move out of the fault core zone. These elementary processes are developed in particular along Riedel's structures and depend on the orientation of the strain surfaces relative to the local stress and depend also on the roughness of each surface type. P-surfaces are smooth and control shearing process. R-surfaces are rough and present two wavelengths of roughness. The long one controls localization of dissolution surfaces and conduits; the short one is characteristic of dissolution surfaces. The dissolved matter can precipitate in the open structures of the hanging wall damage zone, decreasing the connectivity of the macroscopic conduit developed within this part of the fault zone.

Calcium Phosphate Open Porous Scaffold Bioceramics

Calcium phosphate (CaP) ceramics possessing an interconnecting porosity network in the appropriate size range for vascularisation offer the possibility of providing a structural matrix for replacement of diseased or damaged bone. Such bioceramics must possess sufficient mechanical strength to avoid failure whilst offering a bioactive surface for bone regeneration. The objective of the current study was to produce a hydroxyapatite/tricalcium phosphate (HA/TCP) bioceramic that imitated the orientated trabecular structure found in cancellous bone. The structure-property relationship of these bioceramics was then analysed. It was hypothesised that the mechanical properties would be linked to the shape of the pore structure due to the orientation of the open porous scaffolds (OPS) produced. OPS bioceramics possessed an interconnected macroporosity network of 40-70% by volume with bending strengths of 0.30MPa ± 0.01MPa and apparent densities of 0.35g/cm3 ± 0.05g/cm3. Typically, pore sizes in the range of 150-300µm were produced. The fabrication of CaP OPS resulted in a wide range of macroporosity in the correct size range for osseointegration to occur. Elongating the pore structure did not affect the total porosity of the bioceramics. Strengths were low due to microcrack formation on sintering and not due to the shape of the pores present in the scaffold as initially hypothesised.

Molecular networks built from weakly interacting nitro-substituted pentaerythrityl tetraaryl ethers

Crystallization of NO2-substituted pentaerythrityl tetraaryl ethers yields networks of low porosity joined by weak C–H⋯O hydrogen bonds. Such interactions appear less effective than strong hydrogen bonds for directing the assembly of highly porous molecular networks.

Rheological and Morphological Characterization of Triblock Copolymer (PEO-PPO-PEO)-Clay Gel in Aqueous Solution

AbstractThermal gelation and structure properties of high concentration triblock copolymer poly (ethylene oxide)99-poly(propylene oxide)69-poly(ethylene oxide)99 (Pluronic F127)-clay aqueous solutions were characterized by rheological measurements and scanning electron microscopy (SEM). The sol-gel transition temperature, as well as the viscosity of the F127 solution was found to depend both on the concentration of polymer and clay filler. In all cases, Pluronic F127 gels are pseudoplastic, showing the shear-thinning behavior. Above the gel transition, the viscosity of the solutions increased with increasing the clay concentration. The corresponding macrostructure of the gels was studied by lyophilizing thick samples and scanning them with a scanning electron microscope (SEM). A well-ordered network of porosity was observed as a function of polymer concentration and orientation.

Synthesis and characterization of palladium containing membranes based upon polyacrylic acid

Different methods are described to synthesize a highly porous polymer membrane with fine dispersed metal-nanoparticles. The preparation of the porous catalytic membranes happens by crosslinking of polyacrylic acid dispersions with bifunctional crosslinker in presence of palladium particles. Palladium-nanoparticles, stabilized with the block copolymer polystyrene-block-polyethyleneoxide, can be immobilized in the polymer network in different ways. The polymer/metal network can be prepared in the form of thin flat membranes and dried under retention of the porosity and three-dimensional network structure. Different reduction and preparation methods were applied in order to obtain differences in particle size and distribution of the palladium. The morphology of the material was investigated by scanning electron microscopy. Transmission electron microscopy was employed to show the size and distribution of the metal-nanoparticles in the polymeric matrix. The catalytic activity of the obtained membranes was investigated for the gas phase hydrogenation of cyclohexene and propyne.

Study by microtomography of 3D porosity networks in irradiated beryllium

The analysis of gas release modes from irradiated materials during out-of-pile temperature transients and of the related microstructure evolution provides fundamental evidence for developing and validating models of the behaviour of gases in solids. Gas atoms are uniformly generated by nuclear reactions in the lattice. If temperature and/or gas concentration increase, gas atoms diffuse and precipitate into bubbles, then bubbles grow and coalesce until they form at grain boundaries porosity networks connected to the free surface. The formation of such percolation paths is related to the appearance of release bursts where most part of the gas inventory escapes. The morphology of percolation patterns determines the porosity limit necessary to start the percolation stage and finally affects the performance of the material in engineering applications. The gas percolation stage in a weakly irradiated beryllium sample, a 2 mm diameter pebble, has been examined by computer aided microtomography based on synchrotron radiation, with the aim to identify and qualitatively characterise the 3D morphology and topology of open porosity networks.

Comparison of the deformation and failure characteristics of morphologically distinct metal-glass interpenetrating phase composites

Deformation and failure characteristics of two metal-glass interpenetrating phase composite (IPC) systems were compared against a single-phase glass control. The first system (Captek-P) comprised an interleaved arrangement of flake-shaped Au/Pt/Pd particles, the second (Captek-G) comprised loosely packed spherical Au particles. Both materials contained a fully interconnected network of porosity, formed by thermal fusion of particles at contact points. Glass was infiltrated into the porous networks by capillary action at high temperature. Mechanical properties were evaluated using three-point bend tests and compared to data from the glass control. The strength of the glass control (123.47 MPa) was not significantly different to that of either IPC, however both Captek-P and Captek-G IPCs displayed significantly reduced elastic moduli (55.2 ± 10.6 GPa and 48.4 ± 12.4 GPa respectively) compared with the glass (91.5 ± 9.6 GPa). In addition to significantly higher relative toughness than the glass control the IPC materials exhibit plastic deformation prior to failure. Mixed fracture modes were evident on fracture surfaces. Corresponding stress-strain profiles for the materials show well-defined linear elastic regions that make a gradual transition into plastic behaviour. Strength of the glass control decreased by 28% upon exposure to moisture, a feature echoed by the Captek-G IPC system, however not by the Captek-P IPC, indicating that the morphology of the interpenetrating reinforcement can significantly affect the mechanical properties of IPCs.

Great tritium ages explain the occurrence of good-quality groundwater in a phreatic aquifer of an urban area, Lublin, Poland

The phreatic aquifer of the Lublin chalk in the watershed of the Bystrzyca River, eastern Poland, is characterized by waters of good quality. Its hydraulic conductivity is related to a fissure network of low porosity, as much as 0.006 at the outcrops. The good quality of water in this urban setting is surprising because, according to estimates based on Darcy's law, a high seepage velocity would be expected, resulting in rapid transport of pollutants in the aquifer. However, tritium sampling reveals that the mean ages range from about 55 to 92 years in four cases, and about 250 to 350 years in 11 cases. One sampling site is free of tritium, which indicates an even greater age. Such great ages can be explained only by a retardation of solute transport due to matrix diffusion, that is, an exchange between mobile water in the fissures of low porosity and stagnant water in the matrix of high porosity. The delay factor is given as the ratio of total porosity to fissure porosity. In consequence, all types of dissolved constituents and, to some degree, fine suspended matter are delayed in their transport to springs and wells. In addition, non-conservative constituents have longer times to sorb, react, and decay than in the case of transport without a dominant influence of matrix diffusion. Though pollutants are greatly delayed, their accumulation in the matrix and slow diffusion into the fissures contribute to their persistence in groundwater. Regional values of hydraulic conductivity, estimated from tritium ages and known matrix porosity, agree reasonably well with the values known from pumping tests, which supports the interpretation of a dominant influence of matrix diffusion on solute transport.

Estimation of Three-Dimensional Connectivity of Internal Defects in Coatings Using Fractal Analysis

The connectivity of a porous medium is an important topological characteristic, which indicates the extent to which internal defects (e.g., porosity or micro/macrocracking) are connected. Up to now, connectivity has been studied by various stereological procedures based on the “net volume tangent counts” proposed by DeHoff and performed on pairs of consecutive sections of an interconnected structure. However, the drawbacks of these procedures are their use of invasive techniques and manual counting. Connectivity is here studied with fractal geometry instead of conventional Euclidean geometry. The porosity network of a thermal spray sample may be fractal, and so can be at least partly characterized by fractal dimension. Modifications in connectivity could be reflected in changes in the fractal dimension. If changes in the connectivity, as characterized by changes in fractal dimension, can be adequately demonstrated by the computerized analysis of confocal scanning laser microscope (CSLM) images, then the technique may provide a useful, noninvasive way of improving the characterization of thermal spray coatings. The study also seeks to show how connectivity differences affect the mechanical properties of the coating and whether fractal analysis is able to detect these changes in mechanical properties.

Reconstitution du réseau poreux d'un échantillon décomprimé. Mise en évidence d'une anisotropie de connectivité

The porosity network of samples cored in highly stressed granitic material is investigated by mercury injection. In addition to threshold and porous volume classically measured with these techniques, we obtained information on heterogeneity and anisotropy of the porous network. Anisotropy of the crack network connectivity is inferred as the relationship between porous volume measured on classic sample and porous volume measured on a sample partly covered by resin. Mercury injection into samples partly covered by resin is possible only along the core axis.

Fluid circulation in the Ionian fold and thrust belt (Albania): implications for hydrocarbon prospectivity

Within the Ionian zone, which belongs to the external Albanide fold and thrust belt, a surface reservoir analogue was studied with the aim of unravelling the processes which exert an effect on the dual porosity network. Matrix porosity preservation in the Cretaceous to Eocene carbonate turbidite beds relates to early cementation, where the presence of a mixture of micritic and mono-crystalline bioclasts (crinoids and rudists) controls the framework-stabilising development of cements. The presence of these cements explains why these lithologies have not been entirely compacted (as happened for the overlying micrite-dominated lithologies). The underlying bioclast-rich layers also do not possess any porosity since they were entirely cemented.Present-day oil production is mainly fracture-related. Several vein generations have been recognised as well as other tectonic features such as conjugate high-angle or tension joints and stylolites. With respect to the latter, bed parallel (i.e. compactional) and bed perpendicular (i.e. layer parallel shortening or tectonic) stylolites have been differentiated. The spatial relationships between these stylolites and the veins allow differentiation of pre-, syn- and post-kinematic fluid fluxes, which have been characterised based on their petrographical (i.e. cathodoluminescence), geochemical (trace and stable isotope) and fluid inclusion features. This exercise shows that the fluid flow system was rock buffered until the folding and thrusting period. From then onwards the fluid flow system reflects the interaction with fluids which reacted with evaporites which occur as decollement horizons as well as fluid flow systems in relation to the maturation of hydrocarbons. Finally after folding and faulting, the studied anticlinal structure was temporarily emergent during the Miocene. During this period sediment infilled karst cavities formed. Since the latter sediment infill is not compacted but porous, they contribute to the total oil-in place.

Evaluation and development of hydraulic conductivity pedotransfer functions for Australian soil

Pedotransfer functions (PTFs) for predicting saturated hydraulic conductivity (Ks) were evaluated using published Australian soil data sets. Eight published PTFs were evaluated. Generally, published PTFs provide a satisfactory estimation of Ks depending on the spatial scale and accuracy of prediction. Several PTFs were developed in this study, including the power function of effective porosity, multiple linear regression, fractal model, and artificial neural networks. Different methods for estimating the fractal dimension of particle-size distributions showed no significant differences in predicting Ks . The simplest model for estimating fractal dimension from the log–log plot of particle-size distribution is therefore recommended. The data set was also stratified into 3 broad classes of texture: sandy, loamy, and clayey. Stratification of PTFs based on textural class showed small improvements in estimation. The published PTF of Dane and Puckett (1994) Proc. Int. Workshop (Univ. of California: Riverside, CA) gives the best prediction for sandy soil; the PTF of Cosby et al. (1984) Water Resources Research 20, 682–90 gives the best production for loamy soil; and the PTF of Schaap et al. (1998) Soil Science Society of America Journal 62, 847–55 gives the best prediction for clayey soil. The data set used comprised different field and laboratory measurements over large areas, and limited predictive variables were available. The PTFs developed here may predict adequately in large areas (residuals = 10–20 mm/h), but for site-specific applications, local calibration is needed.