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We propose a method to measure the local porosity of porous samples from scanning electron microscopy images in the backscattered electron mode. The porous samples are impregnated with a polymer resin and observed in polished cross sections. Image intensities are calibrated with intensities from pure resin and the bulk phase. The calibration model is justified with Monte Carlo simulations on perfectly homogeneous virtual samples. Uncertainties in measured porosity are given as a function of uncertainties on physical properties of the resin and the bulk phase and on measured signals. The methodology is applied to a series of heterogeneous alumina catalyst supports with varying porosities. A good agreement is found between the averaged local porosity by scanning electron microscopy and global porosity determined by mercury intrusion porosimetry. The use of local porosity statistics allowed the quantitative characterization of the porosity fluctuations of these supports that appeared to be linked with their preparation parameters.
Silicon electrodes with the columnar macroporous structure were investigated to determine the effect of variations in the columnar pore morphology on lithiation and energy storage capacity in Li-ion cells. Several variants of macroporous Si columnar electrodes were electrochemically cycled against the Li reference electrode. The changes in macro-pore size and Si wall thickness of the columnar architecture greatly affected the cyclic Li storage and discharge capacities. A strong correlation of the Li-storage capacity with the ratio of Si wall thickness to pore diameter is found to exist. Specifically, one columnar Si electrode with an optimum macroporous structure exhibited a very high reversible specific capacity of ~1250 mAh/g (total capacity 1.2 mAh/cm2) for over 200 cycles. Electron microscopy revealed that the high reversible Li-storage capacity is due to the macropores accommodating the change in volume of lithiation and providing nearly complete reconstruction of Si walls upon delithiation. The present observations can lead to practical, high-capacity, and damage-resistant Si electrodes for Li-ion batteries.
Boronic ester bonds can be reversibly formed between phenylboronic acid (PBA) and triol moieties. Here, we aim at a glucose-induced shape-memory effect by implementing such bonds as temporary netpoints, which are cleavable by glucose and by minimizing the volume change upon stimulation by a porous cryogel structure. The polymer system consisted of a semi-interpenetrating network (semi-IPN) architecture, in which the triol moieties were part of the permanent network and the PBA moieties were located in the linear polymer diffused into the semi-IPN. In an alkaline medium (pH = 10), the swelling ratio was approximately 35, independent of Cglu varied between 0 and 300 mg/dL. In bending experiments, shape fixity Rf ≈ 80% and shape recovery Rr ≈ 100% from five programming/recovery cycles could be determined. Rr was a function of Cglu in the range from 0 to 300 mg/dL, which accords with the fluctuation range of Cglu in human blood. In this way, the shape-memory hydrogels could play a role in future diabetes treatment options.
This paper reviews the recent development of fabrication methods of porous metals with open-channels. The open-channel metals are fabricated through powder sintering or solidification technique. The template wires are embedded in the sintered or solidified metals, such as aluminum, copper, titanium and its alloys, which are then removed by chemical dissolution or extraction methods. The hole size, hole length and porosity are uniquely controlled by thickness, length and number of template metallic wires, respectively. The pore size ranges from 102 to several 103 μm in diameter. The open-channel metals are characterized by a large aspect ratio of the length to the diameter of the holes in metals. Furthermore, the techniques can fabricate spiral and V-shaped pores in metals. Feasibility and usefulness of each fabrication method are discussed. The methodology for producing the open-channel metals is expected to provide expanded opportunities for application technologies such as functional materials like heat sinks and sound absorbers and light-weight structural materials.
Novel three-dimensional (3D) hierarchical macro- to nano-porous titanium (Ti) and TiMo alloys with sufficient compressive strength (CS) were prepared using NaCl spacer and dealloying methods. The dealloying process was implemented by the heat treatment of TiCu and TiMoCu master alloys in Mg powders. The 3D-hierarchical porous structures were composed of large pores having a mean size of 400 μm with interconnected micro-pores in the size of 10–30 μm, where the pore walls possessed numerous nano-pores with a size range of 10–50 nm. The CS and elastic modulus values were 72.4 MPa and 2.67 GPa as well as 92.62 MPa and 3.36 GPa for Ti and TiMo, respectively. The hierarchical porous structure is beneficial for the fast nucleation of bone-like apatite after immersion in simulated body fluid (SBF). In addition, TiMo samples after NaOH and heat treatments provide better apatite formation after soaking in SBF for a week, in comparison with the samples without treatment.
The adoption of selective laser melting (SLM) for fabrication of porous titanium has resulted in many new investigations into the complex design parameters associated with porous architecture of high spatial resolution. The development of meta-materials has included research into the effects of unit cell architecture (strut versus sheet), porosity, pore size, and other factors on the performance of metallic scaffolds. The current study examined the interactive effects of varying the gyroid sheet unit cell size and overall specimen size on the compressive behavior of Ti–6Al–4V ELI porous scaffolds manufactured via SLM. The increasing unit cell size relative to specimen geometry was found to decrease the compressive strength and stiffness of the overall structure and shift the material fracture mode. The understanding of the relationship between unit cell size and specimen geometry can be used to optimize mechanical properties of implants with constrained volumes and pore/wall size requirements to optimize properties of porous titanium implants for strength and osseointegration.
In this study, uniaxial tensile loading simulations were performed on several single crystalline copper nanoporous (NP) structures with varying relative density (RD) via molecular dynamics simulations. From the results, two distinctive deformation patterns were observed: structures with a low RD went through coarsening, and structures with a high RD did not. During coarsening, dislocations are nucleated because of the high surface stress induced by the thin ligaments. These dislocations drive the merging of ligaments as well as nodes and lead to an increase in the differences between the size of nodes and ligaments. The disproportional nodes and ligaments result in a lowered strength. In addition, larger nodes provide more favorable circumstances for the formation of sessile dislocations, which hinder the movement of other propagating Shockley partials and result in strain hardening. Subsequently, lower RD structures offer anomalously high strain-hardening potential, whereas high RD structures show better strength but poor deformability. These results help us in better understanding the plastic behavior of NP structures as a function of their RD.
In this article, Al75Cu25 (at.%) ribbons were dealloyed by HCl, H2C2O4, H3PO4, and NaOH solutions, respectively, to prepare nanoporous copper (NPC). The dealloying behavior is varied with dealloying solutions, allowing modulating the microstructure and porosity of the NPC. Al75Cu25 ribbons are fully dealloyed in HCl, H2C2O4, and NaOH solutions, whereas they are partially dealloyed in H3PO4 solution. Except the NPC prepared in the NaOH solution, no obvious cracks are traced in other samples. The surface diffusivity (Ds) of Cu atoms along the alloy/solution interfaces is varied with solutions, producing the NPC with different microstructure. NPC with higher specific surface area can be obtained by dealloying the Al75Cu25 ribbons in the HCl solution. Compared with the dealloying in H2C2O4, H3PO4, and NaOH solutions, the dealloying in 10 wt% HCl solution for 25 min at 90 ± 1 °C facilitates the best NPC in this work.
This introduction discusses the conceptual and theoretical framework of The Cambridge History of Black and Asian British Writing, explaining the rationale behind its both linear and lateral structure as well as the selection of its contents. Flagging the difficulties of attempting to contain and articulate such an extensive, variegated, and still emerging field within ‘one’ history, it points to the complex historical and cultural pathways that have conditioned how the different strands of black and Asian writing have evolved. Written to provide readers with a cultural compass to map the often unstable political and historical contexts by which these literatures have variously been framed and named, it points to significant markers and milestones, contiguities and contingencies, which characterise the four centuries of black and Asian writing that this volume covers. One of the challenges of creating such a retrospective history has been to look both backwards and forwards, creating new literary vistas from what have often been limited critical frameworks and reductive political contextualisations.
Diatoms are unicellular photosynthetic algae that autonomously fabricate a porous organized biosilica shell refined in billion years of evolution. They represent an inexhaustible source of low cost, biocompatible mesoporous silica. Despite the major advances in the genomic field, studies on diatom cell biology are still hampered by a lack of cellular tools. In particular, cell staining assays of diatoms viability are still limited or not well performant. Here we provide a phosphorescent organometallic iridium complex (Ir-Fcx) suitable to act as staining agent to detect diatoms viability.
We report a significant advance in thermally insulating transparent materials: silica-based monoliths with controlled porosity which exhibit the transparency of windows in combination with a thermal conductivity comparable to aerogels.
The lack of transparent, thermally insulating windows leads to substantial heat loss in commercial and residential buildings, which accounts for ~4.2% of primary US energy consumption annually. The present study provides a potential solution to this problem by demonstrating that ambiently dried silica aerogel monoliths, i.e., ambigels, can simultaneously achieve high optical transparency and low thermal conductivity without supercritical drying. A combination of tetraethoxysilane, methyltriethoxysilane, and post-gelation surface modification precursors were used to synthesize ambiently dried materials with varying pore fractions and pore sizes. By controlling the synthesis and processing conditions, 0.5–3 mm thick mesoporous monoliths with transmittance >95% and a thermal conductivity of 0.04 W/(m K) were produced. A narrow pore size distribution, <15 nm, led to the excellent transparency and low haze, while porosity in excess of 80% resulted in low thermal conductivity. A thermal transport model considering fractal dimension and phonon-boundary scattering is proposed to explain the low effective thermal conductivity measured. This work offers new insights into the design of transparent, energy saving windows.
Superporous Carboxy Methyl Cellulose (CMC) cryogels were synthesized by chemical crosslinking of linear CMC with divinyl sulfone (DVS) with different mole ratios of CMC repeating unit down to 2.5%. The morphology of macroporous CMC cryogels was visualized by optic microscope and scanning electron microscope (SEM) images. The swelling capacity and pore volume of CMC cryogels were found to increase with the decrease in the ratio of crosslinker to CMC, and the highest swelling capacity and pore volume values were 10825±1799% and 22.1±0.4 mL/g for 2.5% mole ratio of crosslinked CMC cryogels. The blood compatibility of CMC cryogels revealed that blood cells were destroyed with very low hemolysis ratio of 1.09±1% and also showed less thrombogenic activity with 80.2±5.1% blood clotting indexes.
A new finding over the past decade is the stability – and even potential synthesis – of hydrocarbons at depth in Earth. Of course, this has been a highly controversial area of research for decades, but recent evidence has been obtained from natural orogenic geological settings, thermodynamic simulations, and observations of seafloor samples. This chapter reviews this new evidence while highlighting the importance of the physical state of C-O-H fluids contained in rocks on the transport of alkanes like methane, propane, and octane, the impact of pore space and fracture confinement on fluid reactivity, and how reactivity under confinement varies from bulk fluid properties.
Macro-mesoporous zirconium titanate monoliths have been successfully prepared via a sol–gel process accompanied by phase separation, with poly(ethylene oxide) (PEO) as a phase separation inducer and N-methylformamide (NFA) as a gelation accelerator. The size and morphology of macropores are controlled by the PEO and NFA amount. By choosing appropriate starting composition, the co-continuous structure could be obtained. The as-dried gel is amorphous, the pore size is in the range of 0.05–0.5 μm, the porosity is 46%, and the surface area is 111 m2/g. After heat treatment at 500 °C, the gel transforms into the phase ZrTiO4, the macropore diameter decreases slightly, the porosity increases to 63%, and the surface area decreases to 40 m2/g. Moreover, the macroporous structure is well maintained, and the skeleton becomes dense and smooth. The samples have macropores, mesopores, and micropores before and after heat treatment.
The chapter starts by explaining how petroleum reservoirs are formed and gives a brief introduction to various concepts from geology to non-geologists. Next, we discuss the continuum hypothesis and how flow through subsurface porous media is modeled on different spatial scales. An essential part is to develop a description of petrophysical properties like porosity and permeability. We explain how this is achieved in MRST, and outline a few examples of models that give realistic representations of reservoir rocks. This includes the popular SPE10 benchmark and a model of a shallow-marine formation.
Hierarchically porous poly(L-lactic acid) (PLLA)/poly(ε-caprolactone) (PCL) monolithic composites were fabricated by nonsolvent-induced phase separation (NIPS) method without any template for the first time. A homogeneous hierarchical porous structure with relatively large specific surface area containing both mesopores and macropores was confirmed by pore size distribution plots and scanning electron microscopy images, respectively. Fourier transform infrared analysis (FTIR) revealed that PLLA and PCL were physically blended. Differential scanning calorimeter (DSC) analysis further showed that the two components were physically blended but had a slight thermal compatibility. Meanwhile, X-ray diffraction (XRD) tests indicated that the addition of PCL hindered the crystallization of PLLA. Herein, the formation of the mesopores and macropores during the phase separation process was explained from the microscopic point of view according to the results of XRD and DSC. The present monolithic composites with hierarchically porous structures had promising prospect for applications of tissue engineering.
Porosity-graded, conductor- and binder-free porous FeS2 films through the entire thickness were deposited by spray pyrolysis. The film layers deposited at 15 versus 10 L/min are grown in different modes. The film layer deposited at 15 L/min showed Frank–van der Merwe layer-like growth mode whereas the one deposited at 10 L/min showed island growth mode. These growth modes lead to the formation of large pores on the electrolyte side and small ones on the substrate side of the film deposited using 15 and 10 L/min, sequentially. The porosity-graded films showed discharge capacities at C/10 of 879 mA h/g and 754 mA h/g for the 5th and 20th cycles, respectively. Such capacity values are superior to the literature findings for FeS2 powders and nongraded films mixed with conductor and binder additions.
While assessing the environmental impact of nuclear power plants, researchers have focused their attention on radiocarbon (14C) owing to its high mobility in the environment and important radiological impact on human beings. The 10 MW high-temperature gas-cooled reactor (HTR-10) is the first pebble-bed gas-cooled test reactor in China that adopted helium as primary coolant and graphite spheres containing tristructural-isotropic (TRISO) coated particles as fuel elements. A series of experiments on the 14C source terms in HTR-10 was conducted: (1) measurement of the specific activity and distribution of typical nuclides in the irradiated graphite spheres from the core, (2) measurement of the activity concentration of 14C in the primary coolant, and (3) measurement of the amount of 14C discharged in the effluent from the stack. All experimental data on 14C available for HTR-10 were summarized and analyzed using theoretical calculations. A sensitivity study on the total porosity, open porosity, and percentage of closed pores that became open after irradiating the matrix graphite was performed to illustrate their effects on the activity concentration of 14C in the primary coolant and activity amount of 14C in various deduction routes.
Three-dimensional printing (3DP) is becoming a standard manufacturing practice for a variety of biomaterials and biomedical devices. This layer-by-layer methodology provides the ability to fabricate parts from computer-aided design files without the need for part-specific tooling. Three-dimensional printed medical components have transformed the field of medicine through on-demand patient care with specialized treatment such as local, strategically timed drug delivery, and replacement of once-functioning body parts. Not only can 3DP technology provide individualized components, it also allows for advanced medical care, including surgical planning models to aid in training and provide temporary guides during surgical procedures for reinforced clinical success. Despite the advancement in 3DP technology, many challenges remain for forward progress, including sterilization concerns, reliability, and reproducibility. This article offers an overview of biomaterials and biomedical devices derived from metals, ceramics, polymers, and composites that can be three-dimensionally printed, as well as other techniques related to 3DP in medicine, including surgical planning, bioprinting, and drug delivery.
Cordierite foams were prepared by thermo-foaming of alumina–microsilica–talc powder dispersions in molten D-glucose anhydrous followed by reaction sintering at 1400 °C, which exhibited an interconnected cellular morphology and three-dimensional porous cell walls. The cordierite foam had a porosity of up to 96%, and its corresponding thermal conductivity was as low as 0.057 W/(m·K). The foam structures showed a great promise for gas filtration and gas catalytic support. The formation of interconnected cellular morphology, the variations of cell wall thickness, and cell size were explained from the perspective of viscosity and weak points in this paper. The linear shrinkage of cordierite foams having a density of 0.102–0.226 g/cm3 was in the range of 13.0–6.9%. And the compressive strength (0.05–0.28 MPa) was determined by the large cell size (1.1–1.3 mm), ultra-high porosity (91–96%), and characteristic of cordierite.