Micron-sized Pores Research Articles

Mechanical and Microstructure Investigations on Magnetic Pulse Welded Dissimilar AA3003-TC4 Joints

In this paper, 3003Al and TC4 sheets were welded by magnetic pulse welding. The mechanical properties and microstructure of Al/Ti joints were investigated. The results showed that the mechanical properties of welding joints could be enhanced by the increasing effective welded area and transition layer average thickness. Three bonding types were observed in the weld interfaces: solid-state bonding, solid–liquid coexistence state bonding and liquid-state bonding. Three distinct types of defects: cracks along the welding direction, cracks across the diffusion layer, micron-sized pores and shrinkage cracks, occurred in the Al/Ti interfaces with different bonding types. The XRD results showed that TiAl3 and Ti3Al were generated in the weld interface. The cleavage fracture, parabolic dimples and orthogonal dimples existed in the failure surface of different locations.

Nanostructured metal oxide modification of a porous silicon interface for sensor applications: the question of water interaction, stability, platform diversity and sensitivity, and selectivity

Key parameters of a nanostructure modified porous silicon (PSi) template that can affect the development and performance of PSi-based sensors are considered. The importance of pore selection and direct in-situ nitrogen functionalization are emphasized. Metal oxide nanostructured island sites deposited to select, well defined, and reproducible nano-pore walled, micron sized p and n-type silicon pores (0.7–1.5 μ diameter) provide enhanced selectivity. The micron-sized pores facilitate rapid Fickian analyte diffusion to these highly active sites. The metal oxide nanoparticles are trapped by a thin nanopored wall covering preventing their sintering at elevated temperatures. The varying sensitivities of the highly active metal oxide nanostructured sites are well predicted within the recently developed Inverse Hard/Soft Acid/Base (IHSAB) model. Nitrogen functionalization of the nanostructure decorated surfaces provides the conversion of these PSi interfaces from hydrophilic to hydrophobic character. The decrease of water interaction provides greatly enhanced stability. Selectivity can be extended to the measurement of multiple gases using a combination of nanostructured island site determined detection matrices, p and n-type charge carrier variation, time dependent diffusion response, and pore structure influenced sensitivity. The range of variable responses is dominated by the molecular electronic structure of the nanostructured island sites as evaluated using the IHSAB concept. Pulsed mode operation can facilitate low analyte consumption and high analyte selectivity and further provide the ability to assess false positive signals using Fast Fourier Transfer techniques. The modeling of the PSi sensor response with a new Fermi energy distribution –based response isotherm is found to be superior to other isotherms. The rate of sensor response, linearity of measurement, and hysteresis of response are also considered within the framework of the decorated micron sized pore structure.

Designing Multiscale Porous Metal by Simple Dealloying with 3D Morphological Evolution Mechanism Revealed via X-ray Nano-tomography.

Designing materials with multiscale, hierarchical structure is critical to drive the advancement of new technology. Specifically, porous metals with multiscale porosity from nanometer to micrometer sizes would lead to enhanced physical and chemical properties-the micron-sized pores can increase the effective diffusivity of ion transport within the porous media, and the nano-sized pores provide high specific surface area, enabling functionalities that are unique to nanoporous metals. A new ternary precursor alloy selection concept utilizing the different mixing enthalpies is demonstrated in this work for the design of multiscale, bimodal porous copper from a simple, one-step dealloying of Cu-Fe-Al ternary alloy. The nanoporosity in the bimodal porous structure is formed from dealloying of the Cu-rich phase, whereas the microporosity is controlled by dissolving the Fe-rich phase, determined by both the initial Fe particle size and sintering profile. In addition to advancing the materials design method, the multiscale pore formation during dealloying was directly visualized and quantified via an interrupted in situ synchrotron X-ray nano-tomography. The 3D morphological analysis on tortuosity showed that the presence of the microporosity can compensate the increase of the diffusion path length due to nanoporosity, which facilitates diffusion within the porous structure. Overall the focus of the work is to introduce a new strategy to design multiscale porous metals with enhanced transport properties, and sheds light on the fundamental mechanisms on the 3D morphological evolution of the system using advanced synchrotron X-ray nano-tomography for future materials development and applications.

Experimental and numerical simulation of phase change process for paraffin in three-dimensional graphene aerogel

In this paper, melting and solidification experiments were performed on paraffin and paraffin/graphene aerogel (GA) composite. Since phase change process of paraffin in GA skeleton with micron-sized pore structure was difficult to directly observe, numerical simulation was applied with volume average method. The characteristics of phase change process for paraffin and paraffin/GA composite were clearly demonstrated. The temperature-time curves of experimental and numerical simulation were in good agreement. For the melting process, the strong natural convection of paraffin led to uneven temperature distribution. Paraffin cannot be completely melted due to its low thermal conductivity and poor heat exchange performance. GA skeleton could improve the thermal conductivity of paraffin and made it melt completely under the condition of heat exchange with the surrounding environment. For the solidification process, the heat transfer mode was mainly heat conduction, and the GA skeleton reduced the solidification time of paraffin by 21%. Three-dimensional porous structure of GA accelerated heat transfer process, which meant it can be used in the fields of heat storage. The micron-sized pore structure weakened the natural convection, indicating that heat transfer process of paraffin had uniform temperature distribution and could be applied in temperature management.

Rapid photothermal actuation of light-addressable, arrayed hydrogel columns in a macroporous silicon membrane

This paper presents rapid photothermal actuation of light-addressable, arrayed hydrogel columns in a macroporous silicon membrane. Au nanorods are incorporated into thermo-responsive p-NIPAAm hydrogel to utilize surface plasmon-induced local heating by near-infrared light. By measuring optical transmission through the fabricated membrane structure with Au nanorod embedded hydrogel, we have demonstrated that photothermal actuation of the hydrogel can be done in two-dimensional, pixel-like configuration with high spatial and temporal resolutions. Benefiting from the hydrogel volume confinement within micron-sized pores, we have achieved sub-second response time of hydrogel photothermal actuation and its repeatable photothermal actuation on highly localized illuminated area. Considering that each hydrogel column is confined within each pore and different wavelengths of light can be used to induce photothermal actuation of hydrogel’s deswelling characteristics by modifying the physical dimensions of Au nanorods, it has a potential for optically-addressable, multiplexed drug release systems with the rapid response time.

Effects of surface properties of titanium alloys modified by grinding, sandblasting and acidizing and nanosecond laser on cell proliferation and cytoskeleton

Mammal cells detect and respond to physical and chemical signals on the surface of biological materials. The topology, chemical components and free energy of the surface are the main factors that affect cell behavior. In this paper, the surface with different surface properties was prepared by grinding, sandblasting and etching, and nanosecond laser. The effects of surface properties on stem cell proliferation and cytoskeleton were explored. The experimental results demonstrate that cell proliferation is not only affected by surface roughness (Ra and Sa), but also by surface flatness and surface area. Micron-sized grooves prepared by nanosecond lasers induce cells to form the cytoskeleton of high-aspect-ratio. Nevertheless, micron-sized pore arrays prepared by nanosecond lasers can limit the migration and spread of the cytoskeleton. In summary, the formation of the cytoskeleton is affected by multiple energy barriers generated by topology, free energy, and chemical components of the surface.

Microstructural investigation of different nanopore types in marine-continental transitional shales: Examples from the Longtan formation in Southern Sichuan Basin, south China

Variations in pore types, the complexity of pore structures, and strong heterogeneity complicate the thorough characterization of pore networks in marine–continental shales. In this study, a novel 2D image processing method was proposed, expounded, and verified to clarify the geometrical morphologies, formation mechanisms, the size distributions, proportions and the fractal characteristics of different types of pores in marine–continental shales. Six types of pores (inter-particle, intra-particle, organic matter (OM), inter-crystalline, dissolved pores, and micro-fractures) were classified and morphologically characterized. The different types of shale pores had distinct relatively restricted morphologies, formation mechanisms, and size ranges. Nano- and micron-sized pores were controlled by OM pores and micro-fractures, with the size ranging of 6–80 nm and 200–350 nm and 6–10 μm, respectively. Furthermore, the fractal dimension characteristics were investigated on the basis of the 2D binary images, and the results were verified by the fractal findings obtained from the N2 adsorption data. These fracture dimension results demonstrated that the Longtan shale pore structures had strong complexity and heterogeneity, which was strongly and positively controlled by micro-fractures, inter-crystalline and OM pores. In addition, the total organic carbon content strongly and positively influences the development and anisotropy of the nanoscopic pores, which were dominated by OM pores; while the clay minerals content has a minor effect on the total pore development and heterogeneity of shales but a significant effect on the dissolved pore development of shales, whereas brittle minerals inhibit total pore development and heterogeneity of shales but contribute greatly to the development of the inter-crystalline pores.

Combined technology of PCP and nano-CT quantitative characterization of dense oil reservoir pore throat characteristics

The size of pore throats in tight oil reservoirs varies from a few tens of nanometers to several hundred micrometers. This complex and diverse microscopic pore throat structure restricts the exploration and development process, affecting the recovery rate. Size, shape, and spatial distribution of pore throats in tight oil reservoirs are revealed in this paper via a scanning electron microscope (SEM), casting thin-sections, high-pressure mercury injection, and Nano-CT. Results show that the pore type of the Chang 7 tight oil reservoir in the Xin’anbian area is mainly divided into three categories: intergranular pores, dissolution pores, and microfractures. Numerous nanoscale pore throats have developed in this area, which greatly contributes to reservoir capacity and seepage. Pore throat distribution on capillary pressure curves of different samples shows that when the threshold pressure is less than 1 Mpa, there are many micron-sized pores with good connectivity and pore throats form a large tubular shape with a throat radius between 3.6 and 1064 nm. When the threshold pressure ranges from 1 to 3 MPa, there are many nanoscale pores with good local connectivity, intragranular dissolution pores develop, and pore throats are in tube bundles and spherical in shape with the throat radius between 3.6−657 nm. When the threshold pressure is greater than 3 MPa, nanoscale microfractures develop and are connected to neighboring small spherical pores, small spherical nanopore spaces become isolated, vertical connectivity is poor, and the throat radius is between 3.6−242 nm.

Hierarchical self-assembly, spongy architecture, liquid crystalline behaviour and phase diagram of Laponite nanoplatelets in alcohol-water binary solvents

Hydrophobicity and solvation of different charged species are among the various key factors that regulate the self-assembly of colloids, and macromolecules in their suspensions. In this paper, we demonstrate a method to tune the interaction potential and the resulting phase behaviour and microstructure of the states that form by using a combination of Laponite nanoplatelets and alcohols in water. This allows us to exquisitely control the self-assembly process of Laponite nanoplatelets. A new class of soft materials, called nanoclay-organogels, is studied systematically for their aging behaviour, microscopic structure and mechanical properties. Real space imaging techniques depicted spongy architecture with nano and micron size pores inside the gel matrix indicating the hierarchical self-assembly of the nanoplatelets in the aqueous solutions of polar organics. We have extensively examined the dispersion stability, aggregation, gelation and liquid crystalline behaviour of Laponite nanoplatelets in different alcohol (methanol, ethanol, 1-proponaol and ethylene glycol, and glycerol)-water binary solvents, thereby proposing a generalized description of nanoclay in alcoholic solutions, which is poorly probed and marginally understood in the literature. A phase diagram of Laponite® in alcohol solutions is proposed, which clearly demarcates regions of isotropic sol, unstable sol, isotropic gel, nematic/birefringent gel, glass, flocculated sedimentation and liquid crystalline structures.

Improving water management in fuel cells through microporous layer modifications: Fast operando tomographic imaging of liquid water

Polymer electrolyte fuel cells (PEFCs) have been actively developed for a wide range of power generation applications. At the high power densities required for automotive applications, sophisticated water management is vital to further improve cell performance. In particular, the gas diffusion layer (GDL), which includes a microporous layer (MPL), plays a crucial role in optimizing both water drainage and gas transport between the catalyst layer and gas channels. The present work studied the effect of cathode MPL porosity on the water distribution in the GDL. The results show that cells in which MPL materials have larger, micron-sized pores exhibit better performance. Advanced 4D operando X-ray imaging (3D structure plus time) was employed to analyse the water content in GDLs, and demonstrated that the superior performance of cells with large MPL pores is due to the efficient formation of water pathways. These pathways are based on water clusters allowing percolation in the through-plane direction from the bottom to the top of the GDL. Such pathways decrease the liquid water level in the entire cathode GDL. Especially, large MPL pores merge numerous small liquid water pathways in the catalyst layer and stabilize them morphologically, thus creating primary pathways for effective water drainage.

Chemical Compositions and Distribution Characteristics of Cements in Longmaxi Formation Shales, Southwest China

Shale gas resources have been regarded as a viable energy source, and it is of great significance to characterize the shale composition of different cements, such as quartz and dolomite. In this research, chemical analysis and the multifractal method have been used to study the mineral compositions and petrophysical structures of cements in shale samples from the Longmaxi Formation, China. X-ray diffraction, electron microprobe, field emission scanning electron microscopy, cathodoluminescence microscopy and C-O isotope analyses confirmed that cements in the Longmaxi Formation shales are mainly composed of Fe-bearing dolomite and quartz. Fe-bearing dolomite cements concentrate around dolomite as annuli, filling micron-sized inorganic primary pores. Quartz cements in the form of nanoparicles fill primary inter-crystalline pores among clay minerals. Theoretical calculation shows that the Fe-bearing dolomite cements formed slightly earlier than the quartz cements, but both were related to diagenetic illitization of smectite. Moreover, multifractal analysis reveals that the quartz cements are more irregularly distributed in pores than the Fe-bearing dolomite cements. These results suggest that the plugging effect of the quartz cements on the primary inoraganic pore structures is the dominant factor resulting in low interconnected porosity of shales, which are unfavorable for the enrichment of shale gas.

Synthesis of graphene-like passivating carbon layer into nanostructured porous silicon

The paper presents experimental results on the synthesis of graphene-like (Gr) films in gradient porous silicon structures with variable morphology (GPSi-var). Porous GPSi-var layers are characterized by the presence of a nanostructured layer (later nanoporous) on its surface. By increasing the depth of the anodic etching, the nanopores gradually transform into spongy and then into the columnar structure with micron-sized pores. The peculiarities of Gr layers’ synthesis in the walls of the pores throughout the depth of GPSi-var structures are studied. The proposed method of Gr film synthesis in the porous structure allows to form the carbon coating not only on the wall of the through pores in membrane, but also on the inner surface of the closed pores in the GPSi-var layers. It has been established that the composite formation of nanoporous silicon with Gr coating (GPSi-var/Gr) decreases the surface resistance of porous silicon layers by several orders of magnitude. The relatively higher stability of nanoporous composite layers to the impact of aqueous media has been experimentally demonstrated. Besides, it was found that the synthesized Gr layers are formed predominantly on the outer surface of the porous layer and crystal structure of its skeleton.

Higher structures, quantum groups and genus zero modular operad

We establish a biophysical model for the dynamics of lipid vesicles exposed to surfactants. The solubilization of the lipid membrane due to the insertion of surfactant molecules induces a reduction of membrane surface area at almost constant vesicle volume. This results in a rate-dependent increase of membrane tension and leads to the opening of a micron-sized pore. We show that solubilization kinetics due to surfactants can determine the regimes of pore dynamics: either the pores open and reseal within a second (short-lived pore), or the pore stays open up to a few minutes (long-lived pore). First, we validate our model with previously published experimental measurements of pore dynamics. Then, we investigate how the solubilization kinetics and membrane properties affect the dynamics of the pore and construct a phase diagram for short and long-lived pores. Finally, we examine the dynamics of sequential pore openings and show that cyclic short-lived pores occur at a period inversely proportional to the solubilization rate. By deriving a theoretical expression for the cycle period, we provide an analytic tool to measure the solubilization rate of lipid vesicles by surfactants. Our findings shed light on some fundamental biophysical mechanisms that allow simple cell-like structures to sustain their integrity against environmental stresses, and have the potential to aid the design of vesicle-based drug delivery systems.

New Frontiers in Experimentally Observing Detonation Properties

New Frontiers in Experimentally Observing Detonation Properties

Hierarchical porous ceramics with 3D reticular architecture and efficient flow-through filtration towards high-temperature particulate matter capture

Porous ceramics with high porosity and extensive interconnected pores have great application potential in fields ranging from dye removal to high-temperature particulate matter (PM) capture. However, constructing these materials to achieve efficient filtration is extremely challenging. Herein, a novel strategy to create hierarchical-structured porous alumina ceramics (PACs) with three-dimensional (3D) reticular architecture is reported based on polyurethane (PU) foaming method. To ensure the efficient flow-through filtration, carbamate-grafted carbon black is used as the pore-forming agent and assembled into the porous PU framework. Submicron and micron-sized pores on the cell walls are observed in hierarchical-structured PACs. This unique structure enables a high PM removal efficiency (94.1%) at an ultralow pressure drop (20 Pa). Our work has demonstrated great application potentials of as-prepared PACs as an efficient high-temperature PM filter and provided new insights to develop highly effective filter.

Hierarchical dual-porosity nanoscale nickel cermet electrode with high performance and stability.

Nano-structured metal-ceramic materials have attracted attention to improve performance in energy conversion applications. However, they have poor long-term stability at elevated temperatures due to coarsening of the metal nanoparticles. In this work we show that this can be mitigated by a novel design of the nano-structure of Ni cermet fuel electrodes for solid oxide cells. The strategy is to create a dual porosity microstructure, without the use of fugitive pore-formers, with micron-size pores to facilitate gas transport and nanoscale pores to control nano-particle coarsening. This has been achieved using a continuous hydrothermal synthesis and two-stage heat treatments to produce electrodes with micron size agglomerates of nano-structured porous Ni-Yttria-Stabilised-Zirconia (YSZ). This unique hierarchical microstructure combines enhanced electrochemical reaction in the high activity (triple phase boundary density 11 μm-2) nanoscale regions with faster gas diffusion in the micron-sized pores. The electrodes are aged at 800 °C in humidified 5% H2-N2 for up to 600 h. The electrochemical reaction resistance is initially 0.17 Ω cm2 but later reaches a steady long-term value of 0.15 Ω cm2. 3-D reconstruction of the electrodes after 10 h and 100 h of ageing reveals an increase in YSZ network connectivity and TPB percolation. This improvement is well-correlated to the 3-D tomography parameters using a physical model adapted from mixed conducting SOC air electrodes, which is also supported, for the first time, by numerical simulations of the microstructural evolution. These also reveal that in the long term, nickel coarsening is inhibited by the nanoscale entanglement of Ni and YSZ in the hierarchical microstructure.

Laser melting deposition of a porosity-free alloy steel by application of high oxygen-containing powders mixed with Cr particles

Laser melting deposition (LMD) of an alloy steel by application of commercial 12CrNi2 powder with O content as high as 0.53 wt% has been investigated. It shows that the LMD alloy steel contains micron-sized pores. The pore formation, which is assumed to result from gas bubbles due to the reaction of carbon and oxygen in the laser molten pool, can be prevented by mixing the alloy steel powder with an appropriate amount of Cr particles. The result is interpreted based on reaction thermodynamics in the molten pool in combination with TEM observation of the microstructure of the LMDed alloy steel.

Matrix mechanical plasticity regulates cancer cell migration through confining microenvironments

Studies of cancer cell migration have found two modes: one that is protease-independent, requiring micron-sized pores or channels for cells to squeeze through, and one that is protease-dependent, relevant for confining nanoporous matrices such as basement membranes (BMs). However, many extracellular matrices exhibit viscoelasticity and mechanical plasticity, irreversibly deforming in response to force, so that pore size may be malleable. Here we report the impact of matrix plasticity on migration. We develop nanoporous and BM ligand-presenting interpenetrating network (IPN) hydrogels in which plasticity could be modulated independent of stiffness. Strikingly, cells in high plasticity IPNs carry out protease-independent migration through the IPNs. Mechanistically, cells in high plasticity IPNs extend invadopodia protrusions to mechanically and plastically open up micron-sized channels and then migrate through them. These findings uncover a new mode of protease-independent migration, in which cells can migrate through confining matrix if it exhibits sufficient mechanical plasticity.

Development of cellulose based aerogel utilizing waste denim—A Morphology study

Cellulose aerogels with orientated micron-sized pore structure were obtained from denim waste utilizing ionic liquid solvents through dissolution, regeneration and drying. The pore structure of denim-derived aerogels was comprised of a mixture of micron-sized vertically aligned pores and a nanoporous fibrous network. The size and distribution of vertically aligned pores and the nanopores were influenced by the choice of ionic liquid solvent, amount of denim used and drying method employed. A detailed study on the morphology of the cellulose aerogels produced from waste denim is provided.

Optical properties of oakwood in the near-infrared range of semi-transparency.

The spectral absorption and scattering properties of oakwood are retrieved from the measurements of both the normal-hemispherical reflectance and transmittance in the visible and near-infrared ranges of semi-transparency. We employ two alternative methods for the radiative transfer in wood samples: the modified two-flux approximation and the high-order discrete ordinate method. The modifications of both methods take into account the effect of total internal reflection at both surfaces of the wood samples. The analytical approximate solution of the first method gives very accurate results for the absorption coefficient, but the transport scattering coefficient of wood appeared to be systematically underestimated. Fortunately, this error is between 7% and 12%, and that is acceptable for the estimates. The oakwood samples of four different thicknesses were used in the experiments. The effect of the wood cell orientation appears to be insignificant and can be observed in the reflectance from optically thin samples only. There is a considerable decrease in the transport scattering coefficient of oakwood with the wavelength. This effect is explained by a predominant contribution of micron-sized longitudinal pores in oakwood. The latter is used to develop an approximate theoretical model of scattering based on the rigorous solution for arbitrary-oriented cylindrical pores. The model suggested is in good agreement with the experimental data.