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Porous polymer monolith materials of 2-mm thickness were obtained by visible light-induced radical polymerization of oligocarbonate dimethacrylate (OCM-2) in the presence of 1-butanol (10 to 70 wt %) as a porogenic additive. The pore characteristics and morphology of polymers were studied by mercury intrusion porosimetry and scanning electron microscopy. Monolithic polymers with both open and closed pores up to 100 nm in size are formed when the alcohol content in the initial composition is up to 20 wt %. The pore structure in such materials is a system of holes in the bulk of the polymer (hole-type pores). Open interconnected pores with a specific volume up to 2.22 cm3/g and modal pore size up to 10 microns are formed in the volume of the polymer with 1-butanol content of more than 30 wt %. Such porous monoliths are a structure of covalently bonded polymer globules (interparticle-type pores). The free space between the globules represents a system of open interconnected pores. In the transition region of 1-butanol concentrations (from 20 to 30 wt %), areas with both structures and intermediate frameworks, as well as honeycomb structures of polymer globules connected by bridges, are fixed on the polymer surface. It was found that the transition from one type of pore system to another is accompanied by a sharp change in the strength characteristics of the polymer. Approximation of experimental data using the sigmoid function made it possible to determine the concentration of the porogenic agent in the vicinity of which the percolation threshold is observed. [ABSTRACT FROM AUTHOR]

Carbon aerogels have attracted increasing interest as electrode material and conductive template for supercapacitors due to their unique porous structure and strong electrical conductivity. However, the satisfactory strategy for fabricating carbon aerogels with excellent electrochemical performance remains to be explored. Herein, polyimide aerogels with porous fibrous networks were successfully synthesized by ambient pressure drying, and nitrogen-doped carbon aerogel were obtained after high-temperature processing by using the polyimide aerogel as the precursor. The pore structure of carbon aerogel was controlled by adjusting the repeat unit of polyimide molecular chain. When the repeat unit was 60 and carbonization temperature was 800 °C, PA-60-800 exhibits a typical honeycomb porous structure, which contains numerous meso-micro-porosity and provides a large specific surface area > 1000 m2 g−1. In addition, PA-60-800 showed excellent electrochemical behavior with the specific capacitance of 314.1 F g−1 at 0.5 A g−1. After 10,000 cycles of galvanostatic cycling, the electrode still maintains a capacity retention of 98.8%. Moreover, PA-60-800-assembled symmetric supercapacitor display a high energy density of 23 Wh kg−1 at a power density of 535.8 W kg−1. This work proposes an alternative path for the preparation of high-performance nitrogen-doped carbon aerogel electrode materials. [ABSTRACT FROM AUTHOR]

The static and dynamic stability of natural or constructed slopes can be affected by dissolution or dissolution-like phenomena. Their underlying mechanisms, however, remain unclear. New experimental results and discrete element simulations provide particle-level and macroscale information on the consequences of mineral dissolution on slope behavior. At the microscale, load-carrying grain arches develop around dissolving particles, the porosity increases, and contact force chains evolve to form a honeycomb topology. At the macroscale, while vertical settlements are the prevailing deformation pattern, lateral granular movements that create mass wasting are prominent in sloping ground, even under the quasi-static granular loss. Horizontal grain displacement is maximum at the surface and decreases linearly with the distance from the slope surface to become zero at the bottom boundaries, much like vertical granular displacement along the depth. Sediments with smaller friction angles and steeper slopes experience greater displacement, both vertically and horizontally. Slopes become flatter after dissolution, with the reduction in slope angle directly related to the loss in ground elevation, ΔH/Ho. Yet, because of the porous fabric that results from dissolution, vertical shortening is less than the upper bound, estimated from the loss in the solid mass fraction, ΔH/Ho≈SF. Under water-saturated conditions, the post-dissolution fabric may lead to sudden undrained shear and slope slide. [ABSTRACT FROM AUTHOR]

This study demonstrates the utility of thermo-regulated phase separable alumina/camphene suspensions containing poly(methyl methacrylate) (PMMA) microspheres as porogens for the production of multi-scale porosity structures. The homogeneous suspension prepared at 60 °C could undergo phase separation during freezing at room temperature. This process resulted in the 3D networks of camphene crystals and alumina walls containing PMMA microspheres. As a consequence, relatively large dendritic pores with several tens of microns size could be created as the replica of frozen camphene crystals. In addition, after the removal of PMMA microspheres via heat-treatment, micron-sized small spherical pores could be generated in alumina walls. As the PMMA content with respect to the alumina content increased from 0 vol% to 40 vol%, while the camphene content in the suspensions was kept constant (70 vol%), the overall porosity increased from 45.7 ± 0.5 vol% to 71.4 ± 0.5 vol%. This increase in porosity is attributed to an increase in the fraction of spherical pores in the alumina walls. Thus, compressive strength decreased from 153 ± 18.3 MPa to 33 ± 7.2 MPa. In addition, multi-scale porosity alumina objects with a honeycomb structure comprising periodic hexagonal macrochannels surrounded by dual-scale porosity walls were constructed using a 3D plotting technique. [ABSTRACT FROM AUTHOR]

Herein, we fabricated honeycomb ceramics with different porosities and pore shapes via the layer-by-layer deposition of cordierite (2MgO·2Al 2 O 3 ·5SiO 2) particle ink, obtaining proper rheological properties using a direct-writing technology. No collapses as well as minimal cracking and bending were observed in the internal structure of the samples after calcination. We measured and compared the internal porosity and specific surface area of honeycomb ceramics with the same pore shape but different pore dimensions, as well as the same pore dimension but different pore shapes. The samples were both loaded with an γ-Al 2 O 3 washcoat and Pd-based catalyst using the same method for the catalytic combustion of toluene. The different porosity and pore shape influenced the catalytic efficiency. This study may provide some useful guidelines for fabrication of honeycomb ceramics by direct writing technology, which could be used to remove volatile organic pollutants(VOCs). [ABSTRACT FROM AUTHOR]

[Display omitted] • Fe-SA@PNC was developed via a novel chemical vapor deposition strategy. • 3D honeycomb aerogel was prepared employing CNF, ANF and GO through directional freeze-casting and Cd volatilization. • Fe-SA@PNC possess atomically dispersed Fe-N 4 sites and hierarchical pore structure. • Fe-SA@PNC exhibit remarkable ORR activity in Zn-air batteries. Fe-N x C single-atom catalysts have been immensely explored as the most promising ORR catalysts for replacing noble metals. Nevertheless, how to precisely introduce Fe atoms to optimize their spatial distribution and coordination environment in carbonaceous matrices while constructing the hierarchical porous structures to facilitate the mass transport process and ensure the accessibility of Fe-N x sites remain significant challenges. Here, we propose a strategy to prepare porous N -doped carbon aerogels anchored with single atomic Fe sites (Fe-SA@PNC) as highly efficient ORR electrocatalysts via directional freeze-casting and chemical vapor deposition. Fe-SA@PNC exhibit remarkable ORR activity and stability due to the highly stable honeycomb morphology and hierarchical pore structure, as well as the atomically dispersed Fe-N 4 sites in the carbon support. Furthermore, the practical application of Fe-SA@PNC catalysts as cathode materials in Zn-air batteries was demonstrated with encouraging performance. This study provides a promising approach for constructing high-efficiency ORR single-atom catalysts. [ABSTRACT FROM AUTHOR]

Auxetic materials exhibit many superior properties but drawback in low stiffness owe to the substantial porosity. Some narrow-ribs enhanced auxetic honeycombs have been designed for improving the in-plane stiffness. For these narrow-ribs enhanced auxetic structures, local buckling likely appears as the reinforcing walls are designed in low thickness for superior auxeticy. In this paper, a novel narrow-ribs enhanced auxetic honeycomb is designed by embedding rhombus into each cell of the normal re-entrant hexagonal honeycomb (NRHH). Analytical model is built to investigate the elastic behaviors of the new proposed honeycomb under uniaxial compression, in which the incremental method is firstly introduced for post-local-buckling analysis. Numerical simulations are carried out to verify the analytical results. It is interesting that bilinear elastic characteristic is found for the stress-strain and transverse strain-longitudinal strain curves of the new proposed honeycomb on account of the local buckling. Parameters studies are performed and the new proposed honeycomb is proved to exhibit superior mechanical properties compared to other narrow-ribs enhanced honeycombs. Significantly, the incremental method brought forward in the present paper for the local buckling analysis can be popularized to other honeycombs enhanced with narrow-ribs. Thus, the bilinear elastic characteristic is a general feature for these honeycombs. [ABSTRACT FROM AUTHOR]

Development of lightweight ceramic aerogel with enhanced thermal insulation and high temperature resistance is required in the field of thermal insulation. Here, a aerogel-like SiOC ceramic with honeycomb structure was prepared by solvothermal method using polyhydromethylsiloxane (PHMS) as precursor and divinylbenzene (DVB) as cross-linker followed by freeze-drying and pyrolysis. The pore size and homogeneity of the honeycomb structure could be further controlled by the content of DVB through adjusting the crosslinking degree of the PSO wet gel. The aerogel-like SiOC possessing uniform honeycomb structure with the pore size of 20–50 µm and the wall thickness of 3–6 µm is obtained at the mass ratio of DVB:PHMS of 2:1. The aerogel-like SiOC exhibits low density (0.14 g·cm−3) and low thermal conductivity (0.0577 W·m−1·K−1). Moreover, it maintains the honeycomb structure after high temperature treatment at 1400 °C in argon and 800 °C in air indicating its good thermal stability. This work provides a novel route for the preparation of the aerogel-like SiOC ceramic with honeycomb structure and designable overall performance, further expanding its application in thermal insulation. • A novel strategy for developing lightweight aerogel-like SiOC ceramic with honeycomb structure is reported. • Controlling honeycomb-like structure by DVB content. • Realizing low thermal conductivity of 0.0577 W·m−1·K−1. • Achieving good thermal stability of structure at 1400 °C in Ar. [ABSTRACT FROM AUTHOR]

The structure of a freeze-dried material is essential for its ability to preserve and protect biologics such as proteins, cells and other sensitive structures. The structure of a typical freeze-dried matrix can be described as pores surrounded by thin walls where the walls are the encapsulating material (for e.g. cells). The objective of this investigation is to evaluate X-ray microtomography (µCT) as a characterization method to quantifying the matrix of a freeze dried material, and compare it to scanning electron microscopy (SEM). The material consists of maltodextrin, freeze-dried below or above the glass transition temperature of the maximal freeze concentration ( T g ′) and after applying annealing. The SEM images have high resolution and provide an excellent view of the sample. However, it is challenging to perform any image analysis and to ensure that a representative section is presented. The µCT images provide a rather uniform contrast between material and void, allowing for a simple grey-level thresholding when separating structure from the background. A robust image analysis procedure allows the results extracted from a representative sample volume to be evaluated. Further image analysis has been focused on understanding the thickness of the encapsulating structures by estimations of volume-weighted averages of inscribed spheres within the walls. The results show two types of structures: A large pore structure of around 20–100 µm separated by thin walls around 2–3 µm thick, and a finer structure consisting of smaller pockets of air (< 10 µm) packed in a honeycomb like structure. The structures of the samples dried below and above T g ′ have smaller and thinner structures, while material dried after annealing has larger and thicker structures. The structures display comparably small differences between the different drying protocols despite the quite different drying conditions. [Display omitted] • Wall thickness of freeze dried material can be a relevant factor when large biological bodies needs to be encapsulated. • It is possible to use X-ray µCT for characterizing and quantifying the wall thickness of freeze-dried materials. • The annealing procedure provides a structure with larger chambers and thicker wall material. • The wall thickness can be determined both by the measured wall thickness and re-estimated based on the chamber size. • The thickness of the materials are similar despite the very different drying conditions. [ABSTRACT FROM AUTHOR]

Mineral dissolution and solid-liquid phase change may cause settlement or affect the bearing capacity of shallow foundations. The effect of gradual grain dissolution on small-scale shallow foundation behavior is investigated using the discrete element method. Results show that dissolution is most detrimental during early stages, as initially contacting particles shrink and force chains must reform throughout the medium. Porosity tends to increase during dissolution and force chains evolve into strong localized forces with a honeycomb topology. Higher settlements are required to mobilize bearing resistance in post-dissolution sediments than in pre-dissolution ones. Subsurface mineral dissolution beneath a footing under load is the worst condition; in fact, settlements in such cases are higher than when a foundation load is applied on a sediment that has already experienced dissolution. [ABSTRACT FROM AUTHOR]

Currently, the implants used for enophthalmic invagination have the disadvantages of precise filling difficulty, weak filling ability, large surgical wounds, and lack of CT development. Here, a CT-developable orbital stent was manufactured via 4D printing of a shape memory polyurethane composite for enophthalmos treatment. The composite was endowed with good CT development properties via incorporation of gold nanoparticles and nano-hydroxyapatite. Based on the bionic idea and CT reconstruction technique, a 4D printed orbital stent with a bionic honeycomb pore structure and an outer contour matching the orbital coloboma was designed to support the orbital tissue more accurately and stably. CT images of rabbits before and after the 4D printed orbital stent implantation showed better volume-filling capacity compared with the two types of the commercial orbital implants. The three-month follow-up showed the good postoperative result, which demonstrated the excellent performance of the composite in the precise minimally invasive treatment of enophthalmos compared with traditional orbital implants. [ABSTRACT FROM AUTHOR]

Localized regions at the top of the magnetite layer on a 9 %Cr martensitic steel CLAM were honeycombed after exposure to lead-bismuth eutectic (LBE) at 500 ºC for 500–2000 h. The honeycomb structures were composed of many oxygen-poor pores and surrounding net-like branches. Low oxygen concentrations promoted the formation of honeycomb structures in a shorter time and more areas. A model based on the local dissolution of magnetite crystals was proposed to explain the formation process. Honeycomb structures can lead to much oxygen loss in the spinel layer, which may induce pitting corrosion and promote its development. • Honeycomb structures in the oxide scale of martensitic steel are rarely reported in LBE. • Honeycomb structures were composed of net-like branches and oxygen-poor pores. • Low oxygen concentrations promoted the formation of honeycomb structures. • Honeycomb structures led to oxygen loss in spinel layer and may induce pitting corrosion. • Honeycomb structures may be an indicator of local low oxygen concentrations. [ABSTRACT FROM AUTHOR]

Transparent MgAl2 O4 spinel of flat as well as honeycomb structure was fabricated by employing thermally induced gel casting of the slurry with 56 wt% solid loading containing 0.2 wt% of methylcellulose. The green specimens were pressureless sintered to 98%-99% of theoretical density with no open porosity at an optimum temperature of 1700°C. Final densification by hot isostatic pressing of both the specimens at the optimum temperature of 1800°C and 195 MPa pressure enabled further elimination of residual porosities and full densification resulting in theoretical density of 3.58 g/cc. The design of the honeycomb was such that it exhibited a surface area to volume ratio of 0.65 cm2/cm3 and a relative density of 0.69. The hardness of the honeycomb specimens has been found to be 13 GPa, which is at par with the solid specimens processed under identical conditions. Solid specimens of around 4 mm thickness exhibited a transmission of >80% in the visible (0.4-0.8 μm) region. Specimens were also tested according to ASTM procedures and have shown a flexural strength (σf) of 195 MPa and plane-strain fracture toughness ( KIc) of 1.87 MPa·m1/2 as reported in this study. [ABSTRACT FROM AUTHOR]

Abstract: CoCl2 containing honeycomb patterned films were prepared from cellulose acetate (CA)/CoCl2/acetone solutions by the breath figure method in a wide range of humidities. Size and pore regularity depend on the CA/CoCl2 molar ratio and humidity. When replacing CoCl2 with Co(NO3)2 or CoBr2, no formation of ordered porosity in the cellulose acetate films is observed. According to data from scanning electron microscopy (SEM), Energy Dispersive X-ray Microanalysis (EDX), X-ray Diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy, the key role in the formation of honeycomb structures can be attributed to the physical and chemical properties of CoCl2 – hygroscopicity, low interaction with CA, and extraction from CA/CoCl2/acetone solution by water droplets condensed on the surface of the CA/CoCl2 solution. Obtained films are prospective for using in catalysis, hydrogen fuel cells, and optical sensing materials. [Copyright &y& Elsevier]

Abstract: Non-autoclave processing of honeycomb sandwich structures generally leads to poor compaction and high porosity of the skins, along with a decreased skin–core adhesion. The pressure level inside the honeycomb cells plays an important role and is controlled by the permeability to air of the skins. In this work, an initial range of skin permeability to air was explored by perforating the prepregs and adhesive layer selectively. The role of the resulting pressure inside the honeycomb on skin–core adhesion and skin quality was evaluated. Prepreg air permeability was found to control skin–core adhesion through the pressure in the honeycomb and potential outgassing of the adhesive layer. An optimal range of initial pressure inside the honeycomb was found to be 40–70kPa. A universal process window was proposed to determine the time frame of vacuum application leading to an optimal initial honeycomb pressure level. [Copyright &y& Elsevier]

Abstract: The porous Al2O3–TiB2 ceramics from stoichiometric mixtures of Al, TiO2 and B2O3 has been prepared by combustion synthesis technique. Products with high pore contents (86.3%) were obtained using the starting materials containing 10wt% pore-foaming agent (PFA). The finer pores range from 300 to 500μm and the larger ones are in the order of millimeters were obtained in the ceramics. Honeycomb structure micropores and acicular crystal TiB2 were formed at the ceramic pore when PFA added. [Copyright &y& Elsevier]

Hierarchical honeycomb patterns were manufactured with breath-figures self-assembly by drop-casting on the silicone oil-lubricated glass substrates. Silicone oil promoted spreading of the polymer solution. The process was carried out with industrial grade polystyrene and polystyrene with molecular mass M w = 35 , 000 g m o l . Both polymers gave rise to patterns, built of micro and nano-scaled pores. The typical diameter of the nanopores was established as 125 nm. The mechanism of the formation of hierarchical patterns was suggested. Ordering of the pores was quantified with the Voronoi tessellations and calculation of the Voronoi entropy. The Voronoi entropy for the large scale pattern was S v o r = 0.6 − 0.9 , evidencing the ordering of pores. Measurement of the apparent contact angles evidenced the Cassie-Baxter wetting regime of the porous films. [ABSTRACT FROM AUTHOR]