Honeycomb porous structure

Activated carbon, activated charcoal. A form of carbon that has (a) a porous or honeycomb-like structure and therefore a large surface area and (b) high adsorbdvity (certain molecules stick to it). Used to strip out impurities or extract selected compounds. 

In a related approach, these same porous alumina membranes serve as a mask through which O2 plasmas are used to etch underlying carbon films. This etching process produces honeycomb carbon structures that are positive replicas of the alumina-membrane mask. This process has successfully produced honeycomb structures of both diamond and graphitic carbon, with pore sizes in the carbon replica around 70 nm. 

The activated coating layer must possess two additional properties. It must adhere tenaciously to the monolithic honeycomb surface under conditions of rapid thermal changes, high flow, and moisture condensation, evaporation, or freezing. It must have an open porous structure to permit easy gas passage into the coating layer and back into the main exhaust stream. It must maintain this porous structure even after exposure to temperatures exceeding 900°C. 

Stiff lightweight structures such as aircraft wings are made from sandwiches of continuous sheets filled with foams or honeycombs. Open porous structures can form frameworks for infiltration by other materials leading to application of biocompatible implants. Open pore structures are used as supports for catalysts. 

Not all catalysts need the extended smface provided by a porous structure, however. Some are sufficiently active so that the effort required to create a porous catalyst would be wasted. For such situations one type of catalyst is the monolithic catalyst. Monolithic catalysts are normally encountered in processes where pressure drop and heat removal are major considerations. Typical examples include the platinum gauze reactor used in the ammonia oxidation portion of nitric acid manufacture and catalytic converters used to oxidize pollutants in automobile exhaust. They can be porous (honeycomb) or non-porous (wire gauze). A photograph of a automotive catalytic converter is shown in Figure CD 11-2. Platinum is a primary catalytic material in the monolith. 

It is obvious that the honeycomb-like structures can be considered as possible electrodes in electrochemical devices such as fuel cells and sensors due to their very open and porous structure. Analysis of the effect of different parameters of electrolysis given in this section enables to be systematized electrodeposition conditions leading to the formation of this structure type. 

If the concentration of low-molecular liquids (solvents) in the polymers surpasses their compatibility limit, they isolate and form spherical arrangements with a size of 10-20 pm in the polymer structure. When the solid phase volume exceeds that of the liquid, the formed structures are of the closed-pore kind and the liquid phase is distributed within the solid phase as local spherical inclusions [122]. As soon as the liquid phase content surpasses that of the solid, a new honeycomb structure with communicating cavities is formed whose solid phase builds up thin walls that separate the cells. This feature is to a greater extent typical of tough and crystallizable polymers. This is also relevant for systems like PE-MO where honeycomb structures with a pore size of up to several micrometers can be formed under certain conditions (Fig. 4.22) [123]. Such porous structures are perfect for the impregnation of modified additives, e.g. Cl. 

Microspheres prepared by spray drying maintain their spherical geometry with a narrow size distribution with a mean diameter of 2-5 pm. Calceti et al. used suspension solvent evaporation, double emulsion-solvent evaporation, and suspension/double emulsion-solvent evaporation for the preparation of insulin-loaded polyphosphazene microspheres [80], These preparation procedures produced spherical microparticles with a porous surface and a honeycomb internal structure (Figure 11.11). 

The honeycomb of the catalytic converter provides a large surface area to support the catalyst particles and ensures that the gases pass close to these particles. When used as filters the pore (channel) diameter is engineered to suit the purpose. The synthetic bone needs the pores to encourage the intergrowth of regrowing natural bone, but if the pores are too large then the ceramic is weakened. One technique used to provide the porous structure and... 

Several approaches have been developed to fabricate honeycomb porous films [61] (see Fig. 10.3). The most extended approach involves a casting process of polymer solution droplet on a solid support controlling the relative humidity of the chamber (i). In general, at least relative humidity (RH) higher than 50 % is necessary to induce the water condensation and produce highly ordered structures. 

Moreover, some investigations have dealt with the combination of the photonic properties and the ordered porous structure for light-harvesting or emitting. In both cases, light-sensitive honeycomb films based on semi-conductive NPs or conjugated polymers were used to improve the opto-electronic properties of organic thin-film devices [126, 161, 174,176, 190-192]. 

Zhu, L.W., Wan, L.S., Jin, J., Xu, Z.K. Honeycomb porous films prepared fi om pOTphyiin-cored star polymers submicrometer pores induced by transition of monolayer into multilayCT structures. J. Phys. Chem. C 117, 6185-6194 (2013)... 

Chen, S., Alves, M., Save, M., Billon, L. Synthesis of amphiphilic diblock copolymers derived from renewable dextran by nitroxide mediated polymerization towards hierarchically structured honeycomb porous films. Polym. Chem. 5(18), 53105 (2014). doi 10.1039/ C4PY00390J... 

Escale, P., Save, M., Lapp, A., Rubatat, L., Billon, L. Hierarchical structures based on self-assembled diblock copolymers within honeycomb micro-structured porous films. Soft Matter... 

Therefore, it can be seen from the above expression that is closely related to absorption loss (SE ). SE is also important for porous structures (e.g., foams) and for certain type of filled composites (carbon nanofibers [CNFs]/carbon nanotubes [CNTs]/graphene-filled polymers) or for certain design geometries (e.g., honeycomb lattices) [1,2,9,13,81]. It can be neglected in the case of a shield having thick absorbing elements due... 

In order to increase the specific surface area and enhance the effectiveness/ activity of the porous electrodes, it is necessary to reduce the size of the pores, as well as the branches in the foam or agglomerates of copper grains in the honeycomb-Uke structures [26]. One of the ways to improve micro- and nanostructural characteristics of open porous electrodes is the addition of additives to the electroplating solution [26]. The decrease of diameter of holes, as well as the increase of their number in 3D foam copper structures, can be realized by the addition of acetic acid to the copper sulfate solution [26]. Also, the addition of chloride ions dramatically reduces the size of the copper branches in the walls of holes. The reduction in pore size is a result of lowering hydrophobic force of the generated hydrogen gas by adding bubble stabilizer (e.g., acetic acid) that suppresses the coalescence of bubbles, while the decrease in branch size in the foam wall is a consequence of the catalytic effect of chloride ions on the copper deposition reaction. 

The presented disperse or irregular morphological forms of copper may be useful in the production of powders [6, 32], while the honeycomb-like deposit type is due to an open porous structure with the extremely high surface area ideally suited to be used as electrodes in many electrochemical devices, such as fuel cells, batteries, and sensors [48]. 

To increase the specific surface area and enhance the effectiveness/ activity of the porous electrodes, it is necessary to reduce the size of the pores, as well as the branches in the foam or agglomerates of copper grains in the honeycomb-like structures [4]. 

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