High-Porosity Structure

High-porosity structures are useful for various insulating purposes. This kind of structure includes fibrous products such as glass wool, powdered insulated grain, and strongly insulating firebrick. 

1 A typical porcelain body has the composition 50 clay-25 feldspar-25 quartz. Sketch an expected microstructure of such a body, indicating scale when (a) fired to achieve phase equilibrium (1450°C for 6 h) and (b) fired to 1300°C for 1 h. 

2 Describe how you would experimentally determine the fractional porosity, fractional glass content, and fractional crystal content in steatite porcelain containing three phases (pores, glass, and MgSiOj crystals). 

3 From a lineal analysis, eshmate the fraction of porosity present in the porcelain in the following figure. What is the average pore radius  

Kingery, H. K. Bowen, and D. R. Uhlmann, Introduction to Ceramics, John Wiley, New York, 1976, pp. 516-580. 

---

Figure 6 Varying monocrystalline porosities generated by the etching manufactir-ing process whereby characteristic low-, medium-, and high-porosity structures can be processed.

The electronically conductive network in the electrode functions as an internal current collector and can be formed from conductive nanoparticles integrated within a porous matrix or from a continuous rigid backbone. One example is the biopolymer chitosan fabricated with a conductive additive of carbon nanotubes [2,3,8]. Ideally, the electronically conductive network will also provide mechanical stability to the electrode and support the structure against vibrations, fuel flow-through pressures, and other mechanical shocks. The electronically conductive network is essentially an internal current corrector within the anode and, as such, must be electronically wired to the external current collector of the anode compartment with minimal contact and ohmic resistance. The electrode materials described are typically delicate and mechanically soft and must be carefully handled to maintain their open high-porosity structure. 

Figure 13.5. Micrograph of the peripheral zone of a pellet showing the very fine and high porosity structure of the RIM...

Major structural Felted fiber with High-porosity film on Solid urethane sheet with filer Solid polymer sheet... 

TEG macrostructure differs from that of natural graphite it possesses abnormally high porosity and highly developed active surface (40-50 m2/g) (Figure 1). The performed thermochemical treatment leads to an essential exfoliation of graphite matrix with a formation of cellular structure. The thickness of cell s walls is equal to 20-25 nm. The surface of cell s walls contains a lot of macrocracks, outcrops of crystallites, etc. The thermochemical re-treatment was applied to enhance TEG dispersivity. 

In addition to bilayered electrodes with a functional layer and a support layer, electrodes have also been produced with multilayered or graded structures in which the composition, microstructure, or both are varied either continuously or in a series of steps across the electrode thickness to improve the cell performance compared to that of a single- or bilayered electrode. For example, triple-layer electrodes commonly utilize a functional layer with high surface area and small particle size, a second functional layer (e.g., reference [26]) or diffusion layer with high porosity and coarse structure, and a current collector layer with coarse porosity and only the electronically conductive phase (e.g., reference [27]) to improve the contact with the interconnect. 

In addition to the criticisms from Anderman, a further challenge to the application of SPEs comes from their interfacial contact with the electrode materials, which presents a far more severe problem to the ion transport than the bulk ion conduction does. In liquid electrolytes, the electrodes are well wetted and soaked, so that the electrode/electrolyte interface is well extended into the porosity structure of the electrode hence, the ion path is little affected by the tortuosity of the electrode materials. However, the solid nature of the polymer would make it impossible to fill these voids with SPEs that would have been accessible to the liquid electrolytes, even if the polymer film is cast on the electrode surface from a solution. Hence, the actual area of the interface could be close to the geometric area of the electrode, that is, only a fraction of the actual surface area. The high interfacial impedance frequently encountered in the electrochemical characterization of SPEs should originate at least partially from this reduced surface contact between electrode and electrolyte. Since the porous structure is present in both electrodes in a lithium ion cell, the effect of interfacial impedances associated with SPEs would become more pronounced as compared with the case of lithium cells in which only the cathode material is porous. 

Bonded PGA fiber structures with high porosities and area/volume ratios were produced using this manufacturing method and utilizing only biocompat-... 

By far the most studied PolyHIPE system is the styrene/divinylbenzene (DVB) material. This was the main subject of Barby and Haq s patent to Unilever in 1982 [128], HIPEs of an aqueous phase in a mixture of styrene, DVB and nonionic surfactant were prepared. Both water-soluble (e.g. potassium persulphate) and oil-soluble (2,2 -azo-bis-isobutyronitrile, AIBN) initiators were employed, and polymerisation was carried out by heating the emulsion in a sealed plastic container, typically for 24 hours at 50°C. This yielded a solid, crosslinked, monolithic polymer material, with the aqueous dispersed phase retained inside the porous microstructure. On exhaustive extraction of the material in a Soxhlet with a lower alcohol, followed by drying in vacuo, a low-density polystyrene foam was produced, with a permanent, macroporous, open-cellular structure of very high porosity (Fig. 11). 

A wide range of polymeric materials can be prepared from HIPEs. Polymerisation of the continuous phase yields highly porous cellular polymers with a monolithic structure. These are known as PolyHIPE polymers, and possess a number of unique properties including, in most cases, an interconnected cellular structure and a very low dry-bulk density. Their very high porosity favours their use as supports for catalytic species, precursors for porous carbons and inert matrices for the immobilisation of enzymes and micro-organisms. 

Evidence for rubble pile asteroids comes from a variety of observations. The low densities of many asteroids imply that they have high porosities, presumably resulting from the assembly of loose fragments. Spectral variations seen in some S-class asteroids as they rotate also support rubble piles. The variations suggest that portions of the surface have experienced different degrees of thermal metamorphism. Catastrophic collision and reassembly has transformed bodies that formerly had onion shell structures into rubble piles. 

Carbon-fiber based porous materials, namely non-woven carbon paper and woven carbon cloth, shown in Fig. 5, have received wide acceptance as materials of choice for the PEFC GDL owing to high porosity ( 70% or higher) and good electrical/thermal conductivity. Mathias et al.32 provided a comprehensive overview of the GDL structure and functions. In this work, the reconstruction of non-woven carbon paper GDL is presented. 

---