Microstructure pores

One step closer to up-scaling to industrial environments is the multiple-bead reactor shown in Fig. 4.9. Here pellet-type catalyst carriers, so-called beads, are positioned in square containers. The beads are made of alumina and are 1 mm in diameter. Gases are passed over these beads through microstructured pore membranes in the cover and the base plate of the containers. 

Microstructuring of the surface of a polymer membrane on solid support is commonly performed by various lithographic techniques. In previous applications is was not necessary or it was not tested whether the microstructured pores extend down to the neat support surface or whether the lower part of the pore remains filled with bulk polymer of with residues of the lithographic process. It could be shown by FTIR spectroscopic imaging for the first time, that residues remain inside the pores, which chemical origin the residues have and how the microstructuring process can be optimized towards completely empty pores, even if the diameter of the pores does not exceed a couple of micrometers. 

Microstructure (pore, grain, surface, grain boundary, interface, etc.) X... 

In Fig. 10, two PSDs for PSi materials with intentionally microstructured pores are shown. The first sample was obtained by first forming a layer of PS20 for 20 min, corresponding to a layer thickness of 25 pm, immediately followed by the formation of a PS 100 layer for further 20 min (with a layer thickness of about 75 pm). The PSD obtained using NMR cryoporometry (Fig. 10a) shows a bi-modal distribution with two peaks, which are found to be in a reasonable agreement with those measured for isolated PS20 and PS 100 materials. Moreover, the ratio of the areas under the two peaks is in agreement with the ratio of the pore volumes in the two layers expected from the fabrication conditions. 

Power density curve -Microstructure (pore size and distribution, particle or grain size, crystal structure) of catalysts ... 

Abstract This chapter discusses the research and development of porous ceramic membranes and their application as membrane reactors (MRs) for both gas and liquid phase reaction and separation. The most commonly used preparation techniques for the synthesis of porous ceramic membranes are introduced first followed by a discussion of the various techniques used to characterise the membrane microstructure, pore network, permeation and separation behaviour. To further understand the structure-property relationships involved, an overview of the relevant gas transport mechanisms is presented here. Studies involving porous ceramic MRs are then reviewed. Of importance here is that while the general mesoporous natnre of these membranes does not allow excellent separation, they are still more than capable of enhancing reaction conversion and selectivity by acting as either a product separator or reactant distributor. The chapter closes by presenting the future research directions and considerations of porous ceramic MRs. 

Fig. 16.7. Microstructural features of a crystalline ceramic grains, grain boundaries, pores, microcracks and second phases.

Powder X-ray diffraction and SAXS were employed here to explore the microstructure of hard carbon samples with high capacities. Powder X-ray diffraction measurements were made on all the samples listed in Table 4. We concentrate here on sample BrlOOO, shown in Fig. 27. A weak and broad (002) Bragg peak (near 22°) is observed. Well formed (100) (at about 43.3°) and (110) (near 80°) peaks are also seen. The sample is predominantly made up of graphene sheets with a lateral extension of about 20-30A (referring to Table 2, applying the Scherrer equation to the (100) peaks). These layers are not stacked in a parallel fashion, and therefore, there must be small pores or voids between them. We used SAXS to probe these pores. 

Fig. 7. Microstructures of the three primary graphites used in this work (a) H-451, (b) IG-I I, and (c) AXF-5Q. [F]-filler particles, [P]-pores and [C] cracks.

As described above, the code "SIFTING" requires several microstructural inputs in order to ealculate a failure probability distribution. We are thus able to assess the physieal soundness of the Burchell model by determining the change in the predicted distribution when microstructural input parameters, such as particle or pore size, are varied in the "SIFTING" code. Each microstructural input parameter... 

Chakarvarti SK, Vetter J (1991) Morphology of etched pores and microstructures fabricated from nuclear track filters. Nucl Instrum Methods B 62 109-115... 

Membrane reactors are known on the macro scale for combining reaction and separation, with additional profits for the whole process as compared with the same separate functions. Microstructured reactors with permeable membranes are used in the same way, e.g. to increase conversion above the equilibrium limit of sole reaction [8, 10, 11, 83]. One way to achieve this is by preparing thin membranes over the pores of a mesh, e.g. by thin-fihn deposition techniques, separating reactant and product streams [11]. 

The situation becomes quite different in heterogeneous systems, such as a fluid filling a porous medium. Restrictions by pore walls and the pore space microstructure become relevant if the root mean squared displacement approaches the pore dimension. The fact that spatial restrictions affect the echo attenuation curves permits one to derive structural information about the pore space [18]. This was demonstrated in the form of diffraction-like patterns in samples with micrometer pores [19]. Moreover, subdiffusive mean squared displacement laws [20], (r2) oc tY with y < 1, can be expected in random percolation clusters in the so-called scaling window,... 

Concrete is a composite material composed of cement paste with interspersed coarse and fine aggregates. Cement paste is a porous material with pore sizes ranging from nanometers to micrometers in size. The large pores are known as capillary pores and the smaller pores are gel pores (i.e., pores within the hydrated cement gel). These pores contain water and within the water are a wide variety of dissolved ions. The most common pore solution ions are OH", K+ and Na+ with minor amounts of S042" and Ca2+. The microstructure of the cement paste is a controlling factor for durable concrete under set environmental exposure conditions. 

Improved characterization of the morphological/microstructural properties of porous solids, and the associated transport properties of fluids imbibed into these materials, is crucial to the development of new porous materials, such as ceramics. Of particular interest is the fabrication of so-called functionalized ceramics, which contain a pore structure tailored to a specific biomedical or industrial application (e.g., molecular filters, catalysts, gas storage cells, drug delivery devices, tissue scaffolds) [1-3]. Functionalization of ceramics can involve the use of graded or layered pore microstructure, morphology or chemical composition. 

Fabrication processing of these materials is highly complex, particularly for materials created to have interfaces in morphology or a microstructure [4—5], for example in co-fired multi-layer ceramics. In addition, there is both a scientific and a practical interest in studying the influence of a particular pore microstructure on the motional behavior of fluids imbibed into these materials [6-9]. This is due to the fact that the actual use of functionalized ceramics in industrial and biomedical applications often involves the movement of one or more fluids through the material. Research in this area is therefore bi-directional one must characterize both how the spatial microstructure (e.g., pore size, surface chemistry, surface area, connectivity) of the material evolves during processing, and how this microstructure affects the motional properties (e.g., molecular diffusion, adsorption coefficients, thermodynamic constants) of fluids contained within it. 

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