Surface pore dimension

Electron microscopy and image processing Mesoporous or macroporous layers Surface pore dimensions and densities (Stevens et al. 2009) (Ludurczak et al. 2009)... 

Correspondence Between Surface Pore Dimensions from AFM and MWCO m... 

Correspondence between surface pore dimensions from AFM and MWCO is good. In addition, AFM gives surface pore size distribution. 

The stmcture of activated carbon is best described as a twisted network of defective carbon layer planes, cross-linked by aHphatic bridging groups (6). X-ray diffraction patterns of activated carbon reveal that it is nongraphitic, remaining amorphous because the randomly cross-linked network inhibits reordering of the stmcture even when heated to 3000°C (7). This property of activated carbon contributes to its most unique feature, namely, the highly developed and accessible internal pore stmcture. The surface area, dimensions, and distribution of the pores depend on the precursor and on the conditions of carbonization and activation. Pore sizes are classified (8) by the International Union of Pure and AppHed Chemistry (lUPAC) as micropores (pore width <2 nm), mesopores (pore width 2—50 nm), and macropores (pore width >50 nm) (see Adsorption). 

On this basis the porosity and surface composition of a number of silicas and zeolites were varied systematically to maximize retention of the isothizolinone structures. For the sake of clarity, data is represented here for only four silicas (Table 1) and three zeolites (Table 2). Silicas 1 and 3 differ in their pore dimensions, these being ca. 20 A and 180 A respectively. Silicas 2 and 4, their counterparts, have been calcined to optimise the number and distribution of isolated silanol sites. Zeolites 1 and 2 are the Na- and H- forms of zeolite-Y respectively. Zeolite 3 is the H-Y zeolite after subjecting to steam calcination, thereby substantially increasing the proportion of Si Al in the structure. The minimum pore dimensions of these materials were around 15 A, selected on the basis that energy-minimized structures obtained by molecular modelling predict the widest dimension of the bulkiest biocide (OIT) to be ca. 13 A, thereby allowing entry to the pore network. 

On the other hand, the surface fractal dimension characterizes the pore surface irregularity the larger the value of surface fractal dimension is, the more irregular and the rougher is the pore surface. Since the pore structure is closely related to the electroactive surface area which plays a key role in the increase of capacity in practical viewpoint, many researchers have investigated the microstructure of the pores by using fractal geometry. 

Besides the molecular probe method using gas adsorption,107 162 recently, the TEM image analysis method163"167 has been applied to evaluate the surface fractal dimension of porous materials. The most attractive fact in this method is that the pores in different size ranges can be extracted from the TEM images which include contributions from many different pore sizes by the inverse fast Fourier transform (FFT) operation by selecting the specific frequency range.165 167... 

Pore dimensions may have a more subtle effect on decay rate depending on component dimensions and production method of the manufactured material. Products made from pasted starch, LDPE, and EAA (2) typically appeared as laminates of starch and plastic when examined by scanning electron microscopy (Figure 1). The dimensions of inter-laminate channels (i.e., pores) were not uniform and ranged from about 50 to 325 m in cross-section (22). Since flux is dependent on diffusional path area, the smaller pores can be an impediment to movement of solutes from the interior to the surface of the films. Figure 5 illustrates two films in which the laminate units are the same thickness, but differ in length. When the starch is removed... 

Consequently ceramics break easily, mainly because they are so brittle. Defects in the material result in cracks when loads are applied. The main defects are porosity, foreign particles which have been incorporated and surface cracks resulting from the surface treatment of the baked product. For example volume percentage and pore dimensions strongly affect the strength of the object (figure 9.30). 

There are two conventional definitions in describing the fractality of porous material - the pore fractal dimension which represents the pore distribution irregularity56,59,62 and the surface fractal dimension which characterizes the pore surface irregularity.56,58,65 Since the geometry and structure of the pore surfaces are closely related to the electro-active surface area which plays a key role in the increases of capacity and rate capability in practical viewpoint, the microstructures of the pores have been quantitatively characterized by many researchers based upon the fractal theory. 

Specimen BET surface area - I l .rr Micro- Meso- Macro- porosity" porosity porosity" Average pore diameter, Dave Standard Pore radius of the deviation of maximum differential PSD, a pore volume, Surface fractal dimension, tfsurf,SP Low-end thickness, High-end thickness, ad. max... 

The surface fractal dimension c/slirf of the porous materials can be determined from the TEM image by using perimeter-area method54154 159. If the scaling property of the porous materials is undoubtedly isotropic, the 3-D pore surface is simply related to the projection of the 3-D pore surface onto the 2-D surface. It is well known154 155 that the area. I and the perimeter P of the self-similar lakes are related to their self-similar fractal dimension c/pss by... 

Figure 7 demonstrates on a logarithmic scale the dependence of perimeter P on area A of the pores obtained from the binary TEM image of CAS30 in Figure 6b. The (log P - log A) plots obtained from the carbon specimen displayed two straight lines with different slopes that can be divided into region I and II, indicating multifractal geometiy of the carbon specimen. The individual surface fractal dimensions in regions I and II were determined from Eqs. (26) and (27) to be 2.08 + 0.018 and 2.72 + 0.046, respectively. The transition area Ab from region I to II were determined to be 108 nm2, which corresponds to the pore diameter of 12 nm based upon spherical pore shape.

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