Internal area

Considering existing microscopical techniques, one can find that non-destmctive information from the internal stmcture of an object in natural conditions can be obtained by transmission X-ray microscopy. Combination of X-ray transmission technique with tomographical reconstmction allows getting three-dimensional information about the internal microstmcture [1-3]. In this case any internal area can be reconstmcted as a set of flat cross sections which can be used to analyze the two- and three-dimensional morphological parameters [4]. For X-ray methods the contrast in the images is a mixed combination of density and compositional information. In some cases the compositional information can be separated from the density information [5]. Recently there has been a... 

The detailed consideration of these equations is due largely to Kozeny [50] the reader is also referred to Collins [51]. However, it is apparent that, subject to assumptions concerning the topology of the porous system, the determination of K provides an estimate of Ao- It should be remembered that Ao will be the external area of the particles and will not include internal area due to pores (note Ref. 52). Somewhat similar equations apply in the case of gas flow the reader is referred to Barrer [53] and Kraus and co-workers [54]. 

Physical properties affecting catalyst perfoniiance include tlie surface area, pore volume and pore size distribution (section B1.26). These properties regulate tlie tradeoff between tlie rate of tlie catalytic reaction on tlie internal surface and tlie rate of transport (e.g., by diffusion) of tlie reactant molecules into tlie pores and tlie product molecules out of tlie pores tlie higher tlie internal area of tlie catalytic material per unit volume, tlie higher the rate of tlie reaction... 

Another standard industry method for surface area is based on the adsorption of cetyltrimethylammonium bromide (CTAB) from aqueous solution. This is ASTM method D3765-85 (2). This method measures the specific surface area of carbon black exclusive of the internal area contained in micropores that are too small to admit the large CTAB molecules. Eor mbber-grade nonporous blacks the CTAB method gives excellent agreement with nitrogen surface areas. 

Reactants must diffuse through the network of pores of a catalyst particle to reach the internal area, and the products must diffuse back. The optimum porosity of a catalyst particle is deterrnined by tradeoffs making the pores smaller increases the surface area and thereby increases the activity of the catalyst, but this gain is offset by the increased resistance to transport in the smaller pores increasing the pore volume to create larger pores for faster transport is compensated by a loss of physical strength. A simple quantitative development (46—48) follows for a first-order, isothermal, irreversible catalytic reaction in a spherical, porous catalyst particle. 

From surface area to volume ratio considerations, the internal area is practically all in the small pores. One gram of the adsorbent occupies 2 cm as packed and has 0.4 cnP in small pores, which gives a surface area of 1150 m /g( or about 1 mi per 5 lb or 6.3 miVft of packing). Based on the area of the annular region filled with adsorbate, the solute occupies 22.5 percent of the internal pore volume and 13.5 percent of the total packed-bed volume. 

Note all the above definitions relate only to external surfaees internal area, due to porosity, requires further definition. 

Tube OD In. B.W.G. Gauge Thickness In. Internal Area ln.2 Ff2 External Surface Per Ft Length Ft= Internal Surface Per Ft Length... 

Flow through the plates must be laminar, and the critical internal areas are [25,54,61] ... 

Pipe Diam- ness Diameter (In Inches) Internal Area ... 

Nominal Pipe Size Inches Outside Diam- eter Inches Thick- ness Inches Inside Diameter Inside Diameter Funct (In Inches) ions Transverse Internal Area ... 

In many cases, it is necessary to complement physical security by the installation of an intruder alarm system in order to achieve the standard of security commensurate to the risk exposure. The scope of protection to be afforded by the alarm system depends on the security risk, but it may embrace fences, windows, doors, roofs, walls, internal areas, yards and external open areas, and vehicles inside and outside buildings. There is a comprehensive range of detection devices, but the choice of detector is critical to ensure that it provides the desired level of protection and is stable in the particular environment. 

Molds, dies, and other forming tools for metal and plastic processing, especially those involving irregular surfaces and internal areas. 

Another disadvantage of fixed bed reactors is associated with the fact that the minimum pellet size that can be used is restricted by the permissible pressure drop through the bed. Thus if the reaction is potentially subject to diflfusional limitations within the catalyst pore structure, it may not be possible to fully utilize all the catalyst area (see Section 12.3). The smaller the pellet, the more efficiently the internal area is used, but the greater the pressure drop. 

In general, dendrimers of size G-0 through G-3 have open, asymmetric, and flexible structures with effectively no protected internal areas, due to a large freedom of motion in their branches, and they can readily accommodate additional covalent attachments to their surfaces. See Figures 73-7.5 for illustrations of the two-dimension and three-dimension structure of a... 

Internal areas of cast iron and carbon steel bearing housings and oil system components shall be coated with a suitable oil soluble rust preventive. 

The small, spherical particles of ferrihydrite often pack together to form aggregates >0.1 pm across. The aggregated structure and interparticle porosity create difficulties in measurement of surface area because the internal area is not fully accessible to all measurement techniques. It is rare for more than two methods of area measurement to have been applied to the same sample. Pyman and Posner (1978) obtained an area of 250 m g" using both N2 and water BET measurements. With the EG ME method, however, the same sample had an area of 600 m g". These... 

If peUets are packed in a cubic configuration, then there are (2.5 x 10 ) catalyst peUets per liter. The external area of packed spheres in 1 liter is 8 x 10 m. The internal area of these porous pellets is 1.6 x 10 — 1.6 x lO km for 1 liter... 

Porous silicon is under extensive study, largely due to its luminescence properties. For electroluminescence, however, some form of contact has to be made with the Si, and this necessitates deposition of another phase inside the pores of the Si in order to contact as much as possible of the internal area of the high-surface-area Si. With this in mind, CdS has been deposited inside the pores of porous silicon via a two-stage method [73]. Cd(OH)2 was deposited from an ammoniacal bath at pH 8, followed by conversion of the Cd(OH)2 to CdS by treatment with thioac-etamide at pH 8. This was repeated several times until the pores were essentially filled with CdS. The reason that this two-stage process was needed is that either the Si was unstable at the temperatures and pH values needed to deposit CdS from a thiourea solution, or CdS was formed in solution rather than on the Si surface using thioacetamide. 

In the case of a porous catalyst, where the internal area contributes the most to the total area, Ss can be considered to be independent from the catalyst shape and size. Furthermore, the number of catalytic active sites per unit area can be considered a fixed property for a given catalyst. Consequently, the active sites concentration can (n/Ms) be also be... 

Two kinds of wetting must be defined for porous catalysts— internal wetting, which is the amount of internal area wetted by the liquid, and external wetting, which is the amount of the... 

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