Total porosity definition

Absolute porosity, definition, 220 Absolute viscosity, definition, 386 Acid number (total acid number, TAN), definition, 403 Adhesion, definition, 26-27 Adsorbed polymer layers, interaction with droplets, 62 Adsorption definition, 386... 

The total porosity of solids can be estimated by simple pycnometric methods using the differences in surface tension between gases and mercury. By definition, the porosity Pr(%) is given by ... 

In addition to the total porosity, Figure 4 reveals qualitative infonnation about the pore structures in die different films, b the MSQ film widi 1 % by mass porogen, the iqitake saturates at low partial pressures and die adsorption and desorption branches coincide. This is characteristic of the lUPAC definition of micropore filling (pores widths less than 2 nm [9,10]), and consistent with die fectdiat MSQ materials should be inherendymicroporous. 

In resin-coated, impregnated, or laminated nonwoven composites, a small portion of the pores is not accessible (ie, not connected to the fabric surface), and the definition of porosity in above equation gives the so-called total porosity of the fabric. Thus, the open porosity (or effective porosity) is defined as the ratio of accessible pore volume to total fabric volume, which is a part of the total porosity of the fabric. 

The definition above describes the total porosity . Amyx et al. (1960) define total porosity as "... the ratio of the total void space in the rock to the bulk volume of the rock effective porosity is the ratio of the interconnected void space in the rock to the bulk volume of the rock... . 

By definition, light insulating products have a total porosity greater than 45% in volume. Below this value, a refractory is considered to be dense. 

It should be mentioned here that a different definition of the diffusion coefficient is often used in chemical engineering problems, which is more appropriate for the description of reactant or tracer transport. It takes into account the fact that the total fluid contained in a porous substance of porosity e is reduced by this factor relative to the bulk, so that an effective diffusion coefficient D of the reactants is defined such that... 

Pores are found in many solids and the term porosity is often used quite arbitrarily to describe many different properties of such materials. Occasionally, it is used to indicate the mere presence of pores in a material, sometimes as a measure for the size of the pores, and often as a measure for the amount of pores present in a material. The latter is closest to its physical definition. The porosity of a material is defined as the ratio between the pore volume of a particle and its total volume (pore volume + volume of solid) [1]. A certain porosity is a common feature of most heterogeneous catalysts. The pores are either formed by voids between small aggregated particles (textural porosity) or they are intrinsic structural features of the materials (structural porosity). According to the IUPAC notation, porous materials are classified with respect to their sizes into three groups microporous, mesoporous, and macroporous materials [2], Microporous materials have pores with diameters < 2 nm, mesoporous materials have pore diameters between 2 and 50 nm, and macroporous materials have pore diameters > 50 nm. Nowadays, some authors use the term nanoporosity which, however, has no clear definition but is typically used in combination with nanotechnology and nanochemistry for materials with pore sizes in the nanometer range, i.e., 0.1 to 100 nm. Nanoporous could thus mean everything from microporous to macroporous. 

Most solids of high surface area are to some extent porous. The texture of such materials is defined by the detailed geometry of the void and pore space. Porosity, , is a concept related to texture and refers to the pore space in a material. An open pore is a cavity or channel communicating with the surface of a particle, as opposed to a closed pore. Void is the space or interstice between particles. In the context of adsorption and fluid penetration powder porosity is the ratio of the volume of voids plus the volume of open pores to the total volume occupied by the powder. Similarly, particle porosity is the ratio of the volume of open pores to the total volume of the particle. It should be noted that these definitions place the emphasis on the accessibility of pore space to the adsorptive. 

The hygroscopicity of a drug and pharmaceutical substances is a potential parameter to be considered in tablet formulation. The moisture uptake rate is quite variable depending on the type of drug and excipients as well as the environmental conditions. So, a concise definition of hygroscopicity is not possible. Powders can absorb moisture by both capillary imbibition and swelling. The instantaneous water absorption prosperties of pharmaceutical excipients correlate with total surface area while the total absorption capacity correlates with powder porosity [22],... 

Porosity or voidage of a packed bed of powder is defined as the volume of the voids within the bed (i.e. the volume occupied by air) divided by the total (overall) volume of the bed. The void volume includes the pores within the particles if they are porous. The pores in the particles can, however, be excluded from the definition, particularly if the application is in fluidized beds or flow through packed beds because the pores in the particles are in those cases not available to the flow. 

Areal Porosity and Tortuosity. Areal porosity or areosity, Ap, is defined as the effective areal ratio of the open pore cross-section to the bulk space. A more strict definition of areosity was introduced by Ruth and Suman (56). However, the areosity as defined by them is not a property of the porous medium only but a property of both the porous medium and the transport strength of the fluid such as the flow strength and electric current strength. The areal porosity is undoubtedly a very useful quantity for a bundled or ensemble passage model because it represents the ratio of the total passage cross-sectional area to the total cross-sectional area of the porous medium at a given planar section. 

The areal porosity has been invariably considered to be equivalent to the porosity, e, of the medium (I, 31, 33). This is by and large due to the success and popularity of the straight bundle passage models and nonconnecting constricted passage models, in which the ratio of the total open pore area to the total cross-sectional area for the direction under consideration has to be equivalent to the (volume) porosity of the porous medium. However, as it is expected from the difference in the definitions, it is no surprise that Dullien and Mahta (57) found their measured (areal) porosity is significantly different from the measured (volume) porosity with a different technique for the same porous medium sample. 

We arrived at this definition after discovering that other techniques, such as calculating pore size distributions from the BJH method via nitrogen isotherms, do not account for a large portion of the total pore volumes within these types of materials. The amorphous structures seen in SEM images indicate a porosity that is difficult to describe mathematically, whereas the field of microscopy has given us tools that are readily available, which help us to quantify these structures. 

This definition, it should be noted, is somewhat in conflict with the definition of nanoscale objects, which typically have large relative porosities (> 0.4), and pore diameters between 1 and 100 nm. In order to classify porous materials according to the size of their pores the sorption analysis is one of the tools often used. This tool is based on the fact that pores of different sizes lead to totally different characteristics in sorption isotherms. The correlation between the vapor pressure and the pore size can be written as the Kelvin equation ... 

To avoid having to saturate with water or air, one can calculate porosity from measurements of particle density and bulk density. From the definitions of bulk density as the solid mass per total volirme of soil and particle... 

As this book is dominantly concerned with porosity in carbons, current definitions of the terminology of the subject area are given in Table 2.3. Later chapters expand fully on these definitions. The literature is not totally consistent with defiiutions and terminology, and it is unlikely that consistency will happen in the immediate future. 

Different definitions of concentration can be used to characterize the quantity of particles within a fluid. These different definitions are all related to the porosity s, defined as the ratio of the fluid volume to the total volume. They include ... 

Considering the contributions of open and closed pores to the total sample volume, two types of density of a porous sample specimen can be defined. The bulk density, /Obuik, takes contributions both from open and closed pores into account. The apparent density, Papp, considers only the contribution of closed porosity. The definitions of these densities are ... 

The pore volume used in calculating M , in equation 17 includes the entire pore space in the slab. For equation 13 to be valid for porous slabs with inaccessible porosity, the definition of M, can be modified by substituting a new value for the slab porosity. The fraction of total pores which are accessible to the external environment is denoted < )a and is defined ... 

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