Internal pore volume

Scouting and bleaching slightly increase the accessible internal volume, Hquid ammonia treatment of the scoured—bleached cotton decreases it slightly, caustic mercerization substantially enhances accessibiHty, and cross-linking to impart durable press properties reduces this accessible internal pore volume substantially. 

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. 

The separation of a solute of a given size in solution is determined by a distribution coefficient, Ksec, which governs the fraction of internal pore volume of the gel, Vu that is accessible to this solute. The value of the retention volume, Vr, for this solute is given by... 

A comparison of the micropore volume of the coked catalyst samples, shown in Table II, clearly illustrates that the coked-stabilized catalyst sample possesses 70% of internal pore volume, which is almost free of coke and is accessible to nitrogen. On the other hand, the coked-unstabilized catalyst sample showed large reduction of micropore. This indicates a virtual blocking of the internal pores in the coked sample... 

Most surface area determinations are based on measurements of the low temperature adsorption of nitrogen or krypton on the solid and use of the BET theory. This procedure may not give reliable results because the products are chilled well below reaction temperature, possibly resulting in the sealing of internal pores. Volumes of gases adsorbed are sometimes small, as observed for dehydrated alums [37] and decomposed ammonium perchlorate [48], where the areas are consistent with product crystallites of linear dimensions between 1 and 3 pm. The results indicate, however, that little, if any, zeolitic material is formed [36]. The surface area of a solid may also be estimated from electron micrographs. Density measurements may be used to complement area measurements. 

The apparent particle density, pp, is the ratio of the particle weight to the particle volume, or sum of the imaccessible volumes and the internal pore volume. This is the most practical definition. However, it carmot be as accurate as densities usually are because of the difficulty associated with defining accurately the external column porosity (see previous subsection),... 

As described, solid metal ammine complexes can be prepared as very dense materials without any significant internal pore volume, because the porosity needed for ammonia transport is generated as the ammonia release progresses. This allows for ammonia release over large material length scales. Still, the mass transport facilitated by the in situ generated pore structure has to be combined with an understanding of heat transfer resistance, since the ammonia desorption from a metal ammine complex is endothermic. 

The bulk density is not an intrinsic property of coal and varies depending on how the coal is handled. Bulk density is the mass of many particles of coal divided by the total volume occupied by the particles—the total volume includes particle volume, interparticle void volume, and internal pore volume. This allows the density of coal to be expressed in terms of the cubic foot weight of crushed coal (ASTM, 2011c), which varies with particle size of the coal and packing in a container (Table 9.4). In addition, the bulk density of coal varies with rank ... 

Fundamentally, V, is the sum of the void volume occupied by all solutes, a portion of the internal pore volume defined by the size exclusion differential equilibrium constant and a portion of the surface of the column packing defined by the distribution coefficient describing interactions between the column and solute K. This condition leads to the general equation... 

In an article exposing their results [12], they were the first to use the Martin and Synge theoretical derivation to estabhsh the equation relating the solute retention to its micellar partition coefficient. Although their Sephadex G-25 column presented a strong adsorption for some solutes, they were able to obtain straight lines plotting the Vi/(Ve-Vo) parameter versus the SDS surfactant concentration, the subscripts i, e and o refer to the internal (pore) volume of the GPC gel, the solute elution volume and the external (exclusion) volume, respectively. The slope and intercept of the lines allowed them to determine accurately the micellar partition coefficient of the seven compounds studied [12]. They were not interested in the separation ability of the technique and did not go further in this direction. 

The ratio VqA/ c is the total porosity of the column. It is a dimensionless number that should be somewhere between 0.7 and 1. If the ratio is found to be higher than unity, it means the dead volume is overestimated the solute used was retained. If the Vq/Vc ratio is found to be lower than 0.7, the dead volume is too small. The test solute was probably excluded from the internal pore volume of the stationary phase. A practical rule of thumb for the 4.6 mm i.d. column only is [7] ... 

When considering the possible modes of solute retention in SEC it is important to first define the compartmentalization of volumes found within the size exclusion column. The total geometrical volume of the column, Vg, is defined as the sum of the total mobile phase volume, V, and the volume of the packing material or stationary phase, V. The mobile phase volume is further defined as the sum of the volume external to the beads constituting the packing material or the void volume, Vq, and the volume of the channels within the beads, V. The differential solute distribution between the spaces internal to and external to the pores in the column packing material results in the separation of the solutes on the basis of molecular size. In the absence of reversible adsorption, the average elution volume, Vg, is the sum of the void volume occupied by all solutes and a portion of the internal pore-volume defined by the size exclusion equilibrium constant, [Note that this... 

Soft drying under mild temperature conditions leads to homogeneous impregnation and catalyst deposition over the entire internal pore volume of the carrier. 

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