Silica weight fraction, effect

FIGURE 3.15 Adsorption data from Cohen Stuart et al. (1980) for polyvinyl pyrrolidone in water on silica. The effect of polydispersivity is also shown. The weight fraction of component 2 in the mixture is 0.25, M = 1440 for component 1 and 10 for component 2. Reprinted with permission from John Wiley Sons. 

Salamone and Newman (SI) recently studied heat transfer to suspensions of copper, carbon, silica, and chalk in water over the concentration range of 2.75 to 11.0% solids by weight. These authors calculated effective thermal conductivities from the heat transfer data and reached conclusions which not only contradicted Eqs. (35) and (36), but also indicated a large effect of particle size. However, if one compares the conductivities of their suspensions at a constant volume fraction of solids, the assumed importance of particle size is no longer present. It should also be noted that their calculational procedure was a difficult one in that it placed all undefined errors present in the heat transfer data into the thermal conductivity term. For example, six of the seven-... 

The fractionation achieved on the porous silica substrate actually separates according to molecular size and not according to molecular weight. In fact, BBB cannot be considered as a homopolymer in this kind of separation, but must act as a hexapolymer comprised of the six repeat units illustrated schematically in Figure 9. In this case, o/M varies among the fractions not because of an inherent variation of 0/M with M, but because the distribution of the repeat units is not the same for all fractions. In addition, and perhaps even more important, structural imperfections in the repeat units would greatly enhance this effect. 

The results of the studies on the effect of silica particle size on sorption indicate that, in the range of silica diameter of 1.4 X 10 2 to 3.9 X 10 2 cm, there is very little difference in the final amount of plutonium sorbed, as shown in Table III, the total weight of silica being the same for each size fraction. The only differences lie in the surface density of the sorbed species and the rate at which the equilibrium was approached. As the surface area decreased (i.e., as the silica size increased), there was more plutonium deposited per unit area of surface. Also, the smaller size particles with the higher surface areas sorbed the plutonium at a faster rate. These results are difficult to interpret, except with the model of a limited number of sorbable species, all of which are taken up eventually by the silica. They would not, however, be consistent with the model of a limited number of sorbing sites. 

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