Aggregates, porous

Fesch, C., W. Simon, S. B. Haderlein, P. Reichert, and R. P. Schwarzenbach, Nonlinear sorption and nonequilibrium solute transport in aggregated porous media Experiments, process identification and modeling , J. Contam. Hydrol., 31, 373-407 (1998). 

Koch, S., and H. Fluhler. 1993. Solute transport in aggregated porous media Comparing model independent and dependent parameter estimation. Water Air Soil Pollut. 68 275-289. 

Lafolie F, Hayot Ch. (1993). One-dimensional solute transport modeling in aggregated porous media. Part 1 Model description and numerical solution. Journal of Hydrology 143 63-83. 

Ortega-Calvo JJ, Fesch C, Harms H. (1999). Biodegradation of sorbed 2,4-dinitrotolnene in a clay-rich, aggregated porous medium. Environmental Science and Technology 33 3737-3742. 

Millington, R. J. and R. C. Shearer. 1971. Diffusion in aggregated porous media. Soil Science 111 372-378. 

Rao, P.S., Rolston, D.E., Jessup, R.E. and Davidson, J.M. Solute transport in aggregated porous media Theoretical and experimental evaluation. Soil Science Society of America Journal 44 1139-1146. 

An interesting example of a large specific surface which is wholly external in nature is provided by a dispersed aerosol composed of fine particles free of cracks and fissures. As soon as the aerosol settles out, of course, its particles come into contact with one another and form aggregates but if the particles are spherical, more particularly if the material is hard, the particle-to-particle contacts will be very small in area the interparticulate junctions will then be so weak that many of them will become broken apart during mechanical handling, or be prized open by the film of adsorbate during an adsorption experiment. In favourable cases the flocculated specimen may have so open a structure that it behaves, as far as its adsorptive properties are concerned, as a completely non-porous material. Solids of this kind are of importance because of their relevance to standard adsorption isotherms (cf. Section 2.12) which play a fundamental role in procedures for the evaluation of specific surface area and pore size distribution by adsorption methods. 

The rather low value obtained with the copper phthalocyanine, a low-energy solid (line (v)), is probably explicable by some reversible capillary condensation in the crevices of the aggregate, the effect of which would be to increase the uptake at a given relative pressure the plausibility of this explanation is supported by the fact that very low values of s, 1-47-1-77, were obtained with certain other phthalocyanines known to be meso-porous (cf. Chapter 3). 

Several types of aggregate-bed filters are available which provide in-depth filtration. Both gravel and particle-bed filters have been developed for removal of dry particulates but have not been used extensively. Filters have also been developed using a porous ceramic or porous metal filter surface. 

Calcium siHcate hydrate is not only variable ia composition, but is very poody crystallised, and is generally referred to as calcium siHcate hydrate gel or tobermorite gel because of the coUoidal sizes (<0.1 fiva) of the gel particles. The calcium siHcate hydrates ate layer minerals having many similarities to the limited swelling clay minerals found ia nature. The layers are bonded together by excess lime and iatedayer water to form iadividual gel particles only 2—3 layers thick. Surface forces, and excess lime on the particle surfaces, tend to bond these particles together iato aggregations or stacks of the iadividual particles to form the porous gel stmcture. 

It may be pointed out here that estimating ke in terms of the thermal conductivity of the solid (k) and its porosity (e) may be quite difficult, particularly when the porous solid is an aggregate of fine particles. 

Concrete is a composite material composed of cement paste with interspersed coarse and fine aggregates. Cement paste is a porous material with pore sizes ranging from nanometers to micrometers in size. The large pores are known as capillary pores and the smaller pores are gel pores (i.e., pores within the hydrated cement gel). These pores contain water and within the water are a wide variety of dissolved ions. The most common pore solution ions are OH", K+ and Na+ with minor amounts of S042" and Ca2+. The microstructure of the cement paste is a controlling factor for durable concrete under set environmental exposure conditions. 

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