pores


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pores

See sunspots.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Pores

 

interstices or capillaries between the structural elements of a solid. Open pore canals, which permeate the entire volume of a porous body, are differentiated from closed pore cells. The first are characteristic of adsorbents, catalysts, and various filtering materials; the second are prevalent in such substances as foam materials and volcanic glass.

According to the classification system developed by M. M. Dubinin, pores are classed by size into micropores (mean effective radius r < 15–16 Å), intermediate poreso (16–20 < r < 2,000 À), and macropores (from r > 2,000 Á to a pore size visible to the naked eye). There are two types of micropores: fine (r > 6–7 A), as in zeolites and activated carbon, and large (6–7 < r < 15–16 Å), as in certain silica gels. Each pore class has its own principles of adsorption and of other physical phenomena. Micropores correspond to the sizes of molecules or atoms in a solid and do not disturb its homogeneity. For example, the absorption of gases or liquids by microporous sorbents involves permeating the pores of these sorbents; in many way such absorption is similar to diffusion.

Macropores and intermediate pores, found in typically heterogenous materials, substantially exceed molecular size. In polymers, they exceed the size of monomer units in the macromolecule. A reduction in pressure causes a viscous, mass flow of liquids and gases in connecting macropores, whereas only diffusion is possible in micropores.

The aggregate of the size and number of pores in a body, that is, the total space occupied by pores, is termed porosity. Porosity is expressed by the volume of pores per unit volume or mass of the porous body, as well as by the body’s specific surface. Controlled and natural porous substances are widely used in technology. The porosity of rocks and soils determines the intensity and nature of many processes associated with heat and mass exchange in the earth’s crust and on the earth’s surface.

REFERENCES

Gregg, S., and K. Sing. Adsorbtsiia, udel’naia poverkhnost’ poristost’, Moscow, 1970. (Translated from English.)
Dubinin, M. M. “Porous Structure and Adsorption Properties of Active Carbons.” In Chemistry and Physics of Carbon, vol. 2. New York, 1966. Page 51.

L. A. SHITS

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
Based on NMR principles, the transverse relaxation time ([T.sub.2]) is a function of the surface to volume ratio of pores (S/V) which can be expressed by (1) [44, 58], in which [[rho].sub.2] is a constant representing the transverse relaxation strength [38] (or the transverse surface relaxivity [58]).
(2) The low-temperature nitrogen adsorption test found that the typical low-permeability coal seam in the coalfield of South Junger Basin in Xinjiang belongs to the mesoporous medium, which is mainly mesoporous, with a certain amount of large pores, no micropores, and a more complex pore distribution.
(4) Pore porosity reflects the integrity of CPB pores and is the ratio of the pore region to the total image area.
Figure 5 shows the relation between the cooling speed, lamellar spacing, and spherical pore spacing of the two kinds of ceramic pores.
have explored the role of pore surface passivants on the electronic properties of porous SiC systems [14,15].
Curtis, "Imaging pores in sedimentary rocks: Foundation of porosity prediction," Marine and Petroleum Geology, vol.
Caption: A shark's snout contains tiny pores, known as ampullae of Lorenzini, that can sense weak electric fields from prey.
With age, degradation of natural skin proteins results in enlarged skin pores with loss in skin texture.
Sasha Kravchenko, a soil scientist and professor at Michigan State University, studies soils and their pores in different agricultural systems.
In the head region these fishes have similar body neuromasts arranged in a recognized pattern of linear rows, which constitute the cephalic sensorial pores (McDowall, 1970).