Inner surface

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The inner surface of porous or granular solids is a dimensional parameter that is used in various scientific and technical disciplines. It encompasses all of the surfaces it contains , including those that are between grains and within pores. The actual measured variable of the inner surface is the specific surface .

In contrast to this, the outer surface is the surface that can be seen directly from the outside, i.e. that which would be obtained when the material system was packaged.


All porous ( sponge or foam-like ) materials as well as heaps (such as powder and debris ) are pervaded by numerous cavities. Since all chemical reactions essentially depend on how large their area of ​​attack is compared to the volume, the inner surface is of great importance. For example, fine iron filings are highly flammable ( pyrophoric ), while larger pieces of iron are not. The weathering stability of a rock is also largely determined by its size and the number of cracks. There are similar effects with numerous purely physical phenomena, such as capillary action and moisture storage , thermal insulation , light reflection and others.

Technical adsorbents, for example, are often highly porous solids with a heavily fissured inner surface. They have internal surfaces that can be more than a thousand m 2 per gram.

specific surface

The specific surface area (of English. Surface ) is a surface measurement determined.

Mass related

The mass -related specific surface

indicates which surface (in m 2 ) a kilogram of a material has ( unit ).

Volume related

The volume -related specific surface

indicates the surface area A (in m 2 ) of a cubic meter of a material (unit ).

The smallest specific surface (for a given volume) has the sphere:

See also


  • Matthias Stieß: Mechanical Process Engineering 1 , Springer Verlag, Heidelberg 1995, ISBN 3540594132 .

Web links

Individual evidence

  1. VDI 3674: 2013-04 Exhaust gas cleaning through adsorption; Process gas and waste gas cleaning (Waste gas cleaning by adsorption; Process gas and waste gas cleaning). Beuth Verlag, Berlin, p. 7.
  2. Hans Wirth: Properties and selection criteria for adsorbents. In: Dust - cleanliness. Luft , 36, No. 7, 1976, pp. 288-292.