pore

The pore ( Greek πόρος póros , medically also porus : "opening", "hole") is a very small opening, cavity or depression. A distinction is made between micro-, meso- and macropores. The associated material property is porosity .

Occurrence

Pores can be found, for example, in biological tissues such as leaves or skin , where they enable the permeability of air , water and dissolved substances in a membrane . They are of great importance in soil science and hydrogeology , where they play a key role in determining the water and air balance. In addition to the degree of cross-linking of the pores , the pore volume is the most important factor of permeability .

Pores also arise in metals during melting and casting processes . Gases dissolved in the melt still escape while the melt solidifies, so the gas bubbles remain trapped and form pores in the material.

Pores are intentionally created in some fabrics to create an insulating or bulky shape. This is how you produce foam , foamed metals ( metal foam ), foam glass , aerated concrete and aerogels .

In the production of baked goods, pores due to biological, chemical or physical loosening (gas formation due to leavening agents ) are very important, since otherwise the baked goods inside would not be baked through in the given time. Without pores, the baked goods remained inedible. So-called "pore tables" are used to assess bread, with which the density, size and uniformity of pores are assessed.

In the kitchen area, when roasting meat, people often speak of “pores” which are supposed to close when seared, but this is factually wrong, since meat, as muscle tissue, does not have pores per se.

Pore ​​density

The ratio of the number  n of pores to the area  A or the number  n of pores to the length  L gives the pore density :

${\displaystyle {\text{Porendichte}}={\frac {n_{\text{Poren}}}{A}}}$

The specification is made in pores per square inch or metric in pores per cm² .

${\displaystyle {\text{Porendichte}}={\frac {n_{\text{Poren}}}{L}}}$

It is used as a unit of measurement z. B. for filter materials in the unit ppi ( pores per inch , pores per linear inch ). The corresponding size in the metric system is the structure linear density, which is given in 1 / mm. Similar to the line intersection method, the boundaries of the pores are counted along a cut.

Web links

Wiktionary: Pore  - explanations of meanings, word origins, synonyms, translations

Wikiquote: Pore  - Quotes

Individual evidence

1. ↑ pore . In: Duden - German Universal Dictionary . 6th edition, Bibliographisches Institut & FA Brockhaus AG, Mannheim 2007, ISBN 978-3-411-05506-7 .
2. ^ Josef Loderbauer: The baker's book in learning fields . Verlag Handwerk und Technik, Hamburg 2008, ISBN 978-3-582-40205-9 .
3. ↑ skyscan.be (PDF)