Perlite (rock)

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Perlite (volcanic glass) with a white, powdery appearance

Perlite (English: perlite ) refers to an altered (chemically and physically converted) volcanic glass ( obsidian ) in the geosciences and is therefore one of the rocks . It is used as a raw material for many purposes, for example in the construction industry.

Natural occurrence

During the transformation, the hard obsidian is broken down through small cracks into pea-sized glass spheres or shards and then shows the typical pearlitic structure . When water enters along the cracks, devitrification begins , and microscopic crystals of quartz , cristobalite and feldspar are formed from the amorphous glass . In the advanced stage of the transformation, loose rock with a bluish-green, brownish or gray color develops.

Properties and use

Perlite contains 2 to 5 percent water of crystallization and has a density of around 900 to 1,000 kg / m³ (bulk density of the raw perlite). By annealing to approx. 800 ° C to 1,000 ° C, perlite expands to fifteen to twenty times its original volume and then has a bulk density of 50 to 100 kg / m³ and a thermal conductivity of λ = 0.040 to 0.070 W / (m K ).

Perlite, raw or expanded, is used, among other things, in the form of silicone-impregnated beads with a diameter of about five millimeters for thermal insulation, for example as a fill in residential construction, mainly in ceilings or floors and as core insulation . It also serves as fire protection. Expanded perlite is used to a not inconsiderable extent as a filler and aggregate in the building materials industry for the manufacture of paints, varnishes, plasters and dry mortar.

In the production of beverages, expanded perlite is used as a filter aid.

In shipping, perlite is used in the construction of liquid gas tankers for tank insulation. If the perlite is impregnated with silicone, the absorption of water is largely prevented. Perlite in the expanded state can be impregnated with silicone and filled into fabric hoses and used on bodies of water to bind oil that has escaped in the event of an accident.

Perlite is used as an insulating material in refrigeration technology . An example of this is the filling of cold chambers in air separation plants.

In horticulture , it is used as a sterile seed substrate or as an additive for potting soil , which protects against excessive compaction and thus improves air permeability.

Perlite is used as a slag binder in steel production.

A relatively new application of perlite is in the manufacture of anti-perspirant sprays.

It is also used in special toothpastes to remove deposits and discoloration.

Individual evidence

  1. ^ Walter Maresch, Olaf Medenbach: Rocks. New, edited special edition. Mosaik-Verlag, Munich 1987, ISBN 3-576-10699-5 , p. 90.
  2. Knauf Perlite - Physical properties of perlite in its raw and expanded state
  3. Perlite - an overview | ScienceDirect Topics. Retrieved October 4, 2019 .
  4. Entry on perlite in Pharmawiki , accessed on January 28, 2017.

Web links

Commons : Perlite  - collection of images, videos and audio files