Silica sol

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Silica sol is an aqueous colloidal suspension of almost spherical polysilicic acid molecules with 30% to a maximum of 60% silicon dioxide . The word is made up of silica for silicic acids and sol , a synonym for colloid . According to Römpp Lexikon Chemie , it can be stored unchanged for years, according to Holleman-Wiberg , the silica spheres are linked via oxygen bridges to form an amorphous silica ( silica gel ).

Manufacturing process flowchart

Silica sol can be obtained by ion exchange from water glass , by hydrolysis and condensation from silicon, by direct oxidation of silicon or by grinding and peptization of silicon dioxide (mostly fumed silica ). Silica sol obtained from water glass is mixed with a small amount of alkalis , e.g. B. with sodium hydroxide (molar ratio SiO 2 : NaOH approx. 100: 2).

The silicon dioxide is in the form of non-crosslinked, spherical individual particles which are hydroxylated on the surface. The size of the particles is in the colloidal range and, depending on the type, is 5 nm to 75 nm.

It was approved in the middle of the 20th century as a substitute for tannins for the beauty of wine. In oenology it is mainly used to correct tannins and to remove other fining agents such as bentonite , activated charcoal or copper sulphate after their reaction, usually in combination with gelatine or other proteins ( egg white , isinglass and casein ). Covering with gelatine can also be corrected by adding silica sol, as this causes excess gelatine to precipitate . Silica sol is able to bind slimy substances that have a cloud stabilizing effect in the wine . This bond occurs through ion exchange between the silica sol and the mucilage.

Individual evidence

  1. a b Entry on silica sol. In: Römpp Online . Georg Thieme Verlag, accessed on May 27, 2014.
  2. ^ AF Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 102nd edition. Walter de Gruyter, Berlin 2007, ISBN 978-3-11-017770-1 , p. 960.
  3. H. Lim, J. Lee, J. Jeong, S. Oh and S. Lee: Comparative Study of Various Preparation Methods of Colloidal Silica . In: Scientific Research Publishing (Ed.): Engineering . tape 2 , no. 12 , 2010, p. 998-1005 , doi : 10.4236 / eng.2010.212126 .
  4. Otto-Albrecht Neumüller (Ed.): Römpps Chemie-Lexikon. Volume 3: H-L. 8th revised and expanded edition. Franckh'sche Verlagshandlung, Stuttgart 1983, ISBN 3-440-04513-7 , p. 2109.

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