What is silica



As Silicas the oxygen acids of silicon (SiO2 · N H2O). In German it has become common to refer to all possible forms of synthetic silicon dioxide generally as silicic acid.

Orthosilicic acid Si (OH)4 / H4SiO4 is a very weak acid. It is created by the decomposition of silicon tetrahalides with water. Further elimination of water lead to Orthodosilicic acid H6Si2O7 and to Metasilicic acid (H2SiO3). If the last of the water is removed, the silica anhydride SiO is formed2.

In nature, support structures made of silicic acid anhydride occur in plant and animal life, for example in the diatoms that are widespread in the sea (Diatoms) and radiation animals (Radiolarians) and glass sponges (Hexactinellida) as well as horsetail. The silicic acid anhydride skeletons of dead diatoms and radiolucent animals sink to the sea floor, accumulate there and form deposits of kieselguhr (diatomaceous earth) or radiolarian sludge. Deposits from the Miocene contain 70–90% SiO2, 3–12% water and traces of metal oxides.

Silicic acid is also found in groundwater. The rainwater or seepage water that runs down through the soil layers and contains carbonic acid absorbs silica from the silicates of the soil minerals. Therefore, drinking water also contains small amounts of silica. As a food additive, silicic acid anhydride has the designation E 551.

As Silica gel This is the name given to a colloidal silica with an elastic to solid consistency, usually in powder form. She is z. B. used as a drying agent for liquid media.

Silica

About 94 percent silica is made up of silica. Other components are small amounts of iron, calcium, magnesium, phosphorus and aluminum. Silica is produced from sedimented diatom shells (kieselguhr) (broken down, cleaned and ground).

Industrial use

Silica anhydride products, so-called silica gels, precipitated silicas and pyrogenic silicas, are industrially manufactured on an industrial scale.

Silica gels and precipitated silicas are obtained by reacting water glass with sulfuric acid in an acidic or basic medium:

Fumed silicas are produced by the reaction of silicon tetrachloride with water, which is formed in a hydrogen flame, whereby hydrogen chloride gas escapes:


Manufacturer (selection):

  • Degussa AG: Precipitated Silicas (SIPERNAT®, ULTRASIL® and SIDENT®) and fumed silica (AEROSIL®, AERODISP®, AEROXIDS®, as AEROPERL®). Silica is also the base material from which this company's matting agents are made. They are under the brand name ACEMATT® expelled.
  • Wacker Chemie AG: Pyrogenic Silicas HDK®.
  • Du Pont: Precipitated silicas with the brand names LoVel (matting agent) and HiSil (technical fillers, e.g. tires).

Other manufacturers of silica gel and silica:

  • Grace, brand: Syloid
  • Fuji, brand: Sylysia
  • Chemiewerk Bad Köstritz, brand: Köstrosorb
  • Ineos, brands: Gasil, NeoSyl
  • Cabot, brand: Cab-O-Sil
  • Tokuyama, brands: Reolosil, Finesil

Applications of fumed silica

Pyrogenic silicas are used for B .:

  • In plastics and adhesives for thickening / thixotropy, as an anti-settling agent, for reinforcement and antiblocking.
  • Also in paints and varnishes as corrosion protection and to improve scratch resistance.
  • In printing inks to improve printing sharpness and for pigment dispersion.
  • In pharmacy and cosmetics as a consistency regulator, flow regulator and to improve the release behavior of tablets and capsules.
  • Powder made from fumed silica (also: fumed silica) is used as a support core in the production of evacuated insulation materials (VIP = vacuum insulation panels or VIS = vacuum insulation sandwich elements). The highly porous material achieves low thermal conductivity values ​​even with relatively low demands on the applied vacuum (approximately below 10 mbar).
  • Defoamer additive.

Applications of precipitated silicas

Typical applications for precipitated silicas are e.g. B .:

  • Foils for battery separators.
  • Additives to tires, shoe soles and other rubber items (e.g. also cell phone keyboards) to increase abrasion resistance and to improve wet slip behavior and rolling resistance.
  • Additives that improve the flow behavior of feed, soup and beverage powders or other substances that should not be caked (for example the powder in fire extinguishers).
  • Coatings for inkjet papers that allow quick drying and better print quality.
  • Defoamers in detergents.
  • Protein adsorbers in beer production.
  • Matting agent for lacquers, especially clear lacquers in wood and automotive interiors
  • Addition to liquids to improve filtration properties (filter aid, precoat filtration)

nutrition

Silicon is involved in the formation of skin, hair and connective tissue.

Occurrence: Whole grain cereals (e.g. oats, barley, millet, wheat), potatoes, also high-fiber vegetables and fruits as well as in the sprouts of bamboo.

Silica is traditionally offered as a dietary supplement. The commercially available products consist of 80-90% silicon dioxide. Their nutritional-physiological effect has recently been very questioned. There is even a suspicion that ingesting the powder directly can lead to esophageal cancer.

Investigation of silica products Plusminus and NDR Info commissioned an institute for mineralogy at a university in Northern Germany and the Federal Institute for Materials Research to examine ten silica products. The result of both institutes was clear: nine of the ten compounds contained - comparable to normal sand - mainly quartz or cristobalite. Both substances are crystalline forms of silicon dioxide. Finely ground, crystalline silicon dioxide is even considered a "hazardous substance" in other industrial sectors. For example, if quartz dust is inhaled, it can lead to lung tumors. According to the findings of the Fraunhofer Institute for Toxicology in Hanover, a health risk cannot be ruled out if quartz dust is swallowed.

Some consumers are convinced that silica is helpful for the regeneration of skin, hair, nails, teeth, bones and (connective) tissue and therefore also has a (long-term) cosmetic effect. However, so far there is no scientific proof of this.
The amount of silicon dioxide the body needs should normally be covered by a normal diet. Overdosing could possibly promote the formation of kidney stones. However, the scientific evidence for this has not yet been provided either.

Matting agents

Precipitated silicas, silica gel silicas and a pyrogenic silicic acid are used as matting agents in paints. The matting effect consists in the formation of a microstructure during the drying of the paint. The rays of light are scattered in all directions on the resulting mountains and valleys. It can be seen from this that the matting effect depends on the extent to which the paint film shrinks due to solvent evaporation and on the particle size (more precisely on the agglomerate size). The porosity of the silicas also has a certain influence.

See also

  • For nutrition:
    • An overview of several nutritional studies
    • A somewhat cautious study, (Eng.)
    • A slightly euphoric study, (Eng.)
    • Basic research, e.g .:
      • Response surface analysis of rat bone composition changes by dietary calcium and silicon. Shelly McCrady, University of Wisconsin Stout, 2003 (Pdf 2.4 Mb)

Categories: Silicon Compound | Mineral acid | Pharmaceutical excipient