The silicon oxide It is an inorganic solid formed by the union of a silicon atom and two oxygen. Its chemical formula is SiOtwo. This natural compound is also called silica or silicon dioxide..
The SiOtwo It is the most abundant mineral in the earth's crust, since sand is composed of silica. Depending on its structure, silica can be crystalline or amorphous. It is insoluble in water, but dissolves in alkalis and in hydrofluoric acid HF.
The SiOtwo it is also present in the structure of certain plants, bacteria and fungi. Also in skeletons of marine organisms. Besides sand, there are also other types of stones that are silica.
Silica is widely used, fulfilling a variety of functions. The most widespread use is as a filter material for liquids such as oils and petroleum products, beverages such as beer and wine, as well as fruit juices..
But it has many other applications. One of the most useful and important is in the manufacture of bioactive glasses, which allow to make "scaffolds" where bone cells grow to produce bone pieces missing by accident or disease..
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Silicon dioxide SiOtwo is a molecule of three atoms, in which the silicon atom is attached to two oxygen atoms with covalent bonds.
The structural unit of solid silica as such is a tetrahedron where one silicon atom is surrounded by 4 oxygen atoms.
Tetrahedra bond together by sharing oxygen atoms from their contiguous vertices.
That is why a silicon atom shares each of the 4 oxygen atoms in half and this explains the relationship in the compound of 1 silicon atom to 2 oxygen atoms (SiOtwo).
SiO compoundstwo are divided into two groups: crystalline silica and amorphous silica.
Crystalline silica compounds have repeating pattern structures of silicon and oxygen.
All silica crystal can be considered as a giant molecule where the crystal lattice is very strong. Tetrahedra can be linked in various ways, giving rise to various crystalline forms.
In amorphous silica, the structures are attached at random, without following a defined regular pattern between the molecules and these are in a different spatial relationship with each other..
-Silicon oxide
-Silicon dioxide
-Silica
-Quartz
-Tridymite
-Cristobalita
-Dioxosilane
Colorless to gray solid.
60.084 g / mol
1713 ºC
2230 ºC
2.17-2.32 g / cm3
Insoluble in water. Amorphous silica is soluble in alkalis, especially if it is finely divided. Soluble in hydrofluoric acid HF.
Amorphous silica is less hydrophilic, that is, less related to water than crystalline.
The SiOtwo o Silica is essentially inert to most substances, it is very little reactive.
Resists the attack of chlorine Cltwo, bromine Brtwo, hydrogen Htwo and from most acids at room temperature or slightly higher. It is attacked by fluorine Ftwo, hydrofluoric acid HF and alkalis such as sodium carbonate NatwoCO3.
The SiOtwo It can combine with metallic elements and oxides to form silicates. If silica is fused with alkali metal carbonates at about 1300 ° C, alkali silicates are obtained and CO is released.two.
It is not combustible. Has low thermal conductivity.
The main source of silica in nature is sand.
The SiOtwo or silica is in the form of three crystalline varieties: quartz (the most stable), tridymite and cristobalite. Amorphous forms of silica are agate, jasper, and onyx. Opal is an amorphous hydrated silica.
There is also the so-called biogenic silica, that is, that generated by living organisms. Sources of this type of silica are bacteria, fungi, diatoms, sea sponges and plants.
The shiny, hard parts of bamboo and straw contain silica, and the skeletons of some marine organisms also have a high proportion of silica; however, the most important are diatomaceous earths.
Diatomaceous earths are geological products of decayed single-celled organisms (algae).
In nature there are also the following varieties:
- Vitreous Silicas that are Volcanic Glasses
- The lechaterielites that are natural glasses produced by the fusion of siliceous material under the impact of meteorites
- Fused silica which is silica heated to the liquid phase and cooled without allowing it to crystallize
Silica from sands is obtained directly from quarries.
Diatomite or diatomaceous earth is also obtained in this way, using excavators and similar equipment..
Amorphous silica is prepared from aqueous solutions of alkali metal silicate (such as sodium Na) by neutralization with acid, such as sulfuric acid HtwoSW4, hydrochloric acid HCl or carbon dioxide COtwo.
If the final pH of the solution is neutral or alkaline, precipitated silica is obtained. If the pH is acidic, silica gel is obtained.
Fumed silica is prepared by burning a volatile silicon compound, usually silicon tetrachloride SiCl4. Precipitated silica is obtained from an aqueous solution of silicates to which acid is added.
Colloidal silica is a stable dispersion of colloidal size particles of amorphous silica in an aqueous solution.
Silica or SiOtwo It has a wide variety of functions, for example it serves as an abrasive, absorbent, anti-caking, filler, opacifier and to promote the suspension of other substances, among many other modes of use..
It is used for example:
-In the manufacture of glass, ceramics, refractories, abrasives and water glass
-Discoloration and purification of oils and petroleum products
-In foundry molds
-As an anti-caking agent for powders of all kinds
-As a defoamer
-To filter liquids such as dry cleaning solvents, swimming pool water, and municipal and industrial wastewater
-In the manufacture of heat insulation, fire-retardant bricks, and fire- and acid-resistant packaging materials
-As a filler in the manufacture of paper and cardboard, to make them more resistant
-As a paint filler to improve flow and color
-In materials for polishing metals and wood, as it imparts abrasiveness to them
-In laboratories of chemical analysis in chromatography and as an absorbent
-As an anti-caking agent in insecticidal and agrochemical formulas, to help grind up waxy pesticides, and as a carrier of the active compound
-As a catalyst support
-As a filler to reinforce synthetic rubbers and rubbers
-As a fluid carrier in animal feed
-In printing inks
-As a desiccant and adsorbent, in the form of silica gel
-As an additive in cement
-Like pet litter
-In insulators for microelectronics
-On thermo-optic switches
Amorphous silica is incorporated into a variety of food products as a multifunctional direct ingredient in various types of food. It should not exceed 2% of the finished food.
For example, it serves as an anti-caking agent (to prevent certain foods from sticking), as a stabilizer in beer production, as an anti-precipitant, to filter wine, beer, and fruit or vegetable juices.
It acts as an absorbent for liquids in some foods and a component of microcapsules for flavoring oils.
In addition the SiOtwo Amorphous is applied through a special process on the surface of the plastics of food packaging articles, acting as a barrier.
It is added as an anti-caking, thickening, gelling agent and as an excipient, that is, as an aid to tablet various drugs and vitamins.
It is used in a multitude of products: in face powders, eyeshadows, eyeliners, lipsticks, blushes, makeup removers, powders, foot powders, hair dyes and bleaches.
Also in oils and bath salts, foam baths, hand and body creams, moisturizers, deodorants, face creams or masks (except shaving creams), perfumes, lotions and cleansing creams.
Also in night hydration creams, nail polishes and glitters, skin refreshing lotions, hair toners, toothpaste, hair conditioners, tanning gels and creams.
The SiOtwo It is present in bioactive glasses or bioglasses whose main characteristic is that they can react chemically with the biological environment that surrounds them, forming a strong and lasting bond with living tissue.
This type of material is used to make bone substitutes such as those in the face, as "scaffolds" on which bone cells will grow. They have shown good biocompatibility with both bones and soft tissues.
These bioglasses will make it possible to recover bones from the face of people who have lost them by accident or illness.
Very fine silica particles can become airborne and form non-explosive dusts. But this dust can irritate the skin and eyes. Inhalation causes irritation of the respiratory tract.
In addition, inhalation of silica dust causes long-term progressive damage to the lungs, called silicosis..
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