theoretically Silica is a compound of silicon oxide and water.Moreover, the ratio of its components can be quite varied.Therefore, in general terms, they may be represented by the composition formula.Thus silicic acid with the presence of various amounts of silica and water, that is, with different values of the parameters n and m, can easily switch from one state to another.Thus, n and m in this case can be regarded as variables.Theoretically
silicic acid can be prepared by reacting a silicate of an alkali metal (e.g. sodium) and a "strong" acids (e.g., hydrochloric acid).In this way, in the free state have been isolated (prepared), some of these acids: metasilicic, orthosilicic and others.For example, a chemical reaction producing metasilicic acid:
+ 2HCl = + 2NaCl
However receive pure silicic acid is almost impossible.In aqueous solutions (as they are obtained supersaturated) silicic acid in the polymerisation process ceases the basis of formation of colloidal solutions having a relatively short period of existence.Further, from these solutions by coagulation of a gel is formed.Therein lies the use of silicic acid, since it is drained gel to give the so-called silica, which is used as a desiccant and absorbent.In addition, using special stabilizers of colloids prepared resistant colloids (or sols) which are also used in the production.
Silica is poorly soluble, weak and thermally unstable.When heated, the decomposition of silicic acid, which is expressed by the following chemical reaction:
=
It is also a weaker acid than the same coal.By virtue of this silicic acid in aqueous solutions of carbonic acid is displaced its various salts.As an example, it can be seen in the reaction:
= +
salts of silicic acids are called silicates.They are very common in nature.Thus, in the crust mainly comprises silicas and silicates.These include feldspar, various clays, mica, talc and others.Silicates are included in the composition of rocks - granite, basalt, and others.Silicate crystals are such well-known rocks, which, because of their rarity and beauty considered precious like emeralds, topaz and aquamarine.
Most silicates insoluble in water.The only exceptions are sodium and potassium silicates.They can be obtained by alloying with the corresponding hydroxide or carbonate.For example,
+ = +
Aqueous solutions of the salts obtained in this way are known as "waterglass".It is widely used as a binder in the production of acid-resistant concrete, and in addition, used in the manufacture of all known putty and paper glue.As the flame-retardant and water-resistant impregnating them as products treated fabric, wood and paper.
Silicates, a part of which has aluminum, received naming aluminosilicate.These include mica and feldspar, although their structure is much more complicated.Thus, feldspar, except silicon oxide and aluminum oxide also contains oxides of sodium, potassium, and sodium.In the composition of mica, aluminum and silicon in addition, it has a hydrogen, sodium or potassium, but may be, although less common, also calcium, magnesium or iron.
general use of silicates in the present conditions is very broad and diverse.Mountain silicate rocks are used as building materials.Silicates are used as raw materials in the production of cement, fillers various ceramics, glass, and so forth. Mica and asbestos are used for the production of various thermal and electrical insulating materials.
