Silicon(IV) oxide or silica occurs naturally in three main crystalline forms. These crystalline forms are quartz, crystobalite and tridymite. However, the commonest of these forms are quartz. Silicon(IV) oxide can be prepared by heating silicon in air. It can be obtained in a hydrated form such as a gelatinous precipitate, by heating or warming sodium trioxosilicate(IV) with concentrated hydrochloric acid.
The Physical properties of Silicon(IV) oxide are as follows:
- Silicon(IV)oxide exists as colorless crystalline solid in its pure state.
- Silicon(IV)oxide is a macromolecular compound that has the oxygen and silicon atoms linked together covalently in what is known as tetrahedral basic units. In crystobalite, these basic units are arranges just like the way the units in diamond are arranged while in quartz and tridynamite they are arranged in a spiral form around an axis. Silicon(IV)oxide is non volatile which is due largely due to its structure. It is also hard unlike its analogous oxide, carbon(IV)oxide, which is a gas at room temperature.
- Silicon(IV)oxide melts at about 1500ºC.When cooled it forms a glass-like solid referred to as fused silica(quartz glass) which has a very low coefficient of expansion that makes it very heat resistant. Furthermore, fused silica is acid-resistant and is often used in making laboratory apparatus.
The Chemical Properties of Silicon(IV) oxide are as follows:
- Silicon(IV) oxide is insoluble in water and also in all acids except hydrogen hexafluorosilicates(IV)
- Silicon(IV) oxide as an acid oxide dissolves in hot concentrated potassium or sodium hydroxide solution to form the corresponding trioxosilicates(IV) and water.
- It can displace more volatile acid oxides to form the corresponding trioxosilicates(IV) when heated strongly with metallic salts. The displaced oxides usually come off as vapors or gases. Silicon(IV)oxide is non-volatile.
- Silicon(IV) oxide reacts with carbon at very high temperature to yield silicon carbide, SiC. The carbide produced is used as an abrasive due to its hardness.
Uses of Silicon(IV) Oxide
Silicon(IV) oxide has wide applications in medicine, electronics, optical lenses and in the building and construction industries. Below is a list of some of the novel uses and application of silicon(IV) oxide.
- Powdered quartz is used in making silicon carbide, silicon tetrafluoride, lining furnaces, silica bricks and trioxosilicates(IV).
- Fused silica is used in making optical lenses and prisms, scientific apparatus and heat-resistant articles. Fine threads of fused quartz which are very strong are used to suspend component parts in electrical instruments.
- Silicon(IV) oxide in the form of sand is widely used in making mortar, concrete, glass, cement and refractory silica bricks.
- Quartz crystals are used for accurate control of radio frequency transmitters. Large quartz crystals are used for lenses of optical instruments such as binoculars and telescopes because they are transparent to ultra-violet light.
- Kieselguhr absorbs liquids readily and is used as an absorbent for nitroglycerine, which is an explosive, in the making of dynamite. Kieselguhr is used in medicine for making dry anti septic dressings.