Silicon

Silicon has many valuable uses.   It is the most common semiconductor in electronic devices, e.g., transistors.   Extremely pure silicon is prepared by the thermal decompositon of extremely pure trichlorosilane in a hydrogen atmosphere (Siemens process) and by a vacuum float zone process.   The silicon is then "doped" (impurity added) with boron, gallium, phosphorus, or arsenic.   The Czochralski process also is used to prepare single silicon crystals for semiconductors.  The silicon is then cut into wafers and made into transistors, solar cells, rectifiers, and other solid-state devices to be used in the electronics industry.   Silicon can be made into silicones by hydrolyzing a silicon organic chloride, like dimethyl silicon chloride.   Using the hydrolysis and condensation of various substituted chlorosilanes produces a large number of polymeric products (silicones) in liquid and solid form that have many uses.

Silicon as sand and clay are used as building materials, such as cement, brick and glass.   Silicates are combinations of of silicon and other elements, usually oxygen, e.g., SiO₂, (SiO₄)^4-.   They are used in cement, pottery and enamels and in steel.   Silicon carbide is an important extremely hard abrasive. ^{Lide 4-26}   Silicates are extremely abundant in nature and appear in many mineral forms.

Silicon is beneficial, but not essential, to human life.   It keeps bones, cartilage, tendons and artery walls healthy.   On the negative side, siliceous dust breathed in large quantities can cause the lung disease called silicosis, so miners and stonecutters working in that environment must take preventative health measures. ^{Lide 4-27}

Silicon was discovered in 1824 by Jöns Jakob Berzelius.   Silicon is the second most common element in the earth's crust, after oxygen, constituting 25.7% of it.   Since silicon is active, it is not found in free form, but usually as oxides and silicates.   The oxide minerals are sand, quartz, rock crystal, amethyst, agate, flint, jasper and opal.   The silicate minerals are granite, hornblende, asbestos, feldspar, clay, mica, etc.   Silicon is prepared commercially by heating silica (SiO₂) and carbon in an electric furnace with carbon electrodes.   Other methods can be used too. ^{Lide 4-26}