Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: May 1, 2005
Publication Date: January 1, 2006
Citation: Nielsen, F.H. 2006. Silicon. In: Klasing, K.C., editor. Mineral Tolerance of Animals. 2ndd Revised Edition. Washington DC; National Academies Press. p. 348-356. Technical Abstract: Silicon (Si) in its elemental form is a shiny metallic-looking substance that is hard and brittle with a crystalline structure similar to that of diamond. Silicon is the second most abundant element in the earth's crust; 27.7% of the lithosphere is silicon. It occurs in nature mostly in the oxide and silicate form. Silicon dioxide occurs mainly in the crystalline form as quartz or sand. Asbestos, feldspars, clays, and micas are examples of silicate minerals. Silicon is prepared commercially by heating silica and carbon to 1600-1800° C in an electric furnace (Hunter and Aberg, 1975). At this temperature carbon takes oxygen from silica to form carbon monoxide. Silica is the term often used for naturally occurring substances composed mainly of silicon dioxide (SiO2), and silicone (organosiloxane) is the term used for synthetic polymers with a structure of alternating oxygen and silicon atoms (Hunter and Aberg, 1975). Adding water to silicates liberates orthosilicic acid, which apparently is an important biological form of silicon. Orthosilicic acid (Si[OH]4), also known as monosilicic acid or monomeric silica, polymerizes in neutral solutions at concentrations greater than 2 mmol/L. Some lower forms of life and plants may use this reaction to form polymeric silica, or phytolithic silica, for structure and growth. In higher animals and humans, monosilicic acid is thought to be a circulating form of silicon. Precipitated silica, or colloidal silicic acid (approximate formula of H3SiO3), is an insoluble form of silicon and occurs in nature as opal. The condensation of orthosilicic acid to form precipitated silica is a method for making silica gel, an adsorbent.