Topics - Silicic acid
Sillicic acid is the acid that forms the esters and salts called silicates and is rapidly released from inorganic silicates by hydrochloric acid. Silicic acid, however, is inherently unstable and will rapidly condense with itself with the elimination of water forming ‘dimers’, ‘trimers’ and eventually high molecular weight polymers. These polymeric aggregates grow in size until (depending on the environmental conditions, temperature, salt concentration, pH etc.) at a particular size, the hydroxyl groups on the surface of the aggregates begin to condense; the aggregates adhere to one another and the liquid gels. A somewhat complicated treatment of the gel eventually produces the so called silica gel
that is extensively used in chromatography. The aggregates, called ‘primary particles’, are a network of silicon dioxide groups (actually they are better considered as a network of silicic anhydride groups) with hydroxyl groups covering the external surface. Silicon is the second most common element on the earth’s surface and the aluminum silicates represent the clays and shale’s widely present in the earths crust.