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Colloidal silica gel with light opalescence. Silica gel is an amorphous and porous form of silicon dioxide (silica), consisting of an irregular tridimensional framework of alternating silicon and oxygen atoms with nanometer-scale voids and pores. The voids may contain water or some other liquids, or may be filled by gas or vacuum.
Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula SiO 2, commonly found in nature as quartz. [5] [6] In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and abundant families of materials, existing as a compound of several minerals and as a
Amorphous silica is less toxic than crystalline, but not biologically inert, and diatomite, when heated, can convert to tridymite or cristobalite. Silica flour is nearly pure SiO 2 finely ground. Silica flour has been used as a polisher or buffer, as well as paint extender, abrasive, and filler for cosmetics.
Sodium silicate solution is used to inexpensively, quickly, and permanently disable automobile engines. Running an engine with half a U.S. gallon (or about two liters) of a sodium silicate solution instead of motor oil causes the solution to precipitate, catastrophically damaging the engine's bearings and pistons within a few minutes. [27]
Naturally occurring silicon is found in silicate and aluminosilicate minerals. One of the most common silicon compounds found in the Earth's crust is silicon dioxide or silica, which often occurs as quartz. Organosilicon compounds are fairly stable due to the similarity in strength of the Si–C bond to the C–C bond.
[4] [5] [6] Dehydrating the latter yields a hard translucent form of silica with atomic-scale pores, called silica gel, which is widely used as water absorbent and drying agent. Silica dissolves very sparingly in water [citation needed] and is present in seawater at concentrations below 100 parts per million. In such dilute solutions, silica is ...
It is not necessary to freeze the samples, or treat them in any special way because silica is not subject to decay by microorganisms. [10] Natural contexts: Sampling a natural context, typically for the purpose of environmental reconstruction, should be done in a context that is free of disturbances. Human activity can alter the makeup of ...
To attempt to simplify and to stylize a very complex set of various reactions, the whole ASR reaction, after its complete evolution (ageing process) in the presence of sufficient Ca 2+ cations available in solution, could be compared to the pozzolanic reaction which would be catalysed by the undesirable presence of excessive concentrations of alkali hydroxides (NaOH and KOH) in the concrete.