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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.
The lowest-density silica nanofoam weighs 1,000 g/m 3, [58] which is the evacuated version of the record-aerogel of 1,900 g/m 3. [59] The density of air is 1,200 g/m 3 (at 20 °C and 1 atm). [60] The silica solidifies into three-dimensional, intertwined clusters that make up only 3% of the volume. Conduction through the solid is therefore very low.
Hydrated silica is a form of silicon dioxide, which has a variable amount of water in the formula. When dissolved in water, it is usually known as silicic acid . It is found in nature as opal [ 2 ] (which has been mined as a gemstone for centuries), and in the cell walls of diatoms .
Colloidal silicas are most often prepared in a multi-step process where an alkali-silicate solution is partially neutralized, leading to the formation of silica nuclei. The subunits of colloidal silica particles are typically in the range of 1 to 5 nm. Whether or not these subunits are joined depends on the conditions of polymerization.
In acidic solutions, the silicate ions react with hydrogen ions to form silicic acids, which tend to decompose into hydrated silicon dioxide gel. [citation needed] Heated to drive off the water, the result is a hard translucent substance called silica gel, widely used as a desiccant. It can withstand temperatures up to 1100 °C. [citation needed]
Silica gel litter: Made from silica crystals, this litter is lightweight, highly absorbent, and excellent at controlling odors. It requires less frequent changes but can be more expensive.
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
Microcrystalline silica consists of minute quartz crystals bonded together with amorphous silica. Examples include flint and chert . Amorphous silica consists of kieselgur ( diatomite ), from the skeletons of diatoms , and vitreous silica, produced by heating and then rapid cooling of crystalline silica.