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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.
Hydrated silica is a primary ingredient in modern toothpastes, serving as a high performance abrasive during cleaning. [1] 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.
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
Silanols exist not only as chemical compounds, but are pervasive on the surface of silica and related silicates. Their presence is responsible for the absorption properties of silica gel. [6] In chromatography, derivatization of accessible silanol groups in a bonded stationary phase with trimethylsilyl groups is referred to as endcapping.
Silicic acids can be seen as hydrated forms of silica, namely 2 H 2x SiO x+2 = SiO 2 ·(H 2 O) x. Indeed, in concentrated solutions, silicic acids generally polymerize and condense, and ultimately degrade to silicon dioxide and water. The intermediate stages may be very thick liquids or gel-like solids.
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]
Formulation: Since daily sunscreen application is a must, it helps to have a formula that suits your preferences, be it tinted or transparent, or a cream versus a lightweight gel.
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.