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Hydrated silica is a form ofsilicon dioxide, which has a variable amount of water in the formula. When dissolved in water, it is usually known assilicic acid. It is found in nature asopal,[2] and in the cell walls ofdiatoms- hence is found indiatomaceous earth. It is also synthetically manufactured for use intoothpaste as an abrasive to assist in cleaning. Hydrated silica can be dehydrated to producesilica gel[citation needed], which is used as adesiccant. It is also used in various paints and varnishes and in the production ofbeer.[3]
Diatomaceous earth, originally mined as "tooth powder" is a naturally occurring hydrated silica. As a fine gelabrasive, frequently combined with softercalcium carbonate (fromchalk) it helps to removeplaque. Milled to a slightly larger size, the grains are more aggressive and are used intooth bleaching formulations.[4] Hydrated silica is a useful abrasive in toothpastes because it does not chemically interact with other active ingredients, especiallysodium fluoride.[5]
Hydrated silicas can form in nature through biotic processes primarily involving benthic microorganism activity in the oceans.[6] However, there are several abiotic processes that form hydrated silicas, such as precipitating out of solution, forming a diagenetic alteration product, or replacing pre-existing minerals in sedimentary rocks.[6]
In its pure form, as manufactured for toothpaste, it is an odorless, tasteless, white, gelatinous substance, which is chemically inert. One of the primary industrial methods to acquire hydrated silica is through asol-gel process.[7]
Hydrated silicas can be categorized into three main categories based on differences in crystallinity:[6]
One of the most common ways to detect and identify hydrated silicas in laboratory is through near infrared and thermal infraredspectroscopy.[6]
Chemical Formula: SiO2 ·nH2O
Hydrated silicas exhibit a trend of decreasing bonded water molecules as the crystallinity of the silica molecule increases, with microcrystalline quartz's typically containing the least water content and macrocrystaline quartz having negligible water.[6]
Hydrated silica compounds, such as hydrated silica aluminate (HSA), can be combined with traditional flame retardants, such asmagnesium hydroxide andaluminium hydroxide, to increase their effectivity.[8] A hydrated silica compound's effectiveness as a flame retardant is dependent upon the presence of chemically bonded transition metals, commonly iron and titanium[9]
Hydrated silica is listed by the USFood and Drug Administration as "Generally Recognized as Safe"[10]
{{cite book}}: CS1 maint: others (link)Toothpaste:[1]Chemistry:[2][unreliable source?]Opal:[3]Paint/Varnish:[4]Beer:[5]