![]() Silicon carbide in silica fume is in its non-fibrous form, as demonstrated by Scanning Electron Microscopic (SEM) investigations on pre-treated (HF digested) silica fume samples. Respirable crystalline silica (RCS) < 0.1 % The main impurities include carbon, silicon carbide and oxides of alkaline (earth) metals.Īs silica fume is generated from raw materials which inevitably vary in composition depending on the source, the impurities will also individually vary up to a maximum of 5 %, but the total amount of impurities will not exceed 15 %:ĬaO, MgO, Na2O, K2O, Al2O3, Fe2O3, SO3, SiC, Si, C, Cl-< 5 % OCLC 43569399.The primary component of silica fume is amorphous silicon dioxide SiO2 in a range of 85 % - 98 %. ^ Fire retardancy of polymeric materials."Improvement of flame retardancy and thermal stability of polypropylene by P-type hydrated silica aluminate containing lanthanum". ^ Zhang, Sheng Tang, Wufei Guo, Jia Jin, Xiaodong Li, Hongfei Gu, Xiaoyu Sun, Jun ().^ "Hydrated Silica - an overview | ScienceDirect Topics"."Hydrated silica on Mars: Combined analysis with near-infrared and thermal-infrared spectroscopy". The Journal of the American Dental Association. "Baking soda as an abrasive in toothpastes: Mechanism of action and safety and effectiveness considerations". ^ "Hydrated silica gel for stabilization treatment of beer"."Cleaning Power and Abrasivity of European Toothpastes". Hydrated silica is listed by the US Food and Drug Administration as "Generally Recognized as Safe" References A hydrated silica compounds effectiveness as a flame retardant is dependent upon the presence of chemically bonded transition metals, commonly iron and titanium Safety Hydrated silica compounds, such as hydrated silica aluminate (HSA), can be combined with traditional flame retardants, such as magnesium hydroxide and aluminium hydroxide, to increase their effectivity. 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 highest water content. Chemical formula ġ SiO 2 + 1 H 2O → H 2SiO 3 1 SiO 2 + 2 H 2O → H 4SiO 4 2 SiO 2 + 1 H 2O → H 2Si 2O 5 2 SiO 2 + 3 H 2O → H 6Si 2O 7 3 SiO 2 + 2 H 2O → H 4Si 3O 8 3 SiO 2 + 4 H 2O → H 8Si 3O 10 4 SiO 2 + 1 H 2O → H 2Si 4O 9 One of the most common ways to detect and identify hydrated silicas in laboratory is through near infrared and thermal infrared spectroscopy. Microcrystalline quartz (Highest crystallinity).Hydrated silicate glass (Lowest crystallinity).Hydrated silicas can be categorized into three main categories based on differences in crystallinity: One of the primary industrial methods to acquire hydrated silica is through a sol-gel process. In its pure form, as manufactured for toothpaste, it is an odorless, tasteless, white, gelatinous substance, which is chemically inert. 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. Hydrated silicas can form in nature through biotic processes primarily involving benthic microorganism activity in the oceans. Hydrated silica is a useful abrasive in toothpastes because it does not chemically interact with other active ingredients, especially sodium fluoride. Milled to a slightly larger size, the grains are more aggressive and are used in tooth bleaching formulations. As a fine gel abrasive, frequently combined with softer calcium carbonate (from chalk) it helps to remove plaque. Use in toothpaste ĭiatomaceous earth, originally mined as "tooth powder" is a naturally occurring hydrated silica. It is also used in various paints and varnishes and in the production of beer. Hydrated silica can be dehydrated to produce silica gel, which is used as a desiccant. It is also synthetically manufactured for use in toothpaste as an abrasive to assist in cleaning. It is found in nature as opal (which has been mined as a gemstone for centuries), and in the cell walls of diatoms. When dissolved in water, it is usually known as silicic acid. Hydrated silica is a form of silicon dioxide, which has a variable amount of water in the formula. Hydrated silica is a primary ingredient in modern toothpastes, serving as a high performance abrasive during cleaning.
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