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Pyrogenic silica is a fine powder formed by exposing silicone tetrachloride or quartz sand to a pyrolysis process. This produces a powder that exhibits a low overall density with high surface area values and good thixotropic qualities. Pyrogenic silica is used extensively as a strengthening filler and thickening agent in a wide variety of products such as foodstuffs, paints, and adhesives. It also serves as a desiccant and is frequently added to cosmetics and toothpaste due to its respective light diffusing and mild abrasive qualities. Pyrogenic silica has no carcinogenic characteristics but does pose an inhalation risk due to its extremely fine structure.
Silica is an extremely hard silicone oxide found naturally in quartz sand. When exposed to a pyrolysis process, a fine powder made up of microscopic grains of fused silica is formed with a high surface area to bulk density ratio. The pyrolysis process involves exposing the raw silica to very high temperatures, typically in the region of 5,400°F (3,000°C), in the absence of oxygen. The process produces a very fine powder with non-porous particles ranging in size between 5 and 50 nm. The powder also has a very high surface area to bulk mass ratio with values in the range of 50 to 600 m2/g.
The extremely fine and non-porous nature of pyrogenic silica, or fumed silica as it is also known, make it an ideal thickening and bulking agent with outstanding thixotropic qualities. Thixotropic refers to a substances characteristic of reducing viscosity or thickness with extended agitation or shaking. This makes fumed silica an ideal filler for paints, thus causing them to thin out during application and regain their viscosity when left to stand preventing drips and runs. This characteristic is also beneficial in the formulation of printing inks which allow for high definition levels during application. Fumed silica is also a popular filler and reinforcement agent in many coatings, sealants, and adhesives.
When added to foods such as milkshakes, pyrogenic silica lends body without solidifying during preparation or transport. Much like silica gel, pyrogenic silica also possesses good desiccant qualities. The powder is often added to cosmetics due to its light diffusing ability and as a mild abrasive in toothpaste. Pyrogenic silica has no carcinogenic properties but, due to its extremely fine structure, does pose an inhalation risk when suspended in the air. If inhaled in excessive quantities, it can cause irritation of the lungs with associated long-term, irreversible damage.