Fumed Silica is chemically the same thing as sand, SiO2, but it is produced by burning hydrogen with silicon tetrachloride to form Hydrochloric acid and fumed silica. The acid is removed and the final product is white, fluffy and amazing. It looks like microscopic clumps of grapes.
It is used primarily to control the thickness of liquids, their viscosity. Now here is where it gets interesting. Fumed silica is what makes polyurethane "thixotrophic". Meaning, it is low viscosity (thin) under shear and then gets thick without the shear. That's how they make fiberglass boats - by spraying polyurethane (high shear spray gun) onto the outside of the fiberglass hull where it instantly gets thick and stays put.
It makes glycol rheopectic - thick under stress and thin without stress. So, the glycol with fumed silica in it will pour out of a glass, but if you try to stir it, it feels like it turned into a solid.
Which brings us to food. It is used in toothpaste and many foods so they have the "right" thickness. It is used in flour to keep it from getting too clumpy. So, you are ingesting it, probably every day. Have you had your fumed silica today?
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