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Name: Mark
Status: other
Grade: other
Location: NV
Question:
What is the difference between silica flour and silica fume?

Replies:
Hi Mark,

Both materials are pure silica (silicon dioxide). Silica flour is simply made by grinding pure silica sand to a very fine powder. It is used as a cheap filler in plaster and some plastics to add strength, or just to reduce the amount of (expensive) resin needed to fill a mold.

Fumed silica is made in a very unusual way, by reacting silicon tetrachloride in an oxy-hydrogen flame that has an excess of oxygen. A very light, fluffy, pourable solid results. Fascinating stuff, actually! Fumed silica is mainly used as a thixotropic additive to plastic resins and other liquids. For example, when added to an epoxy resin, the resin will not "run" when left to stand, but will still pour if it is agitated. Both forms of silica are essentially inert.

Regards,
Bob Wilson.


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