|MadSci Network: Chemistry|
Hi Carolyn! I bet if the label said it contained 'sand' that you'd be writing to the manufacturer and not to The MAD Scientist! Silicon dioxide [SiO2] and silicate minerals make up 95% of the Earth's crust and the natural forms consist of crystalline, microcrystalline and diatomaceous [from diatoms, the skeleton of tiny marine creatures]. The crystalline sand on a beach has an average particle size of from 2 to about 10 microns. This grain size is visible to the naked eye and, if you ever got some in your eye, could be felt as well by the eye. Synthetic SiO2 is exactly the same compound but is a microscopic particle with sizes as low as 0.007 microns, or 1000 times smaller than beach sand. This material is not found in nature but is synthesized in a chemical reactor. The chemistry is straightforward: Silicon tetrachloride [SiCl4, made from SiO2 and HCl] is hydrolyzed in a flame of oxygen and hydrogen [the same fuel that is burned to launch the space shuttle]. Thus: 2 H2 + O2 + SiCl4 --> SiO2 + 4HCl Why bother to take perfectly good ordinary sand and go through all these gyrations just to make more sand? The answer is in the very small particle sizes that can be obtained with this process. As particle size decreases, surface area increases. As surface area increases more and more water can be sorbed via hydrogen bonding and aggregates of particles begin to form with a structure similar to a bunch of grapes. If this form of SiO2 is added to a candy [or practically any other food] it sets up a jelly-like structure of associated agglomerates that gives a texture and viscosity unattainable via other means. SiO2 is inert and non-toxic and is FDA approved for this use. There are also many other industrial uses. Ken
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