Silicilic acid

When a silicate solution such as sodium silicate is acidified, a gel of polymeric colloidal silicilic acid is formed as an agglomerate of micro-particles. When the gel is heated, water is expelled leaving a hard, glassy structure with voids between the micro-particles equivalent to a mean pore diameter of about 3 nm and an internal surface of about 500,000 m2/kg. As discussed by Everett and Stone(8) these properties may be varied by controlling the pH of the solution from which the gel is precipitated. 

It should be noted that the human body does possess natural barrier systems to prevent aluminum intake. There are various physiological ligands, such as transferrin, citrate, and silicilic acid, which are efficient buffers in preventing the intake of aluminum under natural conditions [28]. Yet the formation of TFA requires only trace amounts of aluminum, and the bioavailability of aluminum to living organisms is increasing. Fluorine, of course, is readily available in drinking water. 

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