Extract

…When heated to decomposition, sodium hexafluorosilicate releases toxic fumes of hydrogen fluoride and sodium oxide, while contact with metals releases hydrogen gas. In water, the compound readily dissociates to sodium ions and hexafluorosilicate ions and then to hydrogen gas, fluoride ions, and hydrated silica. At the pH of drinking water (6.5-8.5) and at the concentration usually used for fluoridation (1 mg fluoride/L), the degree of hydrolysis is essentially 100%. Fluorosilicic acid is a moderately strong acid that can corrode glass and stoneware. Like its salt, its degree of hydrolysis is essentially 100% in drinking water, and when reacted with steam or water or when heated to decomposition or highly acidified, toxic and corrosive fumes of fluorides (e.g., hydrogen fluoride and silicon tetrafluoride) are released. It also reacts with metals, producing hydrogen gas…