# Hexafluorosilicid acid attacks glass?

When HF meets glass, Hexafluorosilic acid is formed (assuming some water is present). It appears that Hexafluorosilic acid and further attack glass? How is this so, considering that all F atoms are "used up" (already bonded to Si atoms)?

http://www.cdc.gov/niosh/ipcsneng/neng1233.html

• $\ce{H2SiF6}$ can decompose into HF in the presence of water fairly easily. I wonder if HF is acting almost as a catalyst, with the fluoride chipping away at the glass, then breaking off, then chipping again, and so on. If the hexafluorosilicic acid were put into water and started to decompose, it ought to provide a source HF to attack the glass, in the right environment. – Jason Patterson Nov 8 '14 at 22:56
• So HF+SiO2 -> H2O*H2SiF6 (or something like that) is reversable? – Kevin Kostlan Nov 9 '14 at 0:46
• Glass isn't exactly $\ce{SiO2}$, but that was my idea. It would effectively be converting glass (big messy molecule that it is) into independent molecules of silicon dioxide. To be clear, that was just my best guess. I've never worked with the stuff and didn't find a mechanism for how it attacks glass when I looked. – Jason Patterson Nov 9 '14 at 1:09
• @Jason: Glass dissolves (your term "independent molecules") up to 100ppm in water but could be more soluble in acid (but HCL would not attack glass due to the slow kinetics) Keep in mind "dissolve" actually indicates a reversable reaction, so it m – Kevin Kostlan Nov 9 '14 at 1:44
• may need a catalyst to proceed to this equilibrium at a reasonable rate (they used finely divided particles). The fluoride probably increases the solubility. – Kevin Kostlan Nov 9 '14 at 2:02