Chemical attack of ZrO2(s) by HF

[quentinflm]

Hi,

I am currently working on the chemical etching of zirconium oxide (ZrO2), but chemistry is not my specialty so a little bit of help would be really welcome =)

The experiment is quite simple : I put a ZrO2 sample in a hydrofluoric acid solution (48% wt) for different times at room temperature, and I study the effect on the surface of the sample.

My aim right now: knowing (theoretically) what are the reactions that can take place, what are the products that actually appear and (maybe the most important) what mass of ZrO2(s) can be dissolved in the solution

My questions : what is the methodology I should follow ? Which kind of diagram should I calculate ? and is there some freeware that can help me for this kind fo work ?

Thank you for your help !

Edited December 11, 2012 by quentinflm

[pippo]

be careful- HF is very dangerous.....

[quentinflm]

I am aware of the risks and I use safety equipment... but yes it's dangerous !

Edited December 12, 2012 by quentinflm

[weiming1998]

The HF reacts with the ZrO2 in a fashion analogous to SiO2, forming ZrF4, which quickly reacts with more HF to form H2ZrF6, or hexafluorozirconic acid, which dissolves in water.

The overall equation is: ZrO2(s)+6HF(aq)---->H2ZrF6(aq)+2H2O
The reaction is mostly likely to proceed until all the HF is used up, so just use stoichiometry to calculate the mass of ZrO2 the HF solution can dissolve. But you can make sure by diluting the HF solution and seeing of the ZrO2 will still react.

[quentinflm]

Thank you for this answer ! that helps a lot. Just one more question : how do you know that it is this reaction that is going to take place ? did you find it in a book ? did you guess it ? did you deduce it from something ? thank you for your help

[quentinflm]

Another thing I was thinking: don't I have to take into account the fact that HF can also form H2F- and H2F2 ?

[weiming1998]

1, I deducted it from the chemistry of silicon. Silicon dioxide dissolves in HF to form hexafluorosilicic acid. Zirconium dioxide acts very similarly to silicon dioxide, and as hexafluorozirconic acid exists, I deducted that it would form. To actually practically test it, heat the resulting solution of H2ZrF6 to dryness. If fumes of HF in addition to water (careful!) is emitted, then the compound is almost definitely H2ZrF6.

2, Yes, but the formation of these ions are negligible and won't affect anything in a 48% solution. H2F2 doesn't exist, as far as I know.