matthill2006 - 7-11-2006 at 21:36
Hi all,
I am looking to remove silica from a strontium titanate/silica composite to leave behind some nanostructured SrTiO3.
The nicest way to do this would be to dissolve out the silica with HF.
My question is: Will SrTiO3 be chemically inert to HF?
Cheers.
guy - 8-11-2006 at 12:47
You might not want to work with HF.
NaOH will do just fine, you will need to heat it though.
matthill2006 - 8-11-2006 at 14:33
NaOH doesn't remove all of the silica from the composite. It is a nanostructured type thing and I think the microporosity of the sample causes the
silica to be entrapped, making it inert to NaOH. With NaOH I am always left with a 20% silica residue no matter how exhaustive the treatment is.
Moreover there was always a sodium residue even after repeated washings...... maybe reacting with the SrTiO3?
Hence the leap to HF!!
not_important - 8-11-2006 at 20:57
Acid washes can remove the alkali residue in some cases. Sometimes the sodium residue can be removed by several leachings with an solution of an
ammonium salt, ammonium nitrate and ammonia mix might be best. Water wash, acid soak, water washm 2 ammonium leachings, water wash several times, dry
and ignite. The ammonium ions replace the sodium, ignition drives them off as gas. There possibly would be a problem with NH4 replacing Sr, so an
alternative to the ammonium leach would be a stronium nitrate one, followed by good rinsing.
It is possible that sodium is replacing Sr to a small degree, or binding to oxygens in the lattice. Simple washing won't displace it, acid washes
replace Na+ with H+, NH4+ or Sr+2 do the same with their ions.
I can't remember if SrTiO3 is attacked by HF, sorry. Best bet would to be to try it on a small scale, and test the extract for both Sr and Ti.
Are you sure that you are not getting a silicate of some type, rather than just simple trapped SiO2? And if NaOH can't reach it, why would HF do any
better?