[jakethepeguk1]

Hello everyone,

I was wondering if anyone can help me. I'm trying to deposit (slowly) TiO2 onto an oxide coated glass substrate using an aqueous solution of TiCl4. It is a 40mM - 80mM solution that is heated to 65 degrees. It forms quite an acidic solution (from the HCl formed when mixing the water with the TiCl4). However, i would like to make the pH closer to 7. Is this possible? Ive tried adding ammonium hydroxide to it, but it precipitates the TiO2 too quickly. Id like to grow the film on the glass substrate slowly, but i don't want it to be too acidic (the acid etches my substrate).

Ive tried buffering the solution, but this hasn't seemed to work. I may be doing something wrong here though.


Any help would be really appreciated!

Thanks

[Fleaker]

Have you opened the bottle of TiCl₄ and seen how much white smoke comes off? That sir, is your titanium dioxide (and a lot of HCl).
I've worked with titanium tetrachloride on a handful of occasions, none of which I really enjoyed. You know something is hygroscopic and rapidly hydrolyzing when it starts sealing itself into its own bottle!



Aqueous solution of titanium tetrachloride?!? Hahahahah!

You'd have better luck going about a different deposition route, perhaps a vapor deposition.
 
You might also think of making a solution of TiCl₄ in a solvent that it is non reactive with (hint: a fully chlorinated organic solvent). Then perhaps you might be able to rig something up where you can allow moisture to ''diffuse'' into the solvent and slowly deposit the titanium onto your substrate.

Shucks, surface scientists these days! Wanting to make aqueous TiCl₄ solutions...

[azmanam]

We use neat tickle4 in our lab fairly regularly.  It's always fun when a bit accidentally drips out of the needle and starts fuming like it's its job right on your glove.

It's not so much fun when you don't clean up your aqueous extracts right away.  Eventually you'll paint the inside of your flask white with, well, white paint.  Doesn't come off so easily...

[jakethepeguk1]

Working with neat TiCl4 is ok if you use it in a fume cupboard, and try not to spill it everywhere. I should have mentioned before that i first dilute the conc TiCl4 to a 2M stock solution by adding it to ice, slowly... to make it easier to work with.

I then dilute the solution further to 40mM which is still sufficiently acidic to etch my substrates, which is very annoying. Using an aqueous solution of TiCl4 is standard for the type of process i am doing, however usually it is on more of a inert substrate, like SnO2 or something.

I will try a different solvent. Can you suggest a safe-ish chlorinated organic solvent which could do the job? Preferably nothing that will attack my central nervous system. I dont mind working with acids (bare HF), but anything that makes my go mad i would prefer to stay away from 

[jakethepeguk1]

Also, if anyone else has a way of depositing TiO2 on an acidic and heat sensitive substrates, that would be great. I would like to keep the temperature low, with a maximum of 250 degrees if possible.

Cheers!! 

[Borek]

I can be completely off here, but I wonder - what if you will start with TiCl₃? Contact with air should be enough for the Ti(III) to get oxidized to Ti(IV). Could be there are other reasons that make this approach completely wrong, but I have no acess to even my own bookshelf at the moment, so can't check it.

[jakethepeguk1]

I have read that TiCl3 still produces a very acidic solution, so i'm going to try and stay away from it. Possibly i may have to find a completely different way of doing this.

ive tried adding ammonium hydroxide to the solution, but it causes the TiO2 to precipitate out too quickly (could be TiOH). I fear i might be going down an impossible path here though.

Any suggestions would be really appreciated if anyone has any other ideas.

Cheers

[Fleaker]

I would try coating your substrate with a readily decomposable organotitanium compound. Hopefully something that is air sensitive and highly prone to oxidation. TiO₂ is quite stable thermodynamically speaking, so it should be a favored product.


Perhaps you should consider making a solution (or rather should I say colloidal suspension/dispersion) of titania in a neutral, easily removable solvent and adding some sort of flocculating agent. You ought to be able to experimentally control how the titania deposits. I have no idea how well it will stick--that is surface chemistry that you will need to figure out.