Is There an Acid That Can Corrode TiO2 Coating?

[mah65]

how to corrode TiO2 ??

Hi guys,

I have a question about TiO2 coating.

I heated (annealed) my alloy, NiTiHf at about 1000 oC, and now a relatively yellow coat is formed on the sample. I think it is TiO2, because its color also proves this point.

I'm looking for a way to remove that undesirable coating. I don't want to polish the sample, because stress may remain it the sample which is not again desirable.

so I'm seeking for an acid to corrode that coating.

experts, what acid do you offer me ?? is there any acid to corrode TiO2 ??

thanx very much

 

[Borek]

In case you don't know correct keywords - Google for "etching TiO2", that's how this process is usually named (not corrosion).

 

[Astronuc]

As Borek mentioned the process is normally called etching (to chemically remove some surface of a material) or pickling. TiO₂ forms a protective oxide on Ti metal and alloys.

The general etchant is nitric acid with a small amount of HF (this is very nasty stuff and is usually done in a polyethylene or other inert container). The HF in solution breaks down the TiO₂ protective layer. The oxide could be blue, green, yellow, orange, pink or red depending thickness. Titanium is anodized (oxidized) for different colours.

Acid wash is followed by an alkali and deionized water rinse to stop the etching and remove the acid.

In commerical operation polishing with fine grit (300 or 600) is done to achieve a shiny surface.


Alternatively, one could use an Ar plasma etching technique.

 

[mrjeffy321]

You can dissolve titanium dioxide using a solution of hydrogen peroxide and a carbonate salt (for example: sodium carbonate). Much safer than using nitric and hydrofluoric acids.

 

[mah65]

thank you so much for your help

I have tried to remove that TiO2 coating by using (HF + HNO3), but surprisingly it did not work !

OK , I will try the other choice,

thank you very much

 

[mah65]

You can dissolve titanium dioxide using a solution of hydrogen peroxide and a carbonate salt (for example: sodium carbonate). Much safer than using nitric and hydrofluoric acids.

this is really strange. none of the solutions worked.

Hf + HNO3 and also H2O2 + Na2CO3 did not work. no reaction happens !

so, what should I do now ?

 

[lightarrow]

this is really strange. none of the solutions worked.

Hf + HNO3 and also H2O2 + Na2CO3 did not work. no reaction happens !

so, what should I do now ?

Maybe it's the Ni and the Hf in the alloy which block the etching with HF: nikel and hafnium fluorides are insoluble. About the second formula, I don't believe it could really dissolve TiO₂.
If you haven't already done it, I would first begin with (in case, hot concentrated) HCl or H₂SO₄ or NaOH. If it doesn't work I would then use melted (NH₄)HSO₄ or melted KHSO₄.

 

[mrjeffy321]

this is really strange. none of the solutions worked.

About the second formula, I don't believe it could really dissolve TiO₂.

I use this to clean out glassware which has been contaminated with TiO2, but that I do not want to damage with HF.

Adding TiO2 to H2O2 should produce a orange-yellow solution, with the H2O2 forming a complex with the TiO2. I am not exactly sure of the chemical mechanism, but the carbonate ions do something which allow more TiO2 to go into solution, otherwise the H2O2 will quickly saturate.

I use concentrated (30% stock solution) H2O2 when do this, but I can dillute it down considerably before use and it still works. I have never tried it explicitly using ordinary household 3% H2O2, if that is what the OP used.

 

[mah65]

If you haven't already done it, I would first begin with (in case, hot concentrated) HCl or H₂SO₄ or NaOH. If it doesn't work I would then use melted (NH₄)HSO₄ or melted KHSO₄.

whould you please give me an exat combination of the solutions I should use ? and what is each concentration ? HCl + H₂SO₄ ... ?

thank you

 

[lightarrow]

whould you please give me an exat combination of the solutions I should use ? and what is each concentration ? HCl + H₂SO₄ ... ?

thank you

I would begin with concentrated H₂SO₄ (98%). You put a little drop on the metal surface and observe, in case you remove it quickly with water. If it doesn't work I would try with the same acid but hot (100°C ~ 200°C).
P.S. Be careful with hot H₂SO₄, don't let a single tiny drop squirt on your skin.

 

[lightarrow]

I use this to clean out glassware which has been contaminated with TiO2, but that I do not want to damage with HF.

Adding TiO2 to H2O2 should produce a orange-yellow solution, with the H2O2 forming a complex with the TiO2.

Probably is a more reactive (non compact) form of TiO₂ because, usually, that reaction happens with titanium salts (TiO₂ already in solution). TiO₂ which has been heated becomes very compact and extremely difficult to dissolve. Usually the method is to melt it with KHSO₄ (first at low temp., the hydrogensulphate becomes pirosolfate, then the temp. is increased to decompose pirosulphate into sulphate and sulphuric anydride which attacks the oxide).

 

[mah65]

As u said, firstly i poured H2SO4 and also HCl separately on the sample, but in each case, nothing happened.

then, I submerged my sample in H2SO4 in a glass container. then put it on the heater to temperatures of 100 - 200, but again, no reaction occurred.

I wonder what to do now ?!

 

[lightarrow]

As u said, firstly i poured H2SO4 and also HCl separately on the sample, but in each case, nothing happened.

then, I submerged my sample in H2SO4 in a glass container. then put it on the heater to temperatures of 100 - 200, but again, no reaction occurred.

I wonder what to do now ?!

Now I would try with molten pyrosulfate. If it doesn't work with it, I give up...
If you don't have potassium pyrosulfate K₂S₂O₇ you proceed as mentioned in my previous post, first decomposing KHSO₄ at low temp. (until it has finished making foam) and then at higher temperatures (over 350°C) to decompose the pyrosulfate in SO₃. The pyrosulfate have to surround completely your block of material.

 

[mugaliens]

whould you please give me an exat combination of the solutions I should use ? and what is each concentration ? HCl + H₂SO₄ ... ?

thank you

I think before you go tinkering with acid combinations, you should learn more about http://en.wikipedia.org/wiki/Acid" !

In general (I'm not a chem-e), I would try a graduated approach, trying successively strong acids. However, I am aware there is a calculated approach to determine the requisite strength, if you're certain it's the titanium-dioxide bond. Again, I'm not a chem-e, and am simply remembering something from third-quarter chem class two decades ago.

 

[manyoolo]

I believe you tried harder, did you succeed?
Can you share with me because am struggling with the same challenge
Emmanuel

 

[mah65]

unfortunately, I have to say that I could not remove that damn layer of oxide! If you could, please let me know. The yellow coating is so anti corrosive! and shows no reaction with those acids! However, the black one can easily be removed using NHO3 + HF + H2O.

 

[manyoolo]

I should admit that this discussion has assisted me.
Finally I managed with conc. HCL with 100oC of temperature
The glass is perfectly clean
Regards

 

[mah65]

What do you mean? did this simple solution worked? Only HCl with 100 Celsius degree temperature?!

What do you mean by glass?!

OK, please tell me about the condition, i.e. the container and any safety measurements I have to consider if I wanted to do carry it out.

 

[manyoolo]

What do you mean? did this simple solution worked? Only HCl with 100 Celsius degree temperature?!

What do you mean by glass?!

OK, please tell me about the condition, i.e. the container and any safety measurements I have to consider if I wanted to do carry it out.

Yeah,
I mean the simple solution of HCL with 100 Celsius degree temperature worked. My case might be quite different from yours because I was trying to wash away TiO2 on a window glass of sputtering unity, the film was thicker.

I also attempted to etch TiO2 thin film from a glass substrate under the same condition, it did not work. Thus I think it work in thicker films and not thin films

-I poured small amount of HCL (the glass can immerse totally) in a beaker
-Soak the glass need to wash
-cover it -I used tissue paper -and leave it in for an hour
-then put the content on oven at 100oC for about 30min
-allowed the content to cool
-rinse the glass with tap water (never add water into acid, do the other way round)
thats what I did!

 

[Nemus]

Titanium is actually a really hard nut to etch. Peroxide, nitric acid and sulfuric acid will only make the oxide thicker. My really fat inorganic chemistry book (Greenwood and Ernshaw) hints at strong hydrofluoric acid. It is just really nasty stuff to handle. Be REALLY careful. Hood, face shield, long goves, the works. Any drop on the skin and it is straight off to the hospital. Deep, necrotic sores after some time.

 

[Borek]

It is not just necrotic sores. HF permeates the skin, goes into blood stream and precipitates calcium, that ends in hypocalcemia. Very painful and nasty way of dying.

 

[FtlIsAwesome]

and now a relatively yellow coat is formed on the sample. I think it is TiO2, because its color also proves this point.

At the risk of sounding like a total noob...

Are you absolutely certain that it is TiO₂? What other yellow material could it be?

 

[m2y]

i had the same problem, if you add some ammonium sulphate into sulphuric acid (5 gr of ammonium sulphate into 10ml of sulphuric acid) u will be able to dissolve it.

 

[mah65]

My Alloy was NiTiHf. Ti Hf are really prone to oxidation. So the oxide must be TiO2, or HfO2 or a combination of these :)