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How to corrode TiO2 ?

by mah65
Tags: corrode, tio2
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mah65
#1
Jan2-10, 06:14 AM
P: 24
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
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Borek
#2
Jan2-10, 07:04 AM
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In case you don't know correct keywords - Google for "etching TiO2", that's how this process is usually named (not corrosion).
Astronuc
#3
Jan2-10, 08:06 AM
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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
#4
Jan2-10, 04:18 PM
Sci Advisor
P: 882
How to corrode TiO2 ?

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
#5
Jan3-10, 02:06 AM
P: 24
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
#6
Jan4-10, 06:35 AM
P: 24
Quote Quote by mrjeffy321 View Post
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
#7
Jan4-10, 10:10 AM
P: 1,521
Quote Quote by mah65 View Post
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
#8
Jan5-10, 02:36 AM
Sci Advisor
P: 882
Quote Quote by mah65
this is really strange. none of the solutions worked.
Quote Quote by lightarrow
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
#9
Jan5-10, 04:47 AM
P: 24
Quote Quote by lightarrow View Post
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
#10
Jan5-10, 06:21 AM
P: 1,521
Quote Quote by mah65 View Post
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 (100C ~ 200C).
P.S. Be careful with hot H2SO4, don't let a single tiny drop squirt on your skin.
lightarrow
#11
Jan5-10, 06:42 AM
P: 1,521
Quote Quote by mrjeffy321 View Post
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
#12
Jan6-10, 07:14 AM
P: 24
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
#13
Jan6-10, 05:00 PM
P: 1,521
Quote Quote by mah65 View Post
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 350C) to decompose the pyrosulfate in SO3. The pyrosulfate have to surround completely your block of material.
mugaliens
#14
Jan6-10, 05:39 PM
P: 595
Quote Quote by mah65 View Post
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 acids!

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
#15
Mar7-11, 02:32 AM
P: 8
I believe you tried harder, did you succeed?
Can you share with me because am struggling with the same challenge
Emmanuel
mah65
#16
Mar7-11, 07:37 AM
P: 24
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
#17
Mar7-11, 09:59 AM
P: 8
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
#18
Mar8-11, 10:48 AM
P: 24
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.


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