Titanium-Alluminum Alloy Oxidation: Why Aluminum Outgrowth Stops

[Mahmood Anwar]

Can anybody explain me why aluminum can not come out / outgrowth stop after the oxidation of titanium-allominium alloy?

 

[Danger]

Welcome to PF, Mahmood.
With all respect intended, I must say that I don't understand your question. Are you referring to corrosion, or difficulties alloying aluminum with titanium, or... what? I can tell that English is not your native language. We get a lot of that here, so everyone is very patient and understanding about it. Take your time, and we'll coax out what you mean.

 

[Mahmood Anwar]

Thank you Danger for your kind clarification.

I just mean that from my series of experiment, I observed that aluminium is not present in the top surface where from the cross -sectional view: Al presents in the bottom layer of the oxidized layer. i.e. question: Is there any explanation that the aluminium is being prevented to come out in the top surface after oxidation of Titanium-Aluminum Alloy?

 

[Danger]

I see. Thanks for the explanation.
I'm not a metallurgist (I'm not a scientist of any kind), but I have a thought about it.
Aluminum oxidizes almost instantaneously, but only on the surface. By that I mean that it won't "rust through" the way iron will.
My admittedly clueless idea is that you are actually alloying aluminum oxide, rather than pure aluminum, with your titanium. If it's already oxidized, it isn't susceptible to the process continuing. I don't see just how that would affect layering, but it's all that I can think of.
I'm sure that someone else here will have a definitive answer for you.

 

[Danger]

I just got around to investigating the oxidation and alloying characteristics of titanium, and it appears that my initial thought is possibly invalid. Titanium forms a protective oxide layer the same as aluminum does. Why I consider that my idea might possibly still be correct is that the oxide layer continues to grow at a slow rate. Perhaps that titanium dioxide, trioxide or whatever simply grows in thickness and thus leaves the aluminum behind in a lower layer.
I really wish that someone else would take over here, because I'm out of my depth.

 

[WARRIOR1]

It could depend on many things, there is a fairly large list of things that the oxidation process is dependent on, and it may come down to whether it is reaction or diffusion limited. It depends from the start on your method of oxidation, which you haven't mentioned. If you are using wet oxidation using steam it may come down to the carrier gas that you are using and the reaction itself. It also sounds like you may not be performing it at a high enough temperature so that it may be reaction limited.

 

[Mahmood Anwar]

Thank u warrior1.
My method of oxidation is without any steam, its a simple process , heating inside furnace in normal environment ( means with the presents of air) and after heating the substrate was air cooled. Really hope , somebody have some explanation...