oxidation of materials exposed to water at high temperatures

[DrMrLordX]

What sort of materials can remain solid while

a). heated to 2500C (or hotter)
b). resist oxidation when exposed to water vapor heated to the same temperatures

I looked at various carbon allotropes but neither amorphous carbon nor graphite seem to fit the bill (maybe CNTs?). I could be wrong, though, and I saw at least one coating available that was supposed to retard oxidation of g. How would tungsten hold up?

I would assume that pressure would also matter . . .

 

[Nathelion]

http://en.wikipedia.org/wiki/Superalloy

Useful?

 

[CycloWizard]

Originally posted by: Nathelion
http://en.wikipedia.org/wiki/Superalloy

Useful?

FTW. The US Air Force (and probably other advanced air forces) are looking into burning fuel at higher and higher temperatures. Therefore, a considerable chunk of research money goes into looking at materials that will withstand very high temperatures, high pressures, and high-humidity environments (since water is a natural product of fuel combustion). The ones that I'm most familiar with are nickel-titanium superalloys, since one of my friends works on them. That said, I don't know much because most of what he does is classified.

 

[wwswimming]

Originally posted by: DrMrLordX
What sort of materials can remain solid while

a). heated to 2500C (or hotter)
b). resist oxidation when exposed to water vapor heated to the same temperatures

maybe ceramics.

they tend to be weak in tension but that can
be partially offset by design.

a friend of mine works for a company that
makes composite structures for aerospace
applications. maybe i'll ask him when i make
my Christmas phone call.

his backyard has a few of the rejects. people
size pieces of graphite in strange shapes, etc.

 

[DrMrLordX]

Originally posted by: Nathelion
http://en.wikipedia.org/wiki/Superalloy

Useful?

Hmm . . . very interesting. The only point I could make against them is that, at least according to the linked article, that current-gen superalloys operate at temperatures as high as 1100C.

Granted, the temperature extremes I specified are absurd by most standards.

Originally posted by: wwswimming


maybe ceramics.

they tend to be weak in tension but that can
be partially offset by design.

a friend of mine works for a company that
makes composite structures for aerospace
applications. maybe i'll ask him when i make
my Christmas phone call.

his backyard has a few of the rejects. people
size pieces of graphite in strange shapes, etc.

I was thinking the same thing, but with my very limited resources/background I could not find anything that would survive the temperatures I specified. I did mind to find some kind of glass-like material capable of surviving temperatures as high as 3000C, but it was proprietary and I can not find the vendor's website again.

 

[CycloWizard]

Originally posted by: DrMrLordX
Hmm . . . very interesting. The only point I could make against them is that, at least according to the linked article, that current-gen superalloys operate at temperatures as high as 1100C.

There are some that go higher, IIRC to around 1500°C. You might also look at metallic glasses. We had a thread about those in here a while ago.

 

[DrMrLordX]

Hmm, interesting. I'm curious about anodized tungsten as well.

 

[DrMrLordX]

Btw, thanks for all the input everyone. Certainly gives me something to consider.

 

[Veramocor]

Alumina (aluminum oxide) gets you to 2000, plus its already oxidized.

 

[NeoPTLD]

Tungsten... doubtful. Try operating a broken light bulb inside an autoclave (filled with saturated steam). I bet it'll flash and burn out instantly.

 

[DrMrLordX]

Tungsten does have a very high melting point, but I would imagine that it would oxidize readily. Also, tungsten oxide has a lower melting point than pure tungsten, so anodized tungsten would likely have very little benefit under such conditions.

I think Veramocor's suggestion may actually be helpful . . . I didn't think of corundum until he mentioned alumina.

 

[PlasmaBomb]

Is this just a thought exercise?

It's just that at those kind of temperatures metals tend to be quite ductile (hense the superalloys stating "low creep"). So your best bet may be to stay with ceramics. You may be able to use an exotic coating on tungsten to help protect it, unfortunately most of the ones I can think of would oxidise at that temp

 

[DrMrLordX]

For now, it's just a thought exercise. It might stay that way, but I do appreciate the feedback.

I did a little looking around and discovered that, realisticaly, corundum will only be useful at temps up to 1500C. Some corundum refactories can be made to provide working temps up to around 1700C (or higher) that won't break down in an oxidizing atmosphere. Coated tungsten sounds interesting but yeah, there's the rub . . . coated with what?

 

[Evadman]

Originally posted by: DrMrLordX
For now, it's just a thought exercise. It might stay that way, but I do appreciate the feedback.

Does this have to withstand constant temps? for example, the flame front in a general automobile engine is 2100 to 2500 degrees, but is contained within an iron block by aluminum pistons and an aluminum head.

2500 is twice the melting point of aluminum, and slightly below the melting point of iron, and yet the materials stand up just fine, generally staying under 300 degrees F. If you hit 500, the aluminum will start to give, and you will end up with failure at the wrist pin.

Is there a way to sink the heat in some fashion in whatever your thought experiment is?

 

[Veramocor]

Originally posted by: CycloWizard

Originally posted by: Nathelion
http://en.wikipedia.org/wiki/Superalloy

Useful?

FTW. The US Air Force (and probably other advanced air forces) are looking into burning fuel at higher and higher temperatures. Therefore, a considerable chunk of research money goes into looking at materials that will withstand very high temperatures, high pressures, and high-humidity environments (since water is a natural product of fuel combustion). The ones that I'm most familiar with are nickel-titanium superalloys, since one of my friends works on them. That said, I don't know much because most of what he does is classified.

Oakridge National Labs does a lot of materials research. I used some of their materials for studying corrosion in black liquor gasification (nasty reducing environment). I had a friend who dealt with high temperature metallics exposed to molten smelt but even that was from 900 to 1000 degrees Celcius.

 

[DrMrLordX]

Originally posted by: Evadman

Does this have to withstand constant temps? for example, the flame front in a general automobile engine is 2100 to 2500 degrees, but is contained within an iron block by aluminum pistons and an aluminum head.

2500 is twice the melting point of aluminum, and slightly below the melting point of iron, and yet the materials stand up just fine, generally staying under 300 degrees F. If you hit 500, the aluminum will start to give, and you will end up with failure at the wrist pin.

Is there a way to sink the heat in some fashion in whatever your thought experiment is?

I can clarify this a bit by adding a bit of information. I'm curious about water thermolysis and the materials that might be needed to contain water while heating it to a high enough temperature at which thermolysis would readily occur. Initially I was under the impression that thermolysis would occur at 2500C or higher, though it seems that it can occur at lower temperatures (though you get a higher % of H2O by volume at lower temperatures and/or higher pressures).

So, yes, the temperature exposure would preferably be constant. Sinking the heat would interfere with the dissasociation of water so, while it would be possible, it would be a bad idea.