Copper breakdown in liguid aluminium in copper crucible 3

[asimpson]

I am doing experiments with liquid aluminium around its melting temperature in a special copper container with 5mm thick walls.

Heating by inconnel immersion heaters.

A while after aluminium melted, copper walls broke down and aluminium poured out.

Could not see this when it happened because apparatus was encased in insulation. After cooling the copper container appeared to have been eaten away in one side rather than melted. No evidence of pooled copper.

Temperature should not have gone above 670c.

What could have happend since melting point of copper is over 1000C well above experimental temperature?

Thanks

 

[Compositepro]

The copper dissolved into the aluminum. Copper is a common alloying ingredient in aluminum. Steel will also dissolve into aluminum. This is why crucibles are usually ceramic.

 

[arunmrao]

PLease check the Al-Cu phase diagram, that shows copper is soluble in liquid aluminum. Suggest you use a graphite,silicon carbide or C.I crucible for melting.

_____________________________________
"It's better to die standing than live your whole life on the knees" by Peter Mayle in his book A Good Year

 

[asimpson]

Thanks guys. That explains it.

A little research or testing could have saved a considerable amount of effort and money. Unfortunately I work with people with a "just do attitude".

I wanted Cu because of its high thermal conductivity. Cant think of a ceramic to match it.

Perhaps a lining of ceramic would prevent interaction but it would have to be thin not to compromise thermal transfer.

 

[cloa]

Aluminium Nitride is about the gold standard (excluding the awkward BeO) in conductive ceramics- only about one quarter of copper's conductivity and wet but not attacked by aluminium.

http://www.anceram.com/pdf/aln_artikel_bull.pdf

 

[asimpson]

Just out of curiosity on the Cu-Al phase issue.

I would have assumed Cu would not have gone into solution with Al until its liquidus temperature 1080c were exceeded.

Is there a temperature above 550c when this may be true?

 

[asimpson]

Would I not have the same problem with cast iron? Solid Fe going into solution with liquid Al?

 

[arunmrao]

You can give a refractory wash to the crucible. Unless you need to completely avoid iron contamination, cast iron will be a cheap alternative.

_____________________________________
"It's better to die standing than live your whole life on the knees" by Peter Mayle in his book A Good Year

 

[EdStainless]

You could even make one from low carbon steel (1002). With a light ceramic wash on the inside it will hold up fine.

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Plymouth Tube

 

[IRstuff]

" would have assumed Cu would not have gone into solution with Al until its liquidus temperature 1080c were exceeded."

No, that's the whole point of having to create eutectic phase diagrams, below is the Al-Fe diagram:

http://legacy.library.ucsf.edu/tid/...id=DBE2E1946F9A1FF87A65D335B63ECA47.tobacco03

Solder is a common eutectic, where the specific composition 62/38 results in the lowest melting point, which is considerably lower than that of lead.

http://www.chemguide.co.uk/physical/phaseeqia/snpb.html

This site has Al-Cu and Al-Si diagrams:

http://pwatlas.mt.umist.ac.uk/inter...hs/microstructures/more-metals/al-alloys.html

Again, note that the Al-Si eutectic dips below 600°C, even though Si by itself has a melting point over 1400°C

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