Material Selection?

[jackson]

Pure aluminium tanks were chosen to store 100% conc. nitric acid on a commercial scale.When 50%v/v HNO3 is used,corrosion happen.Causes?Is it due to oxidation forming Al2O3,but when scratched,exposed aluminium,which reacted with the diluted acid?What type of materials should be selected?Can i select Stainless steel 314 and polyethylene?What other materials can i select and what factors must i consider.

 

[DanTheMan]

I took a course in college on corrosion, and it is a complex subject. Metals can react differently to acidic or basic solutions based on pH.
Likely the aluminum is forming Al2O3 in the persence of HNO3 when it encounters a scratch, but that is not the issue. Aluminum corrodes in the presence of atmospheric air and forms a very thin layer of Al2O3. This layer provides protection from further corrosion because the Al2O3 sticks to the base aluminum. When steel and iron rust the corrosion product does not stick and flakes off. This results in the base metal corroding further in the presence of a corrosive.
I would think Aluminum would atnad up to nitric acid, but I can't find my corrosion text book right now. If any one else can assist please do.
Using a corrosin resistant stainless steel such as 304 may be an option. Nitric acid is commonly used to passivate steel and stainless steel so that they are more corrosion resistant. The nitric acid forms a corrosion product that sticks to the base metal and protects the steel against further corrosion. However once again I don't have my text book to check if you can use stainless steel in nitric acid for long periods of time. Help would be appreciated in this area also.
For further information in the area of corrosion try to find ASCE (American Society of Corrosion Engineers).

 

[MJCronin]

Try the following corrosion forum:

David Hendrix at

http://www.hghouston.com

Good Luck !!!

MJC

 

[DanTheMan]

Oops, that should be NACE at

http://www.nace.org