electronegativity of aluminum and steel 1

[engrnick]

Hi all,

I'm not an expert in corrosion and electronegativity, but I've got a test setup that I made for my client. the fixture is 316 steel and to test the setup my client said "just have some aluminum caps made."

Not thinking too much about it, I had them made. We were gonna use the test fixture for 1-2 days, and I didn't think anything of electronegativity between the steel and aluminum. After 24 hours of letting tap water sit in side the chamber, the caps had a white gunk on it, and the dumped water had particles floating inside. I don't know if it's from the brand new fixture that no one looked inside of, or from the tap water.

My question is, how quickly will a galvanic reaction between aluminum, 316 steel and tap water happen? I'm trying to determine if new steel caps need to be made, or if it might have been dirty water or a dirty fixture.

Thanks!

 

[swall]

It is always better to use like materials when there is exposure to an electrolyte and the potential for galvanic corrosion. BTW, I believe the term you were fishing for is "electomotive force series" not "electronegativity". The latter describes the tendency of one element to pull electrons from an other, whereas "electromotive force series" describes the propensity for galvanic corrosion to occur. To your question--the is no way to answer. How corrosive is your tap water? What temperature? What was the anode area relative to the cathode area?

 

[engrnick]

Thanks for the clarification, it's been decades since I studied this stuff.

The steel fixture is about 7" long and 1.5" diameter, the aluminum caps cover the end of the tube, so the exposed diameter is 1.5".

The aluminum is the anode then, isn't it. hmm.

The temp is room temp, and the tap water is typical LA water. When you mention the area part, now I'm thinking that the aluminum was a bad choice...