×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Fundamental galvanic corrosion questions- zinc/316 stainless

Fundamental galvanic corrosion questions- zinc/316 stainless

Fundamental galvanic corrosion questions- zinc/316 stainless

(OP)
Hi:

I believe the galvanic corrosion questions I have are rather fundamental.

First, I have heard that zinc and galvanic corrosion are used to prevent boat hulls from corroding.  Is metal above the water line not protected from corrosion by the zinc since there is not a "complete circuit" from the metal to the zinc through the water?  If so, this would explain to me why such a method would be useless in preventing corrosion on automobiles.

Second,  I am working with a pivot made of zinc and a 316 stainless rod.  When exposed to a salt fog (ASTM B 117), a white corrosion builds up on the zinc.  Would there be any reason to suspect that part of this build-up is salt?

I have attempted to dissolve it in water to prove that it is indeed not salt and the majority, if not all, of it did not dissolve.  My last question is what might this substance be?

I've tried to dissolve it in Sodium Hydroxide to determine if the substance is Zinc Hydroxide but only about 80% of the substance dissolved.

Thanks,

David

RE: Fundamental galvanic corrosion questions- zinc/316 stainless

first question:

To protect a surface, hull, using a galvanic anodes (eg zinc anodes) there are two requirements to be satisfied:
-The anode need to be in electrical contact with the surface to be protected
-it's necessary that there is an electrical path, thorugh water or soil, between the anodes and the surface
 
So a catohidc protection can't work in air and a galvanic anodes has a range of efficiency, max distance at which the anodes protect the surface and is a function of the resistivity of the medium.
the second question, i think it's a corrosion product of the zinc due to galvanic corrosion between zinc anodic to stainless steel.

http://www.corrosionist.com/Corrosion_Type_Galvanic.htm

S.

http://www.corrosionist.com

RE: Fundamental galvanic corrosion questions- zinc/316 stainless

The contact between the Zn and SS in your system will accelerate the corrosion of the Zn.  The Zn will corrode some in salt fog, adding a more noble metal only makes it worse.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

RE: Fundamental galvanic corrosion questions- zinc/316 stainless

Yes, you should expect salt to be part of the deposits on the parts.  The white deposits are corrosion products - zinc oxide(s) and zinc hydroxide(s).

Regards,

Cory

Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources