tin plating corrosion

[climb1]

i have an aluminum block that is tin plated. starting to show signs of white corrosion. i have been told that it is normal for tin plating to show corrosion based on environmental conditions.

two questions:
1. can anyone confirm or deny that tin plating can corrode?
2. is there an easy test, i am thinking of some chemical that will change color in the presence of tin, that will just show if tin is present?

let me know if more details are necessary.

 

[desertfox]

Hi climb 1

The white corrosion sounds more like the oxide that forms on aluminium.

desertfox

 

[desertfox]

Hi climb 1

Normally the tin plating provides sacrificial corrosion protection of the base material, in your case the aluminium, after a period of time the tin plate cannot protect large area's of the exposed base metal and therefore the aluminium itself will start to corrode.

desertfox

 

[unclesyd]

You might be suffering from "Tin Disease".

Could you come back with more details of your application and environmental conditions seen by the part.

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

 

[climb1]

this is a high voltage connection terminal. the suspect part had not yet been hooked up, so it had been exposed to elements in a matter for a couple of months.it is in louisiana, about an hour north of new orleans. no hurricanes this year.

the part size is about 5in x 5in.

all of your input is appreciated.

 

[desertfox]

Hi climb1

Any photo's of the part? It probably best to get it to a lab I would put my money on sacrificial corrosion but I can't rule out the "Tin Diease".
A picture may help

desertfox

 

[climb1]

attached is the picture requested. only the vertical portion is tin plated. the rust on the bolts is a totally different story.

 

[desertfox]

Hi Again

I found this relating to "Tin Diease"

Tin Disease and History

The transformation of tin into its gray powdery allotrope has presumably occurred enough times in history to provide suitable examples for chemistry textbooks. Many of these accounts may be apocryphal. Many may simply be corrosion processes romanticized into bona fide cases of tin disease. (Tin by itself resists corrosion because of the oxide layer on its surface. If used to coat other metals, tin's corrosion-preventing properties become compromised when its surface is damaged. For example, the corrosion-prone steel of a "tin can" will quickly rust when its thin tin coat is punctured.) In any event, the following list may include valid illustrations of the temperature-dependant transformation of tin allotropes:

and the site it came from:-

http://dwb.unl.edu/teacher/nsf/c10/c10links/chemistry.about.com/library/weekly/aa040300a.htm

Thanks for the photo, well now I am beginning to thnk its "Tin Diease" after all, I'll see what else I can find.

desertfox

 

[stanweld]

It appears that the Tin plate has been only electrolytically deposited withouy remelting. You also don't indicate the Tin ing weight. such coatings can be quite porous. I suggest that you have the oxide chemically analyzed. I have a feeling the aluminum is substrate is corroding.

 

[unclesyd]

The only easily corroded Al alloy with the corrosion product looking like your picture is 2024 Al, especially around salt water.