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 Posted: Mon Feb 25th, 2013 04:36 am
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spotted glass
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It is my understanding that lead and zinc are incompatible.  Can anyone explain what the issues are and is there a problem with the solder and zinc since there is lead in solder?



 Posted: Mon Feb 25th, 2013 05:11 am
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Don Burt
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I've always heard that due to galvanic corrosion, you can't attach zinc to much of anything and expect it not to corrode more at the points of contact. Zinc basically sucks on the anodic scale.

http://www.roymech.co.uk/Useful_Tables/Corrosion/Cor_bi_met.html

But your question is interesting and I'd also like to know the answer. Do solder joints (i.e. tin/lead alloy) on zinc corrode as quickly as zinc touching unsoldered lead? How come you can coat steel with zinc via galvanizing and it resists corrosion better than untreated steel?  

 

 



 Posted: Tue Feb 26th, 2013 02:58 pm
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artfem
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I've always heard that due to galvanic corrosion, you can't attach zinc to much of anything and expect it not to corrode more at the points of contact. Zinc basically sucks on the anodic scale.
 
Don:
I appreciate your comments on Zinc, but it actually plays a very important role in the world of metals.  Zinc properly applied to common steel, a process called galvanizing will protect the steel from rusting because it does not allow the steel to come into contact with water. Most steel is electro-plated today but the best form of galvanizing is hot-dipped.
 
Zinc is used as a sacrificial anode, or a free supplier of electrons, and used to protect more valuable metals from corrosion by sacrificing itself first.  Sacrificial anodes are used on boats, especially in salt water, so that the anode corrodes away protecting the more valuable parts of the boat from corrosion.  
 
http://www.roymech.co.uk/Useful_Tables/Corrosion/Cor_bi_met.html
 
The above link provided by Don is an excellent table to deepen your understanding of galvanic corrosion, the type of corrosion we are discussing here.  The first table indicates the differing electrical potential of many metals.  It is important to note that alloys of the same general material occupy different places on the galvanic chart.  Stainless steel alloy 304 is stronger than alloy 316L but it corrodes more readily. The metals that are more "noble" tend to be more resistant to corrosion than those that are less noble. 
 
The technical explanation of this can be quite lengthy, but a short version is this: electrons orbit around the nucleus of an atom in rings, or more accurately clouds, and have various levels of energy.  The more noble metals have a higher energy level or "stronger" forces, partially a function of how many electrons are in a particular level, determine how readily an atom will give up an electron to an atom of another element.
 
The farther apart any two metals are on the galvanic chart, the greater the electrical potential between them and the greater possibility that the less noble of the two will corrode if the two metals are placed in contact within an electrolyte. The second chart at this site indicates the importance of the electrolyte in this process.  One sees that there is a dramatic difference if the electrolyte is distilled water or sulphuric acid.   
 
But your question is interesting and I'd also like to know the answer. Do solder joints (i.e. tin/lead alloy) on zinc corrode as quickly as zinc touching unsoldered lead? How come you can coat steel with zinc via galvanizing and it resists corrosion better than untreated steel? 
 
The tin/lead alloy behaves quite differently than when zinc is soldered to lead.  The failure point of the zinc/lead came matrix is at the edge of the zinc that is closest to the solder.  This is not a function of the tin/lead solder, the solder simply acts as a conductor between the zinc and lead.  Again, for this failure to occur there must be an electrolyte. If you have a combined zinc/lead panel in a climate controlled condition or in the middle of an arid desert, there will be very little corrosion.  If you live in a marine environment, the corrosion will be quite severe.  I worked on a number of these panels from an area near San Francisco in the early 90's and all of them exhibited severely corroded zinc at the solder joint to lead cames.
Galvanized steel works because the water cannot get to the steel surface. 



 Posted: Tue Feb 26th, 2013 03:34 pm
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Rebecca
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I'm not sure if I am understanding the question, but what I think is being asked is if you make a window completely in zinc, are the solder joints at risk. The answer is yes. There is still a zinc/lead interface because of the lead in the solder. I have had zinc windows come for repair with all of the joints broken and the whole thing in pieces. As Art said, it depends on the environment. Some cabinet doors, that have only been exposed to an indoor environment are fine, while windows exposed to the weather have fallen apart.

Rebecca



 Posted: Tue Feb 26th, 2013 03:47 pm
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Don Burt
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Thank you Art. That's good information. I feel bad now about insulting zinc. It is undeserving of being denied classification of a noble metal. Sacrificing one's electrons in defense of underlying metal is as noble a metallurgical gesture as I can imagine.



 Posted: Tue Feb 26th, 2013 11:32 pm
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spotted glass
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So, if a stained glass panel is made with lead, but has a zinc border for strength and will be hung in an interior environment, not installed, is there a serious concern about corrosion?



 Posted: Wed Feb 27th, 2013 03:38 am
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Steve
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I am curious about the misconception of a "zinc border for strength"? interior or exterior, doing an edge in zinc for strength I feel is a false sense of security. The corrosion will take a very long time, but will happen. Just happens faster with exposure to moisture. If hte panel built is insatlled in a frame, then it does not matter what is on the border, if it is hung by the metal frame of the panel, the strength is marginal at best.
To answer your question about the integrity of the joint with solder to zinc, somebody will have to repair it at some point.



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