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topic 3501

Does UV light have a tarnishing effect on silver?


(1999)

I am having a silver tarnishing problem with a lamp causing the brightness to go down. Does UV light have a tarnishing effect on silver? I know that sulfur does. However, I have performed an EDS analysis on the tarnished surface and I could not detect any traces of sulfur.

How about polyester resins, do they have sulfur in it?

Jaime LLinas
Houston, Texas


(1999)

Jaime, I do not think UV light is the problem with your silver tarnish. UV light can only accelerate chemical reactions but it is not a chemical itself. In addition to sulfur compounds, other chemicals also cause copper corrosion, such as ammonium, acid with oxygen, nitrogen oxide, and so on. It is not surprising to me that you did not detect sulfur on your tarnished silver surface. EDS analyzes about 1 micron depth of surface material and detection limit is about 0.5% a/a. Only single layer sulfur can lead to silver tarnish, which means sulfur content on the tarnished silver surface within one micron depth is much lower than the detection limit of EDS. I guess you can detect the existence of sulfur on your tarnished silver surface you do XPS or AES analysis which is truly surface analytical tool. Ling

Ling Hao
Minden, Nevada


(1999)

According to the lamp supplier, Because the failed lamp reflector has darkened (black) it seems it is burnt or tarnished but actually, it is discoloration of the silver. He further indicated that heat from the light source was the culprit to this discoloration. Is the discoloration mechanism a corrosion phenomenon or is it a burning phenomenon? What can I do to confirm failure mechanism?

Jaime LLinas
Houston, Texas


(1999)

If it is burnt, the main component of the black stuff on silver surface should be silver oxide. If it is tarnished, the black stuff should be mainly silver sulfide. Surface analysis will provide you with answer. Visually, silver oxide is truly black, while silver sulfide is slightly greyish black.

Ling

Ling Hao
Minden, Nevada



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