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Electropolishing Zirc-2 for nuclear applications - sulfur contamination question

January 24, 2012

Q.
I work in the nuclear industry and recently received an inquiry about electropolishing. It was handed down to me based on industrial cleanliness grounds, but unfortunately I have no background in electrochemistry. After a literature search and a lot of reading I am no further along. We are getting more details, but I'd like to get out ahead of this.

A supplier of ours is switching their electrolyte from Na₂NO₃ to Na₂SO₄ (I'm not sure if it's pure sodium sulphate or a mixture containing ... I'm thinking the latter.) They electropolish Zirc-2 components for us that then go into a reactor. Sulfur (of any kind) is not permitted on any of our components. My question is will this switch lead to sulfur contamination on our components?

At those temperatures and currents, will elemental sulfur be in the solution? Will it accumulate at the electrode (how does stirring the solution effect this, etc.?) Na₂SO₄ is water soluble but sulfur is not. If sulfur is present in the bath, rinsing with water will be insufficient to remove it, correct?

I know Nb superconducting RF cavities have a lot of problems with sulfur contamination (H₂SO₄ and HF solution) - does this sort mechanism come into play with Zirc-2?

Baring any show stoppers, what would be a good way to test for the presence of sulfur from coupons? methanol [affil links] wipedown? Ultimately I'd want an XPS (otherwise known as ESCA) analysis done, but any responses will help me with questions I should be asking.

Thanks!

Kyle Haygarth
engineer - Lynchburg, Virginia, USA