plating, anodizing, & finishing Q&As since 1989
Silver Plate Surface Contamination
June 10, 2010
We are a medical device manufacture that utilizes silver plated parts for our product.
Recently we have been experiencing an issue with sulfur contamination on our Ag part (as verified by EDS.)
Our Ag part is plated per Mil spec QQ-S-36S TYPE II, GRADE B, .001" THICK, over a 0.0002" Nickel plate preceded by a copper strike over our base material which currently is SS303.
The parts are cleaned post plating by DI water only
I was hoping to receive some advice on the possible source before speaking directly with our vendor.
1) Plating additives? My understanding is that sulfur-containing suppressors are used in some plating packages and possibly in brighteners as well.
2) Residual anti-tarnish from previously plated parts? (we HAVE had some residue on the parts that is removed by Heptane.)
3) Migration of Sulfur from the SS303 Base material? (we switched from brass due to other issues.) The migration of sulfur SEEMS unlikely; SS303 was recommended by vendor.
I deeply appreciate any insights I might receive.
Chemist in Manufacturing - Austin, Texas, USA
August 8, 2010
Besides plating additives or anti-tarnish residues, sulfur could also come from silver tarnish film formed on unprotected silver surface with the present of oxygen and sulfide simultaneously.
Chemical reaction as below:
4Ag + O2 + 2H2O + 2Na2S ---> 2Ag2S + 4NaOH