Problems with electroplating

[Ladeira]

Hey guys. I'm back to SFN with a very boring issue.

 

I'm doing some pretty nice copper electroplating on stainless steel pieces using a solution containing 250g.L^-1 CuSO₄.5H₂O, 0.05 mol.L^-1 H₂SO₄ and 0.1 g.L^-1 SDS. As it is for codeposition of suspended particles, it is desirable to use a dispersant (SDS) and EDTA.

 

I usually use a temperature of 28°C (82ºF) that is mostly related on the articles I've seen, but somehow, when I used a temperature of 50°C (122°F) which is still OK for this kind of electroplating and took the sample to EDS analysis on a SEM, there was a big peak of Cl (15% wt. of the surface). Question is: WHAT THE HELL IS CHLORINE DOING HERE?

 

I don't know if it's about the temperature, but anyhow there shouldn't be any chloride in this solution.

 

Even if there was, how would it be joining the plate?

 

So, I tried using the simplest method around, testing the solution with AgNO₃. Ha! So it gave me a precipitate that seemed to be white (though it surely could also be gray). I really thought 'oh it's AgCl then'. I filtrated it and took it to the oven at 600°C (1112°F). Then took it to EDS analysis. And what did I have? Pure METALLIC SILVER!

 

Now I don't really know what to do. What is reducing Ag⁺ to Ag⁰? And now, how to explain Cl on the plate?

 

Some informations:

 

1. Dry acrylic paint, acrylic, stainless steel and carbon electrodes gets to be in contact with the electroplating solution.

2. There are two procedures before the plating (anodic activation and nickel strike), both of them include a solution with HCl but it's impossible that the HCl gets to contaminate the copper plating solution as everything is very washed from a procedure to another.

3. Would the distilled water be contaminated with chloride? Sounds good but still does not explain how there was Ag⁰ and no AgCl.