Electroless nickel coating of confined spaces

I am conducting some experiments with the electroless nickel (EN) coating of the free machining brass (high lead contain material, which is not good for coating but I must use this material).
After surface cleaning and etching procedure, once the brass is submerged in the EN coating solution, I apply approx. 2V DC to kick off the process (for first 20 seconds). Positive is connected to mild steel anode and negative to brass.
I have successfully kicked off my process and obtained good quality coating for scenario I (a few times), outlined on the attached draft, but only at 'outside' brass surface (as expected).
In scenario II (see draft) I am not able to kick off the process on 'inside' or 'outside' surface.
Finally, in scenario III, where brass is cut into two halves, I was able to kick off the process at all surfaces of the brass and get the EN coating ('inside' and 'outside').

I do not understand why I cannot kick off the EN coating process for scenario II.
The inside cavity of the brass is small, thus there is limited amount of nickel in the solution there for coating, but would that be the reason of no coating at all?
Any ideas why?

P.S. Inside and outside surfaces of the brass are cleaned, etched and rinsed with use of the same procedure.

Please help. Thanks.



Science Advisor
Gold Member
You need active agitation .

Mild application of ultrasound would be ideal but failing that use a standard lab vibrating table .

Real etching and plating systems often have full circulation of the electrolyte and/or active jetting of the electrolyte onto the surfaces being worked on .

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