4
$\begingroup$

I am experiencing partial coverage of a part during a DIY home zinc plating operation and was hoping someone here may be able to identify the cause of this.

I am using a solution of household vinegar and epsom salt to zinc plate some pieces during a motorcycle restoration but I am having difficulty getting the zinc to deposit on an area of a specific part.

On accompanying picture of a footpeg mount it is evident where the plating has not adhered.

I have done multiple runs and cleaned the part thoroughly between each run and even oriented it in different directions to the zinc anode and even connected my cathode connection point directly to the area not accepting any zinc all to no avail and was wondering if anyone has any ideas on what may be happening here and how I may resolve the issue. (My guess is there is an electrical or magnet field being generated by the "sides" of the part and preventing plating in this area as all other areas not visible have zinc adhered from the first run)enter image description here

$\endgroup$
5
  • 1
    $\begingroup$ have you used any stirring? $\endgroup$
    – permeakra
    Feb 13 '16 at 19:45
  • $\begingroup$ Sorry I didn't mention that. Yes, I have stirred the solution before and during use and the part has been fully submerged in the solution and during I also use an aquarium bubbler to keep the solution moving. Although I have also tried it without the bubbler after noticing this problem and have even reoriented the mount (pictured) in different orientations to the anode still to no avail $\endgroup$
    – Stuart
    Feb 13 '16 at 20:05
  • $\begingroup$ If you look close at the image, it will be evident that not only the surface facing you is not plated, the inner sides are not plated either and it appears the absence of plating follows the contour of the sides which lead me to believe there is possibly an electrical issue (magnetism or other) between the sides preventing the plating of this area. (just a guess) $\endgroup$
    – Stuart
    Feb 13 '16 at 20:08
  • 1
    $\begingroup$ Ions of zinc move following electrical gradient. Between the inner sides the gradien is very low if exists at all. I'd guess that either very intensive stirring or moving the anode close into the inner space should work. Otherwise, if the part is not very large, you can try to put it into melted zinc. Its mp is rather low and zinc can be easily smelted using propane torch or even common wood flame. Hell, I even melted it once using common alcohol flame. $\endgroup$
    – permeakra
    Feb 13 '16 at 20:39
  • $\begingroup$ @permeakra thanks for commenting. I'd like to extend our conversation by adding that this piece is relativetly small (would fit in the palm of your hand) and I have positioned it directly in front of the anode and it plated the edges facing the anode (pictured) as well as the back side which is against the paper in the photo but I can't get it to adhere to this inner area and the sharp line where the plating ends makes me believe something else is at work $\endgroup$
    – Stuart
    Feb 13 '16 at 22:36
1
$\begingroup$

It is hard to imagine this would be due to an electric field or a magnetic field.

I would say this has to be a different material or coating in the region where you are having bad coverage.

Would it be possible to sandpaper this piece to get rid of any potential coating? Even leftover glue from some sticky on top would cause an issue.

You could also try to electrochemically clean the surface immediately prior to the plating. Applying a highly cathodic potential should lead to some electrolysis that would evolve hydrogen gas which would knock any impurities off the surface.

Either method could roughen the surface somewhat, I don't know enough about motorcycles to say if this would be a dealbreaker.

$\endgroup$
2
  • $\begingroup$ I thank you immensely for your contribution. I'd like to add that I have wondered if there was a difference in materials at play but the piece appears to be made of the same material throughout. Regarding sandpapering the piece; I have done similar by aggressively running it into a spinning wire wheel and it appears to be bare metal across it's entire surface which I've then cleaned multiple times with Kerosene - > Brake Clean -> MEK and then Distilled Water before submerging in the solution and after plating the unplated area even develops light rust as can be seen in picture $\endgroup$
    – Stuart
    Feb 15 '16 at 14:48
  • $\begingroup$ I do like your suggestion regarding electrochemically cleaning the surfaces before plating to increase their cathodic potential and I may visit this in the near future. Thanks $\endgroup$
    – Stuart
    Feb 15 '16 at 14:51
0
$\begingroup$

I think your problem is called "throwing power" in the industry. That is a reason professional platers have chemists to modify bath chemistry . And maybe electrode design.

$\endgroup$
2
  • 1
    $\begingroup$ Would you care to elaborate? An answer of this length is pretty much just a comment. $\endgroup$
    – orthocresol
    Nov 2 '20 at 1:56
  • $\begingroup$ I was was trying to identify or name the cause. I have zinc plated test coupons but have no technology background in plating. $\endgroup$ Nov 2 '20 at 16:16

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.