Nickel experiment gone awry

[jon]

Hi! This is my first post, so be gentle.

I am a hotel engineer, and I've been using the nickel kit for several weeks now with excellent results, saving thousands in plating costs. So when my 12-year-old daughter needed a subject for her seventh grade science project, I thought plating would be a slam dunk. She could plate samples for various time periods and compare the deposition rate with theoretical values.

We carefully cut sheet brass into eight 1" squares. We used a micrometer with 0.0001" precision to measure their "before" thickness, which was uniformly 0.0200" for each sample. We then plated them at fifteen minute intervals at a closely-monitored 140 mA, that is 70 mA/sq. in.

Here's the rub; every sample, whether plated for fifteen minutes or an hour and a half, has turned out to measure 0.0209". What is cutting off deposition? The current has stayed pretty constant-- within 2 or 3 mA as measured through a multimeter.

[cprocess]

One theory - unless you are replinishing the plating solution, you are plating out the available nickel ions in the solution. As the nickel metal concentration decreases, the plating efficiency decreases as well.
Another thought, make sure you have good solution movement. The solution needs to move around to make sure enough nickel metal is always available at the part to plate. Also, nickel becomes less conductive as the thickness builds, so the solution movement will help overcome the potential resistance at the solution/part interferace.
Also, check the pH of the solution before plating each panel. As you plate, the pH increases so may need adjusting to maintain the same plating efficiency.
The last thought is that since you are plating very thin deposits at this milliamp current, it may be difficult to get an accurate thickness reading with a micrometer caliper.

Hope this helps. If not, maybe it will give some insight on topic to research for the science project, thus better understanding how nickel plating works.

[lcaswell]

If you stop the nickel plating cycle at any time, no more nickel will deposit. You'll need to activate the old nickel layer with Pickle #3 (battery acid/water) to increase the thickness.