Fun with Chemistry (anti-corrosion)

[graham-xrf]

So, it absolutely is possible to do what you are suggesting. It appears that the rectifier control is the trick and the rest is plumbing, chemistry, tooling and setup.

This feels like it is absolutely in the wheelhouse of hobbyists from my point of view. Now to find a rectifier...

OK - decoding what is going on with the "pulsed" plating. Stop the video at the places where you get a view of the power supply display readings. e.g. at 6:57. See that at the time it was running 2.88 amps, and had been casually set to approximately 9 volts, and that it had delivered 2.55 Ampere-Hours worth of electrons. There is no sign of where it gets it's "pulsed" capability from.

Now - extracted from another paper, I find the following text..

Electro nickel plating involves a wide range of current density levels. Current density directly determines the deposition rate of nickel to the base material—specifically, the higher the current density, the quicker the deposition rate. Current density, however, also affects plating adherence and plating quality, with higher current density levels delivering poorer results. Therefore, the optimal level of current density depends on the type of base material and specific type of results the final product requires.

One way to avoid working at lower current densities is by employing a discontinuous direct current to the electroplating solution. By allowing between one and three seconds of break time between every eight to fifteen seconds of electrical current, high current densities can produce a higher level of quality. A discontinuous current is also beneficial for avoiding over-plating of specific sections on the base material.

So the answer is , if you have the patience to put up with a longer plating time, the lower current density (without pulsing) will deliver a highly adherent coating. Short bursts of higher density can make a thicker coating, faster, and with stress, adhesion, and hardness qualities that depend on all the bath parameters, and the pulsed duty cycle.

In the text, they describe pulse cycle periods of 8 seconds to 15 seconds, with ON time between 1 second and 3 seconds. If I were trying it, I might try pulse cycles as short as 0.5 seconds period.
20 whole seconds seems a big maximum, but we go with it for now.

The actual current you hit it with should likely not be more than you might allow when going for the faster, if poorer, quality deposition, on a non-pulsed supply.

[Edit: Hmm.. it turns out to be more complicated than that. Even though the use of current pulses in the plating process is used, it might be essentially an electro-less process. The current pulse and duty cycle is too low to be the main delivery of deposited metal. The effect of the pulse every few seconds is to re-start an electro-less process which has slowed down - a normal characteristic. Pat US3,264,199 (1966)]

 

[vtcnc]

Zinc is electropositive w/ respect to iron and will corrode instead of the iron. The zinc electroplate that is used on fasteners is too thin to be of much value. When iron is galvanized, it is hot dipped and has a fairly thick coating.

Copper can be plated on iron. In fact, when chrome plating, copper was first plated, then nickel, then the chromium. Steel MIG wire is coated with a copper electroplate. You can actually plate copper on iron by just dipping the iron into a copper sulfate or copper chloride solution.

Many visitors to our factory think we nickel plate our cast iron parts in our factory with a copper strike first - because of their knowledge of chromium plating. We don't. Just Nickel on cast iron. Our products are commercial can openers. We find that the business end of the can opener suffers corrosion before any abuse to the cast iron bar itself. But that is a use-case example, not a good discussion about plating. I suspect that for many hobby machinists - static, load bearing or decorative pieces are good candidates for nickel plating without much worry of corrosion.

@graham-xrf - cleaning, we use a caustic soap to remove organics, then hot acid bath, then hot rinse before going into the nickel bath. Getting rid of the organics (carbon, dirt, oil, etc.) is paramount for good adhesion.

 

[vtcnc]

@RJSakowski : OK - I got it wrong then.
What happens without the help of a battery or power supply seems to be all about which has the greater (natural) electrode potential, (compared to hydrogen) ... I think. This stuff can get complicated. You make a solution, and already it is no longer the straightforward ingredients.
It "dissociates" splitting up into some Ni++ and (other stuff)- -
Not all mind, but only some proportion in an "equilibrium", which can get urged on by a battery.

I think, if there are other metals encountered, one will be the winner - Hmm. I did some chemistry at school, but I must have slept through this one.

I am still feeling quite stoked about the way that plating went onto the end of the shaft, and I am already dreaming of diverting whatever I can in the way of other household plastic containers to the new secret cellar purpose.

And yes - I do want to attempt some of THIS stuff! (thanks @vtcnc ).

Wow! Was that a piece of 3M Scotch Brite pad he was using to deliver the solution?

It could be felt.

 

[graham-xrf]

Nickel strike is the standard first go-to process prior to laying on most any other metals. It's the first thing plating shops do, and they push back when you veto nickel.
Difficult in the case of of aluminum, where the favourite way in is via "double zintec". What happens second time around is not the same as the first. Then copper, as precursor to more metals.

Nickel first strike is cheap, easy, self-limiting, and thin, and given the electrode potential, it will go on most other metals. e.g. the thick "chrome" plating on your motorcycle exhausts is mostly nickel, to go under a very thin layer of shiny chrome, and the chrome is "micro-cracked", with the cracks reaching in only as far as the nickel, to relieve the peel-off stresses, and still be corrosion free.

One thing I have always known about nickel is to steer well clear of it in any part of a process to plate RF microwave kit involving transmit power. Nickel is a transition metal, and I did not think it to have semiconductor properties, but unless one can guarantee that there is total complete coverage of all the nickel by the next metal, the slightest pinhole, burred screw thread, hole anywhere - anything that exposes the nickel metal junction to moisture will generate the father and mother of radio frequency intermodulation distortion and unwanted signal mixing products. I have spent years insisting that nickel be excluded in built kit.

It's nice to have the beautiful green stuff on my side this time!