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Cobalt infused gold coating


I've recently been doing a lot of research in magnet coatings, and found out something interesting which I'd like to share.

Now, regularly, even pure gold is far from being a perfect coating, but I've recently found out about the use of cobalt in gold electroplating.

Ok, so at first - why?

Cobalt improves adhesion of the deposited gold, and also increases the final hardness.
Elemental cobalt is also ferromagnetic, which would improve the layer adhesion even more, but due to its low quantity, the magnetic effects are likely to be negligible.

Industrially, cobalt is often used to improve hardness and survivability of galvanic gold coatings, forming about 0.1-0.3% of the final alloy.

Pure gold has Knoop hardness of 60-85, while cobalt-gold plating has Knoop hardness of up to 300 (usually 200-250), which makes it more than 3 times harder.

Also, since it can be electroplated, the availability and price would be almost the same as regular gold coatings.

Now the hard part - determining whether cobalt additives are actually viable for a subdermal implant.

In the past, cobalt was used in metal on metal hip implants, but nowadays it's mostly been ruled out due to its toxicity, since the motion and stress of the implant caused mechanical degradation and intake of the material. It's important to consider that those were high-content cobalt alloys.

Cobalt ions are toxic in high quantities in the body, with an LD50 of about 150mg - 500mg per kg of body mass, however, it is also present in the body naturally, mostly in form of cobalamine (vitamin B12) with the recommended daily intake of about 5-8 micrograms per day.

Let's consider a disc magnet of 1x2mm and coating thickness of 20 microns and cobalt content of 0.5%.
That gives us about 48.3455 micrograms of cobalt per magnet. A lot of this cobalt would be locked inside the crystal, and even then, absorption of exposed cobalt would be quite slow. Still, at roughly 50 micrograms, the amount of ALL the cobalt that would be deposited is not that far away from the recommended daily dose.

I'm not going to say that it is absolutely safe, but for me, it is safe enough to try it.

What do you guys think?


Displaying all 6 comments
  1. Interesting. Do they sell any or have you contacted any magnet companies? I would like to know what you find. And what your tests results are.

  2. @SimplyTom said:
    Interesting. Do they sell any or have you contacted any magnet companies? I would like to know what you find. And what your tests results are.

    I haven found any pre-coated magnets, but a lot of companies sell cobalt-gold plating solutions.

  3. Mmmm how much? I might go in on it with some people if anyone wants.

  4. Yeah. I've seriously wanted to try electroplating. There are so many things I want to try.

  5. Ok, I confirm that this technology is easy and affordable to do within home environment. I first cleaned the magnets in concentrated solution of NaOH, then HCl, then again in NaOH to neutralize any leftover acid and grease. I plated it at 2.8 volts for 2-20 minutes (experimented a lot with the duration)

    I implanted a magnet coated with a dense layer of cobalt-gold (my supplier claims that the Co content is less than 1% for any reference).

    I removed the magnet and inspected it after 3 days. The coating is still solid and uniform. There are no signs of rejection in the site whatsover, the tissue is healing very nicely.

    I reinserted the magnet and I'll post further updates as the time passes.

  6. @delta12 who was your supplier?

Displaying all 6 comments