Adventures in Electroplating

I'm working on a project and wanted to add something special to some of the 3d printed parts. I had originally wanted to do Lost-PLA/investment casting and make some bronze parts. But after looking at the price tag for a kiln and nice furnace, getting started was going to be > $1000 to make anything nice.

So, I decided to go halfway between that and metallic silk PLA prints, i.e. electroplating.

What is Electroplating?

If you put a "metal salt" into water, the metal salt breaks up into a positive metal ions (cations) and the associated negative ions (anions) of that salt. They float around and are happy, that is, until you run some electrical current through the water.

To run current through the water, you need to make it conductive (pure water is not particularly very conductive by itself!) So we will normally add something to the water that will make it conductive, but also not interact much with the metal salt in solution.

The metal cations(+) are attracted to the cathode(-) that we stick in the water. The anions(-) are attracted to the electrical anode(+). We need to use both positive and negative electrical terminals in order for the current to flow and for interesting things to happen.

When the metal cations get to the cathode, the electrons are donated to the copper ions which are reduced (given electrons) and the copper attaches to the cathode. A similar thing happens in reverse on the anode which is oxidized. There are a lot more details, but this gives you the gist.

If we have a copper salt in water, attach something conductive to the cathode, and drop an anode in the solution as well, and then finally make the solution conductive, the copper will come out of the solution and deposit as solid metal on the cathode, one atom at a time! Given enough time, power and metal salt, the entire conductive area of the cathode will be covered in a solid metal coating. Cool, right?

So How Does One Do It?

If you are smart, you buy a kit. If you are short on patience, you try the DIY approach with whatever you can (or can't?) find at local stores. I generally find that starting with DIY is good for learning the basics and then I graduate to the commercial stuff so that:

1. I can appreciate the "good stuff"
2. I have some idea of the reason for the more complicated commercial processes or equipment

So I did both. I attempted to get the DIY stuff and ordered some supplies at the same time. I also did not order the absolute best supplies (yet?)

Basic DIY Method

There are several ways to do this, but the one I chose used the following items:

• Nitrile gloves + chemical resistant goggles
• Copper sulfate root killer (pure blue crystals), no foaming stuff
• Sulfuric acid (battery acid refill from auto store @25-30% concentration)

WARNING. This is dangerous stuff. This can kill, burn, blind, poison, and generally leave you in bad shape if you are not careful. It's debatable if I should even be using this particular chemical. This article is meant to be educational, hopefully entertaining, but not instructive. Find an official source before you try this yourself.

Moving on...

• Distilled water.
• Copper wire.
• DC power source, preferably with a current limiter.
• Something conductive you want to metal plate.
• HDPE container

Put on safety gear. The HDPE container is filled with distilled water and copper sulfate in "scientifically determined" quantities. To that some sulfuric acid is carefully added to make the solution conductive. You hang the item you want to be plated on one side of the container (cathode). On the other you have your copper wire (anode). Set the power supply to some number of volts between 1-3. Set the current limiter to the magic value. I wanted things to go slowly, so I used 0.5A.

Well, that was how it was supposed to go. Except they didn't have the root killer (I found some elsewhere at a different store at a later date). But I did have a bunch of copper tubing. So I decided to try to make my own copper sulfate.

Diversion 1: Making Copper Sulfate

The great thing about using sulfuric acid with copper sulfate is that, well, as copper is deposited to the cathode, if you use a copper anode, the copper is oxidized at the anode which degrades it. This is fortunate for a couple reasons:

1. We don't want anything other than copper in the solution that will contaminate the chemistry. So copper is good!
2. The copper is oxidized during the electrolysis to copper oxide. This reacts with the sulfuric acid to produce copper sulfate (yay!) and normal copper (meh!).

We can take the normal copper and figure out what to do with it later.

Even without copper sulfate, with the copper anode I thought I'd try to do the electroplating with just moving the copper from the anode to the cathode. What I got was:

• A very light blue and weak copper sulfate solution.
• Copper metal precipitate at the bottom of the container
• What looked like red copper(1) oxide covering the cathode.

This copper sulfate was not nearly as dark as the solutions I'd seen online. It seemed like to get reasonably fast electroplating, I'd need a solution with more copper sulfate in it. If only I could convert the copper precipitate into copper sulfate.

Diversion 2 - Using the Copper Precipitate

Sulfuric acid cannot directly dissolve copper metal to make copper sulfate. However, one can add hydrogen peroxide to sulfuric acid to make something called Caro's acid a.k.a. "Piranha Solution" that through a two step (catalytic?) process converts copper into copper(ii) oxide and then into copper sulfate.

The problem is, it is extremely exothermic and needs to be put in an ice bath to keep from getting out of control. So, yeah, maybe someday, but not today!

But I did see what seemed like a more tame pathway which was using sodium bicarbonate, hydrogen peroxide and heat to convert the copper to copper(ii) oxide and then copper carbonate. The copper carbonate could then be combined with sulfuric acid to produce copper sulfate.

I tried it and it seemed to work. It made a very nice light blue colored precipitate which I isolated and eventually combined to make some very dark copper sulfate. It was pretty saturated and some crystals even formed at the bottom of the container in the subsequent 24 hours.

Delivery

By the time I had gotten my homebrew copper sulfate worked out, my first delivery arrived. A five pound package of copper sulfate powder.

I mixed a new solution, added the acid and was ready to try again. But there is on part that I left out. If I want to electroplate a 3d print, how do I make it conductive?

<< Rewind << to << Conductivity << Part

3d printer is a generic term. There are many types. If you want to know more, Google that stuff. I use FDM printers. They use thermoplastic filament to form the prints. Most thermoplastic is NOT conductive. There is some conductive filament available, but I don't think it is terribly conductive and I've seen people have poor results with it online.

I had seen others report success with homemade graphite slurries and other conductive paints. I tried paint with zinc in it (galvanizing), but I think that had some chemical interactions and it may not be possible to plate copper on zinc.

I also tried isopropyl alcohol with graphite powder. That didn't seem to work well and was very messy. But that test was with my weak copper sulfate, so perhaps that is worth a retry.

When my copper sulfate arrived, soon after I got some commercial spray paint that contained graphite. You just spray it on, let it dry, and your part should then be conductive.

First Success

With the new solution and conductive paint, I did another run. I ran a Benchy for about 24 hours. When it came out, it was sort of a pink or salmon color with what looked like some oxidation and rough spots. But after some sanding and some very crude polishing, the polished side was a nice hard layer of copper!

I feel like I'm on the track to getting better results.

The next steps I'll take are:

1. Add some polyethylene glycol to the solution. I've read this helps.
2. Use a larger container and put the electrodes further way from each other.
3. Potentially use less acid to lower the "throwing power" to get more uniform coating.
4. I purchased a platinum covered titanium mesh anode to try. This should not degrade like copper or graphite anodes and not affect things chemically.
5. I'd really love a fume hood to do this stuff in. There shouldn't be a lot of dangerous fumes from this particular chemistry, but I really had fun experimenting.
6. I got a programmable power supply. I'd like to experiment with programs where I vary the voltage or current to see how that affects the speed and quality. I can easily imagine an annealing curve to optimize quality vs time spent plating.

I hope you've enjoyed this. Thanks for reading!

p.s.

Intro Image with Annotations + Legend

1. Nomex (heat resistant) glove
2. Programmable power supply
3. Hydrogen peroxide (3%)
4. Pyrex measuring cup with copper(ii) oxide + sulfuric acid
5. Heating plate
6. Copper carbonate precipitated out of, but still with solution
7. Copper tube (anode) - (Hahah, hooked up incorrectly to negative.. should be positive. Who staged this photo!!!)
8. Copper wire for suspending item to be plated (cathode) - (Again, hooked to red.. should be black!!!)
9. Copper sulfate solution (homebrew #2!!!)
10. Acidified copper sulfate solution (homebrew #1)
11. Sulfuric acid
12. Eye protection
13. Nitrile gloves
14. Eye dropper/stirrer!
15. Sodium bicarbonate (baking soda) for unintentional acidic incidentals

Covered Chemical Reactions

1. 
Cu + H?SO? -> CuSO? + H?O + Cu?

Copper + 30% sulfuric acid became light blue copper sulfate solution and deposited a non-metallic red powder copper(I) oxide on the cathode as well as on the bottom of the container.  


2.
Cu?O + H?SO? -> CuSO? + Cu

The copper(I) oxide was put into more sulfuric acid, generated a small amount of copper sulfate and appeared to make normal copper powder?


3.
Cu + NaHCO? + H?O? -> CuCO? + ?(NaOH + H?O)

The copper powder was mixed and heated with sodium bicarbonate (NaHCO?) and hydrogen peroxide (H?O?) to make copper carbonate.

The hydrogen peroxide acts as an oxidizer, oxidizes the copper to make copper oxide which then reacts with the carbonate ions to make copper carbonate.  


4.
H?SO? + CuCO? = CuSo? + H?O + CO?

The copper carbonate separated and was mixed with sulfuric acid (H?SO?) to create more copper sulfate (CoSO?).