Safer electroplating solution 1
Robert Murray-Smith posted a video describing an electroplating solution here:
which uses safer chemicals for electroplating than most traditional methods. According to the patent, US 7235165 B2,
the solution has some very interesting properties:
- it uses chemicals that are safe enough to be used as food additives
- the metal ions can be removed from the solution easily by using a carbon anode and plating in reverse. So, for example, a solution that has just plated copper can have all the copper ions redeposited on the copper anode and then a nickel anode can be used with the same solution.
- a variety of metals can be plated, such as copper, nickel, zinc, silver, gold, iron, lead
- alloys can be plated such as manganese-nickel alloys (Monel), stainless steel, brass
- alloys can be produced by providing anodes of different metals (zinc and copper for brass, for example)
- a variety of substrates can be plated on to such as aluminum, steel, copper, brass, steel, stainless steel, lead, zinc, nickel
That is a very interesting set of claims!
There is a range of effective compositions for the plating solution, but the 'standard solution' composition that I will base the experiments off of is:
32g Oxalic Acid
10g Trisodium Phosphate
4g Ammonium Sulphate
950 mL Deionized Water
For a start, I used water from my water filter, which is not deionized. Maybe it will turn out to be necessary later.
Time to start a series of experiments. It took some time to get the kinks worked out. Here is a run-down of the notes:
I was able to reproduce copper on stainless spoon. The first coating was nonadherent. I assumed the TSP in the solution and copious amount of bubbles produced during the 'copperification' of the solution would clean any residuals off of the spoon (just came out of the dishwasher). That was wrong. Thanks to Dan Gelbarts' suggestion of using AJAX for surface prep, the repeated attempt produced a great, strongly adherent copper coating on 18-0 stainless.
In a subsequent experiment, I tried reverse-running with opposite polarity for a short time to surface clean the stainless. That only resulted in some deposit on the stainless that needed to be scrubbed off.
I note that the copper very quickly gets covered by verdigris like coating, constantly increasing the voltage required to hold current.
I also note that after running the reverse current with carbon Anode to put the remaining copper back on results in all the deposits of the verdigris like coating to disappear from the copper, but that stuff just drops to the bottom of the container. Even after several hours the blue color does not disappear from the solution.
I have a cadmium anode, so I will likely try to put that onto copper next (easy to see because of color difference).
Chrome anode still on the way....
Comment from Robert on these results:
"I got similar results with copper - i found you needed to play with the oxalic acid concentration a bit and the current density - the patent recommends 1 amp per square inch - i found this to be far too much and 100milliamps per square inch with an extra 10% oxalic acid worked well - it was a lot slower though. Bath temp has a role to play too - With different combinations you need to alter the temp 60C seemed to work well for me"
I also found that much lower current than in the patent is indicated.
None of the things I tried yielded Cadmium plating onto either copper or stainless.
Nothing I tried with the nickel anode resulted in a plating of any sort. Stainless steel stayed pristine. Two different types of steel samples both got covered with some yellow-greenish layer, but it has no corrosion resistance and does not look like nickel anyway. Plating onto copper also failed.
Also, trying to remove the ions (color) from the plating solution by running with reverse polarity using a carbon anode failed just like it did with the copper plating (though there at least the copper plate itself worked...)
Plating copper onto aluminum works, but no amount of surface prep causes it to adhere well, as far as I can tell....
All depositions have been done at room temp so far.
Chrome results up to now:
Chome on stainless leaves the surface dull. Not sure if we just roughened that up or actually deposited anything.
Chrome on copper does not work.
Ah, also using carbon as anode to get the nickel back out of the solution did not work.
Small update on chrome:
Upon turning on the current a dark orange-brown region develops around the chrome anode. This appears to be heavier than the solution as it flows to the bottom with no visible movement to the cathode. This material then appears to slowly dissolve into the solution; upon turning off of the current the orange-brown area slowly disappears.
Leaving this to sit over night the solution turned into a dark black-purple-blueish thing. When engaging the current to try to plate a steel parallel, the orange-brown stuff starts coming off the anode again.
Not clear yet if any plating actually occurs in either color area...
I am having some doubts about the claims of the patents at this point....
Comment from Robert
"I have plated Cu onto Steel, Cu onto AL, Cu onto Pb Al onto Cu, Pb onto Al with various amounts of success"
Update: Chrome plating also a no-go.
But maybe with higher temp next week....
That chrome plating solution got very dark purple-ish when left standing for another day. I used a heater to get this solution to 38C. With low current over several hours a nice, uniform, dark gray, matte coating formed on a steel parallel I used as the cathode. I don't have anything on hand to test for chrome, so I don't know what that coating actually is. But it is strongly adherent and no amount of scrubbing with stainless-steel wool has any effect on it....
Started trying to do nickel one more time.
Plating nickel on steel or copper at 60C failed.
Even letting the nickel sit in the solution for a few days first did not help (like it seemed to do for the chrome).
chrome at elevated temps and onto copper next....
Ok, whatever the dark gray deposit was... copper sticks to it ok, but not as good as to plain steel. I went ahead and tried to deposit copper onto my chrome anode directly, and the result was the same as for aluminum. shiny copper on top that could easily be wiped off....
At 70C the chrome will not deposit on steel or copper...as before at lower temps.
Ok, I did zinc plating, and the result is that on copper and steel I see severe corrosion of the target part instead of plating. Stainless steel seems to coat as well with zinc as it did with copper.
Bath temp about 65C.
Soo... we can plate stainless with copper and zinc. We can plate plain steel with copper. We can plate nickel with copper.
Pretty nice, but the patent led me to expect more...
Working on putting stainless onto brass right now. One thing I have noticed is that at room temperature not all the ingredients seem to dissolve. However the patent mentions the standard formula for plating as low as 16C. I started with 11C water and slowly heated and stirred - I don't get complete dissolution until about 25C.
Ok. With a 37C bath, 8.7V potential difference, 1A current, 1 in^2 brass cathode and 20 in^2 304 SS anode, I get a tenacious black deposit on the brass rod over a time period of 30 mins. I cannot take that deposit off with stainless steel wool, though I can make some scratches here and there. I needed a file to clean the rod off.
The solution turned to a pale greenish yellow.
I cleaned the rod and am decreasing the current density from 1 to 0.1 A/in^2.
The voltage to accomplish this is now at 2.1V
2 Hrs later no visible steel deposit. a little dirty yellow deposit. Cleaned the rod up, increased the current density to 0.5 A/in^2. Now at 6.6V
1 Hour later light gray deposit on one side of the rod. Cleaned it off. Lowered the current density to 0.25. Bath temperature crept up and stabilized at 42C over the past couple of hours. Voltage now 3.5V. The bath has a beautiful deep green color now. The stainless anode shows signs of decomposition.
A bit over an hour later some yellow-green gunk has built up. Under that was the same gray stuff as before. Looks like stainless on brass won't work with these parameters.
I replaced the brass rod with a copper strip to see what happens.
Another hour or so. There is a silvery-gray deposit about the right color on the copper. This may have worked!!! This is the last update for today. Bedtime. Will use the same bath tomorrow to see if I can get a good deposit on properly prepared copper.
The stainless anode was definitely electro-etched. Looks like it has been sandblasted with very fine grit.
The bath is very dark now.
Ok, next day. I put in a copper clad coin, left the solution at 23C and left it for 45 mins. The result is that on the surface a lot of gunk appears that can be wiped/washed off. Under that is a nice uniform dark gray iron-color coating. At first I thought we had etched away the copper coating, but a scratch test verified that the copper is still there.
The little bit of gray stuff that accumulated on the copper strip last night looks like it has rusted, so I put some water onto the coin to see what happens. There is a lot of cloudiness in the solution, so it is possible that we only transfer the iron and precipitate some of the alloying elements out as sludge.
The voltage on the coin was 4.4V and the current density at about 0.3 A/in^2
I have a number of these coins, so I will increase the temp slowly and see how that affects the result.
Ok, one more coin. Was in an hour. Bath temp up to 43C. Result as before nice clean gray coating over easily cleaned off gunk.
Next coin. Temp going higher...
Result: Temperature up to 59C. Nice deposit as before. some of the previous deposits on the other coins show rust under moisture exposure.
One more coin. Turning up the heat.
Temp up at 62C. Two hours later, same type of deposit.
Placed coins on moist towel. Some show signs of rust already.
Stuck the brass rod back in. 2 hrs later, under yellow crud, got a thin gray coating reminiscent of the one on the copper coins. Leaving the rod in moist environment to see if rust develops. Bath temp was 63C.
So far it looks like the earlier coins do in deed show signs of rust. The later ones do not yet.
New test: The patent mentions 6 or 12V batteries as source, so I went from constant current to constant voltage. Now there is a copper coin being plated at 12V. Current density about 5x as before.
Ok. Last report for today. The high-voltage high-current deposit avoids the gunk buildup, but results in a much darker coating. The coating can be cleaned up with SS wool.
Added the coin to the moist towel for corrosion testing.
Well, all the coins show at least some rust. But,
Finally some success. I put a steel parallel into the by now deep green-black solution and ran the plating at 60C for a couple of hours. A stirring bar was moving the solution and the short edge of the parallel was pointing into the stream. Along that side and the bottom short edge there was a great buildup of stainless steel. That edge looks a little like the bottom of an ice skate now, with a hollow in the center and a knife edge of sorts along the edge. I suspect that the agitation was resulting in less bubbles moving right along that edge. The deposit there was bright, can't be corroded, and is about 5 mils! thick.
I am going to make the guess that the deposition voltage is important, and that bubbling has to be kept under control. So I see two ways of making that happen. First, decrease the concentration of chemicals in the bath. Or, second, use a much wider container to separate the electrodes. The second one is probably better with respect to uniformity (more even field distribution), but my glassware dictates that I go the first route right now.
Ok, fresh solution at 1/4 concentration. I ran plating into a steel parallel at 12V and 72C. It looks like I got a nice decorative plating effect in one area fading into brown and then black rust. Since it looks like the area of lowest current density gave the best result, I dialed down the voltage to 10V with a new parallel.
After 1 hour at 10V, I can see an area right around the waterline where good plating seems to have occurred. Also on one side this are extends about an inch below the waterline. The rest had crud on it that came off with SS wool. So either voltage or concentration seems to be the controlling factor.
one more test at 8V...
The result at 8V is identical to the one at 10V as far as I can see. Maybe I will dilute the solution by a factor of 2.
I actually diluted by a factor of 3. That reduced the current density by 3 as well. However, only close to the surface can I consistently get a good plating. Stainless steel can corrode in oxygen poor environments. And of course all the bubbling and agitation at the top could introduce oxygen there. I can turn up the stirrer and have it suck in air.....
Aerating did not help. If anything it made it worse, though that could have been due to the much greater liquid flow.
I diluted by a factor of 2 one more time for a total of 6. 120 mins of plating time. No visible stainless plating. So it looks like stainless can be done, but it is not clear how to get a decent coating.
I had more more idea. The patent mentioned increasing the oxalic acid to avoid black oxide films, so I changed the composition from 32 to 40g. At 6V and 70C no stainless deposits, but a 1/8 inch thick mass of black crud does. The crud is easily scraped off but under it there is not sign of stainless steel.
Also, I am operating on the assumption that we need a high voltage coupled with low current density. To that end I took the solution from the last experiment (for convenience) and put it in a much larger container (to be able to separate the electrodes further). Then I diluted the solution by a factor of 2, because the fluid level was too low and because previous experiments lead me to believe this won't have any effect other than to reduce the current density further.
30 mins later: now we are talking! There was a thin crust of a checker-pattern of yellow and black. Kind of like the yellow was a complete coat and the black was paint that dried and cracked and contracted. Anyway. I cleaned that off with SS wool and I may actually have a decent SS coating underneath. The color seems right, but it reminds me of when I put copper onto SS. You can see the discoloration after 30 mins or so, but it is not copper color after a long time (remember that I needed very low current density for a good copper coating). Anyway, I put the thing back in, and I guess I will just clean the crud off every 30 mins or so and see if I can get any sort of good SS coating that way.
Looks like the discoloration was not SS. Increasing the voltage to 20V to see what happens...
Well, the deposit looks sort of mottled, but I don't see any rust on it a day later.
I also used my last bit of oxalic acid on my last clean parallel to make a full strength solution to test with 30V but a large enough distance between the electrodes to keep the current down. No visible sign of deposit. Rust all over the next day...
The lack of success made me double check everything. It turns out that the product that I bought "TSP Trisodium Phosphate" by Savogran is not pure. While the package does not mention it, the MSDS mentions only 75% TSP, the rest is some other compound. Don't use this!:
Soooo.... I probably have to redo the experiments. I have pure TSP on order. :/