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Ok, lets try to go for stainless steel deposition one more time.
Experiment 1;
New standard solution; T=60C; Anode stainless steel angle of unknown composition; cathode: steel parallel, prepared by AJAX scrubbing. Approximate submerged cathode area: 3 in^2
10:50 : start; current 1.5A
10:58 : On steel parallels the standard solution always starts out creating a dark gray layer, current or not. By this time much of that layer is gone. The submerged layer sort of looks like a topographical map going from gray to shiny.
11:56 : There are a lot of little flakes floating around. These flakes are yellow, the same color as elemental sulfur. They seem to grow on the parallel and then detach. The solution is clear and deep green.
12:22 : stop; T=60C. Yellow deposit on parallel. Sulfur? removed deposit with SS wool
15:12 : rust showing on sample
15:14 : restart; T=23C; parallel scrubbed clean; added 5g of oxalic acid to solution
15:45 : stop remove sample; T=41C; more yellow deposit.
16:05 : add 3g TSP; continue
16:53 : remove & clean; some yellow deposit, but the color of the parallel under that now is about right for stainless steel. The solution is now deep green-black. put cleaned sample back in.
17:18 : T=53C
17:28 : remove and clean; some sulfur; very shiny underneath.
19:17 : stop; a little more yellow deposit; some blackening along one edge; along some edges and especially under the blackened part something definitely built up. At sharp edges there is a lot more deposit than in flat areas.
The following note on electro-polishing stainless steel:
http://www.worldstainless.org/Files/issf/non-image-files/PDF/Euro_Inox/Electropolishing_EN.pdf
notes that "it can take a couple of days before the passive layer develops its full thickness", so the cleaned and dried part is left to sit in air for at least an hour.
Next, I took some pictures with a microscope.
Here some pictures of an unaltered parallel.
Here equivalent areas of the plated on parallel.
Some extra pictures of plated area:
Clearly some metal deposited. But it looks like there are areas without adherence, and that the deposit in general is porous.
20:20 : a large drop of water is placed on part of the stainless plated area of the parallel
Next day:
Some rust shows on area of water drop. To check against the potential need to passivate for a longer period of time:
09:00 : stainless area of parallel is wetted again.
10:39 : more rust. Stainless deposit clearly porous or otherwise incomplete.
Experiment 2:
Use existing solution. Solution is transferred to stainless bucket. Bucket is heated, but not stirred. Current is set to 0.25A. New parallel is prepared with AJAX. Approximate plated area: 2 in^2.
08:27 : start; T= 33C
09:29 : T=44C; yellow coating; not removed, parallel placed back in after taking picture.
10:34 : T=54C; yellow coating; not removed, parallel placed back in after taking picture.
11:51 : stop; yellow coating. Looks like there is a black coating underneath. Cleans up easily with stainless steel wool. It is light gray and shiny under the deposit. Could be stainless steel.
The microscope seems to tell the story that - along the sharp corners at leas - there is noticeable plating. For the rest, it's a bit hard to tell. Certainly there is no porosity, which is good. The color is also right. Along the inside edge of the hole, I did not de-oxidize nor clean too well. And there it looks like there is some bad plating, with cracks.
Time to test this with a water drop.
19:45 Water drop shows some rust. The rust easily wipes off, though and one can see the bare metal underneath it. It seems fairly clear now that there really was a layer of something on top.
The microscope tells the same story, on the left half is the area where the rust removed the top layer. On the right half is still plated area.
Experiment 3: Use the same solution to plate on to a copper coin. Since it seems to hard to plate on top of steel, I want to try to see if copper is an easier substrate. To that effect, I have AJAXed a copper coin and placed it into the bath. Approx area: 1/3 in^2. Current 0.25A. Left it in approx 1 hour:
Result: There is a dull gray coating on the penny after removal. After cleaning up with a bit of AJAX, the plating looks shiny and about the right color for stainless.
Of course, one concern is whether the plating bath simply removed the copper plating from the coin. However the microscope pictures are pretty definitive about this not being the case.
20:24 : Put water drop on deposit to check for corrosion.
Next day.
09:05 : Rust on coin. Since the copper cannot rust brown, the deposit itself must have rusted....
Conclusions: While metal definitely deposits from the stainless steel anode to the cathode, we cannot yet make a corrosion resistant plating on either steel or copper.
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