Safer electroplating solution 6
A disagreeable fact about this electroplating solution is that the anode cruds over with an ugly deposit and sooner or later part of that starts floating in the solution. Lou, from the goldrefiningforum.com forums suggested that these are oxalates and to use sulfamic acid instead.
I thought that was a good suggestion, especially since the patent stated that the oxalic acid can be replaced by any polyfunctional acid, and so I did some experiments replacing the oxalic acid with sulfamic acid.
The sulfamic acid has a density of 97.1g / mol
The oxalic acid has a density of 90.0-126.0 g/mol depending on whether it is anhydrous or not.
not knowing the water content in my oxalic acid, I chose a 1:1 replacement by weight.
24 g sulfamic acid
7.5 g trisodium phosphate
3 g ammonium sulfate
750 ml water
Experiment 1: try plating copper onto stainless steel
I am not using the heater on this one, but the water did come from a heated water filter, so the starting temperature was at 73C
15:11 : start; 0.5A; area 1-2 in^2
15:21 : stop; dull copper plating; buffs up easily; sticks strongly even though I did not prepare the spoon with AJAX or anything.
Experiment 2: try to plate copper onto a steel parallel
parallel prepared with sandpaper.
15:53 : start; T=43C; 0.1A
15:55 : copper is visible on the parallel. the anode still looks good!
16:15 : stop. copper rubs right off the parallel.
Experiment 3: plate copper onto brass
the brass target was prepared with stainless steel wool and AJAX.
16:19 : start. T=35C; 0.1A
16:58 : stop. there is a dull copper coat on the brass. It buffs right out. Great coating.
Experiment 4: Plate copper onto aluminum
the aluminum was prepared by stainless steel wool and AJAX.
17:02 : start ; T=27C
17:19 : nice copper coat, but it rubs off easily.
Experiment 5: Plate copper onto a chrome vanadium wrench.
Wrench prepared with AJAX.
17:25 : start; T=27C
17:42 : stop. full copper coating, but rubs right off. However the surface under the copper coat looks discolored.
Experiment 6: replace the Anode with a nickel anode, keep the same solution and plate onto a stainless spoon. The hope is that at first copper plates out, but eventually nickel.
17:51 : start; copper plates onto SS spoon quickly.
18:25 : lots of copper, no visible nickel
19:23 : even more copper, no visible nickel; increase current from 0.1 to 0.3A
21:08 : even more copper, no visible nickel; stop.
Next day, left it running for several more hours at 0.6A; The nickel anode dissolved quite a bit, but with no crud building up. There is a very thick copper buildup on the cathode, but no sign of nickel.
Experiment 7: plate brass onto stainless/copper
The cathode is a stainless steel spoon partially plated with copper.
Using a fresh sulfamic acid based solution.
08:55 : start; 0.2A
09:05 : dark matte copper deposit on spoon on both copper plated and stainless areas.
10:41 : Lots of loose copper deposit, metallic flakes floating around (zinc?). Burnishing shows copper deposited on both stainless and copper areas. no brass. The brass anode is dark, but wipes clean easily.
Conclusion: It looks very much like sulfamic acid is a great substitute in this solution for copper plating. Neither the nickel nor the copper anodes built up any deposit and the solution was clear and colored as opposed to turbid.
I do note that some nickel plating baths are based on nickel sulfamate.
One production method for this is to treat nickel powder with sulfamic acid (US pat. 3620669):
So it makes sense that the nickel dissolves. Maybe I should look into these plating baths for a hint of how it might be made to stick as well....
Nickel sulphamate, Ni(SO3N2)2: 40-60 oz/gal (300-450 g/l)
Nickel chloride, NiCl26H2O: 0-4 oz/gal (0-30 g/l)
Boric acid, H3BO3: 4-6 oz/gal (30-45 g/l)
But can this actually directly plate stainless steel?