[aksaraf]

Hi everyone! I've been struggling a bit with an issue related to platinum plating. Any and all advice is welcome! I am getting a little desperate at this point.

I've been machining aluminum parts (5 cm²) for a device I'm working on, and because they're going to be involved in electrochemical processes, I've elected to plate them with platinum, because platinum makes for an excellent counter electrode. I've been able to plate up to nickel just fine, but the platinum is not plating in metallic form, but rather its porous platinum black form. I'm not entirely sure what I'm doing wrong, so I am here asking for help. Let me walk you through my steps.

1: The machined part is deburred, sanded, and sonicated in soap and water for 5 minutes.

2: The part is sonicated in DI water for 5 minutes, and then sonicated again for 5 minutes in ethanol.

3: The part is dried with an air gun and soaked in nitric acid for 1 hour to roughen the surface.

4: The plating solutions are sonicated for 5 minutes to remove dissolved gases in solution (zincate, copper strike, copper bright, nickel, platinum).

5: The part is dipped in 3 vats of DI water before beginning the electroplating process.

6: The part is immersed and treated in each of the solutions on the table. Between each solution, the part must be immersed in 3 vats of DI water for 30 seconds to 1 minute to remove residual plating fluids, and the water must be replaced as needed.

7: The part is immersed in Zincate solution (electroless) at temperature T = 30C, agitation at 0 RPM, Voltage V = 0 V, Current I = 0 A, Time t=1 min

8: The part is immersed in Copper Strike solution (basic) at temperature T = 50C, agitation at 900 RPM, Voltage V = 1 V, Current I = 0.5 A, Time t=30 sec

9: The part is immersed in Copper Bright solution (acid) at temperature T = 50C, agitation at 900 RPM, Voltage V = 1 V, Current I = 0.5 A, Time t=10 min

10: The part is immersed in Nickel solution at temperature T = 50C, agitation at 900 RPM, Voltage V = 4 V, Current I = 0.2 A, Time t = 15 min

11: The part is immersed in Platinum solution at temperature T = 50C, agitation at 900 RPM, Voltage V = 3 V, Current I = 1 A, Time t = 30 min

12: The part is soaked in DI water for 30 minutes, left to air dry for 30 minutes, and annealed on a hotplate overnight.

13: The part is sonicated in DI water for 5 minutes, and the part is left to air dry.

If anyone has any ideas on how to properly plate the platinum, I'll happily listen / read! Thank you all so much in advance!

[Hunter2]

What I can see is that you use the highest current 1 A for platinum. Try to go down and extend the time.
On the other hand which platinum solution do you use.

[aksaraf]

Alright, I'll drop the current by half and maybe double the time. And as for the solutions, I'll provide all of my solutions, with my known active ingredients, and the SDS.

Zincate (ZnO2): https://caswellplating.com/content/sds/Zincate.pdf

Copper Strike (proprietary): https://products.riogrande.com/content/Safety-Data-Sheets/335163-SDS.pdf

Copper Bright (CuSO4): https://products.riogrande.com/content/Safety-Data-Sheets/335001-SDS.pdf

Nickel (NiSO4 and NiCl2): https://products.riogrande.com/content/Safety-Data-Sheets/335078-SDS.pdf

Platinum (H6N4O4Pt): https://products.riogrande.com/content/Safety-Data-Sheets/335504-SDS.pdf

[pcm81]

Have zero experience with platinum plating, however here is what i observed with other metals:
At high current you end up with an effect platers  call "burning" or "burned deposit". This is basically a deposit of metal hydroxide and it happens when concentration of metal ions in the solution is too low for the current density that is doing the plating. The extra current gets used for electrolysis of water, producing hydroxyde whych then deposits as metal hydroxide on the part. To combat this, reduce current, increase concentration of metal ions in the solution or may be improve agitation to reduce depletion of ions in that local area.

[Borek]

To combat this (..) increase concentration of metal ions in the solution

That's a risky idea, too high a concentration of a "free ion" often means low quality, porous surface. From my understanding best coating can be done with high total concentration, but low concentration of the easily reducible cation (so when the cation is actually complexed, preferably in a high stability complex which is also labile).