Parts turn black in Wood's Nickel Strike

A. A guess. The parts are anodic to the rack. What is your rack made of?
Is there any possibility that your Wood's Strike tank is electrically backwards?
What is the voltage at the part, not the rack?
If you are heavily gassing with 50% HCl, try a lesser percentage. 25 or 30% with a bit longer etch time should work just as well without the heavy gassing.

A. Hi, Steve

What you have to do is turn on your rectifier before you dip in the parts

"Electrodeposition: The Materials Science of Coatings & Substrates"
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A. Hi, Steve. I have never heard of citric acid for activation, only for its opposite, passivation. If you can get access to a copy, Jack Dini's "Electrodeposition" ⇨
has an outstanding chapter entitled "Adhesion" with a lot of quantitative data about Wood's Nickel adhesion onto stainless.

Regards,

A. If you really have the part anodic in the Woods strike (positive lead), then the parts will come out of the tank black or spotted and you will not have any nickel strike on them.
3 volts might be OK for a small load and give you the amps per sq ft that you are looking for, but otherwise it is a bit low. Anodically, it takes much less voltage to get an amperage than it does cathodically (forward).

Long ago, research on the best adhesion out of a normal Woods Strike, was at 90 amps per sq ft. Adhesion falls like a rock above about 100 ASF.

A. James has described a probable good fix for the smut. A possibility could be that the parts aren't truly clean; strong acids working on oils will be a mess. It would be best to know exactly what stainless you are dealing with, and its work history. Passivating with citric acid is the last thing you'd want to do, Steve; yes it will probably eliminate the smut, but there's more to plating onto stainless: you'll have no adhesion.

What you need to do to plate stainless steel is clean it completely, acid treat it to bite off the passive outer layer, then retain an active surface for long enough to get plating going onto an active surface. That's what Wood's Nickel Strike does: simultaneously activate while getting a thin layer of fresh plating down.

A. Copper is not a good rack material if it is bare. If it is covered with tape or plastisol or some other good masking, it is OK. I would still make the contact points out of brass or stainless or even titanium. If they are small, piano wire contacts might work. We used home made racks out of brass rod for rack material in a great number of plating solutions. They were gradually eaten away, but at a rate that was slower than iron or copper. It also carries a lot more current for a given size than SS or iron. PS, You will use a lot less current, waste less plating solution, not pollute your tanks and have a lot less grief if you plastisol your racks (except the contact points). Consider buying a good rack from one of the professional rack companies to get ideas for your own later racks. Most good rack companies will design a rack or modify a stock rack if they can see one of your parts and know how you are going to plate it IE: the complete process. James Watts - Navarre, Florida A. Years ago I used to plate a lot of stainless steel components, including many different alloys. Occasionally we'd have an adhesion problem on a weld area, or the back of a part that had a weld on the front. Wood's nickel wouldn't touch it. We came up with a solution using potassium permanganate ⇦ this on eBay or Amazon [affil links] at close to boiling (I don't remember the concentration). This was merely a several minute "dip", not electrified, that solved the problem. George Brackett III - Maine

! Permanganate is really a messy tank to operate. It works by oxidizing the carbon from the weld operation. It prepares the surface so that the follow on chemicals can work to activate the surface. It is in the standard practices manual for most airplane overhaul manuals.

A. Hi Steve,

Try the following process .
I believe you doing over acid treatment an this is producing the smut.

1- Anodic Electrolytic Cleaning
2- Alkaline Periodic reverse Cleaning.(cyanide activation)
3- Acid dipping HCl 10% 30 sec (rinsing not required)*
4- Wood Nickel Strike 6-10 amp/dm2
5- Electroless Nickel

Remarks:
Nickel Strike do not deposit well on rough surfaces.
Nickel Strike must be chemically OK. 120 g/l NiCl2 + 240 ml/l HCl
Check the Anodes conditions and electrical contacts.

A. If your part is gassing in 50% HCl and gassing in the Wood's strike before you apply current then you are not plating on 400 series stainless!

A. Hi Sakthivel. Yes, Wood's Nickel Strike is already the correct approach, and your composition sounds workable, and close to that suggested by Don Baudrand. Your current density didn't come through in your e-mail, but as long as it's in the range that Don suggests, it ought to be okay.

I strongly suspect you are missing something, rather than that the conventional Wood's Nickel won't work for you, but it is not easy to know from such a brief description exactly what it is. Are you sure the parts exhibited no water break as they came out of the rinse before Wood's Nickel, and are you sure you're not over activating and generating that slightly black color as a smut in the acid tank, and that you are using sulfur-free anodes?

Regards,

A. Do NOT do the anodic cycle, that is plating copper onto the anodes, and contaminating the solution with copper. Go straight cathodic with the part. Take out the anodes when not in use to prevent the metal from climbing.

A. 1. HCl way too low.
2. 3 volts is not enough to activate, all you are doing at 3 volts is plating copper in the lows.
3. Apparently you left the anodes in while idle and the metal concentration increased thereby changing the low efficient "strike" into a high efficiency "plating" solution.