Plating nickel on nickel

A. I would agree that it may be a problem taking this method to production. If you could keep the sulfuric acid clean by dummying, you may have a better chance. As soon as any copper or other metal builds up in the sulfuric acid, you will start plating a non-adherent smut which will be a problem.

A. I don't like to use the words direct and reverse, however, what you are doing makes good adhesion, Make the part CATHODIC in the clean electronic grade sulfuric acid using bagged carbon anodes. Be aware that any sulfuric soluble impurities (iron, copper, zinc,) either coming in with the sulfuric acid or dragged in by you, will co-deposit but not adhere over old nickel oxide, and then your deposit will blister off. Also the addition of about 1/2 oz/gal very clean and pure ammonium bifluoride will enhance the adhesion. Any metallic impurities will compromise this process, and it will also compromise a Sulfamate strike or a Woods Strike. Theoretically the only difference in the results from electrolytic plain acid versus a metallic strike is that NOW you must transfer to the plating tank more rapidly.

A. I am aware of the fact that cyanide sounds like a four letter word but in case that you have cyanide in your premises, a cathodic activation in an alkaline cyanide solution is the best way to activate nickel and to enable plating nickel on nickel. If you stick to the sulfuric acid activation, use the previous reply and add fluorides. I recommend to activate in the sulfuric acid only when parts are activated cathodically.(what you call direct).

A. Hi, we run a Pulse Reverse Nickel chloride process. We are able to run reverse for e.g. 5 min. and then start up the electroforming process, without the item leaving the bath. This could solve all your problems.

Thank you very much Tom, Robert, Sara and Lars for your comments. The part is already plated and everything has gone OK. It was 1 piece, 8 tons, but only 1 piece. The sulfuric was as clean as possible and the dead time was as short as we could.

Thanks again,

A. I don't think the approach you want to use is extraordinary, Gary. Bumper platers have, for years, replated internal rejects without stripping the nickel; it's the environmentally savvy thing to do if it works. With luck, it involves no more than running the parts through the preplate cycle, then through a nickel strike tank, then plating. Obviously, the parts must be properly reactivated or peeling will be a problem.

A. You will need to go through a good cleaning cycle and use a nickel strike, such as Wood's nickel. If the nickel contains lots of organics, you may need to machine it to give a rough surface.

A. Gary
You might consider using a cathodic cyanide nickel activator if this is amenable with your overall process. Most any supplier would have their version of this chemistry.

A. Gary,

I have used acid salts containing fluorides, hot @ one pound per gallon, soak time depends on how passive your bright Nickel is, but at least 5 minutes. Consult supplier for the proper tank and heater materials used.

A. Hi,
In my opinion re-activating nickel is very touch and go. We always use a copper strike plate over the existing nickel and then re-nickel and we have never had a problem.

Cheers,

A. This is how I do it:

Hot alkaline cathodic cleaner
15% sulfuric dip - 1 min
Cyanide cathodic cleaner - 1 min
15% sulfuric dip - 1 min
Woods Nickel strike - 20 secs

Works every time.

A. You might want to check out my response to question #36845 in section 2B I have used this method quite a bit, we can plate stainless without a Wood's nickel strike. We use a Macdermid product by the name of Metex LDA,ammonium bi-fluoride & HCl -- maybe worth a shot. We activate for 2 minutes in this acid and, of course, we soak clean it and then go I the electrocleaner -- but we do make contact.

A. Hi, Bob. The typical nickel activation process is "Wood's Nickel", which is nickel chloride based (32 oz/gal Nickel Chloride, 12 oz/gal Hydrochloric acid). There is also a nickel sulphamate strike (which may be more compatible with your nickel sulphamate plating); the ratio of nickel to acid is probably similar, but I don't know the exact numbers without researching it.

If you use the search engine to look for "Wood's Nickel" and "nickel sulphamate strike", though, you find some variations on both of these formulations. Good luck.

Regards,

You may endup by passivating your part

Bob, Unfortunately you give very little detail of your process - perhaps it is sensitive information or just an oversight. Either way, not knowing your process makes giving an answer a bit like shooting a bow and arrow in a totally dark room and hoping to hit the target.
Anyway, Ted is correct about using a nickel strike. You need to reactivate the nickel surface prior to further metal deposition otherwise subsequent layers will delaminate. You also need to activate the nickel before you use a nickel strike, so a quick anodic treatment in a good acid activator normally does the trick. The level of activation will be dependent on your nickel electroforming bath and what additives you are using. I used to also give a few seconds anodic treatment in the nickel strike before reversing the polarity to the more conventional cathodic polarisation. This ensures the surface is active and suitable for receiving fresh nickel and making it adhere. There are numerous nickel strikes around, but the most common ones are Woods nickel and sulphamate nickel; formulations for both are available in any good text book, the internet or your chemical supply house.

A. Chiu,
If you are using a Woods nickel strike a brief reverse in the bath (seconds not minutes) will leave the surface slightly etched with a micro roughness ideal for maximum adhesion. A good indication that the anodic cycle was correct is to observe the surface. There should be a uniform color without burns, streaks, patches or excessive roughness and totally hydrophylic for a perfect water break test. You should start the cathodic step (forward) immediately after this. Then move to the following steps w/o delay.

A. As you have discovered, nickel can be very difficult to reactivate so that you get good adhesion. If the nickel deposit contains any additives, it becomes even harder to reactivate. However, often nickel can be reactivated by using the correct procedure. Reactivation of nickel should not be considered to be a full scale production process, but only one for remedial operations, as it is fiddly, time consuming and the process can run the risk of cross contamination from different solutions, as clean water rinsing should be minimised.
Firstly, ensure the nickel is totally free of any surface contamination; this is done by giving it a thorough chemical and electrochemical clean using both alkali and acid cleaners. If possible give the nickel a good scrub with a chalk slurry and then rinse it off before going into the aqueous clean stages. Your aqueous cleaning can be commercial products from your supply house, but it is important that the acid cleaner is a strong one (typically equivalent to at least 10% sulfuric acid. One good one I used was a mix of 25% HCl and 13% formic acid (HCOOH) at about 30C for at least 60 seconds. At no stage should your nickel surface be allowed to dry out or passivate, so rinses should be in slightly acid washes, sing the same acid as the process sequence. Once clean, the nickel can be reactivated in a good nickel strike. The most common one is Woods nickel (240g/l NiCl2, 125g/l HCl at 2-4A/dm2 and room temp.) Use the Woods nickel in both cathodic and anodic phases, say 10 seconds anodic, followed by 60 seconds cathodic. Do this for about five or so minutes. An alternative, that may be quite good, but I never compared them, was to use 20g/l NiCl2 with 30% H2SO4 at 8 Volts cathodic for 20-30 seconds; there may be some benefit is also using reverse polarity here too. Either way, ensure that your final cycle is cathodic! Once you have reactivated the nickel, transfer it to your main nickel bath. Depending on your plating bath (sulphate based, chloride based, fluoborate based or sulphamate based), you may want to consider using a compatible acid rinse between the strike and the main bath.

A. I suggested to Bob Adams that he reactivate his parts in the sulfamate nickel bath. I have some clients who do this and all report good results.

Using the plating bath to activate the parts has many advantages:
1. it is impossible for the parts to dry between activation
and plating
2. rinsing is not required

This works for parts that have not been machined, formed, heat treated or had other secondary operations performed after the first plating. Basically you are reactivating a clean plated nickel surface that has been exposed to air for about 4 hours or less.

You should try it before going to more extensive reactivation.

A. Pat, I agree with you about the benefits of reactivating in the plating bath and under the right conditions, I would agree with you.
My last response was more directed towards Chui Tao rather than Bob Adams; Chui's question was much vaguer than Bob's and with less detail, so I gave a broader answer.
As far as Bob is concerned, from my experiences of nickel electroforming, the only reasons for reactivating the nickel are after the workpiece has lost polarisation or there has been a need to carry out a processing step off-line. If polarisation has been lost by a loss of power and it is simply a power cut, as long as the workpiece has not been removed from the bath, then in-situ reactivation is possible, but only as long as it doesn't affect the mandrel and contaminate the bath.
The only real problem with reactivating in a sulphamate bath is that anodic polarisation will require a higher chloride level in the bath, since the deposited nickel will not be S-depolarised and will hence need chloride to ensure good polarisation and no passivation. If there is inadequate chloride in the bath, the workpiece runs the risk of passivation with nickel oxide and this will certainly cause delamination.
However, one of the best things about sulphamate baths is that they produce low stress deposits, but chloride induces stress, so you want to keep it as low as possible.
Electroforming with nickel sulphamate allows you to use a zero chloride bath, but most electroformers, us being a cautious breed, tend to add a bit of chloride, just for luck!
If the workpiece has been removed from the bath for off-line processing, it will certainly require extensive re-processing to ensure total and complete reactivation and the elimination of delamination

A. Trevor

I always enjoy reading your comments and find them very helpful.

Frequently the reason for reactivating is because the part has to be taken out of solution for a thickness measurement or shields and auxiliary anodes need to be repositioned. reactivating after these processes is easy.

I think there is a common misunderstanding that electrodeposited nickel does not anodically dissolve without chloride. This is partially true. Nickel plated from a watts bath (without additives) is very pure and corrosion resistant. Nickel plated from a sulfamate bath is low stress because it always contains some sulfur and the sulfur makes the nickel less corrosion resistant similar to S nickel anodes.

A. Simple one to try in the lab is 20-30% H2SO4, Cathodic, 50 ASF (min), (try not to go over 5V in achieving this...) for 2-4 min. Watch out for etching.

No rinse, relatively quick transfer time.

Plate

Only works with relatively "clean" nickel deposits which I would assume you have out of an electroforming bath. May alleviate the need for a strike completely.

Try it out in the lab first, easy to do, if it works great, if not you are only out a few dollars of Sulfuric.

A. Yes. I've used the Canning activation process with good results more than a dozen times.

However, after stripping the chromium, you must buff, at least lightly, the nickel, then clean (scrub, if necessary, but no current), rinse, rinse, Canning activation, rinse and go right quickly into nickel plating.