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Titanium hooks on nickel anodes dissolved
October 18, 2011
We run a nickel strike tank at room temperature at 28 oz/gal of nickel chloride with oval bar 'pure' nickel anodes. Our anode to cathode ratio is minimum 4-10 so we have plenty of anode surface area. Additions of nickel to the baths are never required, nor are dilutions. Strike is performed for 5 minutes at 3-6 volts and coating is quality.
Problem: The threads of our titanium hooks holding the bar anodes are corroding?/dissolving?/melting? and dropping the anode bars and bags to the bottom of the deep tanks.
The anodes are never removed from the plating solution and shouldn't passivate in the bath.
The fact that I never have to add nickel chloride to the solution would indicate to me that my anodes are not passivated, although that is not a certainty since my tanks (solution volume) is huge relative to my short usage of the tanks. Even if my anodes are passivated, titanium anodes in nickel baths are inert, right!
I see no way titanium is galvanically corroding with the nickel.
The melting temp of titanium is near 3000 F, we're talking 60 amps max going through 8-10 hooks and anodes and the room temp solution is circulating well around the anodes so melting seems out of the question.
I had my metallurgical lab analyze the remains of the hooks and they are pure Ti.
Any thoughts?
Plating tech support - Oklahoma City, Oklahoma, USA
This is a common occurrence. The titanium is reacting with the chloride in the solution and the positive electricity speeds up the process.
The cure is to mask off the lower half to 2/3rds of the titanium with tape or masking lacquer or hot wax.
- Navarre, Florida
October 19, 2011
Good day, Art.
I have operated and have done maintenance on Wood's nickels. I have found using ovals is extremely expensive. My solution was to use R material as 3 feet X 0.5 feet slabs and attach the slabs with plastisol coated titanium hooks and nuts/bolts.
Even with the plastisol coating, the titanium hardware was compromised. I did not bag the slabs, as R material does not produce any sludges, and without the bag you can always monitor the anode conditions. Even though it is time consuming, I always removed the anodes at shift's end, because at 12% HCl, nickel metal is always rising. Regular decants of solution were required at 32 oz/gal for my process. You have not indicated your HCl conc. If I could suggest, I would try and keep the Titanium hooks out of solution. I started using bagged titanium baskets with S rounds, and sludges were a problem. Guess what? The titanium baskets dissolved pretty quick.
Hope this helps.
Regards
- Toronto Ontario Canada
First of two simultaneous responses -- October 20, 2011
Thank you. Will do.
Art Cambell- Oklahoma City, Oklahoma
Second of two simultaneous responses -- October 20, 2011
First of two simultaneous responses -- October 21, 2011
I have never used R nickel, so do not know what it is anymore.
S rounds are very very bad news for a Woods strike tank.
I preferred to use rolled depolarized nickel anodes and use bags with only small problems after coating the hooks. Decanting not required. Electrolytic nickel should work OK also and may not need to be bagged.
I did carbon treat the strike tank periodically to hold the smell down and it would work better.
- Navarre, Florida
My solution was to use monel hooks instead of titanium.
Jon Barrows, MSF, EHSSC
GOAD Company
Independence, Missouri
Second of two simultaneous responses -- October 21, 2011
Put a sump tank underneath the strike tank. When you are done using the strike, just drain it down into the sump where it can filtered and readied for the next use.
Jim Schwartzmyer- North Tonawanda, New York, USA
October 27, 2011
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