A Toxic project - CADMIUM Plating flaking off - Page 1
Forum section: electronics / repair

author: innkeeper
author_rank: Unknown
timestamp: November 28, 2018, 09:08:52 am
content: I have an old and very sought after tube tester i am restoring where the internal frame that the switches and transformers are mounted to are cadmium plated which is oxidized and is flaking off. the cadmium plating on the frame has turned to a yellowish green powder and in some places a whitish powder. the user side is all aluminum so no problems on the outside.I've been doing a bit of digging on the internet, and it seems the yellowish green stuff is likely cadmium sulfide. in any event, I know cadmium is very toxic stuff.my first instinct was to remove that frame and just strip it and re-plate it but. removing that frame it would be a horrendous task, and would likely result in me needing to rewire a good portion of the tube tester and frankly, I'm not wanting to do that.So i am putting it out there to see what options there might be and ideas to deal with this. I can't see leave it,as the stuff is flaking off, and there are small flakes and powder in the bottom of the case its in. if I brush it off I will leave exposed iron that's going to rust, not to mention that brushing it off will likely put cadmium dust in the air. if i don't remove the frame, there will be areas i can't reach to clean most likely under were the switches mount. most of the subframe is welded together as one piece with a few screwed on plates to hold the transformers in place

author: helius
author_rank: Super Contributor
timestamp: November 28, 2018, 05:54:28 pm
content: You could try coating it with an anti-corrosive acrylic lacquer, like the ones used to preserve bronze statues. If the plating is relatively strongly attached it should keep it from flaking off wholesale.

author: innkeeper
author_rank: Unknown
timestamp: November 28, 2018, 06:49:07 pm
content: Quote from: helius on November 28, 2018, 05:54:28 pmThat could work.from what I am gathering from various places, cadmium plating is usually very resilient. the problem comes in when it is exposed to some acids. the box itself was made of plywood, and the outgassing likely caused the initial issues. Probably not something that was on their minds when this was built in 1952. then just time and environment did the rest.with that in mind, I would guess id have to remove the current scaling and surface oxidation. there is certainly some cadmium plating still well attached, what is scaling off and creating the dust layer is cadmium that has oxidized.sealing it would likely work in keeping it from oxidizing further. but I am not sure how well lacquer would hold up over another 65 years. I don't want this to be a temporary fix, but its definitely a fix worth considering.

author: helius
author_rank: Super Contributor
timestamp: November 28, 2018, 07:46:23 pm
content: Some conservators believe that Incralac should be removed and recoated every 10 years, but that seems much too conservative (no pun intended). I think the lacquer can be made more permanent if it is covered with Johnson's wax, and of course if aesthetics aren't important and UV exposure isn't a factor then it should be more long lasting.

author: innkeeper
author_rank: Unknown
timestamp: November 28, 2018, 07:48:12 pm
content: anyone know about brush electroplating and good metals for long-term corrosion resistance?I've been doing some reading about brush electroplating. this would allow me to plate metal without removing it.I'm not sure if it would plate to both the steel and cadmium. but, my thought here is if I can get the oxidation off and then plate over it, it might be a resilient coating.the downside is, i'm not sure just how clean I have tog et the metal to do that. making the laquer method more attractive.this is sounding a lot like asbestos abatement lol.

author: SeanB
author_rank: Super Contributor
timestamp: November 28, 2018, 08:05:30 pm
content: To get the dust a vacuum cleaner with a HEPA filter in good working order will be the best way to handle the dust. Preferably also route the exhaust of the vacuum cleaner outdoors as well so any fine powder that gets through will be outside safely and not in the indoor air. Change the filters after cleaning and wash the vacuum inside and out as well, including the suction hoses. Then you can look at using some sort of conformal coating to hold down the non flaking corrosion products.To replate you have to strip down to bare metal, etch and degrease then plate again, a lot of work. Rather just paint with some polyurethane varnish and leave at that, it will be fine inside the case, and take the case, clean it as well inside, sand lightly while vacuuming out the dust, and use the same polyurethane varnish on it. For the longest life use a 2 part automotive clearcoat instead, you can brush it on with little issues if you do not care too much about appearance, and they will last decades. Automotive 2K clearcoat with a retard thinners will take the longest time to cure ( around an hour in cool temperatures, about 10 minutes at 30C) when applied, probably best to use, and does cure water clear and does not yellow with age.