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Old 16th Jun 2018, 8:52 am   #21
Craig Sawyers
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Default Re: Zinc and Cadmium Plating

Quote:
Originally Posted by dseymo1 View Post
Apparently, it can occur in relatively high concentrations in coal (and thus smoke and soot), and tobacco, so I suspect that much of the general population has already exceeded those levels.
There are all sorts of stuff in coal. One of the original sources of Germanium was from flue soot.

And arsenic was a by-product of tin and copper smelting. So at the mine head tin ore was roasted to drive off sulphur and valuable arsenic, and then children were sent up the chimney to brush out the arsenic soot. In the 1800's. The Cornish tin and copper mines produced half the world's arsenic - 3000 tons per year. Heaven knows what happened to the children.

All a bit off-topic, other than that times have fortunately changed regarding toxicity.
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Old 16th Jun 2018, 9:05 am   #22
Philips210
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Default Re: Zinc and Cadmium Plating

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Originally Posted by The Philpott View Post
Slightly destructive, but- a wad of kitchen roll soaked in a weak electrolyte placed on the surface, with a piece of zinc on top, check for a cell voltage across the two? If an avo 8 shows nothing or virtually nothing i would say it's zinc..
Hi.

That seems a very reasonable way to check. What would be a suitable electrolyte to soak the paper towel in?

Regards,
Symon
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Old 16th Jun 2018, 10:06 am   #23
M0FYA Andy
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Default Re: Zinc and Cadmium Plating

First catch your piece of zinc...………….
Are the cases of dry cells, AA etc, still made of zinc these days?

Andy
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Old 16th Jun 2018, 10:30 am   #24
John M0GLN
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Default Re: Zinc and Cadmium Plating

I've just tried it with a galvanised screw and with both aluminium and brass samples as I don't have any cadmium plated bits to hand, I used freshly squeezed lemon juice ( I've watched Masterchef ) and a Fluke DMM as I wasn't sure that the area of zinc, about 6mm dia, would be large enough to supply sufficient current for an Avo and I got good results, close enough to the expected ones considering I was trying to hold the screw steady with just a drop of lemon juice in between.

John
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Old 16th Jun 2018, 11:18 am   #25
John M0GLN
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Default Re: Zinc and Cadmium Plating

I've just redone the test using some kitchen roll as 'The Philpott' suggests and with samples of the only 2 guaranteed pure metals I have, lead and copper, the result I get with lemon juice is 0.45V which is pretty close to what it should be with copper at +0.34 and lead at -0.13.
That's a good method of testing, I've used the electrochemical series quite a few times to check the suitability of different metal combinations but never the other way round.

John
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Old 16th Jun 2018, 12:47 pm   #26
Philips210
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Default Re: Zinc and Cadmium Plating

Hi.

This sounds very promising. I suppose galvanised steel would be OK for the Zinc test plate. I wonder what the expected emf for a zinc cadmium pair would be with acetic acid as the electrolyte.

Regards,
Symon.
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Old 16th Jun 2018, 1:41 pm   #27
kalee20
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Default Re: Zinc and Cadmium Plating

Ideally, the electrolyte should make no difference, as long as it's weakish and conductive.

The downside is, it will have to attack the passivation layer before it gets to the bare metal plating.

Wiki lists the standard electrode potential of -0.4V for cadmium and -0.7618V for zinc, so the two should give a reading of 0.36V - ish.

If there's a scratch and the underlying steel is exposed, things could get more complicated! I'd like it to think that the Zn-Fe (or Cd-Fe) pair action would fill in the crack, nullifying it (which is what the plating is supposed to do, after all), but someone more knowledgeable on electrochemistry will hopefully comment!
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Old 16th Jun 2018, 2:49 pm   #28
Philips210
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Default Re: Zinc and Cadmium Plating

Thanks kalee20 for the figures that's helpful.

Regards
Symon.
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Old 16th Jun 2018, 3:23 pm   #29
M0FYA Andy
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Default Re: Zinc and Cadmium Plating

I've ordered a piece of zinc so I can try this method.
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Old 16th Jun 2018, 4:40 pm   #30
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Default Re: Zinc and Cadmium Plating

Oh, just too late! If anyone else is needing a lump of zinc, it is what car wheel-balancing weights are usually made of these days, now lead is controlled. (A few are steel, and you can weed them out with a magnet). OT - but I have melted them with scrap copper to make brass Some came from the street as I cycle to and from work - surprising how many must fall off.
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Old 16th Jun 2018, 5:17 pm   #31
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Default Re: Zinc and Cadmium Plating

Many years ago a friend of mine had a nicad burst in his pocket, from fit young man to skinny weak fellow in a few weeks, not nice. This was obviously a large acute dose. He did get somewhat better a year or so later not back to his former self though.

Cad plate is stable (that's why it's used) and quite safe if not abused, don't sand, grind, lick etc.. For long term handling use gloves. I wouldn't think the minor contact with it in our hobby is of any consequence. Like all safety advice should be, understand what you are doing. None of this "I have read the leaflet and it doesn't mention anything about the new extension lead I have just plugged in and using it as hammer outside in the rain".
 
Old 16th Jun 2018, 5:49 pm   #32
Philips210
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Default Re: Zinc and Cadmium Plating

Hi

That's a nasty experience. I guess the NiCad was a PP3 that was shorted by coins or keys. Does the cadmium part get readily absorbed through the skin?

Regards
Symon.
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