|
General Vintage Technology Discussions For general discussions about vintage radio and other vintage electronics etc. |
|
Thread Tools |
11th Jun 2018, 5:09 pm | #1 |
Nonode
Join Date: May 2007
Location: Preston, Lancashire, UK.
Posts: 2,511
|
Zinc and Cadmium Plating
Is there any easy and non-destructive way to ascertain whether a steel chassis was plated with zinc or cadmium when it was made seventy years ago? The finish is dull and grey, which makes me think zinc, but I'm not sure what colour old cadmium plating would be.
Modern zinc plating looks quite different, but I believe that is caused by 'brighteners' used in the plating bath. Many thanks, Andy |
11th Jun 2018, 5:29 pm | #2 |
Dekatron
Join Date: Sep 2007
Location: Oxfordshire, UK.
Posts: 4,311
|
Re: Zinc and Cadmium Plating
I think the industry standard way of doing this these days would be by X-ray fluorescence. Hand-held analysers are now available https://www.bruker.com/products/x-ra...dheld-xrf.html and the last time I popped into quite a small plating shop they had a desk-top one for routine use.
At school I remember that in the 6th form we did transition metal analysis using 2D-chromatography, the last stage of which involved developing the filter-paper chromatograms in flowing hydrogen sulphide gas. The metal sulphides have distinctive colours. Cadmium sulphide for example is the famously bright 'cadmium yellow'. Unfortunately for us the fume hood in which our H2S Kipp's generator was running had developed a fault and rather a lot of H2S escaped into the lab. The first thing it does is to paralyse your sense of smell, so we weren't really aware how bad the problem was getting. The second thing it does is to kill you. Poisoning was avoided when a teacher came into the lab, practically choked on the stink, slammed the hood door shut then rushed us all outside into the fresh air. No harm seemed to have been done. I suspect that would get onto the news these days, assuming of course that schoolchildren are still allowed access to poisons. Cheers, GJ
__________________
http://www.ampregen.com |
11th Jun 2018, 8:26 pm | #3 |
Nonode
Join Date: May 2007
Location: Preston, Lancashire, UK.
Posts: 2,511
|
Re: Zinc and Cadmium Plating
GJ, thanks for your interesting reply, unfortunately I don't think either meet my criterion of 'easy', by which I meant 'something I can do at home without spending money'!!!
Your mention of H2S is appropriate - the chassis belongs to a Fishpond Indicator, a unit of the pioneering H2S ground-mapping radar...……. We did all sorts of things in the school chemistry and physics labs back in the 60's which are banned nowadays, I know it's easy to remines about the 'good old days', but school science was fun and fascinating then. Andy |
11th Jun 2018, 8:41 pm | #4 |
Octode
Join Date: Dec 2017
Location: Morden, Surrey, UK.
Posts: 1,560
|
Re: Zinc and Cadmium Plating
Military kit would most likely to be cadmium, especially in those days, I would have thought.
Zinc and Cadmium are both grey initially, I think, it is the passivation process that turns them the brighter gold colour. |
11th Jun 2018, 9:40 pm | #5 |
Nonode
Join Date: Dec 2012
Location: Kirk Michael, Isle of Man
Posts: 2,350
|
Re: Zinc and Cadmium Plating
Ref GJ's#2, at school we had a terrible chemistry teacher (he could not control us, so no work was done). In Jan, he was gone, a new teacher who read the riot act, and we could see he meant it. He then got on with hammering chemistry into us (thankfully). When we had cause to make H2S in the Kipps, he told us about the effect on smell. In fact he got caught at his own school or university. He left the drawer too far up, and was slowly being gassed. He came around to hear his teacher or lecturer saying "Poor Manson, he might have been killed". He hammered that message into us as well. I still remember it more than 60 years later!
Les. |
11th Jun 2018, 10:13 pm | #6 | |
Dekatron
Join Date: Sep 2007
Location: Oxfordshire, UK.
Posts: 4,311
|
Re: Zinc and Cadmium Plating
Quote:
XRF units are more common than you might imagine. There probably isn't one around your home , but if you're prepared to go outside then a quick Google finds this lady https://www.uclan.ac.uk/staff_profil...williamson.php who seems to be using XRF. I wouldn't be surprised to find that there's an XRF rig at UCLan. Cheers, GJ
__________________
http://www.ampregen.com |
|
11th Jun 2018, 10:49 pm | #7 |
Dekatron
Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
Posts: 7,087
|
Re: Zinc and Cadmium Plating
I'd go with that - military stuff would have the best protection, and cadmium plating is a very effective anti-corrosion coating on steel. If you know the provenance (and the age being 70 years old), you can make an inspired guess.
|
11th Jun 2018, 10:54 pm | #8 |
Dekatron
Join Date: Aug 2016
Location: Colchester, Essex, UK.
Posts: 4,108
|
Re: Zinc and Cadmium Plating
Highly likely to be Cad plated.
Any zinc deposition of that era would have been done galvanically, so is polishing an area and looking for that signature crystalline appearance (under magnification) an option? 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.. |
12th Jun 2018, 3:01 am | #9 |
Dekatron
Join Date: Dec 2007
Location: Haarlem, Netherlands
Posts: 4,203
|
Re: Zinc and Cadmium Plating
Cadmium plating tends to have a bit of a yellowish/greenish tinge sometimes (might be an effect of oxidising). For example, look at some Philips chassis or screws.
|
12th Jun 2018, 4:59 am | #10 |
Banned
Join Date: Jun 2015
Location: Mareeba, North Queensland, Australia
Posts: 2,704
|
Re: Zinc and Cadmium Plating
A small problem arises with modern plating!!. Passivated zinc chromate is the modern plating seen in all sorts of places. Its identical to Cadmium in colour once its on the metal.
Check a modern wood screw bought from virtually anywhere, and it looks like cadmium plating. Check a modern chinese guitar amp chassis. Its gold coloured and looks identical to Cadmium plating. On large areas ( over a few square inches/or sveral 10's of millimeters) passivated zinc chromate will have a blueish tint when held to the light at an angle, Cadmium is even in colour. Joe |
12th Jun 2018, 7:53 am | #11 |
Dekatron
Join Date: Nov 2010
Location: Oxford, UK.
Posts: 4,991
|
Re: Zinc and Cadmium Plating
All the linkages underneath Garrard decks from the 50's though to the 70's at least, were cadmium plated.
People who do high quality restorations of the 301 and 401 decks dismantle all the linkages and send them to be stripped of the cadmium and replated with zinc. So I think on balance the OP's metalwork is likely to be cadmium plating. It was the generic passivation technology back then. In fact even in the 80's when I was developing equipment for defence purposes, connector shells - even D connectors - were cadmium passivated. |
12th Jun 2018, 5:50 pm | #12 |
Guest
Posts: n/a
|
Re: Zinc and Cadmium Plating
D38999 mil spec connectors even today have the option of zinc as opposed to cadmium.
|
12th Jun 2018, 8:15 pm | #13 |
Nonode
Join Date: May 2007
Location: Preston, Lancashire, UK.
Posts: 2,511
|
Re: Zinc and Cadmium Plating
Thanks for all the replies, I think I have to conclude that there is no easy way to tell without access to university-level laboratory facilities.
The reason I was interested is that this particular chassis needs some repairs to reverse modifications made when it was repurposed as something else, maybe part of an early TV set. Although I'm not a health and safety obsessive, I'll take sensible precautions such as not breathing any dust, not eating or drinking whilst working on it, and washing my hands frequently, as I'm aware that cadmium is a whole lot more toxic than zinc. I'm thinking of making the repairs by soldering, which will mean getting back to clean steel where necessary. Andy |
15th Jun 2018, 12:35 pm | #14 |
Dekatron
Join Date: Dec 2007
Location: Haarlem, Netherlands
Posts: 4,203
|
Re: Zinc and Cadmium Plating
As far as I know there is an easy way to tell, but it only goes one way. If it looks slightly yellowish/greenish it is cadmium, but if it looks zinkish it can be both. Never seen or heard about a goldish colour, though.
|
15th Jun 2018, 1:22 pm | #15 |
Octode
Join Date: Dec 2017
Location: Morden, Surrey, UK.
Posts: 1,560
|
Re: Zinc and Cadmium Plating
Both Zinc and Cadmium can be plain or clear. passivated, which looks greyish or colour passiivated, which normally starts off yellowy gold but soon fades. I don`t know of any reliable visual way to differentiate between Zinc or Cadmium plating.
|
15th Jun 2018, 9:05 pm | #16 |
Dekatron
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 16,536
|
Re: Zinc and Cadmium Plating
That cadmium plating is potentially nasty is a given, but is there any empirical evidence to say how likely one is to suffer as a result of cleaning up old electronics at a hobby level?
__________________
....__________ ....|____||__|__\_____ .=.| _---\__|__|_---_|. .........O..Chris....O |
16th Jun 2018, 2:16 am | #17 |
Dekatron
Join Date: Dec 2007
Location: Haarlem, Netherlands
Posts: 4,203
|
Re: Zinc and Cadmium Plating
Ah, that explains why I've never seen it. I've only seen old chassis.The yellowish greenish tinge I see regularly on old Philips stuff, doesn't look goldish.
|
16th Jun 2018, 7:03 am | #18 |
Dekatron
Join Date: Nov 2010
Location: Oxford, UK.
Posts: 4,991
|
Re: Zinc and Cadmium Plating
The HSE's recommendation for working with Cadmium and its compounds are:
– cadmium and cadmium compounds (except cadmium sulphide pigments) – 0.025 milligrams per cubic metre of air averaged over an 8-hour period; – cadmium sulphide pigments (respirable dust) – 0.03 milligrams per cubic metre of air averaged over an 8-hour period; – cadmium oxide fume has also been assigned a short-term exposure limit. This exposure limit is measured over a 15-minute period and has been set at 0.05 milligrams per cubic metre of air; 0.025mg/m^3 is 25 parts per billion (ppb) - a very low level indeed. Craig |
16th Jun 2018, 7:19 am | #19 |
Retired Dormant Member
Join Date: Dec 2007
Location: Shropshire, UK.
Posts: 3,051
|
Re: Zinc and Cadmium Plating
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.
|
16th Jun 2018, 8:25 am | #20 |
Heptode
Join Date: Apr 2016
Location: Cheltenham, Gloucestershire, UK.
Posts: 875
|
Re: Zinc and Cadmium Plating
There are several ways of applying Zinc viz: a) sheradising i.e. baking in the powdered zinc - resulting in a variegated finish b) hot dip, and c) electro-plating. All result in a silvery coloured finish - which fades to a metallic grey. Zinc paints [eg. "Galvafroid"] are also available .....
Cadmium plating [which can be electro or vapour blast] tends to result in a pale golden finish ..... which also fades to a dull metallic grey .............
__________________
Red to red, black to black. Throw the switch and stand well back! |