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Conductive foam problem

Seeing someone else's post on foam problems reminded me. Years ago I had 3 A4 size sheets of black conductive foam covered with ICs and for storage placed one each in a new manilla envelope with details written-up on them. Stored with open flaps, vertically in a drawer of a filing cabinet indoors, not in a shed. A few years later came to use one and all the pins on all the ICs were affected by rust to the point that some were rusted away totally. Gummed flaps on envelopes were fine unstuck and no other traces of damp. Anyone else experience of this?

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

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Reply to
N Cook
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yes

but I have no idea of the cause

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Reply to
CJT

ICs

later

I should have added it was the soft rather than more rigid foam type. Anyone know what chemicals, initially anyway, are in conductive foam ?

Reply to
N Cook

Sounds like the dreaded black wire corrosion of the past

Possibably caused by the carbon black in the insulation / foam.

Hugh

Reply to
Hugh Prescott

ICs

later

Interesting but the 'rust' I observed was standard iron oxide brown in colour - not necessarily rust as such but certainly that colour.

Reply to
N Cook

My guess would be that something in the foam is corrosive, or that the foam attracts moisture. Rust isn't surprising since ICs often have tinned steel pins. Are all the ICs made by the same company? Andy Cuffe

snipped-for-privacy@psu.edu

Reply to
Andy Cuffe

I don't know the answer, but I'm surprised you didn't have a bigger problem.

I find that black foam deteriorates with time. I was going through a box of old ICs recently, and some of the ICs once well protected were loose because the foam had crumbled.

The mroe recent pink and more solid foam has stood up better.

Which may be why there was a switch to the pink foam.

Michael

Reply to
Michael Black

ICs

later

I'd never heard that term so I've done a bit of looking into it today. I've always assumed the black sooty deposit found in conjuction with copper sometimes, is copper sulphide but putting "black wire corrosion" and "copper sulphide" in search engines turned up nothing.

Some years I asked a chemist what this black and insulating material was likely to be that I often find on 20 or 30 year old switches that because it insulates and unless the wiping type contacts break through it, stops the switch action. He said likely Copper Sulphide, in my instances the suphur from air borne polution and in BWC presumably from battery sulphuric acid vapours. Any thoughts ?

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

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Reply to
N Cook

damp.

corrosion"

sulphuric

or even spelt Copper Sulfide and BWC no references

Reply to
N Cook

The black tarnish that you find on old switch contacts is most likely silver sulfide, since many switches were (and still are) silver plated. It's the same stuff that gets on your good silverware after having eggs over easy for breakfast, and then letting the egg residue stay on the silverware for a while. Eggs are heavy in sulfer content (Remember the rotten egg odor? It's hydrogen disulfide).

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Reply to
DaveM

silver

for

It's

in

I've added rec.antiques.radio+phono as their territory probably

I rarely come across silver plating on the switches I replace/recondition. Usually the black deposit I find is on function and wave change switches. Usually made by Alps company 1 or 2 lines of brass? contacts set in paxolin, then sliding phospher-bronze? U channel slider contacts located in black plastic slider and all housed in tin-plate? cover

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

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Reply to
N Cook

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