"Hugh Prescott" wrote in message
...

"N Cook" wrote in message
...
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
http://home.graffiti.net/diverse:graffiti.net/



Sounds like the dreaded black wire corrosion of the past

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

Hugh




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
http://home.graffiti.net/diverse:graffiti.net/