On 03/03/2017 21:08, Benderthe.evilrobot wrote:

"John Robertson" wrote in message
...
On 2017/03/03 12:28 PM, wrote:
Mpfffff..... Some clarification required.

FINE silver plating (most of it) *will not* tarnish from exposure to
air, nor will it form sulphur compounds - without other contributing
factors. Sterling silver (.925 silver) is an entirely different matter.

What is going on here electro-galvanic (galvanic action) *corrosion*
of the copper plating under the silver - and most things
electro-silver-plated other than brass are first copper-plated to
guarantee proper adhesion.

The black material noted is CuO, not tarnished silver.

Peter Wieck
Melrose Park, PA


Thanks, we've had many an Eprom with corroded legs that are from the
70s, in some cases the legs break off inside the IC sockets when the
EPROM is removed. Also this is common on some other ICs used in the
early 80s, such as Galaga which has Namco custom ICs, where again the
legs are corroding right off them.

Is there any way to arrest the process? Be nice to have something to
dip the legs into to cancel the corrosion, similar to using white
vinegar and water (50/50) to neutralize alkaline battery leakage
corrosion.

No idea whether its related - but when I serviced VGA monitors, I often
encountered brown glue that was probably applied to prevent components
from fatiguing their leads.

This stuff eventually became brittle and crumbly - and highly corrosive.
It frequently etched away component leads.

Once brittle it was fairly easy to chip away, but in the early stages it
was elastic like contact adhesive, and lighter brown like Evo-stik.

Very often a component like a resistor would come out encased in this
stuff and the leads completely eaten away.

sorry wrong followup.
You failed to mention it going conductive