John:

There is much less Tin dissolved in MEA than in Caustic.

And, if you include the fact that most proprietary MEA based strippers also
contain inhibitors, these systems CAN, but do not always, dissolve less
Copper than Caustic.  Caustic will inherently dissolve essentially no Copper,
but it does tarnish real badly, because the Copper is being oxidized, but not
dissolved.

A properly formulated MEA based stripper will dissolve the Copper on the
surface that is already oxidized, but no more.  Many MEA based strippers
dissolve not only the already oxidized Copper, but promote oxidation of even
more Copper, especially in a spray chamber, where the dissolved Oxygen from
the air helps this out nicely.

Now, the funny part of this is that it is not the MEA that is promoting
Copper dissolution, it is rather the Ethylene Diamine, or some similar
analogue, which is usually in there as well.

Rudy Sedlak
RD Chemical Company

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