Harvesting SMD IC's with rework station.

Good theory, but probably not. All of the IC's on the tray in my photo are new and have never been soldered. I also use non-corrosive rosin flux and am fairly good about cleaning off any flux with solvent after soldering (and de-soldering). My photo is from one of the trays of IC's that remained after I tossed about 5 other black foam pads full of rotted IC's. Every IC had severely corroded leads. Bend the lead and it just breaks. Except for the gold plated leads, the other IC's were only damaged where they contacted the black foam.

It's not easy to see on my photo, but when I pull out an IC from the foam, some of the foam comes with the leads. It's not unusual to pull out a small chunk of foam with the IC. I'm not sure of the significance, but it does indicate that whatever chemical reaction was involved also causes the foam to harden.

I'm still mystified what would attack gold plated lead.

My bet would be that it was some sort of electrolytic action, rather than a purely chemical reaction.