I've just seen this five year thread; this is the first time I've visited his group, and Google won't let me reply to a post that old. If it's of any interest, there was, and probably still is, a process for attaching track circuit bonds to rail ends using a thermit-like process, which produced some sort of copper/bronze metal. I don't know the composition of either the mixture used, or the metal produced. This process was quite common at one time, especially on third-rail electrified lines, where very heavy bonds had to be used, as they carried not only the track circuit current, but also the traction return current, but the need for such bonds has been much reduced by the use of continuous welded rail.