I believe the possibility that tritanium is an isotope of titanium (one extra neutron, perhaps?) has long been suggested. It follows with the theory that "duranium" is actually "depleted uranium".VOY Season 4, Ep# 74: "The Raven"
TUVOK: There are no lifesigns. Tritanium decay suggests it has been here for nearly 20 years.
Misc: Tritanium decay? This means tritanium is radioactive, with such a short half-life that it can be accurately dated to within a few years!
I would suggest, however, that these are both alloys and that Federation naming standards for materials have long since diverged from anything modern.
Assuming that it's not a radioactive isotope, I would suppose that tritanium tends to slowly break down in an atmosphere. Since there are apparently microscopic life forms in space that "feed" on materials like tritanium, it's probably an exothermic reaction. With the right chemicals, it might be possible to rapidly corrode the hull of a Federation vessel.
Is there any precedent for such a material?