These elements have been suggested before, but I think I've figured out how they can be useful in tpt.  I even changed the name of one of them and the abbreviations of both of them:

1.) Potassium (POTM)

When POTM comes into contact with empty space, it's life gets set to 75 and decreases by 1 every frame.  When that life value reaches 0, the POTM becomes AMTR (AMTR produced in this way has a ctype of POTM and does not destroy the POTM.)  Any POTM that's not touching empty space will not undergo this process.  You can set it's life value to any number you want, to make the process shorter or longer as you please.  Like rubidium (solid or liquid,) POTM explodes into FIRE upon contact with WATR, FIRE, or LAVA.  But unlike rubidium (solid or liquid,) it explodes into PLSM (not FIRE) upon contact with PLSM.  Unlike most explosives, it does not explode with heat.  Instead, it melts into LAVA at a temperature of 1832F.  LAVA will not trigger POTM if the LAVA has a ctype of POTM, but it will melt it into LAVA.  When molten POTM comes into contact with molten SALT, the molten POTM absorbs the molten SALT and becomes molten PSLT (see below.)  POTM is a solid.

2.) Potassium salt (PSLT)

It's actually potassium nitrate, but I think potassium salt sounds better.  PSLT is, obviously, a powder.  Unlike POTM (see above,) it does not decay into AMTR.  PSLT splits into FIRE and SALT upon contact with WATR, FIRE, and LAVA.  PSLT splits into PLSM and SALT upon contact with PLSM.  The resulting PLSM will; of course, melt the resulting SALT into LAVA.  When PSLT comes into contact with WOOD, both the PSLT and the WOOD turn into GUN.  The WOOD has to be at both a tmp of 872 and a tmp2 of 872 for this to work.  PSLT melts into LAVA at the same temperature as POTM.

AMTR and GUN currently can't be made via reactions.  But with these new elements, they can.  New factories that make AMTR and/or GUN could be revolutionizing.

NOTE:  the reason why I chose this kind of WOOD is because in real life, the recipe for gunpowder is potassium nitrate, charcoal, and sulfur.  Tpt has yet to add sulfur, but the type of WOOD mentioned above simulates charcoal.  We could certainly use a new challenge when it comes to factories in tpt.