Neutron absorbing element - MERC or GOLD
Heavy water - GLOW
If the elements you propose do not have any other unique properties, elements with their properties already exist.

@EnganK (View Post)

 Isnt heavywater DEUT? or is glow just better?

Of course, DEUT, being deuterium oxide, is technically heavy water. However, in terms of the proposed functionality, GLOW is much closer to heavy water, being a chemically passive liquid often used in reactor cooling loops.

maybe COLF/ cooling fluid, which would slowly cool down elements it touches when they go above the COLF's temperature, which could help people make more ambient heat friendly stuff, and would be cool (pun intended) for weapon cooling and thermal weapon resistant armor

 

also magnesium/ MAGN, just a heat trigered bomb, 'cause magnesium acts a lot like bomb with the sparks and little expolosions

Why are you writing this in existing threads instead of creating your own?

COLF already exists in the game as FRZZ/FRZW. It's literally a liquid that cools down over time.
MAGN can be somewhat simulated with ICE(BOMB) or SNOW(BOMB).