The closest you can get it nitr turning into water at a high temperature. There might be a way but i don't think it is possible.

I think that you can do that the way explosives turn into EMBR and FIRE

I'm not really sure if this helps, but I made an element that explodes into another a while back:

 local a = elements.allocate("QUENTIN" , "EXPL")
elements.element(elements.QUENTIN_PT_EXPL, elements.element(elements.DEFAULT_PT_BCOL))
elements.property(elements.QUENTIN_PT_EXPL, "Name" , "EXPL")
elements.property(elements.QUENTIN_PT_EXPL, "Description" , "Does Cool Stuff")
elements.property(elements.QUENTIN_PT_EXPL, "MenuSection" , 5)
elements.property(elements.QUENTIN_PT_EXPL, "Gravity" , 0)
elements.property(elements.QUENTIN_PT_EXPL, "Falldown" , 0)
elements.property(elements.QUENTIN_PT_EXPL, "Flammable" , 0)
elements.property(elements.QUENTIN_PT_EXPL, "Explosive" , 1)
elements.property(elements.QUENTIN_PT_EXPL, "Diffusion" , 0)
elements.property(elements.QUENTIN_PT_EXPL, "Weight" , 100)
elements.property(elements.QUENTIN_PT_EXPL, "Advection" , 0.1)
elements.property(elements.QUENTIN_PT_EXPL, "AirLoss" , 0.95)
elements.property(elements.QUENTIN_PT_EXPL, "Loss" , 0.15)
elements.property(elements.QUENTIN_PT_EXPL, "Temperature" , 295.15)
elements.property(elements.QUENTIN_PT_EXPL, "HeatConduct" , 255)
elements.property(elements.QUENTIN_PT_EXPL, "MenuVisible" , 1)
EXPLUpdate = function(i, x, y, s, n)
local clife = tpt.get_property('life', x, y)
if clife > 1 then
for cx = -1, 1, 2 do
for cy = -1, 1, 2 do
tpt.create(x + cx, y + cy, 'stne')
sim.pressure(x/4, y/4, 40)
end
end
tpt.set_property('life', clife - 1, x, y)
elseif clife == 1 then
tpt.set_property('type', 0, x, y)
elseif s > 0 then
for cx = -1, 1, 2 do
for cy = -1, 1, 2 do
if tpt.get_property('type', x + cx, y + cy) == 4 or tpt.get_property('type', x + cx, y + cy) == 49 then
tpt.set_property('life', 100, x, y)
return true
end
end
end
end
end
tpt.element_func(EXPLUpdate, tpt.element('expl'))

I hope it helps some...