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I'm researching a way a dragon could expel a substance that freezes things it comes in contact with. I've seen two posts here on the WBSE with this theme, but both said about the animal evolving to have this feature and I think this might limit a little bit on how this could happen. Also, I've seen responses suggesting using liquid nitrogen, but liquid nitrogen doesn't freeze a person, if it does, it takes a long time, you can't use it as a weapon in battle.

Now the question: could an animal expel a substance that freezes the things it touches and is effective in battle?

  • My dragon he is created, did not arise from evolution;
  • It's a carnivore, I don't know if that matters, but it's there in case you need to know;
  • The substance will be expelled together with the water, so if the water freezes it may incapacitate the target, even a little, or create ice blocks("hail") that have fallen on those below;
  • The substance cannot be toxic, as the animal will be mounted and it will not be good if the rider ends up intoxicating nearby allies;
  • The substance has to be easy to make and store, not something that would depend on super machinery to manufacture and store.
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    $\begingroup$ And here I thought you wanted a creature that would shit ice cubes! Alas... $\endgroup$
    – elemtilas
    Commented Oct 19, 2021 at 1:15
  • $\begingroup$ Does it have to be water ice, other wise you could use hot ice $\endgroup$
    – Nyra
    Commented Oct 19, 2021 at 1:31
  • $\begingroup$ You might find this reference useful. letstalkscience.ca/educational-resources/stem-in-context/… $\endgroup$ Commented Oct 19, 2021 at 2:24
  • $\begingroup$ Don't knock liquid nitrogen. It's dangerous stuff to "play" with, and it can also asphyxiate ehs.research.uiowa.edu/liquid-nitrogen-handling. As a warmer alternative, dry ice shards cause physical damage + cold burns $\endgroup$
    – DWKraus
    Commented Oct 19, 2021 at 3:12
  • $\begingroup$ I think you'll need to drop the requirement of this fast-freezing of a human. this is simply not possible in a battle setting. A (best-case) unarmored human with 100kg water content @35degC needs to have (100*333 + 100*4*35)kJ, so about 47MJ of heat removed before being all ice. To do that in 10 seconds 5MW would need to leave the human during that time. that is not feasible, if you do not have the human as a very thin paste on a large surface, and in that case, whats the point in freezing them.... ? $\endgroup$
    – bukwyrm
    Commented Oct 19, 2021 at 12:42

3 Answers 3

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A reasonable solution seems to be large quantities of liquid propane dumped onto the target.

  • Propane can be maintained liquid at about 10atm at 20-30C.

  • Has a high vapor pressure - 8 atm at 20C, so any liquid propane will vaporize as fast as it can.

  • Each kg of liquid propane will need 428kJ to evaporate (latent heat of evaporation) and will freeze about 0.2kg of water (latent heat of fusion for water: 2,260kJ/kg).

To completely freeze an 80kg human with 70% water, one will need to douse the human with about 250kg of liquid propane (and better keep it thermally isolated from the environment, so that the heat is extracted from the human. I suggest putting it into a barrel, isolated by some blankets).
At about 580 kg/m^3, it means a wee bit under half a cubic meter of liquid propane.

Do I need to mention one should avoid naked flame or sparks during the freezing process?


Of course, you can try other liquids with a high vapor pressure, like liquid carbon dioxide, nitrogen or helium, but the storage is gonna be a harder problem. Avoid liquid ammonia, though, its dissolution in water is exothermic.


Are you sure you want a tanker filled with cryo liquids as an animal?

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  • $\begingroup$ Ammonia IS a very good refrigerant, goodway.com/hvac-blog/2009/08/… if you organism can use an internal compressor system. then is can be exhaled as poison gas, and it's flammable, so it could produce fire. In AD&D terms, that's the bulk (white, green, red) of dragon breath. Cold is still the hardest to justify. Good answer, BTW. $\endgroup$
    – DWKraus
    Commented Oct 19, 2021 at 3:05
  • $\begingroup$ @DWKraus I though about it, but it's too chemically active (especially against proteins) and a bit towards corrosive when you mix it with water (which ammonia simply loves to do). Dousing the victim in ammonia may resemble more of a chemical attack than a cryo one. $\endgroup$ Commented Oct 19, 2021 at 3:12
  • $\begingroup$ This is supposed to be a breath weapon, so maybe destructive isn't so bad. The water expelled could be super-cooled internally, then expand on exhalation, freezing on contact. The ammonia never leaves the beast or touches the water. Oh, I almost forgot "Acid" breath, as ammonia would give you the (black) corrosive breath weapon as well! I'm seeing a common ammonia-utilizing ancestor to all evil dragon types. Plus ammonia is a lifting gas, so maybe used in dragon flight... $\endgroup$
    – DWKraus
    Commented Oct 19, 2021 at 3:21
  • $\begingroup$ That dragon better be made of non-biological substances, at least on the part that filters and liquefies ammonia. And don't try supercooled water if you intend to have a moving dragon. Actually, you may want to think of a jet formation that uses teleportation, so that the supercooled water molecules don't get opportunities to change their mind and huddle together $\endgroup$ Commented Oct 19, 2021 at 3:37
  • $\begingroup$ And how would the animal get the propane? $\endgroup$ Commented Oct 19, 2021 at 9:43
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You might not need a chemical to produce the ice, you could have a chamber full of superchilled water. This is water cooled below it freezing point but it doesn't have a nucleation site to freeze from so it stays as a liquid, but as soon as it hits something that is can crystallise around (most thing work, it is far harder to stop it freezing) it starts to freeze. enter image description here

To Stop it freezing in you dragon the chamber it is stored in would have to be very smooth, possible a grown protein structure. To cool the water you might be able to use a system described in this answer

hopefully that helps

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    $\begingroup$ And make sure your dragon sits perfectly still until the attack, moderate agitation may cause a sudden increase in the superchilled water volume. $\endgroup$ Commented Oct 19, 2021 at 3:19
  • $\begingroup$ Your dragon might keep the water compressed, allowing the water to stay liquid, then it gets cold as it expands. $\endgroup$
    – DWKraus
    Commented Oct 19, 2021 at 3:24
  • $\begingroup$ @DWKraus that is a Cool idea $\endgroup$
    – Nyra
    Commented Oct 19, 2021 at 3:29
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    $\begingroup$ @DWKraus You know how water is practically uncompressible and that ice has 10% more volume. The problem... umm... boils down to what pressure one will need to maintain to compress water by 10% and if, at that pressure, you won't still get some sort of the 19 possible crystalline structures of ice. But all is not lost, it may actually work if you dissolve in the water a good amount of suspension of belief ;) $\endgroup$ Commented Oct 19, 2021 at 3:56
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    $\begingroup$ @AdrianColomitchi looking at the phase diagram for water, i think the pressure would have to be ~1000 atmospheres to have a significate affect on the freezing temperature. So while possible I don't think it is practical. $\endgroup$
    – Nyra
    Commented Oct 19, 2021 at 4:21
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I know Bombardier beetles expel 2 chemicals to create a hot explosion. A quick google search produced this

We show that liquid polyoxacyclobutane −[CH2–CH2–CH2–O]n– when mixed with water at room temperature precipitates solid cocrystals of the polymer and water. Cocrystals can also be formed by simply exposing the liquid polymer to saturated humidity. This appears to be the only known example of nonreacting liquids combining to form a solid cocrystal, also known as a clatherate, at room temperature. At high temperatures, the same polymer–water mixtures phase separate into two coexisting liquid phases. This combination of cocrystal formation and LCST-type liquid–liquid equilibrium gives rise to an unusual, possibly unique, type of phase diagram.

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  • $\begingroup$ Their spray does not produce an explosion, but the reaction is quite exothermic. $\endgroup$
    – DrMcCleod
    Commented Nov 17, 2021 at 13:56

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