Liquid to solid crystal when exposed to air [closed]








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Im working on a prototype weapon based on the [needler from the Halo series](https://youtu.be/-SdRoTj5u-Y). And yes while I do realize that this game series is fantasy, I still find it fun to try and recreate working versions of what is in the game. 


I have a concept worked out to keep the crystalline ammunition in a liquid tank and then use compressed air to fire. The liquid will be pushed through perforated holes to for the crystal ammunition. But I don't know of any chemical or compound that turns from liquid to solid, preferably crystalline when exposed to air. If someone could help me with such a substance I would greatly appreciate it.


