[Bloodtrain]

Hello. I realize this is probably a strange question but I need to know of a material or substance that I would leave in a cold temperature and would implode after a few hours or days because of it. Does such a thing exist?

[Arkcon]

We can start to try to figure this one out.  Why don't you start by defining implode?  What things implode?  I suppose a sealed metal can, evacuated of air, ends up crushed by atmospheric pressure.  But solid items don't do that, and that's not even an implosion.

We have rules, on this forum, against discussing explosives.  But a "rules lawyer" would jump right in and say they want an "implosion" which is totes diff, dawg.  However, if you're expecting some force, from minumal effort, then you want much the same thing as an explosion.

[Bloodtrain]

It is for a concept in a story, I'm sorry if what I'm asking isn't allowed here. Basically, I would have something like an urn be put under a cold condition (not incredibly cold) and within one or two days, because of something inside the urn that reacted to the cold and imploded/exploded, the urn would break.

[Corribus]

As you may guess, things don't usually become MORE unstable as they are cooled. Thankfully, chemistry is nothing if not chock full of exceptions. Off the top of my head, one possibility that comes to mind is oxygen, which is known to be highly unstable/explosive when cooled to liquid or solid form. This is a common laboratory hazard with the use of vacuum lines and liquid nitrogen cooling traps. Vacuum pulls air into the trap, oxygen condenses into liquid, small spark or trace bit of organic material, kaboom.

[Borek]

Start with a tin box, with vacuum inside (for whatever reason - just put in some boiling water so that it pushes the air away, then close the box and once it is cooled it has a pretty low vapor pressure inside) cooled down it can get attacked by the tin pest and break. Not that I would expect a serious implosion, but it will definitely break.

Actually any vessel that is close to its structural limit can break after some time because of material fatigue, so using the trick with water opens plenty of possibilities.

[Enthalpy]

Fill butane, propane, pentane... in the urn to replace the air.
Design the urn so that it collapses (for instance by buckling) with less than 1atm difference outside-inside.
Isolate the urn enough (with soil maybe) that it takes the desired time to cool the gas so the pressure sinks. The insulator shall not prevent buckling.

[Enthalpy]

Or with a double-walled urn like in a hydrogen gun.

The inner space is void (zero atmosphere) and the intermediate space, between both walls, at about half an atmosphere. When you let air leak in the intermediate space, the inner wall collapses as it withstands 0.5 but not 1.0 atmosphere difference. Then the pressure drops in the intermediate space and the outer wall collapses for the same reason.

Some bimetallic thing, or a paraffin thermostat, or anything else, can create the leak at cold.

Or you put electronics in it. Too easy.

[pcm81]

a can with sodium and a glass test tube with water inside. Water freezes, test tube cracks. Cold spell goes away, ice melts, water leaks out of test tube, comes in contact with sodium and... BOOM!!!

[Arkcon]

Annnd, we're done.  There are rules against explosives.  They apply to everyone, no matter the situation -- yes, even those people writing stories, and yes, even something as obvious as over inflating a balloon.  The information can be used to hurt oneself or someone else.