Re: Wood's metal and styrofoam

Matt Giwer wrote:
It melts at 158 degrees F. I always heard about it and bought some on a whim. (unitednuclear.com -- no connection whatsoever) So I tried it. I microwave heated some water, not to boiling and but I did not measure the temperature, in an unused styrofoam cup, dropped in some small pieces and it melted. I rolled it around the bottom and rather viscous/little surface tension/not like mercury but quite liquid. NOTE: I added the metal AFTER the water was hot and I rolled it around.

Well that was a waste of $10, I says to myself.

So when it cools I pour it out over my hand to catch the metal. It doesn't come out. In fact it is stuck to the bottom. In fact when I break it loose from the bottom, very slight pressure, the styrofoam is indented with the shape of the metal blob. It had slightly melted the styrofoam. There is no styrofoam stuck to the metal.

WTF,O?

Styrofoam cups do not melt in normal use. In fact I use the same one for coffee (black) for weeks until it starts getting brittle but it never melts.

The metal is heat conductive obviously but it can never get hotter than the water. Given convection I can't see how a temperature difference between the water and metal could occur but even if it did how it could cause this.

The blob was small to begin with and spread out a lot NOT as mercury would behave so there was a trivial amount of weight for the metal. Besides if pressure mattered I would expect to see dents from spoons and forks after eating food heated in a cup which I have never observed.

The indented area was the shape of the metal as it cooled with no signs of melting where I had rolled it around.

I heated the water before adding the metal so it had nothing to do with microwave heating.

It was a never before used cup so there was no existing damage to make worse.

Any suggestions on why this happened that can be tested?

I'm down to saying a chemical reaction but that is not my field. And I don't see metals reacting with plastic at this temperature so that would be just hand-waving.

Uncle Al and Huang

I have been thinking on your replies with a hope of finding a way to test them.

The idea of the density of Wood's metal while possible is not likely. I did move it around on the bottom of the cup but the depression is only where it cooled. As it cooled it was in a thin layer NOT like mercury. Thus the density would have to translate to weight to leave the depression. The differential weight between four inches of water and four inches of water with a thin layer of metal would appeal to be negligible.

Even if mechanical bonding occurred I do not see how that would cause a depression. As I noted, no styrofoam was stuck to the metal.

As to a temperature difference as a result of conductivity of the metal, however much greater convection of the water should have made that negligible. The metal was added to the hot water not water to the metal in a cup so the temperature could never get higher than the water at any time. Even if the water were added after the metal the surface of the styrofoam would have instantly become the temperature of the water with the temperature of the metal lagging so the metal should have been on a mound BUT

I did get the metal to move around after melting and it was only where it cooled that a depression formed. While it was moving its temperature would have been identical to the water.

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