Reply #32: Melting points [View All]

[plaguepuppy]

That's a cool animation, and eutectic mixtures are an interesting phenomenon. You can also think of it as plotting the melting point over an x-y plane that represents the different ratios of the ingredients. The eutectic points represent local minimums on such a plot. And of course you are not just limited to mixtures of two ingredients,

As a kid I was a true mad scientist with a booby-trapped basement lab (set off only once, by my mother). I had an alcohol lamp and a nice big crucible with a handle that I used to melt lead in, making a nice big crucible-shaped lump. Also spent a lot of time making a variety of things that went boom. My favorite was potassium iodide, a very touch-sensitive compound made from iodine and ammonia. Just dropping a piece on the floor would set it off, scattering smaller pieces that would make little crunching noises as you walked on them.

But even with a bunsen burner lead or solder were the only metals I could get to melt - not counting magnesium ribbon, which I spent many happy hours burning.

Based on this intensive hands-on heavy metal exposure I have a good sense of what it takes to melt various metals. It's true that hydrocarbon fuels will do the job, but only if well mixed with the right amount of air. As anyone who has played with gas motors knows, getting the right mixture in the right place at the right time is not a trivial accomplishment. To suggest that you could generate such temperatures by smashing a container of fuel against a building indicates not enough physics and too much exposure to action movies.

In the real world engineering is governed by the gods of FUBAR: if you try to get a complicated system to behave in some predetermined way you will first experience all the other possible outcomes and all the ways it can avoid the outcome you want. This is just the opposite of action movie physics, where for example a machine gun bouncing down a flight of stairs manages to go off at just the right moments to kill all the bad guys. In the real world the opposite would be safer to bet on, but most likely it just wouldn't go off.