In our summer camp (more info here, natch) we have an awesome demonstration that heats an iron wire via a variac that demonstrates the solid state phase transition from BCC iron (at room temp) to FCC iron (at higher temperatures).
This video heats wires of various metals at - I think - constant voltages - and observes a few interesting things:
- copper wire produces a green flash at the moment of melting
- magnesium ribbon rose as it heated and expanded (rather than sagging) at first
- molybdenum wire produced a series of evenly spaced 'balls' (unduloids) before melting and breaking
I've seen something somewhat similar to the molybdenum balls when the iron wire melts and fails. Each end of the iron wire creates one single ball of iron on its end where the wire failed. We don't get the repeated drops like molybdenum, but the metal balls are familiar to me.
I appreciate the explanation of the formation of unduloids forming via partial melting and surface tension pulling the molten surface together. Sounds good enough to me.
I do wish they had repeated the 90 degree turned experiment with the molybdenum wire - not just with the copper wires.
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