I have an organic chemical (can't say due to an NDA) that has a nominal melting point of 28 °C. When I raise it above this temperature, it melts, but then it will stay a liquid indefinitely at lab temperature (≈22°C), and in the fridge (4 °C) for at least a week. When put in the freezer (-20 °C), it will freeze, and then stay a solid at lab temperature indefinitely.

Is there an explanation for this phenomenon? I'm assuming this may have something to do with the kinetics of the crystallization, but I've never seen something with this level of hysteresis.

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    $\begingroup$ Supercooling is a pretty common thing with organics. $\endgroup$ – Ivan Neretin Mar 1 '19 at 15:58
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    $\begingroup$ We even exploit this to make hand warmers. Sodium acetate is easy to supercool and needs a "kick" to start crystallisation. Small sealed pouches are sold as hand warmers. They contain a flexible metal disk that when clicked kicks off crystallisation and this releases heat. The solid push can be reused by warming it and melting the solid. It stays liquid when cooled. $\endgroup$ – matt_black Mar 1 '19 at 17:43

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