I go through a lot of ice. I really don’t like drinking anything that is above 33 F, and 32 F is soo much better. Because of that, I believe I go through more ice than your average person.
Every so often, when I get a tray of ice cubes out of the freezer I have one or more cells of the ice cube tray exhibiting an odd ice formation: A spear of ice usually about two cm long, sticking anywhere from 65° from the horizontal to full 90°.
I realize that ice is a crystalline structure and that, especially in purer waters, ice formation will take on shapes that coform to the natural crystal that ice falls into.
But this still seems to be very odd. The more I think about it, the more I think that it has to be a case of using the thermal energy released from the freezing water to actually raise the water molecules to a higher potential energy state. (Yes, an inch isn’t much, but it’s still an increase.)
Whatever else is going on with the formation of ice cubes, I am well aware of the normal progression. First the extremities of the cell freeze: The surface, and those portions of the cell touching the ice cube cell wall. From there, while the heat of fusion will have some effect on the forming ice, the major concern is that the majority of the heat loss is through the surface of the forming ice cube - simply because the air there can be heated, setting up a small natural circulation convection current.
For the first 50-60% of the freezing process, as the water freezes it will also be extruding dissolved and entrained materials from the ice (Primarily entrained air, actually - that’s what the screen on domestic water faucets does, after all.). This is why the upper portion of your ice cube is clearer, and harder, than the lower portion. Eventually, of course, the remaining liquid water is saturated, and cannot be forced to take more of the contaminants* from the ice, and so the ice matrix has to form to surround the contaminants. Which is why the lower half of one’s ice cubes are cloudy, and more brittle compared to the upper half.
There’s a reason for me to mention this process, because what gets me is that I really, and truly, cannot fathom how those ice spears form. Based on what I believe to be the process for ice cube formation, the spears have to begin forming while the surface of the ice cube is still liquid, or partially so, and then have to wick more fluid onto the spear to keep it growing.
So, how does that happen? Next time I get a spear in my ice, I’ll try to remember to take a photo so that I’ll be able to show the Teeming Millions what’s going on.
FWIW, I usually filter my water using a Brita water filtration system, and let the filtered water sit in my fridge until I empty another ice cube tray, so the water is going into the freezer at about 34 F. (Yes I keep my fridge cold, too. I will admit I’ve had veggies freeze in the past.) I don’t know whether that’s a factor, or not, but I figure I’ll give the best data I can.
*Note: using the term contaminant to simply mean anything that’s not H[sub]2[/sub]O, not making a judgement on whether the contaminant is dangerous or unwanted.