Nate Holt's Blog

July 5, 2009

Ice-cube Tray Phenom

Filed under: Musings — nateholt @ 9:40 am

(note: originally appeared in July 2006 on the old blog)

I’ve noticed some strange things growing in my ice-cube tray. It doesn’t happen all the time, maybe one out of every 40-50 cubes. Here’s a two-fer:

ice_spike_002

The valve controlling the refrigerator’s ice maker broke and I was too cheap to fix it… went back to the old-fashioned manufacturing method of low-tech ice cube trays. But I did install an under-sink reverse osmosis water filter and started creating extra-clean cubes. Taken together, this weird phenomenon began to appear. Ice spikes shooting straight out of the tops of random cubes at odd angles. Defying gravity.

ice_spike_001

Had to figure this out. What’s the explanation?

Water expands as it freezes, about 10% (remember grade school and the iceberg talk?… they look big but another 90% is hidden below the surface…). This had to be a clue.

Let’s say I put the ice cube tray into the freezer. The top of the water surface is exposed to the cold air blowing over it in the freezer compartment and starts to freeze quickly. The liquid water below drops more slowly toward the freezing point and starts to expand as it closes in on the freezing point of water at 32F / 0C. But the top surface of the cube is already pretty much frozen, so pressure builds and something has to give. In most cases the whole top surface of the semi-frozen cube pushes up a bit. Look at the close-up above. The cubes on the left-hand side are especially pushed up.

But, in rare cases… maybe there is a tiny weak spot in the top of the cube that the slightly warmer water, under pressure due to expansion below, oozes up through. As this water oozes out, the outer surface of the “ooze” keeps freezing while the inner water oozes up even higher. Maybe this process builds these weird looking ice needles.

UPDATE: I am not (totally) nuts.

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