The life of an ice tray

Below 40 degrees, water stops shrinking

When we fill the ice tray with water, within hours tiny peaks begin to form.
  • When we fill the ice tray with water, within hours tiny peaks begin to form.
  • Image by Rick Geary

Dear Matthew Alice: There is a phenomenon that is occurring in our freezer at work that cannot be explained, at least not by us. When we fill the ice tray with water, within hours tiny peaks begin to form. By the next morning there could be a peak of ice 1/2 inch high. A stalagmite of ice rising out of the ice tray! Is there a logical explanation, or is this place wackier than I thought? — David Braxton, San Diego

Those choices are hardly mutually exclusive. Though I’ll admit the Society for Computer Simulation doesn’t sound like the land of zany hi jinks to me. Anyway, while the rest of you are trying to reduce all of life to mathematical models, the water in your ice tray in your freezer is following its own unique path. Unique for most liquids, anyway. Cool down most liquids and they’ll get denser and shrink. So will water, until it dips below 40 degrees Fahrenheit. As it reaches the freezing point, it begins to expand. So ice crystals occupy more space than the water from which they were formed. Since the crystals cling first to the sides of the ice tray, then accumulate toward the center, you can often end up with those characteristic ice peaks. Freezing water develops an extremely strong chemical bond and exerts a lot of pressure, enough to crack a car’s engine block if you decide to take a motor tour of Antarctica and forget to fill up with antifreeze.

If you leave the tray untouched in the freezer for a few weeks, your cubes will do another unique thing. They’ll disappear. Water is one of the few substances that will go from a solid to a gas without first becoming liquid. If there’s a lot of air movement around the ice, it will vaporize even faster. That’s the principle behind self-defrosting reefers; air is blown into the freezer compartment periodically to zip away any ice crystals that have formed. Of course, the moving air vaporizes your ice cubes too. There’s even an example of this in nature. While you’re tooling around Antarctica, stop by the Dry Valleys, a desert-like stretch of terrain that’s kept ice-free by 200-mile-per-hour winds.

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