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So I have been freezing ice a lot recently, and I will come out and say it, as it turns out it is, albeit unlikely, it is sometimes possible for ice to "explode." I was not so aware of this before, but from now on I consume my ice beverages with deliberate care.

The first action I have taken is to make sure no bubbles are visibly present before freezing.

I was thinking about how one might reduce these frozen bubbles when making ice with ice trays and a freezer (the bubbles are sometimes a few millimeters across). I was thinking perhaps the bubbles are more likely to form if there are more dissolved minerals and other compounds commonly found in tap water. I think it is time to review osmosis to see if anything will shed light on this idea. My first instinct was to distill water and freeze it to see if there would be less bubbles, but since there will always be dissolved gases even in a freezer it does not follow that this will greatly affect anything.

Is it the case that at lower temperatures water will not be able to hold as many dissolved gases? If that is the case, then it might be worthwhile to lower the temperature of ice in the fridge or to a temperature just above freezing and allow the solution to stabilize, and then put it in the freezer.

Your insight is appreciated, thank you.

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2 Answers 2

up vote 4 down vote accepted

IIRC, the solubility of virtually all gases in water decreases with temperature. This is the reason why heating water will result in bubble nucleation, and this can be exploited to produce very clear ice by boiling water, perhaps several times, before putting it into the trays.

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To minimize the air bubbles in ice, either 1) hold the water under a vacuum or 2) 'degas' the water with an ultrasonic cleaner before freezing.

1) Holding the water under a vacuum will pull the dissolved gases out of solution. The will diffuse to the air-water surface, and then be vacuumed away.

2) An ultrasonic cleaner will vibrate the liquid at ultrasonic frequencies. Vibrating water-gas mixtures at the right frequency will drive out dissolved gases in much the same way that an earthquake will drive ground water out of water-saturated soil (ie liquifaction). Many such ultrasonic cleaners even have a 'degas' setting for just such a purpose.

Note also:
* Water will freeze as soon as it dips below 0 degrees C (assuming it's pure water, it's not being agitated, and it's at standard atmospheric pressure). So, cooling the ice at a lower temperature freezer will make the ice form quicker. Thermodynamically then, it's creating a greater temperature difference between the air-water interface and the center of the water, so the heat flow out of the ice will be greater, and water will reach 0 degrees C sooner. * Gases do not immediately dissolve into water. Assuming you had water with absolutely no dissolved gas it takes some time for the gas atoms/molecules at the air-water interface to dissolve into the center of the water. -- So I guess this means, assuming you degas the water, forming the ice in a lower temperature freezer will help, too.

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