Can you melt ice in a microwave oven?

[Mr__Bill]

The problem here is your looking at the change of state to validate the heating and not measuring the temperature of the ice. Put -40 Deg F ice in microwave and it will heat to +30 at about the same rate as +40 Deg F water will heat to +110.

Now explain why hot water freezes faster than cold water!


Bill on the Sunny Oregon Coast where all the ice comes from the freezer

[Alex Franke]

So to summarize -- and let me know if I'm getting this wrong -- a microwave oven does in fact have a difficult time melting ice but only because anything has a difficult time melting ice -- this is because it takes a lot of evergy to change the state from ice to water, no matter what is providing the energy. Plus the warmer something is, the less energy it takes to make it even warmer, unless it must change state during the process, so comparing the relative temperature changes between ice and water wasn't really a fair test of how well it was working.

And are we concluding that a microwave can excite a water molecule in ice just as easily (and just as effectively) as it can a water molecule in liquid water? This still seems counterintuitive to me -- espectially since so much enerty is required to break the crystal structure and melt the ice in the first place...

[Alex Franke]

If microwaves can't melt ice because the water molecules are "locked," then how do they cook frozen dinners?

I didn't mean to imply that a microwave oven might be totally ineffective against ice (although that's pretty much what I did imply). But I did think that it would be far less effective than other means -- that's what I meant by "it probably won't work very well." Poor choice of words on my part.

But doesn't a crystal structure pretty much imply that the molecules are held into relatively predictable positions?

I would guess that the more impurities there are, and the weaker the crystal structure is, the easier it will be for the ice in those parts to melt. Once some if it melts, those parts will start heating up faster and melting what's around it.

But it doesn't seem like this would be an even melting throughout -- seems like it would be far more spotty.

I do know what when I set the microwave on defrost, it uses a lower power and turns off frequently -- perhaps to let pockets of heat dissipate?

[cgallery]

I do know what when I set the microwave on defrost, it uses a lower power and turns off frequently -- perhaps to let pockets of heat dissipate?

Exactly. It allows the temperatures in the food to equalize.

When I asked the "how do frozen dinners cook" I wasn't denying that ice doesn't melt in an microwave. I was trying to say that the temperature inside your microwave is (typically) room temperature. The ice cube starts melting, and the energy imparted by the microwave oven heats this water which further melts the ice.

Here is the real experiment: Take your microwave oven outside when the temp. is below freezing. NOW try melting an ice cube in it. Unless there is some liquid water present, I don't think it will work.

[newood2]

I don't have a microwave so I warm up my ice cubes in a pot on the stoves. Stir slowly until they come to a full boil in less than a minute.

[dkerfoot]

BTW, do microwaves make things colder in Australia?

No, but I bet the platter rotates the other direction...

[gerti]

A microwave can not melt ice. Room temperature does that, and the microwave takes it from there and things kind of snowball.

[LCHIEN]

My microwave does a fine job melting ice.

I put this GE microwave on time cook with 8 cubes in a bowl. I used an infrared thermometer with a narrow 10° aperature., Stopped the microwave every 20 seconds to make a reading as fast as I could and then continued on the same timer. I scanned to find the coldest spot, After 40 seconds there was very little ice left as it gradually melted. After 80-100 seconds there was some bubbling as it was trying to boil. The temperature never exceeded 93C; full boil is 100C. I didn't measure the volume but most of the water was still there and had not yet boiled away.

My conclusion is that the smaller slope of the intital temperature rise was due to the heat of fusion being met by the energy going into it, just as I predicted.
After 40 seconds it was mostly melted and the more rapid rise is as I expected as the energy goes drectly into raising the temperature. Finally it levels out as it approaches 100C and most of the energy no longer raises the temperature but goes to satisfying the heat of evaporation.

Who says a microwave won't melt ice?