Ice transparent to microwaves ?

Molten glass absorbs microwaves quite well. You need to get it pretty hot with a blowtorch and then microwave it whilst still lossy. Beware you might set off the thermal fuse of the microwave and stop it working.

I believe this phenomenon was something to watch out for with high power vacuum tube RF amplifiers and perhaps a reason for the popularity of ceramic envelopes for high-power tubes.

Chris

On a sunny day (Fri, 24 Jan 2014 00:35:50 +1100) it happened Chris Jones wrote in :

Red hot anodes occasionally melted the tube glass. I have had tubes like that. Not sure there were microwaves involved, as it was audio or TV tube, here an example:

The anode gets hotter than the glass melting point, the glass melts locally, and air flows in, stopping the electron current.

hed

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Ice does not allow eddy currents needed for heating by absorption. Evidentl y the ions are "frozen" in place. Materials transparent at 10 micron (RT he at waves) are a few non-polar types - polyethylene and FEP (teflon-like) fi lms are fairly transparent. A good absorber there is Silicone, since it has broad internal movement lines . (stretch, rock, etc.)

A trick you can amaze your friends with is to boil an egg in the microwave. Simply add some salt to the water surrounding the egg, and it becomes opaq ue. If you use ordinary water, the egg explodes.

Ice does not allow eddy currents needed for heating by absorption. Evidently the ions are "frozen" in place.

** Pure water has no ions and microwaves heat the (polar) molecules directly.

This link has a good summary of the principles involved.

See the text under pic 4.

" .. ice is practically microwave transparent, since the water dipoles are constrained in a crystal lattice and cannot move as freely as in the liquid state. "

.... Phil

Hi Phil, I have found that my microwave does NOT heat pure water well, and addition of salt makes a big diff.

** So your oven produces special, salt loving microwaves ???

FYI:

I just heated 100cc of tap water in my oven for 60 seconds.

The water temp rose by 63 degrees C.

Same again, with a teaspoon of table salt added.

Exact same temp rise.

.... Phil

"David Eather"

** ROTFL !!!!

I call a post " Lunatic Alert " and just look who turns up less than 20 minutes later.

Must be like the Pied Piper and the rats.

... Phil

"Tim Williams"

** Irrelevant to the subject.

The lunatic OP has supplied no case.

.... Phil

I stand corrected. I thought there was a big difference, base on personal observations rather than measurement. I was using reverse osmosis water with fairly high resistivity, but I don't know if that made a difference. My apologies to you and your microwave. JB