Subject: Re: Microwave absorbers - I need some
From: dwilkins@orion.polaristel.net (Don Wilkins)
Date: Sep 06 1996
Newsgroups: sci.chem

On Thu, 05 Sep 1996 16:24:00 GMT, rsndww@rohmhaas.com (Dave Whitman)
wrote:

>usmlkpbn@ibmmail.com (Drew Child) wrote:
>
>>I am looking for information on substances that convert microwaves to heat,
>>are transparent to visible light, and boil above 450F.  Absorption
>>doesn't have to be very high and doesn't have to be a specific mechanism
>>(e.g., electronic excitations).  For example, water would do, except that
>>it boils too quickly.
>
>>Can anyone tell me of some possible materials or provide a lead as to
>>where to look?

You didn't mention the wavelength of the microwaves which certainly
will make a difference in the answer.

If you are referring to a microwave ovens designed for cooking then
silicon carbide is an excellent absorber. With proper insulating
bricks and a silicon carbide suscepter you can easily melt glass in an
ordinary kitchen microwave oven.

The frequency in these devices was selected to utilize the absorption
by water molecules but other substances absorb to varying degrees.
Water absorption was selected because of the presence of water in most
foods.

Much of this work was done in the 1950s and early 60s. One
investigator was Jim (probably James) Beggs. I still recall being
served hotdogs cooked on a paper plate in the hallway of the General
Electric Research Laboratory by Jim who was completely out of
character with a tall chef's hat. What is second nature today was
almost unbelievable at the time.

In general any molecule with a permanent dipole or magnetic moment
will absorb microwaves, the amount of heat generated will depend on
the match between the radiation wavelength and the absorption bands
among other things.

I too have seen lists of materials and their susceptibility but the
memory dims and the references are not at hand. With the time period
and the name of at least one prominent investigator you should be able
to dig up the information. There was also a lot of work on microwave
spectroscopy at about the same time.