RogueRose - 8-4-2017 at 19:23
I needed to melt some paraffin to coat some wicks and seal a cardboard tube so I used 1/2 a candle made from a small dixie cup (mouth rinsing after
brushing teeth size). The candle had a .5x.5" piece of Al can wall material to hold the wick to the bottom and a cotton wick - this was inside a
larger dixie cup to catch the paraffin that was to melt.
Microwave is 1200w and I put it in for 45 seconds on high. it was maybe 90 degrees at most after this. 45 seconds later no difference. Another
cycle, same thing but the paper cup it was in was getting hot on the bottom. I made sure the settings were correct on the microwave and did it for 1
min. No change. I did about 40-50ml of water for 45 seconds and it was steaming. I did 80 seconds for the paraffin finally and no change at all. so
3, 45 second intervals, one 1 minute and one 80 second and it was at most 90 deg F. This was all done with maybe 2-4 seconds between cycles after 3rd
cycle I tested with water, then right back to paraffin. I quicly moved it to a metal cup and used a blow torch and it melted but it didn't seem like
it had absorbed any heat prior as it was a normal melt rate. Inside the unit the glass wasn't hot, the sides were normal, so it was really odd.
I tried heating water later and it sure heats it up fast on the same setting so I know it isn't the microwave.
I know water is supposed to get excited and heat food, but I've seen microwave kilns for working with glass, so it doesn't seem that water is needed..
Anyone know what's going on?
I looked online and there are how-to's making candles with a microwave and it says use 15-20 second cycles (didn't look at this first)
I read somehwere about borated paraffin used in stopping electrons or neutrons or something?? IDK if it is the paraffin that does some of this and
the boron helps a lot or what, but IDK what the heck is going on here.
Twospoons - 8-4-2017 at 20:40
Some compounds absorb microwaves (2.45GHz) well, and some are virtually transparent. Polypropylene is used in a lot of microwave safe containers,
simply because it is transparent to microwaves, and therefore doesn't heat up. I would guess the same is true of paraffin wax. Adding a susceptor ,
such as iron oxide, will absorb the microwaves and melt the wax. There are ceramic bowls with iron oxide added just for this purpose in microwave
ovens.
violet sin - 9-4-2017 at 00:39
just microwave water to melt paraffin, like a second tupperware double boiler kind of thing. the water will heat just fine without buying anything
special.
RogueRose - 9-4-2017 at 08:24
Thanks for the replies. I'll try some other materials and that is probably why the microwave setups come with what looks like a ceramic crucible of
some kind for it. But that doesn't negate the fact that the paraffin seems extremely resistant to that wavelength and I wonder if it has applications
that could be useful.
[Edited on 9-4-2017 by RogueRose]
[Edited on 9-4-2017 by RogueRose]
PirateDocBrown - 9-4-2017 at 08:26
Microwaves heat by interacting with the dipole moment of water's rotational libration modes. However, at normal temps, the normal levels are several
thousand times the energies provided by the radiation (i.e. water emits and reabsorbs at the blackbody radiation level at ambient temps), so no
ordered absorption is observed. Instead, the energy is simply randomized into heat.
The problem with long carbon chains in microwave radiation is that their dipole moments and rotation energies are wildly different from water, and so
do not interact.
[Edited on 4/9/17 by PirateDocBrown]
Dr.Bob - 18-4-2017 at 17:52
Hydrocarbons have almost no dipole moment or polarizable groups, so they don't absorb microwaves well, either in a kitchen or chemical lab microwave.
In a home microwave ovens this can lead to feedback which can destroy the tube. This is well known and used to control heating of some items in
industrial microwaves, such as those used to heat the glues in plywood and other polymers. In the lab, a drop or two of DMF, DMSO, or an alcohol will
improve the absorption of microwaves.