Epoxy and the microwave; interesting

[prfesser]

Caution: do NOT do this in the kitchen microwave. I don't find epoxy odor to be particularly strong or objectionable...but then I've worked with amines (long-dead-fish smell), carboxylic acids (rancid butter + old goat pee), and other really stinky compounds over the years.

Got a gallon of old EPON 815C epoxy resin from a friend, and have a quart of Versamid 140 curative sitting on the shelf. Both are at least 15-20 years old. I've used epoxy with Versamid before, and full cure required at least 48 hours at room temperature. In a hotbox at 140F it took several hours at least.

As a test I mixed two 30 gram portions, 2:1 and 3:2 epoxy:Versamid. Put them in the microwave for just fifteen seconds. Both were then too hot to touch, and were glass-hard within half an hour.

As a chemistry geek I know that microwaves have been used for years to accelerate chemical reactions, and certain reactions are more susceptible to microwaves than others. Just didn't expect such a dramatic decrease in cure time.

If you want to experiment with microwaves and epoxy, use an old microwave and do it outside or in a separate workshop.

Best,
Terry

 

[DAllen]

Need to try this out with some JB Weld.

On a related note...Every microwave is a metal detector.

 

[StreuB1]

Need to try this out with some JB Weld.

On a related note...Every microwave is a metal detector.

JB Weld has steel powder in it. I would highly recommend against that.

If you do though, please video and post up. I want to see it in action!!

 

[David Schwantz]

Nope, no metal in JB Weld anymore, wink wink.

 

[KenECoyote]

I've microwaved old 2-part epoxy resin that had solidified to "reconstitute" it back to fluid and it worked well, but from what I recall, the same article/post that mentioned this also noted that it may weaken the epoxy. Ymmv

 

[StreuB1]

Nope, no metal in JB Weld anymore, wink wink.

Ahh yes yes!!! I always forget, that was the old formula, the new current formula contains no metal and is 105% microwave safe!! Yes indeed!!!

You should indeed go microwave half a tube's worth today and film it so we can all see that it is now microwave safe. Yes, maybe you should do it this morning so we can watch the video while having our coffee.

Get after it, we're waiting.

 

[cls]

Makes sense... 2.5GHz ovens work on the hydrogen, and epoxy resin has lots of hydrogen.

However, 30+ years of my not being careful about epoxy has led me to be super careful these days. Maybe I shouldn't heat up the allergens and breathe them!?

 

[MClark]

When I used to microwave epoxy I found if unmixed one part would heat way faster than other.
Typically used 1/2 second per gram.

 

[prfesser]

Makes sense... 2.5GHz ovens work on the hydrogen, and epoxy resin has lots of hydrogen.

However, 30+ years of my not being careful about epoxy has led me to be super careful these days. Maybe I shouldn't heat up the allergens and breathe them!?

<lecture mode on>

As it turns out, the frequency, 2.54GHz, isn't a special frequency for hydrogen or water molecules. Some molecules or groups on molecules are polarizable; they have, or can be made to have, a + end and a - end. Absorbed microwaves cause rotational vibrations in polarizable molecules. The vibrations essentially cause friction between moving molecules, which results in heat.

Some materials are more susceptible to microwaves than others. Water, sugars, and oils/fats heat quite rapidly.

Quiz on Friday.

Best,
Terry

 

[dhbarr]

<lecture mode on>

As it turns out, the frequency, 2.54GHz, isn't a special frequency for hydrogen or water molecules. Some molecules or groups on molecules are polarizable; they have, or can be made to have, a + end and a - end. Absorbed microwaves cause rotational vibrations in polarizable molecules. The vibrations essentially cause friction between moving molecules, which results in heat.

Some materials are more susceptible to microwaves than others. Water, sugars, and oils/fats heat quite rapidly.

Quiz on Friday.

Best,
Terry

Magic, got it.

No but seriously, makes me think interesting thoughts about sugar alcohols....

 

[BDB]

<lecture mode on>

As it turns out, the frequency, 2.54GHz, isn't a special frequency for hydrogen or water molecules. Some molecules or groups on molecules are polarizable; they have, or can be made to have, a + end and a - end. Absorbed microwaves cause rotational vibrations in polarizable molecules. The vibrations essentially cause friction between moving molecules, which results in heat.

Some materials are more susceptible to microwaves than others. Water, sugars, and oils/fats heat quite rapidly.

Quiz on Friday.

Best,
Terry

You beat me to it.

Several years ago I had an undergrad in my lab who was working on some microwave chemistry. I just gave him cash out of my wallet to buy about half a dozen microwaves off Craigslist, and we blew them all up. A salesman from Biotage convinced us that his research-grade microwave wouldn’t have the same issues, so he loaned us one of his demo units, in the hope that he would get a $25k sale. One week later, we returned it after blowing up so many reactions that it could no longer be repaired.

 

[cwbullet]

My wife would kill me if I did it in the kitchen microwave. Interesting idea.

I heat my epoxy in a bottle warmer. It works well at speeding the reaction a little and also will liquify hardened hardner.

 

[cls]

Water, sugars, and oils/fats heat quite rapidly.

Full of hydrogen... Like the long chain molecules in epoxy resin... As I said.

 

[dhbarr]

Full of hydrogen... Like the long chain molecules in epoxy resin... As I said.

Elemental hydrogen is covalent nonpolar. So is hydrogen disulfide. I don't have any handy, but presumably a microwave wouldn't work especially well on these.

 

[BDB]

Full of hydrogen... Like the long chain molecules in epoxy resin... As I said.

Microwave frequencies excite the energy states associated with molecular rotations. IR frequencies excite bond vibrations, like O-H and C-H bonds. X-rays are required to excite the electrons of individual atoms.

 

[Funkworks]

... Some molecules or groups on molecules are polarizable; they have, or can be made to have, a + end and a - end...

I completely agree, but just to zoom in on this part: unless they are symmetrical, molecules are all polarizable to some degree. In some cases, a molecule can be simplified as a simple arrow, a vector called "dipole moment", that can be plugged into electro-magnetic equations. This allows physicists to do all sorts of modelling. It can also be said that molecule rotation and vibration is the heat.

 

[cls]

Elemental hydrogen is covalent nonpolar. So is hydrogen disulfide. I don't have any handy, but presumably a microwave wouldn't work especially well on these.

Non polar is indeed the key; for example PVC has some H but is not polar and isn't heated by microwaves.

Anyway, spin of the polar molecules is only part of the story. High electrical permittivity materials, like metals, are heated by radiothermy.

 

[T-Rex]

Back to the OP, many years ago I put some epoxy in the microwave and turned it on. It started to boil before it hardened. At the time I was fascinated by the shape, a frothy boil frozen in time. Looking back it was not the smartest thing to do in the kitchen....

 

[jqavins]

Non polar is indeed the key; for example PVC has some H but is not polar and isn't heated by microwaves.

And the presence of hydrogen isn't necessary, as well as not sufficient. Though I'm drawing a blank on liquids or solids that are polar molecules without hydrogen, but there are plenty of gases. Liquify some NO₂, for example, and it should be warmed up in a microwave oven just fine (probably).

CORRECTION: N₂O₅ is liquid at room temperature, but I wouldn't to mess with it.

 

[cls]

though I'm drawing a blank on liquids or solids that are polar molecules without hydrogen,

Yeah, me too, no ideas. Maybe Terry has some ideas. Doesn't matter much, though, for normal folks the rule of thumb for microwave heating is the hydrogen. But even that's too hard, easier to just say water, fats, metal.

 

[dhbarr]

CORRECTION: N₂O₅ is liquid at room temperature, but I wouldn't to mess with it.

Any liquid can be microwaved at least once

 

[Grog6]

Way back in the 80's when I went to electronics school, they told us that microwaves only worked on the hydrogens bonded to the oxygen in water; some bs about vibrating the hydrogens, creating heat. But Bacon works well in a microwave, so it's not much related to water...

 

[Grog6]

I have heard you can melt Uranium in one, but never tested it.

 

[KenECoyote]

 

[jqavins]

But Bacon works well in a microwave, so it's not much related to water...

There"s plenty of water in bacon. But it"s not the water anyway. I was told, when microwave ovens in homes were new, that the frequency, 2.54 GHz according to Terry, is an absorption line for water. but that"s not it either.

 

[cls]

But Bacon works well in a microwave, so it's not much related to water...

Bacon has a lot of fat, with polar hydrogen.

 

[BDB]

All 4 of the bonds in methane, CH4, have a dipole. What is the dipole of the overall molecule? Will it absorb microwave energy?

 

[Funkworks]

All 4 of the bonds in methane, CH4, have a dipole. What is the dipole of the overall molecule? Will it absorb microwave energy?

IR frequencies can make the + and - parts move in opposite directions so methane has vibrational modes at IR frequencies:

https://www.chem.purdue.edu/jmol/vibs/ch4.html
https://webbook.nist.gov/cgi/cbook.cgi?ID=C74828&Type=IR-SPEC&Index=1#IR-SPEC
As for microwaves, you made me look for , and find , this:

“A tetrahedral(T4) molecule like CH4 was conventionally assumed (Herzberg, 1945) to have no permanent μ in its ground vibronic state, by virtue of the high symmetry in this state. Consequently, CH4 was not expected to have pure rotational transitions, i.e., transitions in which only its rotational quantum numbers change. Spectra of CH4 in the far-infrared and microwave regions were thus thought to be forbidden.
…
In 1971, it was theoretically predicted that pure rotational transitions in the vibronic ground state of Td molecules could occur as the result of a small μ arising from vibration-rotation interactions (Fox, 1971) or, alternatively, from centrifugal distortion effects (Watson, 1971; Aliev, 1971). This μ was measured (Ozier, 1971), by molecular-beam techniques, to have the magnitude (5.38+0.10) x 10"6 D for 12CH4.”

https://www.cambridge.org/core/serv...e-in-the-atmospheres-of-the-outer-planets.pdf
I'll now.

 

[jqavins]

"In 1971, it was theoretically predicted that pure rotational transitions in the vibronic ground state of Td molecules could occur as the result of a small μ arising from vibration-rotation interactions (Fox, 1971) or, alternatively, from centrifugal distortion effects (Watson, 1971; Aliev, 1971). This μ was measured (Ozier, 1971), by molecular-beam techniques, to have the magnitude (5.38+0.10) x 10^-6 D for ¹² CH₄.”

(I fixed the notation for the magnitude of the moment.) Surprising and interesting. For scale, water's value is 1.84 D, so about 342,000 times greater.

So for all practical purposes:

Will it absorb microwave energy?

No, it will not. Unless you want to impart to it 1 J for every 304 kJ imparted to the same mass of water.

 

[OverTheTop]

The Arrhenius equation applies in so many domains.
https://en.m.wikipedia.org/wiki/Arrhenius_equation