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I'm working with microcrystalline wax that I would like to be able to microwave to heat up. I've found that wax doesn't seem to microwave, with the most common answer I've come across for why being that it doesn't contain any water.

Adding water doesn't seem like a valid solution in this instance, since even if I could add it to a wax mixture, it would eventually dry out anyway. Therefore, I'm looking for an additive that, once mixed in with the melted wax, will allow me to microwave it after that point. The mix ratio isn't all that important as long as it's kept below 30 percent or so, although this would depend on the additive.

In searching for a potential solution, I came across a concept called the "dielectric constant". Unless I'm misunderstanding, the higher this number the greater the capacity for heating in a microwave. Looking up numbers, this seems to make sense as the DK of paraffin (the closest material I could find to microcrystalline) is around 2, whereas water is around 80.

A potential material I found was titanium dioxide. I'm getting different numbers, but it seems to have a DK somewhere in the 100-300 range. Before going out and buying some, is it feasible that I could use this as a filler for my wax that would allow it to be microwaved?

If not, or if I'm on a completely wrong track with the dielectric constant concept, are there are other suggestions on how I could solve this problem?

Matt
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  • Why cannot add water just before warming? Cheap, easy, easy to remove unlike TiO2 – Greg Oct 30 '16 at 12:38
  • Well I am looking for a filler for my wax regardless, so if TiO2 meets both my needs (filler and microwavable) then it's no issue to add at all. I'm not even sure how I could add water. I could always use a water-bath / bain-marie, but that detracts from my need for convenience, which is the purpose of making this microwavable in the first place. – Matt Oct 30 '16 at 13:06
  • I would try graphite powder. It is conductive so it should absorb microwaves. – electron positron Jul 27 '23 at 17:15
  • I think you are onto something with the idea of thinking about the dielectric constant, though not quite the right thing. Polar molecules and salts can greatly increase microwave absorption (salty foods often microwave unevenly as the surface absorbs so much of the energy)... – matt_black Jul 27 '23 at 19:55
  • Whether you need to include the salt or material in the wax is unclear. It might be possible to create a vessel that will warm enough to melt wax if made of the right materials. Something simpler than the carbon-lined alumina kilns used to get 1,000 °C from microwave heating might work. – matt_black Jul 27 '23 at 19:59

2 Answers2

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Microwave heating works best on polar molecules, such as water and alcohols, as it then causes the molecules to rotate or "jiggle" violently. Waxes are nonpolar, so heat poorly, but if your application can use fatty acids in the mixture, such as palmitic or stearic acid, you might try mixing some into the microcrystalline wax. The dielectric constant is not significant in your application.

However, the longer the fatty acid molecule, the less effective it is in absorbing microwave radiation and converting it to heat, and on the other hand, the shorter molecules have strong odors and do not mix well with wax... do not use butyric acid for that reason. The suggestion of using an absorbent container, by @Li Zhi, seems to be more effective.

DrMoishe Pippik
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  • I actually have some stearic acid I could use, but I may need to use this wax with a latex mould, and from what I've read latex and stearic don't work well together. Alternatively, I also have access to lanolin which is a long-chain fatty acid, but I can't find any information about whether it could be used with latex safely or not. I'm assuming not since it's also considered an acid. Thanks for the help though, I may end up just going with lanolin or stearin and just try to avoid latex moulds. – Matt Oct 30 '16 at 22:41
  • Would triglycerides not work then @DrMoishe Pippik? Coconut has fairly short chains. Also what about glycerin, or some kind of ester or vitamin E. – Joseph Hirsch Dec 29 '16 at 23:51
  • Powdered sand? I am sure silicon dioxide heats up without water – Joseph Hirsch Dec 30 '16 at 00:42
  • No, SiO2 is the main ingredient in glass, which does not heat much in a microwave. – DrMoishe Pippik Dec 30 '16 at 19:33
  • Are you sure. I remember reading about a fire started in a microwave from sand heated in a paper towel. Also, I have ceramic dishes that get hot with nothing in them. It could be due to metallic content though, iron in the sand and cobalt maybe in the ceramic. – Joseph Hirsch Jan 07 '17 at 03:34
  • I just tried and I got Silicate sand to heat up pretty well. Also found this: http://physics.stackexchange.com/questions/136219/will-a-microwave-heat-sand @DrMoishePippik – Joseph Hirsch Jan 07 '17 at 03:38
  • So my bone china bowls get hot but my ceramic ones don't. – Joseph Hirsch Jan 07 '17 at 04:01
  • It's a matter of what absorbs energy best: if you have a glass bowl or mug of water and equivalent container filled with sand in the microwave at the same time, the water will absorb most and the glass and sand stay cool. If there's nothing else but sand, or even Teflon, that will absorb the radiation. See http://www.rfcafe.com/references/electrical/dielectric-constants-strengths.htm for absorption coefficients. N.B. high-lead glass and glass with metallic ornamentation behave differently. – DrMoishe Pippik Jan 08 '17 at 01:08
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You are, imho, on the completely wrong track. Microwave ovens are "tuned" to be particularly effective in heating (transferring energy to) water. For the simple reason that our foods almost universally contain it (but try to heat dried beans in a microwave, or even cooking oil). Wax is, of course, similar to cooking oil and won't be efficiently heated in that way.It is possible that you can find some additives which heat the MC wax efficiently without substantially changing its properties. I've no idea why you'd want to go this route, primarily because efficiency will be proportional to additive content, and at high enough concentrations to be effective, you're not going to have MC wax anymore...unless you get really really lucky (snowball's chance in Hell, I'd say). There are a multitude of microwave dishes that will themselves heat up in a microwave. Use one of them.

Li Zhi
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  • Actually I may test this out but I seem to remember silicates and sand heating up in the m w. Silicon or powdered sand? – Joseph Hirsch Dec 29 '16 at 23:55
  • Actually microwave energy is also strongly absorbed by conductive additives and salty materials. They are not as fine tuned to water as you might think. – matt_black Jul 27 '23 at 20:00