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Material to retain heat Answered

Hi everyone,

: I thought of something I could make for an Instructable. To keep the idea until I publish, I'll exclude the actual idea. I need a material for this project that will retain heat from a microwave oven for ≥20 to ≥30 minutes, Ideally Id like to keep the Temp around 180 degrees Fahrenheit.

What can I use for this? We all know metal cant go in the microwave. Ideas??




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1 year ago

Hey all,

I really appreciate the help. ok so if I take sodium silicate pentahydrate, & enclose in quarter inch of ceramic covering would that be help hold the heat & be acceptaable?

I like the SALT idea. Could I enclose that within ceramic one layer salt & outside layer ceramic??

Jari b


Reply 1 year ago

No matter what you enclose to deal with heat you need to consider expansion, possible steam and even cooling down effects.
Some things might turn liquid, get sticky, seal your porous container and so on.
There is really only one way to find out - try it out...

Had another thought and maybe you can combine one with the other.
For example using clay as a binder and your prefered choice to be heated mixed into it.
Basically creating a solid heating block of sorts.

And by the way: metals are no problem in a microwave at all.
Comes down to surface area and how the surface is created.
Around here quite a few microwave dishes come in containers made from aluminium foil and the foil won't spark or such things.
Years ago I did som "what could go wrong" experiments with an old microwave.
I was surprised that most metal things did not do anything expect getting hot.
Only if too small and with a bad surface, like crunched up aluminium foil balls or a fork it gives a lot of sparks.
Couldn't get any with decent sized stuff that had no sharp edges or corners.


1 year ago

You do know though that a microwave does not produce heat?
It heats mainly water molecules and materials that act similar at 2.4GHz.
You would need a material that is fully translucent to WiFi but has a high insulation rating.
I would start by putting insulation materials in the microwave so they cover a glass of water.
Water needs to heat up as usual but the material around must neither get hot nor reflect microwaves.
Most glass is fine, so maybe glass and glass or rock wool will do it for you...
For the filling check what Seamster already suggested.
Dry rice, corns and such heat up in the microwave and hold heat for a while.
But the temps you seek might be well above what you can do with plant material.
Some salts might work though.

Jack A Lopez
Jack A Lopez

1 year ago

Have you seen the Wikipedia page for, "Phase change material",
You know, a pot of melted stuff, at its melting point, has to give up that latent heat as it crystalizes. So, one way to search out your material, might be find one with a melting point close to your target of 180 F, which is about 82 C, for those of us who speak Celsius (or Centigrade).

Also if you could find a material with that melting point, AND have it be non-toxic, AND cheap, AND also a good absorber of microwaves.

That sodium silicate pentahydrate, it looks like a good candidate, even if its melting point is a little lower than your target, at 72.2 C (162.0 F). I am guessing it will absorb microwaves, since it has 5 water molecules in its structure. If not, it is probably miscible with water. I mean, get it a little bit wet, and it probably will absorb microwaves.

Some of those really long chain paraffins look good too, like "Paraffin (34-Carbons)", at 75.9 C (168.6 F). However, paraffin by itself is not going 'sorb microwaves by itself. I don't think. I am guessing you would have to heat it indirectly, with some material that does 'sorb microwaves.

Also liquid paraffin is flammable, so there might be some fire danger there.

You'll notice this part of the table has a whole bunch of other organic solids, but I suspect a lot of these are more toxic than you want to use. Like for example, Alpha napthol has good melting point at 96 C (205 F), but if it smells anything like naphthalene (moth balls) or phenol, then it is really just too nasty to use.

Actually regular naphthalene,


has a melting point around 80 C (176 F). But can you imagine liquid naphthalene at 80C? That stuff smells so nasty, as a solid, at room temperature. The vapors coming off that liquid would be positively awful.

I wonder if Jory Caron and his friends ever tried microwaving moth balls?