Why a mug handle gets very hot when microwaved

  • #1
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Summary:

Two different ceramic coffee mugs heat up drastically different, why?

Main Question or Discussion Point

I have two coffee mugs (I have many more, just not in this example :biggrin: ). I often microwave cold coffee from earlier in the day. Mug "A" when microwaved for a minute produces hot coffee and a warm outer mug. Mug "B" produces hot coffee and a lava hot outer mug that will give you third degree burns on your hand :eek:. They look fairly similar. I am pretty sure they are both ceramic. The only obvious difference is that mug "B" is much lighter in weight.
 

Answers and Replies

  • #2
sophiecentaur
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Conductive (medium resistance - not a short circuit) glaze in the one that gets hotter? They sell ‘browning’ plates for microwaving bacon etc. with resistive stripes in the bottom. “Lava hot”!
 
  • #3
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My guess would be that more water molecules are encapsulated in mug B.
 
  • #4
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My guess would be that more water molecules are encapsulated in mug B.
I agree. Especially in older mugs, imperfections in the glazing allow the ceramics inside to get saturated with water. "Microwave safe" mugs and bowls have closed cell structures that prevent water intrusion.
 
  • #5
Bystander
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"Corelle" and some other "ceramic? How breakable is the "lava" producer? Corelle is nearly indestructible, but produces razor sharp shards.
 
  • #6
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How breakable is the "lava" producer?
It chips very easily
 
  • #7
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It chips very easily
Glazed "pottery" perhaps? So what is/are the difference/s between "ceramic ceramics" and "glaze finished ceramics?"
 
  • #8
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Glazed "pottery" perhaps? So what is/are the difference/s between "ceramic ceramics" and "glaze finished ceramics?"
I never heard of "ceramic ceramics" but I believe the answer you are looking for is what i mentioned earlier. If a material has closed cells, then it does not absorb water when immersed. Think of open cell foam compared to closed cell foam. Glazing covers an open cell material with a waterproof coating.
 
  • #9
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I never heard of "ceramic ceramics" but I believe the answer you are looking for is what i mentioned earlier. If a material has closed cells, then it does not absorb water when immersed. Think of open cell foam compared to closed cell foam. Glazing covers an open cell material with a waterproof coating.
I think the production process plays a role, too. How dry was the material before glazing? This certainly depends on temperature and duration, and maybe even on the glaze itself.
 
  • #10
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One of the hottest parts of the mug is the handle, if that helps.
 
  • #11
sophiecentaur
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How dry was the material before glazing?
I think that the first stage of firing has to chase all traces of water out or, once glazed, the pottery will burst. I reckon that , if people don't like the idea of unsuitable glaze then it has to be ingress of water later on.
One of the hottest parts of the mug is the handle, if that helps.
Possible answer: The main body of the mug is in contact with the water / coffee to keep its temperature to well less than 100C. The handle would have no such heat sink nearby to keep it 'cool'.
 
  • #12
Summary:: Two different ceramic coffee mugs heat up drastically different, why?

I have two coffee mugs (I have many more, just not in this example :biggrin: ). I often microwave cold coffee from earlier in the day. Mug "A" when microwaved for a minute produces hot coffee and a warm outer mug. Mug "B" produces hot coffee and a lava hot outer mug that will give you third degree burns on your hand :eek:. They look fairly similar. I am pretty sure they are both ceramic. The only obvious difference is that mug "B" is much lighter in weight.
Just tossing this out there but..one of those ceramic existences's resonates closer with the microwave frequencey...?
 
  • #13
Just tossing this out there but..one of those ceramic existences's resonates closer with the microwave frequencey...?
If one is..say 5 times(or 50 or 500) exactly the frequency of the microwave it may "express" itself.
 
  • #14
jim mcnamara
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Do not microwave the "hot handle" cup it is not microwave safe.

From quora:
I’ve answered questions like this previously, and the reason that the handles on coffee cups, as well as the
cups themselves, and perhaps the dishes made by the same manufacturer become hot in a microwave is because of improperly formulated glaze on the ceramic material. In my lab, as part of a class-action suit against a big-name dinnerware manufacturer whose dishes said “microwave-safe”, I found the temperature of the coffee cuphandles reaching temperatures of approximately 300°F, even when filled with coffee when microwaved. The culprits in the glazes are usually heavy metals.

Proper formulation has been known for at least 40 years, but much of this dinnerware is made in China and, for some reason, the manufacturers, most commonly small companies, simply have no knowledge of all the technology that was developed decades ago. When the proper formulations are followed, the dinnerware only gets warm, and often that’s due to heat transfer from the food that’s being heated in the microwave.
https://www.quora.com/Why-do-the-handles-of-some-coffee-mugs-get-hot-in-the-microwave-quickly-while-others-dont
 
  • #15
sophiecentaur
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ne of those ceramic existences's resonates closer with the microwave frequencey...?
RF to Heat transfer doesn't need a 'resonance' in particular. It can be a simple broadband Resistive Loss. Some structures in a ceramic item could involve resonant cavities but I'd bet the effect is independent of shape.
 
  • #16
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Do not microwave the "hot handle" cup it is not microwave safe.

"The culprits in the glazes are usually heavy metals. "
This leads me to my next question. Should I even be drinking out of this thing? Is the glaze safe toxic wise? It was a gift from a friend who traveled in Israel.
 
  • #17
OmCheeto
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This leads me to my next question. Should I even be drinking out of this thing? Is the glaze safe toxic wise? It was a gift from a friend who traveled in Israel.
It's hard to say. Maybe the glaze uses safe metals, like the ones used everyday:

In some situations, metal placed inside a microwave can become very hot, a fact food manufacturers cleverly take advantage of, notes Ross. Some microwavable soups and pies are packaged with a thin metallic layer under a non-metallic lid, so the food trapped against the metal browns nicely.
 
  • #19
Materials with NH bonds will heat up in a microwave also just as will materials with OH bonds like water or alcohol. There's a great experiment where three bowls of plastic pellets are put in a microwave. The three bowls contain polyethylene, polyester and nylon. The nylon will set on fire while the polyethylene and polyester remain cool.
Also, ice has about 1/1000 the microwave absorption of water. So melting just ice is difficult while when the ice starts to melt, the water will absorb strongly. This can produce hot spots in microwave melting of frozen materials.
 
  • #20
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Funny thing... I was vacationing a few weeks ago, and the rented-beach-pad had a bunch of ceramic coffee mugs waiting to be used. It was 4 AM the following day, and rather than make a fresh pot of coffee, I thought I'd just microwave the last bit in the pot. In it went, set the timer on 2 minutes, and voila! DING!

I reached in and grasped the mug, lifting it up. With the usual time-reaction-delay, I heard sizzling, and intense burning. I put (not dropped!) the mug back onto the glass microwave plate. And thrust my now-singed fingers under the cold tap.

Within seconds, all three fingers (one of which was a thumb) had large blisters.
Damn!

Here we are, some 3 weeks later, and there's still a 3rd degree missing-skin patch on one of the blistered healing skin sections.

MORAL OF THE STORY ... Never ever trust a microwaved ceramic anything. Test it before grabbing. You'll save yourself weeks of pain and super-sensitive new flesh.

Just Saying,
GoatGuy
 

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