bz
ch100-5.chem.lsu.edu> wrote:>> bz
ch100-5.chem.lsu.edu> wrote:> ....
>>>> Lots of cheap cups with handles have an embedded wire in the handle
>>>> which makes manufacture easier.
>>
>>> No wire in the handle on this cup.
>>
>>> I have never seen a ceramic cup with wire in the handle.
>>
>> Break it open and look.
Yeah, but it isn't that one, is it?
Somewhere in Purdue there must be an X-ray machine...
> nb: since the cup is Corning Corelle, it is actually technically a glass.
> However, glasses are ceramics.
Technically yeah.
BTW, "Corelle" is a trade mark, not a defined material.
Most Corelle products are three layers of two different glasses which
makes them thin, tough, and fairly resistant to thermal shock.
Some Corelle products have decorative gold (at least it looks like
gold) trim and those can't be used in microwave ovens.
> [quote from
>
http://chemed.chem.purdue.edu/genchem/topicreview/bp/materials/ceramic4.htm
> l]
> "The term ceramic comes from the Greek word for pottery. It is used to
> describe a broad range of materials that include glass, enamel, concrete,
> cement, pottery, brick, porcelain, and chinaware. This class of materials
> is so broad that it is often easier to define ceramics as all solid
> materials except metals and their alloys that are made by the high-
> temperature processing of inorganic raw materials."
> [unquote]
>>>> Did it occur to you to wonder why only the handle got so hot
>>
>>> Did I ever say that ONLY the handle got hot? The cup got hot too but
>>> the heat went into heating the water in the cup. That kept the
>>> temperature down.
>>
>> So the cup was filled to the brim and only the handle got "red hot"?
> I said [quote] Some ceramics get very hot in a microwave oven. I once
> picked up a cup of tea from the oven, only to find that the handle was just
> short of red hot.
> [unquote]
> I did NOT say the handle got "red hot". Please be accurate when you quote
> me. I make enough mistakes on my own without someone helping by misquoting.
> The cup need not be filled to the brim. It takes a lot of calories to heat
> water. It only takes a few calories to heat ceramic IF the ceramic has a
> low heat capacity.
> Understanding the distinction between temperature and heat is critical to
> understanding how the handle can get much hotter than the body of the cup.
> The handle can only lose heat(calories) through conduction [to the body of
> the cup and to my finger], radiation, and convection through air
> circulation. The body of the cup loses heat to the water in the cup.
> If the ceramic receives uniform heat due to the microwaves, the handle
> will get much hotter (higher temperature) than the body of the cup.
By that logic the body of the cup above the water line should be quite
hot.
Was it?
Have you never seen the old "I bet I can boil water in a paper cup"
camping trick be done?
You put a paper cup of water in the camp fire. The water boils below
the water line and the paper cup above the water line burns.
>>> Ceramics are dielectrics.
>>> Many ceramics were developed before 'the age of microwaves'.
>>
>> No kidding?
>>
>>> Some of those ceramics have high dielectric losses at microwave
>>> frequencies. This cup had high dielectric losses.
>>
>> Doubtfull.
> More likely than the wire in the handle that you suggested.
Yes, most glasses get conductive when the temperature is high enough,
but those temperatures are far beyond what one reaches in sucessfull
cooking.
So what?
>> Most common ceramics have quite low dielectric loss.
> Many do. Some don't. Corning's Corelle apparently doesn't. If you have a
> reference showing that 'Most common ceramics have quite low dielectric
> loss', I would like to see it.
> But regardless of whether or not 'most' have low losses, the material in my
> Corelle cup has high losses and gets hot quickly in a microwave.
Sigh.
We are talking about losses low enough for a piece of kitchenware
not to get significantly hot in a microwave oven, not building
precision microwave devices.
Either get the cup in question X-rayed or do the experiment.
Put the empty cup in the microwave with another container of water
and nuke for a while.
Does the entire empty cup get hot or just the handle?
>>>> Pure ceramics don't get hot in microwave ovens.
>>> You are clearly outside your field of expertise.
> First, what is a 'pure ceramic'? As most ceramics consist of a mixture of
> compounds, I can only guess that by a pure ceramic that you meant one that
> did not contain a wire. In which case, you are clearly wrong when you say
> "pure ceramics don't get hot in microwave ovens."
Nothing other than ceramic and glaze in the construction and no conductive
trim or glaze.
> The only ceramics that I have familiarity with are the barium titanate
> formulations that we used in our capacitors when I worked for Sprague.
> Which ceramics are you familiar with and what bearing does your familiarity
> have on the hot handle I encountered on my cup?
The ceramics commonly used to make things like cups, bowls, etc.
I've had several cheap promotional coffee mugs with wire in the
handle as well as an Asian tea pot.
>>> Why do you think that modern plates and cups say 'microwave safe' on
>>> the bottom?
>>
>> Mostly marketing, the same reason you find it on glass kitchenware.
> NO! It is a matter of safety.
> There are glasses and ceramics that can be used in the oven.
> There are glasses and ceramics than can be used on the stove.
> There are glasses and ceramics that can be used in the microwave.
> Some can be used in all of those places. Some can't.
> I know from painful experience that one should pay attention to whether or
> not a cup is 'microwave safe'.
The use of kitchenware depends on the material, to state the obvious.
Generally, only materials with low thermal expansion, i.e. not likely
to shatter from thermal shock, can be used on a stove or in an oven.
If you can use it on a stove or in an oven and it has no metal
"parts", such as decorative metallic trim, it is usually safe to use
in a microwave oven.
--
Jim Pennino
Remove .spam.sux to reply.
