Jocelyn McAuley on sun 29 apr 01
I guess I'll throw in my experience while we're on this subject :)
(and ways to avoid it at the bottom of my message- ceramic spoons!)
I was microwaving a gelatin solution in an erlynmeyer flask in the lab
where I work. I removed it from the microwave and dropped in a magnetic
stirring rod, and BOOM! Hot gelatin was flying everywhere. Fortunately
(for embarrasement's sake, not safety's!) no one else was in the
lab. Cleaning up puddles of cooled gelatin from the lab bench, floor and
myself was fun.
So, how do we avoid such impending doom?
http://rabi.phys.virginia.edu/HTW/ has the How Things Work Website, a
collection of such questions answered by a Physics Professor.
Here's his take on superheated liquids from microwaves:
If you're looking for a way out of this hazard, here are my
suggestions. First, learn to know how long a given amount of liquid must
be heated in your microwave in order to reach boiling and don't cook it
that long. If you really need to boil water, be very careful with it afte=
r
microwaving or boil it on a stovetop instead. My microwave oven has a
"beverage" setting that senses how hot the water is getting. If the water
isn't hot enough when that setting finishes, I add another 30 seconds and
then test again. I never cook the water longer than I need to. Cooking
water too long on a stovetop means that some of it boils away, but doing
the same in a microwave oven may mean that it becomes dangerously
superheated. Your children can still "cook" soup in the microwave if they
use the right amount of time. Children don't like boiling hot soup anyway=
,
so if you figure out how long it takes to heat their soup to eating
temperature and have them cook their soup only that long, they'll never
encounter superheating. As for dad's coffee water, same advice. If dad
wants his coffee boiling hot, then he should probably make it
himself. Boiling water is a hazard for children even without superheating=
=2E
Second, handle liquids that have been heated in a microwave oven with
respect. Don't remove a liquid the instant the oven stops and then hover
over it with your face exposed. If the water was bubbling spasmodically o=
r
not at all despite heavy heating, it may be superheated and deserves
particular respect. But even if you see no indications of superheating, i=
t
takes no real effort to be careful. If you cooked the water long enough
for it to reach boiling temperature, let it rest for a minute per cup
before removing it from the microwave. Never put your face or body over
the container and keep the container at a safe distance when you add
things to it for the first time: powdered coffee, sugar, a teabag, or a
spoon.
Finally, it would be great if some entrepreneurs came up with ways to
avoid superheating altogether. The makers of glass containers don't seem
to recognize the dangers of superheating in microwave ovens, despite the
mounting evidence for the problem. Absent any efforts on their parts to
make the containers intrinsically safer, it would be nice to have some
items to help the water boil: reusable or disposable inserts that you
could leave in the water as it cooked or an edible powder that you could
add to the water before cooking. Chemists have used boiling chips to
prevent superheating for decades and making sanitary, nontoxic boiling
sticks for microwaves shouldn't be difficult. Similarly, it should be eas=
y
to find edible particles that would help the water boil. Activated carbon
is one possibility.
_______________
He goes into more depth on the subject than I've revealed here. Included
are videos of microwave superheating experiments.
Since metal spoons in microwaves don't work, we as ceramicists could make
and provide ceramic stir spoons (or something similar) that one leaves in
their coffee cup as they microwave their beverage. As mentioned in the
above excerpt, this would be similar to "boiling chips", and prevent this
=66rom happening.
Cheers
Jocelyn
--
Jocelyn McAuley ><<'> jocie@worlddomination.net
Eugene, Oregon
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