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Re: Pyrex "Explosion" Conserves Energy?

On Tue, 20 Feb 2001, Polvani, Donald G. wrote:

While I'm only kidding about energy not being conserved, I really don't
understand the mechanism which caused such a violent event to occur. My
chemist daughter tells me that Pyrex glass should be capable of going from a
warm oven into a freezer. She would heat quartz (not Pyrex) tubing up to
600 deg C and then thrust it into ice water. I was only trying to go from a
warm (not hot) burner to one at room temperature.

The cold heating element might only touch the glass at very small regions
on its surface, so conductive cooling would be huge at these regions. How
is this different than dipping hot glass in cold water? The peak value of
internal force might be similar, but the gradient of force would be very
different. (Or does the geometry of a small cooled spot lead to larger
forces as well as larger gradients?)

Also, you don't need visible cracks in order to trigger complete breakup.
Tiny surface scratches and chips might be enough. Old glassware seems to
break more easily than new glasswhere when dropped, and I've always
suspected that accumulated surface damage is the cause.

Isn't there a lecture demo where a "Prince Rupert's Drop" is touched to
corundum powder to trigger its shattering?

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