Re: Borosilicate glass -- easy fracture?

Gordon Couger wrote: 
Uncle Al wrote:

Sporkman wrote:

I was under the impression -- perhaps false -- that "Pyrex" and other
borosilicate glasses didn't fracture as easily as natural untempered
glasses, but a light impact resulting in a very sharp concoidal sliver
from the inside rim of one "ovenware" top that we have made me think
again.  Isn't most "ovenware" tempered?  I know tempering is an entirely
separate consideration from composition, but are untempered
borosilicates any more or less apt to fracture or shatter than regular
glass?




Pyrex doesn't temper given its small coefficient of thermal
expansion.  If it were tempered and you had cracked it, it would have
exploded into rounded shards.  Try dropping Corelleware onto concrete
(wear goggles).

If you ding Pyrex it chips.  It is definitely stronger, harder, and
more survivable than soda lime glass.


What is Corelleware anyway? It is the most unbreakable ceramic dinner ware ever saw.

Gordon 


I snipped this off of a site on residual stress.....

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A final example of residual stress is the secret to the strength of Corning’s Corell Ware ceramic used to make dishes. This ceramic is actually a combination of a crystalline ceramic center coated on
both sides with a glass ceramic. This layered composite is processed at very high temperatures and then allowed to cool slowly. It turns out that the coefficient of thermal expansion of the crystalline ceramic is greater than that for the glassy outer material, which means that as the composite cools the center shrinks more than the outer part, causing the inner part to be loaded in tension and the outer part to be loaded in compression. This pre-stressing of the outer material strengthens the material since in order to produce sufficient tensile loads in the outer surface to cause cracks to form and grow one has to first apply a sufficient load to get back to a stress of zero.


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