shanlo wrote at 2007-01-08 23:08:23
I have no explanation but I just had my Pyrex dish explode in the oven. I can't believe how much glass is spread all over my oven. I will not use Pyrex dishes again. Thanks for posting your question.
Tyrone wrote at 2008-02-11 01:43:23
Dear Susan and Alex,
Alex's theory as to the voids sounds reasonable for how the material would start to crack. When the chicken was placed in the center of the pan and moved from the oven, the center of the pan was higher temperature on the inside than the outside after some cooling. At this point, stresses are acting outwardly from the center of the pan due to thermal expansion. One of the mentioned voids is a perfect place for stresses to intensify and propagate a fracture. This does not account for an exploding glassware though. If the manufacturer did not anneal the glass, it is possible that residual stresses are present in the thicker portions of the pan. This is usually around the edges. When a critical fracture from before meets this area, it is possible that the direction of fracture could change to facilitate an easing of residual stresses thus causing this explosion like behavior. Remember, an explosion is a release of energy. Residual stresses can have a lot of energy.
Good luck with future glassware
Rhomphaia wrote at 2009-10-13 12:32:57
Alex made a mistake in his answer. Pyrex USED to be made of Borosilicate glass. It is now made of heat treated soda lime glass, which has three times the thermal expansion of borosilicate glass, and thus, is three times more likely to fail due to thermal shock. All American Pyrex is now made from soda lime glass (European Pyrex is still made from borosilicate glass).
That is the bad news. The good news is that soda lime glass has double the mechanical strength of borosilicate glass, and thus, is only half as likely to shatter due to physical impact.
So, three times more likely to shatter from thermal shock, but only half as likely to shatter from physical impact.
Odds are, it really was thermal shock that cause that sudden and violent shattering.
chrism wrote at 2013-06-08 09:12:05
Based on my own experience I suspect that the problem is not solely due to thermal shock. Twice in the last 30 years I've had flat Pyrex dishes explode on me at room temperature. Neither dish was was under any stress or subject to localised heating. Both split into long thin shards with hardly any pieces recognisable as the original. Both dishes were 1970s vintage so I assume that they were made to the original formulation. It almost seems as if there are internal stresses in the material that overwhelm the integrity of the dish as it ages, is heated and cooled, and picks up a few scratches.