Glass baking tray explosion

That's tempered glass. It's under intentional stress from heat-treatment, and it shatters into small pieces that are relatively blunt. The non-laminated safety glass in car windows does the same thing.

Your dish probably is Pyrex. I don't know if all Pyrex is tempered, or not. But it is heat-treated.

The old Pyrex did not make little pieces. Big chunks go flying. I turned on the wrong burner about 50 years ago, and 2 baking dishes were stacked on top of the electric burner I turned on. Shortly, and I was around the corner luckily, there was a major explosion of glass.

Interesting read here

, is the tray recently made and of US origin. I've used European Pyrex cookware recently over a naked flame with no problems. IIRC the borosilicate is less prone to thermal shock failures because the COE is very much lower than soda lime glass.

An amusing science experiment is using a blowtorch to melt drips of molten glass from a glass rod and allow the drips to fall in a bucket of water.

The glass drips are quenched in such a way that the glass 'skin' is highly stressed, if you break one of these glass droplets it explodes.

A neat little booby trap - drop a handful in someone's toolbox.

Yes, see here

's_Drop . If you have the balls have one set off in your hand, sort of feels like beings high fived very very hard. Got to do a few for a mate sometime soon.

I do not know what was the material, the tray was likely purchased at Wal-Mart, so I suppose that it was made in China.

I will retrieve some pieces to see if it is thermal shock resistant.

i

My money's on uneven stress caused by uneven heating by the surface burner under the dish. Glass baking dishes are heated evenly by oven heat. Heating them unevenly on a surface burner will make them go BOOM, alright. DAMHIKT!

And now YKHYKT too.:)

Thinking Pyrex glass was borosilicate glass (low TC) resistant to heat induced stress, I went to Wikipedia:

"Orignally Pyrex was made from thermal shock resistant borosilicate glass. In 1998 Corning sold its consumer products division.......Pyrex kitchen glassware is now made of soda lime glass...."

Jerry Pournell was right.

Kevin Gallimore

?

Pournelle is known for revising Sturgeon's Law.

Sturgeon pointed out that "90% of science fiction is crud".

Pournelle expanded it to "90% of everything is crud".

Kevin Gallimore

When I was a kid my mother served strawberries and cream in a glass bowl. Just as the spoon lightly touched the bowl the bowl exploded with the shards travelling across *two* rooms and (apparently round the corner) onto the balcony. Interestingly no-one was injured.

Took a while to clean the strawberies off the walls...

David and Ian, that was facinating. I melted and bent a bit of glass from my chemistry kit back in the day but never dropped it into water. The fun I missed ;(

Wes

-- "Additionally as a security officer, I carry a gun to protect government officials but my life isn't worth protecting at home in their eyes." Dick Anthony Heller

Ditto that. It expanded in the center and the cracking rim led to the explosion and thrust to the other dishes.

-- The reasonable man adapts himself to the world; the unreasonable one persists in trying to adapt the world to himself. Therefore, all progress depends on the unreasonable man. -- George Bernard Shaw

I bet it took some time to clean the underwear too. Scary stuff.

So, in your case, it was basically existing stresses in the glass, right?

i

I will get some glass rods and will try just that. Seems fascinating. Probably will try it in the front yard where no one usually runs barefoot.

i

John, this is tempered glass. It's under compression on both surfaces and under tension in the middle, as a result of heat treatment. It makes the glass much tougher and resistant to cracking by bending, whether the bending is mechanical or heat-induced. It's something like prestressed concrete in the way the surface compression has to be "unloaded" by a lot of tension before an actual tensile force is applied to the surface of the material.

Here's a brief description from Wikipedia:

"Toughened or tempered glass is glass that has been processed by controlled thermal or chemical treatments to increase its strength compared with normal glass. Tempered glass is made by processes which create balanced internal stresses which give the glass strength. It will usually shatter into small fragments instead of sharp shards when broken, making it less likely to cause severe injury and deep lacerations. As a result of its safety and strength, tempered glass is used in a variety of demanding applications, including passenger vehicle windows, glass doors and tables, as a component of bulletproof glass, for diving masks, and various types of plates and cookware.

"Toughened glass is physically and thermally stronger than regular glass. The greater contraction of the inner layer during manufacturing induces compressive stresses in the surface of the glass balanced by tensile stresses in the body of the glass. For glass to be considered toughened, this compressive stress on the surface of the glass should be a minimum of

69 MPa. For it to be considered safety glass, the surface compressive stress should exceed 100 MPa. The greater the surface stress, the smaller the glass particles will be when broken."

Glass is one of the strongest structural materials in existence. Unfortunately, it's extremely vulnerable to surface scratches and imperfections. By applying compression to the outer layers, those inevitable imperfections aren't subjected to tensile stress until the actual tensile stress on the tempered glass is quite high.

From information others have posted here, the material that Pyrex was once made from, borosilicate, which is very resistant to heat stresses, has been replaced by a common type of glass, and the strength and heat resistance has been restored somewhat by tempering. But it sounds like Pyrex ain't what it used to be.

"ian field" wrote in news:qBNxm.58441$ snipped-for-privacy@newsfe27.ams:

Ah yes. Prince Rupert's Drops. Lots of fun. We used to make them in the high school chem lab. A lot of them would explode in the water after zipping around a bit, but the ones that didn't were fished out & cherished. They had long thin tails, and they were amazingly tough. If you snap off the tail or crush it with pliers, kablooey!

A friend of mine had a small box with a bunch stored in it. He forgot about them & found the box several years later. Most of them had exploded spontaneously at soem point in the past.

A larger scale version is the Bologna Bottle. These are tough enough to drive nails on the outside, but are easily scratched on the inside. When you do, (you guessed it) kablooey!

Doug White

Well, that's my something new for today. :)

I've got several glass baking dishes round the place. One for sure is Pyrex, but it's old as the hills, so I think it is borosilicate. I've shattered tempered auto glass and CRT fronts by heating one area and allowing it to cool naturally. After a while cooling, BANG!

So I figured that would apply to the baking dish in question.

It ain't what you know that gets you in trouble: Its what you know that just ain't so - Twain(?)

Does anyone remember the GE group that went around the country in the

1950's and put on science assemblies in High schools?

One of the demos was exactly the thing Doug wrote about. Pounded several quite large spikes into a 2X4 and then gently dropped a small chunk of carborundum into the flask and exactly, KABLOOEY!.

They also did a demo of a pulse jet engine. Shook the whole school. I loved those assemblies!

Paul