🚀 go-pugleaf

WEBER@JEDI.SSD.LMSC.LOCKHEED.COM (Kevin Weber) writes:

>I once saw a rather amazing display of the effect in question.  A professor
>of mine took two 1/2 inch glass rods.  One he slammed against a table top
>which caused the rod to obviously shatter into a million pieces (yes, he
>did it in a contained area behind a shield).  The next rod he immersed into
>an acid solution (concentrated sulfuric I believe) then rinsed the rod.  He

Hydrofluoric

>slammed it agianst the table.  It did not break!  

Yes, see my earlier article re our lab demo

>Thinking back, you could conclude that the presence of moisture is not the
>sole cause of crack propogation, but also crack geometry.  The acid would

Yes, this is standard fracture mechanics.

>round the crack tips and prevent propogation.  Correct me if I'm wrong out
>there (and I'm sure you will) but this may be the one result of tempered
>glass, in addition to getting rid of crystalline defects.

I guess it's possible the heat might blunt the cracks, but the
heat treatment of glass works by another main mechanism:  it puts compressive
residual stresses into the surface, which tend to close up cracks.  To see
this, try grinding back the surface of a Duralex glass (hotel glasswear)
on SiC paper: once you expose the tensile residual stresses underneath,
you better watch out!  (WEAR SAFETY GLASSES FOR THIS ONE!)

|  jeff@minmet.uq.oz.au	      |  Jeff Gates,   Dept Mining	   |   _--_|\
|  Ph. direct: +61 7 365 3726 |        & Metallurgical Engineering |  /      B
|  Ph. Dept: +61 7 365 3738   |  University of Queensland 	   |  \_.--\_/
|  Fax: +61 7 365 3888	      |  Brisbane   Qld   4072   Australia |	    v