Interesting question.

Pouring the glass directly on liquid Nitrogen, seems that you will not have control of the cooling rate since:

-Heat exchange at the glass surface mut be poor

-You dont control glass thicknesswhich also determines the cooling rate

I find it better quenching the glass melt on a metal plate cooled with liquid nitrogen, and thinner films for higher cooling rates.

Thank you so much Dr Miguel Prado for your answer! Can you please recommend some literature where the suggested method has been discussed or applied..

Mohammed,

quenching your glass in liquid nitrogen will lead to the formation of a gas "cloud" of nitrogen gas around the glass that will make the quenching less efficient. Quenching in a waterbath filled with ice cubes might be another solution to achieve better quenching efficiencies.

Thank you Mathieu Hubert for your answer! By the way, I use a freezing mixture of ice, ethanol and NaCl (kept at approximately -11°C) to quench TeO2 pure glass.

Mohammed, try:

http://en.wikipedia.org/wiki/Melt_spinning

Thank you again Dr Miguel Prado!

The concept of melt spinning is highly interesting especially in the case of conditional glass formers such as pure TeO2 glass, but unfortunately the equipement in question is not available in my laboratory!

On the other hand, I look forward to try quenching upon a N2-cooled metallic plate as you have suggested in your first reply!

@ Zaki,

As u mentioned u tried quenching on an ice mixture, does ur sample formed a glass in this condition?? I too tried such quenching with 90% pure tellurite glass composition but i didnt get glass rather i got an opaque sample. Also, i have used just an Ice slab for quenching rather than a mixture of ice, ethanol and NaCl.

Dear Naziya,

Yes, as I mentioned, I obtained glass by dipping the bottom of the crucible into the mixture. Does 90% represent the purity of your TeO2 powder?

@ Zaki

90% represents the amount of TeO2 powder in the batch in mol%. In my case i poured the melt directly on the ice slab rather than dipping crucible in the ice cold water.

Normally, the addition of a second component to TeO2 is expected to provide a favorable condition for tellurite vitrification... Though, I guess that devitrification could take place in the case of quenching voluminous melts.

@ Zaki

Thank you