Complexes of Mg, Sr, Ba, adn Al have been used to dope aluminum fluoride glasses as a way to improve optical properties. (Ozuturk (1998) One draw back to these glasses is the tendency of crystal formation and phase separation due to florine evaporation and acid corrosion of the crucible upon casting.
Slow cooling is desired to achieve good optical properties and desired shapes. As the mixture cools, a competition between the glass and crystal state ensues. Slow cooling can sabotage the vitrification (glass) formation. The crystal formation should be as slow as possible. Ozuturk (1998) studied the impact of Ba(PO3)2 on relationship between the cooling rate (R) and the energy of activation (Ea) for long chain structures characteristic of glass.
A. Ozuturk (1998) studied formation of glasses in the system AlF3 M F2 -Ba(PO3)2 (M = Ca, Mg, Sr, Ba) as a function of Ba(PO3)2 content. Increasing the molar percent of Ba(PO3)2
- increased glass formation
- decreased the critical cooling rate for glass formation from 98 ± 7 (0 mol %) to 2 ± 0.5 (1.5 mol%) C /sec
- improved glass structure by linking broken chains present in the structure
- changed from short chains of AlF6 groups to long chains of PO3F and Ba(Ca, Mg, Sr)P2O7 groups
- lowered the Ea for formation of the long chain structures.
- A Structure of AlF6 as a single molecule and as a crystal. B. Resonance structures of P2O7 C. Lewis dot structure of P2O7 .
Infrared transmission analyses of selected borophosphate glasses revealed the basic structural groups remained intact during the crystallization process.
The influence of Ba(PO3)2 on the formation characteristics of fluorophosphate glasses
A. Ozturk
Journal of Materials Science 33 (1998) 73-76
