Glass Stability of Alkali and Alkaline Earth-Silicate and -Germanate Glasses

Reference Presenter Authors
10-033 Jeanini Jiusti Jiusti, J.(Federal University of Sao Carlos (UFSCar)); Mattos, M.N.(Federal University of Sao Carlos (UFSCar)); Andreeta, M.R.(Federal University of Sao Carlos (UFSCar)); Zanotto, E.D.(Federal University of Sao Carlos (UFSCar)); Glass-stability (GS) is a measure of how slow is the crystallization of a glass upon heating and it is inversely proportional to the critical cooling rate (Rc) for glass formation. GS is an easily measurable and yet significant parameter for exploring the glass forming ability in the development of new glass compositions having unique or improved properties. Although many efforts have been made to understand this matter, the role of network modifier elements in oxide systems is not entirely elucidated. In this study, we explore the GS of binary silicate and germanate glasses containing alkaline or alkaline earth metals. We used the Hruby parameter, KH=Tx-TgTl-Tx - where Tg, Tx, and Tl are the glass transition, crystallization onset, and liquidus temperature - to compare the influence of these modifiers in both systems. We collected literature data and performed DSC analysis of glasses produced in our laboratory. It was not possible to determine the GS of Rb2O and Cs2O containing glasses due to the absence of a DSC crystallization peak. Nonetheless, we found that the GS increases with the atomic radius (Cs>Rb>K>Na>Li) and continuously decrease with increasing R2O content. We observed the same tendency for the alkali-germanate glasses; however, a minimum GS occurs at approximately 20% of R2O. Regarding the alkali earth (RO), our analysis did not show a significant difference between Mg/Ca/Sr/Ba silicate and germanate glasses. Due to their high GS, we could not determine the KH of the pure glass-forming oxides, but we observed an overall higher GS for the silicate glasses, with KH reaching 2.0, while the germanates show KH < 0.4. In general, there is a good correlation of our findings with what we observed at glass melting/quenching practice in the laboratory. We are studying other systems (phosphates, aluminates, tellurites, and borates) to determine whether the modifiers have an overall role in the glass stability of all oxide glass forming systems.
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