Glasses Technology

Potassium borosilicate glasses were prepared in families having the general formula of RK//2O·B//2O//3·NSiO//2, where R is the ratio of potassium oxide to boron oxide and N is the ratio of silicon dioxide to boron oxide. The glasses wereprepared for values of R ranging from 0 to 7.0 in the families N=0.5, 1.0, 2.0,and 4.0. ^29Si MAS-NMR measurements were performed on these glasses to determine the shortrange order around the silicon atom. a model of proportional sharing of the added potassium oxide between the silicate and the borate groups was suggested. This model was tested against other suggested models where proportional sharing begins after a minimum amount of potassium oxide, R//0, and was observed to provide a better fit to the ^29Si chemical shifts obtained. As was observed in the ^29Si MAS-NMR studies of the RLi//2O·B//2O//3·NSiO//2 glasses, the proportional sharing model with R//0=0 is in stark disagrement with that proposed by the ^11B NMR studies of the alkali borosilicate glasses. This problem is as yet no understood. Since K//2CO//3 was used as the starting material for K//2O, its was observed that at large R values, R?R//CO//2, where R//CO//2=2.3 for N=1, R//CO//2=4.0 for N=2, and R//C2=5.0 for N=4, CO//2 was retained in the melt in thefashion similar to that observed for other high-alkali borate and silicate glasses. The N=0.5 family did not exhibit retention at the compositions studied. ^29SI MAS-NMR could be used to determine where CO//2 retention began in composition

Martin, Steve W.?Ajay Bhatnagar.?