Properties of Ca -(Y)- Si - Al - O - N - F glasses: Independent and additive effects of fluorine and nitrogen

Thirty glasses of composition (in equivalent percent) 20-xCa:xY:50Si:30Al: (100-y-z)O:yN:zF, with x = 0, 10; y = 0, 10, 20, and z = 0, 1, 3, 5, 7 were prepared by melting and casting. All glasses were X-ray amorphous. Glass molar volumes (MV) decreased with nitrogen substitution for oxygen for all fluorine contents and, correspondingly, glass fractional compactness increased. Fluorine substitution of oxygen had virtually no effect on molar volume or fractional glass compactness for the three nitrogen contents tested. Young's modulus and microhardness were virtually unaffected by fluorine substitution for oxygen while nitrogen substitution for oxygen caused increases in these two properties. Glass-transition temperature and dilatometric-softening point values all decreased with increasing fluorine substitution levels, while increasing nitrogen substitution caused values for these thermal properties to increase. Correspondingly, the thermal expansion coefficient increased with fluorine and decreased with nitrogen substitution levels. Using property value differences between glasses containing fluorine and the corresponding glass containing 0 eq.% F enabled 24 data points to be used to determine the effect of fluorine on T_g,dil and T_DS. The trends were linear with a gradient for both properties of the order of -22°C (eq.% F)^-1. For the nitrogen effect, 20 data points were analyzed for trend effects. As expected from earlier work, all trends had good linearity. Gradients were for T _g,dil and T_DS +2.5°C (eq.% N)^-1, which are fairly similar to previous results in oxynitride systems. All of the data collected and its analysis clearly shows that the substitution effects of fluorine for oxygen and nitrogen for oxygen are independent and additive with the fluorine substitution. The property trends of the glasses are discussed in terms of their implications for glass structure.