Physical properties of sodium borogermanate glasses compared with the sodium borosilicate system

The glass forming range of the sodium borogermanates was examined as a func tion of R (molar ratio of soda to bora) for fixed K families (where K is th e molar ratio of germania to bora). Glass formation has been extended to 70 mol% soda well beyond that previously reported. Density and the glass tran sition temperature (T-g) were measured on a large number of samples spannin g the newly observed glass forming limits. The resulting property trends ar e discussed in terms of models for the atomic arrangement. Key comparisons are made between this system and the corresponding technologically importan t sodium borosilicates. It was found that the molar volume trends are remar kably similar in the two systems whereas T-g shows two distinct regions of interest. Below about 30 mol% soda, T-g varies considerably for the two fam ilies' whereas above this soda content the values are essentially identical and independent of K These data are discussed in terms of models developed for the sodium borosilicate system based on the work of Dell & Bray and Ma cKenzie et al.