NITRIDATION OF GLASSES IN THE SYSTEM R(2)O-MO-P2O5

Nitrided glasses with the composition 25R(2)O.20MO.55P(2)O(5) (R = Li, Na, K, M = Ba, Pb) were prepared by treatment in an anhydrous ammonia atmosphere between 650 and 800 degrees C for periods of 3 to 40 h. Th e nitrogen content of the glasses increases linearly with the treatmen t temperature; as a function of time, the N-2 content tends toward an upper limit, which depends on the temperature. The nitrogen introducti on into these glasses causes an increase in the transformation and sof tening temperatures, microhardness and toughness, while the expansion coefficient decreases slightly with the nitrogen content. However, the rise of the hydrolytic resistance of the glasses by near two orders o f magnitude is the most important change caused by nitrogen introducti on. The structural study by IR spectroscopic and the analysis of the g lass weight losses during the thermal treatment reveal that nitrogen r eplaces the bridging oxygens in the phosphate network.