Nitridation Effect on Properties of Stannous-Lead Phosphate Glasses

Stannous-lead phosphorus oxynitride (Sn-Pb-P-O-N) glasses were prepared by remelting under an anhydrous ammonia atmosphere. Glasses that contained up to ∼4.2 wt% (9 at.%) of nitrogen were obtained. The rate of nitrogen dissolution was studied as a function of remelting time (3–66 h) and temperature (400°–600°C). The onset nitridation temperature was extrapolated to be 315°C; higher nitridation temperatures accelerated nitrogen dissolution. Nitridation of the stannous-lead oxyphosphate (Sn-Pb-P-O) glasses decreased the dissolution rate in water and the thermal expansion coefficient; however, it increased the dilatometric softening temperature, the glass-transition temperature, the microhardness, and the density. The chemical durability of the nitrided glasses increased more than four orders of magnitude with 3.0 wt% of nitrogen content. An increase in the lead oxide content in the stannous phosphate glasses also improved the chemical durability. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy suggested that nitrogen replaces the terminating hydroxyl ion and the bridging and nonbridging oxygen atoms in the PO4 tetrahedra to form the functional groups –NH<, –N<, and –N=, which leads to enhanced crosslinking of the glass network. Quantitative results regarding these bondings have been given.