Chemically durable nitrided phosphate glasses resulting from nitrogen/oxygen substitution within PO4 tetrahedra

Nitrided phosphate glasses were prepared from phosphate melts, with molar compositions 15R2O–15K2O–15R′O–5Al2O3–50P2O5 and 12R2O–12K2O–20R′O–6Al2O3–50P2O5 (R = Li or Na; R′ = Mg, Ba or Zn), exposed to flowing ammonia for up to several days. The effects of nitrogen incorporation on glass properties were determined by measuring glass transition temperatures, thermal expansion coefficients and dissolution rates in water as a function of the nitrogen content. Nitrogen incorporation increases the glass transition temperature, decreases the thermal expansion coefficient and decreases the dissolution rate in water. Due to the properties of the oxynitride glass medium, Ag2O added to a nitrided glass is reduced at ≈Tg to form metallic Ag particles, about 1 μm in diameter. Changes in the properties of phosphorus oxynitride glasses result from the strengthening of the glass network by P–N bonds substituting for P–O bonds.