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

Nitrided phosphate glasses were prepared from phosphate melts, with molar c ompositions 15R(2)O-15K(2)O-15R'O-5Al(2)O(3)-50P(2)O(5) and 12R(2)O-12K(2)O -20R'O-6Al(2)O(3)-50P(2)O(5) (R = Li Or Na; R' = Mg, Ba or Zn), exposed to flowing ammonia for up to several days. The effects of nitrogen incorporati on on glass properties were determined by measuring glass transition temper atures, thermal expansion coefficients and dissolution rates in water as a function of the nitrogen content. Nitrogen incorporation increases the glas s transition temperature, decreases the thermal expansion coefficient and d ecreases the dissolution rate in water. Due to the properties of the oxynit ride glass medium, Ag2O added to a nitrided glass is reduced at approximate to T-g to form metallic Ag particles, about 1 mu m in diameter. Changes in the properties of phosphorus oxynitride glasses result from the strengthen ing of the glass network by P-N bonds substituting for P-O bonds. (C) 2000 Elsevier Science B.V. All rights reserved.