Oxidation behaviour of Li–Na–Pb–P–O–N oxynitride phosphate glasses

The oxidation behaviour of different oxynitride phosphate glasses, elaborated by thermal ammonolysis of oxide base glasses with composition (25 − x/2)Li2O·(25 − x/2)Na2O·xPbO·50P2O5 (0 < x < 50), has been studied in air by thermogravimetric analysis and differential scanning calorimetry. The oxidation of the nitrided powders proceeds first from a surface oxidation, followed by a bulk oxidation controlled by diffusion. As the nitrogen content increases, the sintering becomes slower and the surface oxidation is greater. The second step, which depends on the particular composition, takes place once the glass viscosity has decreased enough to allow oxygen diffusion inside the glass particles.