OXYNITRIDE SURFACE-LAYERS ON SODIUM AND LITHIUM METAPHOSPHATE GLASSES

Oxynitride layers can be created on the surface of NaPO3 and LiPO3 glasses by heat treating these glasses in dry ammonia near the glass transformation temperature. The chemical durability of these glasses increased several times with the formation of oxynitride surface layers, but the improvement was less than that for bulk nitrided glasses because of the small thickness of the oxynitride surface layer and the presence of the non-cross-linking NH and NH2 species. When a glass is heated in flowing ammonia, an oxynitride surface layer forms by the dissolution and diffusion of NH3. The maximum nitrogen content depends on the solubility of ammonia in the glass and the nitriding temperature. The bridging oxygen/non-bridging oxygen ratio in the oxynitride surface layer, as determined from the deconvoluted O1s and N1s spectra, is consistent with the mechanism proposed for the nitridation of bulk alkali metaphosphate glasses. © 1990.