Oxy-Nitride Glasses

The so-called oxynitride glasses can be obtained by melting phosphate salts in an atmosphere of ammonia, or alternatively by melting a nitride such as Mg3N2 with sodium metaphosphate. 

Increased glass transition temperatures, hardness and chemical durability are claimed for these nitrided glasses in which some of the O atoms have been replaced by N or NH. The N atoms are capable of three connections and may therefore participate in extra cross-linking (12.65b) or tighter bonding to neighbouring P atoms (12.65c). 

The chemical durability, solubility and thermal expansion of these glasses have been shown to be related to their N content. In alkali metal glasses of the metaphosphate composition, it appears that up to 50% of the O atoms may be replaceable by N (see 5.388). 

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