Phosphorus oxynitride PON

Phosphorus oxynitride, PON, is a useful starting product, as a phosphorus and nitrogen source, to prepare various nitridooxophos-phates, in particular phosphorus oxynitride glass compositions (211). Moreover, it shows as a material excellent chemical stability with potential applications in several domains. In microelectronics, for example, PON has been used to form by evaporation insulating films for the passivation of III-V InP substrates and the elaboration of MIS (metal-insulator-semiconductor) structures (190, 212-215). PON could have also valuable properties in flame retardancy (176,191,216). 

To conclude, it is pleasant to consider the regular evolution from 0 to 4 of the number of bridging atoms in the following series of phosphate compounds, which is nicely completed by the phosphorus oxynitride PON (237). 

Phosphorus oxynitride (PON) is the name for a family of closely related materials that have been around for over 100 years. They are not well known but are thermally very stable and may be considered as future flame retardants and for intumescent formulations since PON is analogous to ammonium polyphosphate. It can be made from inexpensive starting materials such as ammonium phosphate, melamine phosphate or urea phosphate just by prolonged and intensive heating. 

Condensed phosphoramides with linear, cyclic, or cross-linked structures are produced by the reaction of POCI3 with ammonia. The higher molecular weight products are insoluble in water and on fnrther heating are converted to a cross-linked insoluble polymer, phosphorus oxynitride (PON)j (25). Phosphorus oxynitride can be made by prolonged heating of melamine phosphates (26), urea phosphate (26), or ammonium phosphate imder conditions where ammonia is retained (27). Phosphorus oxynitride is an effective flame retardant in those polymers, such as nylon 6, which can be flame retarded by exclusively char-forming condensed-phase means. However, phosphorus oxynitride is ineffective (at least by itself) in those... 

Following ternary phosphorus oxynitrides, which involve only phosphorus as a cationic element, quaternary and higher oxynitrides will be described. A number of other solid-state PON compounds are under study and, when considering the richness of the phosphate crystal chemistry and the additional degree of freedom given by the presence of nitrogen, it is very probable that many new nitridooxophosphate compositions will be found in the near future. 

Although a chemical substance with the PON formulation was reported as early as 1846 (186), this phosphorus oxynitride was not well known for a long time. That is essentially due to some difficulty in its preparation and to the X-ray amorphous character of the commonly obtained powders. 

Millers and Vitola (217) have mentioned different crystalline phosphorus oxynitride compositions that are located in between PON and... 

Upon heating, melamine-based salts dissociate, and re-formed melamine volatilizes in a manner similar to pure melamine. However, in the case of melamine salts, a larger portion of melamine undergoes progressive condensation than does pure melamine therefore, the condensed-phase contribution of the salts is larger. If the anion contains phosphorus, the phosphoric acid released will phos-phorylate many polymers and produce a flame retardant effect similar to that of other typical phosphorus-based additives (see above). Melamine condensates and phosphoric acid react further at temperatures above 600° C, where triazine rings are opened and cross-linked. A (PON) type of structure known as phosphorus oxynitride is formed. Phosphorus oxynitride is very thermally stable and in some polymers can contribute to condensed-phase mechanisms. ... 

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