Sodium metaphosphates, NaPO

Sodium metaphosphate, NaPOs.—The metaphosphate is prepared by the interaction of sodium nitrate and phosphoric acid at 330° C.20 It is a white, vitreous mass, almost insoluble in water, and melting21 at 617 2° C. It is sometimes called Maddrell s salt, after its discoverer.22 The semihydrate, NaP03, H20, is formed by heating sodium ammonium hydrogen phosphate at 160° to 170° C., and subsequently raising the temperature to 320° C.23 Tammann24 has proved the existence... 

Monobasic sodium phosphate is chemically stable, although it is slightly deliquescent. On heating at 100°C, the dihydrate loses all of its water of crystallization. On further heating, it melts with decomposition at 205°C, forming sodium hydrogen pyrophosphate, Na2H2P20y. At 250°C it leaves a final residue of sodium metaphosphate, NaPOs. 

Figure 5.3 is a phase diagram for sodium polyphosphates from tetrasodium pyrophosphate, Na4P207, to sodium metaphosphate, [NaPOs]/ . At this point it is... 

Sodium Polymetaphosphate. Graham s salt "sodium hexametaphosphate glassy sodium metaphosphate Hy-Phos. (NaPO. A mixture of polymeric metaphos-... 

It occurs as a white, crystalline powder. It is a high-molecular-weight sodium polyphosphate composed of two long metaphosphate chains (NaPO-j) that spiral in opposite directions about a common axis. The NajO/ILOj ratio is about 1.0. It is practically insoluble in water but dissolves in mineral acids and in solutions of potassium and ammonium (but not sodium) chlorides. The pH of a 1 3 slurry in water is about 6.5. 

As is seen, in the NaPOs-NaCl system similar to Mo(V) and W(V) polyhedra of the same composition and structure are formed that predetermines possible similarity of their electrochemical behavior. Indeed, in the system studied the values of tungsten and molybdenum reduction potentials were proved to be almost identical and more positive as compared to the phosphorus reduction potential (Fig.4). In addition, solubility of molybdenum and tungsten trioxides was found to be fairly high and the binary system metaphosphate-sodium chloride rather low-melting. 

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