Chain Lengths of Phosphate Glasses

Crystallization and recrystallization drives impurities out of a melt to surfaces of crystals. Each time a system is crystallized, more and more water is lost. As water is lost, bulk compositions more nearly approach an R of unity. All metal oxides in excess of unity contribute as chain terminators and breakers. 

Unlike the sodium systems, melt history has less influence on potassium Kurrol s salt systems mentioned above. Potassium trimetaphosphate is not a phase diagram entity. Potassium phosphate melts with R values of unity are very difficult to quench to glasses, because they crystallize very rapidly. If potassium phosphate melts are cooled slowly, long-chain polyphosphates, [KPOsln, are the only crystals to form. No other crystals are thermodynamically stable in this portion of their phase diagram and Kurrol s salts dominate a large area of this diagram. 

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