Thermal behavior of various zinc cyclo-phosphates

The thermal behavior of various zinc cyclo-phosphates (zinc cyclo-tri-, Zn3(P3O9)2·11H2O; cyclo-hexa-, Zn3P6O18·10H2O; cyclo-octaphosphates, Zn4P8O24·20H2O; abbreviated as ZnP3m, ZnP6m, and ZnP8m, respectively) were investigated with thermogravimetry–differential thermal analyses (TG–DTA), X-ray diffractometry (XRD), and high-performance liquid chromatography-flow injection analysis (HPLC-FIA). With increasing of temperature, cyclo-triphosphate changed to short-chain phosphates at 200 °C, and then further changed to cyclo-tetraphosphate, finally changed to insoluble highpolyphosphates (Pinsol.) at 700 °C. The behaviors of cyclo-hexaphosphate were similar to those of cyclo-triphosphate except of temperatures of transformations to cyclo-tetraphosphate. On the other hand, cyclo-octaphosphate dehydrated of almost all crystallization waters at about 100 °C, and decomposed to ortho- (P1), di- (P2), tri- (P3), oligo- (P4–P20: Poligo), and soluble polyphosphates (