Effect of Water Vapor on the Formation of Lithium cyclo-Hexaphosphate

Article abstract of DOI:10.1246/bcsj.64.2353

The effect of water vapor on the formation of lithium cyclo-hexaphosphate Li6P6O18 (P_6m) from trilithium hydrogenpyrophosphate monohydrate Li3HP2O7*H2O was investigated by means of DTA-TG, X-ray diffraction analysis, isothermal heating with electric furnace, and HPLC.Li3HP2O7*H2O lost the water of crystallization at about 180 deg C to give anhydrous Li3HP2O7.At 300 deg C the disproportionation of Li3HP2O7 anhydride to Li4P2O7 and Li4P4O12 (P_4m) proceeded faster under humid conditions than under dry air, and subsequently P_4m increased with a decrease in P₂ and soluble polyphosphates (P_poly).At 400 deg C, P_4m changed largely to P_6m under humid conditions.In these reaction processes, water plays an important role as catalyst in the cyclization by dehydration of the end group and in ring opening by attacking the P-O-P bond.At 450 deg C, the amounts of P₂ and P_6m were almost equal under both humid and dry conditions, because all of P_4m thermally changed to P_6m.