THERMAL BEHAVIOR OF VARIOUS COBALT CYCLO-PHOSPHATES

Abstract

The thermal behavior of various cobalt cyclo-phosphates, Co₂P₄O₁₂·8H₂O(P_4m), Co₃P₆O₁₈·14H₂O(P_6m), and Co₄P₈O₂₄·18H₂O (P_8m), was investigated using TG-DTA, HPLC, X-ray diffraction analysis, and IR. P_4m decomposed perfectly to short-chain phosphates and oligo phosphates (P_oligo:chain length n=5-14) with the elimination of water of crystallization. With an increase in temperature, their phosphates condensed to insoluble highpolyphosphates (P_{high poly}). The decomposition of P_4m proceeded faster under humid air than dry air. P_6m, also decomposed to short-chain phosphates and P_oligo (n=7-14). Although the water vapor accelerated the decomposition of P_6m, it prevented the condensation of phosphates. At temperatures above 540°C, all the phosphates changed to P_{high poly}. P_8m lost the most of water of crystallization to decompose to short-chain phosphates and oligophosphates at about 150°C. An increase of oligo phosphates (n=9-17) and soluble polyphosphates (n=18-20) was observed at 400 °C. Under a higher water vapor pressure, the decomposition of P_8m proceeded rather faster than in a lower one, while the rate of condensation reactions slower than in the higher one. At 400°C, a little amount of P_6m formed. At higher temperatures, all the phosphates changed to P_{high poly}.