The “Overcondensation” of Phosphate Ions and the Formation of Conjugate Metal Oxide upon the Thermal Dehydration-condensation of Hydrogenorthophosphates

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Abstract
On the thermal reaction of H3PO4 or NH4H2PO4 with metal salts, such as Na2CO3 or Mg(OH)2, the “overcondensation” of the phosphate anions and the conjugate formation of metal oxide were observed. The “overcondensation” was defined as a formation reaction of the phosphate with a larger polymerization degree than that of the product to be expected from the [MO or M2O]/[P2O5] mole ratio of the starting mixtures. The “overcondensed” tetrametaphosphate and the conjugate oxide, magnesium oxide, were detected on the thermal condensation of MgHPO4·3H2O and of a mixture of NH4H2PO4 or H3PO4 and Mg(OH)2. The “overcondensed” tripoly- and trimeta-phosphate were found in the course of the formation reaction of Na pyrophosphate from a mixture of Na2CO3 and NH4H2PO4.