Abstract
Tetracalcium phosphate (Ca4 (PO4) 2O) was studied with respect to its preparation, thermal change, hydration and catalytic characteristics.
Reaction products by heating the stoichiometric mixture of Ca2P2O7+2 CaCO3 in air were as follows : Ca2P2O7+2CaO (≥650°C), Ca3 (PO4) 2+CaO (≥700°C), 1/3 Ca10 (PO4) 6 (OH) 2+2/3 CaO (≥ 800°C), and Ca4 (PO4) 2O (≥1200°C). When Ca4 (PO4) 2O was heated up and then cooled down gradually in air, the reaction Ca4 (PO4) 2O→1/3 Ca10 (PO4) 6 (OH) 2 +2/3 CaO_??_Ca4 (PO4) 2O occurred, where the first process started at 300-420°C with absorbing H2O vapor in air, and the second reversible process at 1200°C for the forward reaction and at ca. 1050°C for the reverse. The reverse reaction could be prevented by rapid cooling or by using dry atmosphere. Actually, Ca4 (PO4) 2O was prepared in air by rapid cooling from 1350°C. The formation of hydroxyoxyapatite (Ca10 (PO4) 6 (OH, O) 2) was suggested at 850-1200°C. The hydration activity of Ca4 (PO4) 2O was lower than that of α-Ca3 (PO4) 2, and higher than that of β-Ca3 (PO4) 2· For the catalytic thermal decomposition of 2-propanol, Ca4 (PO4) 2O was a typical basic catalyst, However, it was considered that Ca4 (PO4) 2O changed into a mixture of 1/3 Ca10 (PO4) 6 (OH) 2+2/3 CaO during the catalytic experiment.
