The solid-liquid reaction of α-Ca3(PO4)2 and Ba(H2PO4)2 solution proceeds to successively precipitate BaHPO4, “X” phase and DCPD (CaHPO4⋅2H2O), depending on the sluggish dissolution of α-Ca3(PO4)2. The process experiences three exothermal flows accompanying a three-step decrease in electric conductivity. Chemical analysis of the liquid phase together with X-ray diffraction (XRD), thermogravimetric and differential thermal analysis (TG-DTA) and scanning electron microscopy (SEM) of the residue were conducted to clarify the reaction mechanism. As a result a suitable method for isolating the new compound “X” was examined. The “X” phase was isolated, for example, by stirring a suspension composed of 0.6g α-TCP and a mixed solution, 500ml of 14.2mmol·dm-3 Ba(H2PO4)2(aq) and 300ml of 15.0mol·dm-3 Ca(H2PO4)2(aq), for several hours. The chemical formula of the “X” phase was BaHPO4⋅CaHPO4⋅H2O and its crystal structure was monoclinic with unit-cell parameters, a=1.0656nm, b=0.7802nm, c=0.9605nm and β=104.26°.
The Ceramic Society of Japan