Hardly soluble calcium phosphate compound is able to dissolve easily by stirring with an aqueous suspension containing a strongly acidic ion exchange resin, H-R. However, CaHPO4·2H2O (DCPD), an intermediate, precipitates during the dissolution process of tetracalcium phosphate [Ca4 (PO4) 2O, TetCP] or α-tricalcium phosphate [Ca3 (PO4) 2, α-TCP], accompanied with a decrease of electric conductivity. In this paper, the dissolution process of six kinds of calcium phosphates was followed by simultaneous measurement of calorimetry, conductivity and pH. Precipitation of DCPD by the reaction between TetCP and Ca (H2PO4) 2 solution proceeds quantitatively. The fact is applied to determine the standard formation of enthalpy (-4779.0 kJ · mol-1) of TetCP.
Synthesis of pillared montmorillonite organic polymer porous hybrid and its unique adsorption properties were investigated. Polyvinylalcohol (PVA) or furfurylalcohol (precursor of furan resin, FF) were used as an organic polymer to intercalate under coexistence with montmorillonite in distilled water. In order to form pillar, intercalated montmorillonite was dipped into polyalminum chloride aqueous solution with shaking, followed by firing at 300-700°C in N2 atmosphere for immobilization of polymer and dehydration of polyalminum ion. Interlayer spacing was evaluated from XRD patterns. In the case of PVA, the interlayer spacings greatly increased from 1.3 for montmorillonite to 2.2 nm on the intercalation. In the case of FF, the spacing little increased to 1.6 nm. Specific surface area increased steeply by firing above 300°C. Maximum surface area of around 150 m2. g-1 was obtained in the sample with PVA fired at 700°C. On the other hand, amount of adsorbed H2, N2 or O2 reached maximum at 600°C. Since carbonization degree increased with firing temperature, the adsorption ability was considered to be attributed to organic species