The exothermal behavior in the hydration process of calcium phosphate cement

The exothermal behavior in the hydration process of calcium phosphate cement (CPC) and their effect factors were investigated systematically. One CPC formulation is composed of tetracalcium phosphate (TECP) and dicalcium phosphate anhydrous (DCPA), and its hydration reaction is an exothermic reaction. Hydration includes five processes, namely, the start, induction, acceleration, deceleration and the terminating process. The introduction of hydroxyapatite (HAP) as crystal seed shortens induction and advances on the reaction peak position, which resulted from the introduction of crystal seed that reduced the activation energy of heterogeneous nucleation. The increase in temperature not only makes the reaction advance but also enlarges it. The activation energy of the hydration reaction is 176kJ/mol by calculation. The particle size of the raw material and the ratio of calcium to phosphate in the specimen have large effects on the hydration process. Decrease in particle size of TECP and in the ratio of calcium to phosphate resulted in marked acceleration of reaction and made the reaction peak advance evidently, but the effect of particle size of DCPA is not so remarkable. Based on the heat liberation in the hydration of CPC specimens taking Ca/P as 1.5 and 1.67, the standard mole enthalpies of formation of TECP and calcium-deficient hydroxyapatite are -5908 and -11,119kJmol(-1), respectively.