Effects of sulfate, pyrophosphate, and citrate ions on the physicochemical properties of cements made of beta-tricalcium phosphate-phosphoric acid-water mixtures

Several additives were selected to increase the setting time of calcium phosphate cements made of beta-tricalcium phosphate (beta-TCP; beta-Ca-3(PO4)(2))-phosphoric acid-water mixtures, The effects of the additives, i.e., sulfate, pyrophosphate, and citrate ions, ie presented in this study, The results show that they all increased the setting time of the cement, Their effectiveness at increasing the setting time is in the order pyrophosphate > citrate > sulfate, The effect of sulfate ions on the setting time is increasingly large below a concentration of 0.1M. Above that concentration, calcium sulfate dihydrate (CSD; CaSO4 . 2H(2)O) crystals nucleate and act as nuclei for dicalcium phosphate dihydrate (DCPD; CaHPO4 . 2H(2)O) crystals, which are the normal product of the setting reaction, This decreases the setting time and decreases the DCPD crystal size, resulting in an increase of the tensile strength of the cement.