Effect of particle size on carbonate apatite cement properties consisting of calcite (Or vaterite) and dicalcium phosphate anhydrous

Calcium carbonate (CaCO₃) has been known as one of the components of carbonate apatite (CO₃Ap) cement. Calcite is one of the polymorph of CaCO₃ with big particle size and excellent stability. In contrast, vaterite has small particle size and a metastable phase. To discover the effect of particle size on the properties of CO₃Ap cement, this study investigated the different particle size of vaterite; calcite from vaterite, which has almost similar particle size and shape with vaterite; grounded calcite and ungrounded calcite. The powder phase of calcite or vaterite combined with dicalcium phosphate anhydrous (DCPA) was mixed with 0.8 mol/L of Na₂HPO₄ solution in 0.45 liquid to powder ratio. The paste was packed into a split stainless steel mold, covered with glass slide and kept at 37°C and 100% relative humidity for a period of time. XRD and FT-IR analysis revealed that CO₃Ap cement consisted of vaterite and DCPA transformed to pure B-type CO₃Ap in 72 hours while CO₃Ap cement that consisted of calcite with different particle size was not completely transformed to CO₃Ap even until 240 hours. We concluded that CO₃Ap cement consisted of vaterite with small particle size and metastable phase properties is more effective as starting material due to its fast transformation to CO₃Ap.