SODIUM PHOSPHATE-DERIVED CALCIUM-PHOSPHATE CEMENTS

Calcium phosphate cements (CPC) were synthesized by the acid-base reac tion between sodium phosphate, NaH2PO4 or -(NaPO3-)-(n), as the acid s olution, and calcium aluminate cements (CAC) as the base reactant at 2 5 degrees C. The extent of reactivity of -(-NaPO3-)-(n) with CAC was m uch higher than that of NaH2PO4, thereby resulting in a compressive st rength of > 20 MPa. Sodium calcium orthophosphate (SCOP) salts as amor phous reaction products were responsible for the development of this s trength. When this CPC specimen was exposed in an autoclave, in-situ a morphous --> crystal conversions, such as SCOP --> hydroxyapatite (HOA p), and Al2O3 . xH(2)O --> gamma-AlOOH, occurred at approximate to 100 degrees C, while the rate of reaction of the residual CAC with the ph osphate reactant was increasingly accelerated by hydrothermal catalysi s. Based upon this information, we prepared lightweight CPC specimens by hydrothermally treating a low-density cement slurry (1.28 g/cc) con sisting of CAC powder, -(-NaPO3-)-(n) solution, and mullite-hollow mic rospheres. The characteristics of the autoclaved lightweight specimens were a compressive strength of > 9.0 MPa, water permeability of appro ximate to 5.0x10(-3)) milli darcy, and a low rate of alkali carbonatio n. The reasons for such a low carbonation rate reflected the presence of a minimum amount of residual CAC, in conjunction with the presence of HOAp and gamma-AlOOH phases that are unsusceptible to wet carbonati on.