Calcium phosphate powders synthesized from solutions with [Ca2+]/[PO43-] = 1 for bioresorbable ceramics

Abstract

Calcium phosphate powders for manufacturing bioceramics were synthesized via precipitation from stock solutions of (NH4)2 HPO4 and Ca(NO3)2, or CaCl2 or Ca(CH3COO)2 with [Ca2+]/ [PO43-] = 1, without pH regulation. Properties of powdered samples, including density and microstructure of ceramics sintered at 900, 1000, 1100°C, were studied. The following pairs of precursors such as Ca(NO3)2/(NH4) 2HPO4, CaCl2/(NH4) 2HPO4, Ca(CH3COO)2/ (NH4)2HPO4 gave both insoluble calcium phosphates and the corresponding by-products of synthesis - NH4NO3, NH4Cl, NH4 CH3COO. These by-products were released from the calcium phosphate precipitates in the course of heating to the temperature of sintering. Owing to specific buffer properties of the solutions being formed during synthesis, the pH value varied in a wide range during the precipitation process leading to different final values of pH and, thus, to different target phase(s) after annealing at 900 - 1100°C. After sintering, the samples based on the powders synthesized from Ca(NO3)2/(NH4)2 HPO4 consisted of β-Ca2P2 O7, whereas the samples based on the powders derived from CaCl2/(NH4)2HPO4 were composed of β-Ca2P2O7 and β-Ca3(PO4)2, and the samples based on the powders synthesized from Ca(CH3COO)2/ (NH4)2HPO4 contained only β-Ca3(PO4)2. All the powders can be considered as the precursors for fabrication of bioceramics with enhanced resorption. © Versita Warsaw and Springer-Verlag Berlin Heidelberg 2009.