Phase formation and evolution in the silicon substituted tricalcium phosphate/apatite system.

摘要

The sintering of silicon doped calcium phosphate ceramics prepared from a basic colloidal hydroxyapatite (Ca(5)(PO(4))(3)OH or HA) precipitate mixed with silica over 800 degrees C yields a phase mixture of tricalcium phosphate phases (TCP) designated Si-TCP, beta-TCP and a silicon substituted dehydrated apatite (Si-Ap). The Si-TCP phase is defined as a combination of a silicon stabilized TCP in which the silicon content attains a saturated value (Ca(3)(P(0.9)Si(0.1)O(3.95))(2) or Si-TCP(sat)) and alpha-TCP (Ca(3)(PO(4))(2)). Si-TCP(sat) has the same crystalline space group (P2(1)/a) as alpha-TCP, but with characteristically different lattice parameters due to the substitution of silicon in tetrahedral phosphorus sites. The nucleation and growth kinetics of Si-TCP in samples of composition 0.2mol SiO(2):mol HA (0.2:1) and 1mol SiO(2):mol HA (1:1) can be understood in terms of the initial growth of alpha-TCP at a silica-HA interface followed by a transformation to Si-TCP(sat) or beta-TCP. A thermodynamicmodel for the formation of Si-TCP(sat) predicts a nucleation temperature of 795 degrees C, in close agreement with experiment. If sufficient silicon is available, the alpha-TCP transforms to Si-TCP(sat) during extended sintering. In the absence of sufficient silicon, the alpha-TCP transforms to beta-TCP.