Phase formation and evolution in the silicon substituted tricalcium phosphate/apatite system.
The sintering of silicon doped calcium phosphate ceramics prepared from a basic colloidal hydroxyapatite (Ca5(PO4)3OH 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 (Ca3(P0.9Si0.1O3.95)2 or Si-TCP(sat)) and alpha-TCP (Ca3(PO4)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 0.2 mol SiO2:mol HA (0.2:1) and 1 mol SiO2: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 thermodynamic model 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.
Reid
J W
JW
Department of Physics, Queen's University, Stirling Hall, Queen's Crescent, Kingston, Ont., Canada, K7 3P6. joel.reid@millenium-biologix.com
Pietak
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Sayer
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Dunfield
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Smith
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D001031:Apatites / Q000737:chemistry*; D001672:Biocompatible Materials / Q000737:chemistry*; D002130:Calcium Phosphates / Q000737:chemistry*; D002516:Ceramics; D017886:Durapatite; D006882:Hydroxyapatites / Q000737:chemistry; D007700:Kinetics; D008422:Materials Testing; D008956:Models, Chemical; D012822:Silicon Dioxide / Q000737:chemistry*; D013696:Temperature; D013816:Thermodynamics; D013997:Time Factors; D014961:X-Ray Diffraction
D001031:Apatites; D001672:Biocompatible Materials; D002130:Calcium Phosphates; D006882:Hydroxyapatites; D012822:Silicon Dioxide; D017886:Durapatite; C020243:calcium phosphate; C018392:tricalcium phosphate