title: Electron spin resonance in silicon substituted apatite and tricalcium phosphate.
abstract: Impurity centers associated with silicon have been observed in the phase mixture of silicon substituted apatite (Si-Ap) and silicon stabilized tricalcium phosphate (Si-TCP) using electron spin resonance (ESR). Two unique centers occur upon addition of SiO2 to the calcium phosphate system: an orthorhombic center with g-values 2.0072+/-0.0001, 2.0024+/-0.0001 and 2.0003+/-0.0001 (Si-h1) and a center with tetrahedral symmetry having g-values components 2.0054+/-0.0001 and 1.9992+/-0.0003 (Si-h2). Both centers are hypothesized to be characteristic of defects associated with silicon in the Si-Ap phase. Through comparison of the intensity of F-OH centers in undoped calcium hydroxyapatite (HA) prepared with various levels of OH occupancy, a relationship is demonstrated between the ESR intensity of an F-center signal with g = 2.0019+0.0004 (F-OH) and the OH occupation of HA. Relative changes in the intensity of ESR signals Si-h1 and F-OH are consistent with a chemical model describing the substitution of SiO4(4-) for PO4(3-) in HA with the creation of OH- vacancies as charge compensation, resulting in a mixed phase composition of Si-Ap and Si-TCP that results when a hydroxyapatite precipitate (HA) is heated in the presence of added SiO2.
authors.affiliation: Physics Department, Queen's University, Stirling Hall, Kingston, Ont, K7L 3N6, Canada. alexis@physics.queensu.ca
authors.forename: Alexis M
authors.initials: AM
authors.lastname: Pietak
authors.forename: Joel W
authors.initials: JW
authors.lastname: Reid
authors.forename: Michael
authors.initials: M
authors.lastname: Sayer
mesh_terms: D001031:Apatites / Q000032:analysis / Q000737:chemistry*; D001672:Biocompatible Materials / Q000032:analysis / Q000737:chemistry*; D018786:Bone Substitutes; D002130:Calcium Phosphates / Q000032:analysis / Q000737:chemistry*; D002516:Ceramics / Q000032:analysis / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D008422:Materials Testing; D008968:Molecular Conformation; D011208:Powders; D012825:Silicon / Q000032:analysis / Q000737:chemistry*
chemical_list: D001031:Apatites; D001672:Biocompatible Materials; D018786:Bone Substitutes; D002130:Calcium Phosphates; D011208:Powders; C018392:tricalcium phosphate; D012825:Silicon