Colour centres in plasma-sprayed hydroxyapatite.
Very pure hydroxyapatite is diamagnetic and shows no electron paramagnetic resonance (EPR) spectrum. Plasma-sprayed coatings made with such a pure hydroxyapatite contain paramagnetic point-defects. Irradiated deposits show a strong EPR absorption assigned to an O2- anion adjacent to a calcium vacancy, with anisotropic parameters, g1 = 2.004, g2 = 2.013 and g3 = 2.038. The EPR spectra and colour fade away following thermal annealing. These features are discussed in terms of point-defects in the hydroxyapatite crystal structure.
F+ centre in (Ca-Sr) carbonated hydroxyapatites
Abstract Powdered samples of synthetic carbonated hydroxyapatites with variable amounts of strontium substituting for calcium, obtained by precipitation, were studied by ESR at the X-band frequencies after heating at 400°C for 24 h, X-irradiation and annealing at 150°C for 30 min. The F+ centre spectrum exhibiting orthorhombic symmetry was recorded between RT and 120 K, with ≃2. When the amount of carbonate inside the samples increases, the spectral intensity has the same behaviour than that of the quantity of O2- vacancies calculated from results of chemical analysis. Our results are a confirmation of the existence of two different mechanisms of charge compensation when CO3 2- substitutes for PO4 3-, and they also show that Sr ions are not located in cation sites adjacent to carbonate ions.
France in the Middle Ages 987-1460 : from Hugh Capet to Joan of Arc
Translatora s Note. Foreword. List of Illustrations. List of Genealogical Tables. Part I: The Inheritance: . 1. The Empire. 2. The Frankish People. 3. The Principalities. 4. Disturbances. Part II: Lordship:. 5. The Village. 6. The Castle. 7. The Church. 8. King and Lord. Part III: Origins of State and Nation:. 9. The Great Age of Progress. 10. Louis VII. 11. Philip Augustus. 12. The South. 13. The Thirteenth Century. 14. The Fourteenth Century. 15. The Maid of Orleans. Epilogue. Chronology. Bibliography. Index.