Claude Carel

A synthetic aragonite-based ceramic as a bone graft substitute and substrate for antibiotics

Abstract The present material is a non-sintered porous synthetic carbonate in its metastable modification under ambient pressure, i.e. aragonite, for bone reconstruction and drug carrying. The crystal structure, density, morphology and granulometry of the synthetic aragonite are characterized. The powdered aragonite is used for processing non-sintered porous ceramics. The influence of process parameters on porosity is investigated. In vivo biocompatibility, resorption and bone formation have been evaluated after implantation of selected materials in femurs of sheep. Preliminary results show a mineralization of the implant sites and the complete resorption of implants at 6 months. Two antibiotics Metronidazole and Gentamicin were incorporated into materials without alteration or degradation. This incorporation of therapeutic agents in the first stages of the process, and particularly before compaction, allows a controlled drug loading of the biomaterial.

Re-examination of the non-stoichiometry and defect structure of copper(II) oxide or tenorite, Cu1±zO or CuO1±ϵ: A short review

Abstract Four sets of compositional data with a departure z or ϵ from the stoichiometry of tenorite Cu 1± z O or CuO 1± ϵ are re-examined for possible point defects. Correlations z ( p O2 ) at equilibrium solid⇔pure di-oxygen – when they can be computed – indicate the presence of either oxygen vacancies or copper interstitials or clusters of them. Some recent data after quenching are in favor of copper interstitials. Few data concerning tenorite prepared by decomposition of a salt, by oxidation of copper and by CVT in sealed tubes have generally been interpreted in the literature as indicating copper deficiency. In those oxides a large departure from the stoichiometry indicates a complex behavior likely due to several point defects possibly ordering at short and/or long range, and including chemical impurities in the case of sealed tube preparation. It is, however, in fact likely that the defect structure of such samples involves the two sub-lattices. Cu 3 O 2 - or Cu 4 O 3 -like clusters can even be envisaged.

Evolution structurale de monoxydes non-stoechiométriques du type wüstite: Simulations et relations entre paramètres structuraux

Abstract For nonstoichiometric monoxides M 1− z O (or M O x ) of the wustite type, it is possible to forecast the trend of experimental graphs representing the parameters a of the cubic cell or the temperature factor B vs temperature θ or composition z (or x ). A criterion for the experimental accuracy allows to justify the existence or not of a curvature on the graphs. The parameter a is calculated a priori for wustite ( M = Fe) vs z . A model gives the law of variation of a vs some ionic species and the ratio ϱ = (z + t) t ; t is the rate of intertitials. The law is a = a 0 [1 − 1 3 β∗z] . The calculated value obtained for β∗ agrees well with the experimental mean value 〈β〉 = 0.28. This model applies to the monoxide Mn 1− z O for which the calculated value of β∗ is close to 〈β〉 = 0.29. In a second model, the cell volume is defined as being the weighted mean of the volumes of distorted and undistorted cells. With knowledge of β∗ and ϱ, it is possible to evaluate the mean radius of a vacancy for each oxide. The factor B is the sum of two contributions B Th ( θ ) and B St ( z ). This latter varies linearly with z . The coefficient p = ( ∂B ∂z ) θ can be calculated a priori from simulations of the shifts resulting from clusters of point defects. Knowing β∗, p may be located between 3 and 10 A 2 according to the assumptions. The experimental value for the wustite under equilibrium conditions is p = 4.2 A 2 . An empirical relation between B Th ( θ ) and a ( θ ) is discussed from the point of view of Gruneisens law. When the molar heat C p is known, it is possible to evaluate the mean force constant D = 0.78 mdyne/A for the bonds in Fe 1− z O. The compressibility coefficient χ 0 is then obtained. It can be compared with the measured value from the literature, at 25°C under zero pressure.

Structural evolution study of substituted wüstites Fe1 − z − y (Ca, Mg)yO

Abstract Polycrystalline samples of magnesio- and calciowustites Fe (1 − z − y ) Me y O with Me = Mg or Ca, were investigated using neutron diffraction experiments. The effective chemical composition was controlled by taking into account Vegards law for the cell parameters as functions of z and y . The site occupancies were refined: the ratio P SRO = ( z + t )/ t was found to increase with increasing Ca substitution while the diffuse scattering of the diffraction patterns decreased. The P SRO was found to be independent of the level of Mg substitution. The model previously proposed for clustering of defects in pure wustite is justified: the evolution of the defect structure is interpreted in terms of size effects and surface energy changes of the clusters.

Structural evolution of manganosite: comparison of properties of nonstoichiometric manganese and iron monoxides

Abstract Accurate measurements of the lattice parameters of polycrystalline manganosite Mn 1− z O lead to the conclusion that the magnetic lattices of the stoichiometric MnO and Mn 3 O 4 , which appear during the cooling process, do not interact. The X-ray energetic shifts and the morphology of the manganosite are described for multilayer samples obtained by oxidation of the metal. The reactivity of the two isomorphic monoxides, Mn 1− z O or manganosite and Fe 1− z O or wustite, is interpreted in terms of the elastic constant C 44 . The clustering of the point defects, the deformation energy, and the comparative plasticity or brittleness are discussed in terms of this constant for both monoxides at high temperature and after quenching.

Determination of some anisotropic elastic coefficients of the compound YBa2Cu3O6.7F0.3

Abstract The orthorhombic compound YBa2Cu3O6.7F0.3 noted F-(123) is obtained by chemical addition of 0.3 flourine atom into the pure (123) compound with 6.7 oxygen atoms. The high pressure study by neutron powder diffraction at low temperature leads to volumic expansion coefficients at 295 K αv=43 and 47×10−6 K−1 under ambient and 4.9 kbar pressures respectively, a compressibility pressibility coefficient χv=5.4×10−12Pa−1, i.e. a bulk modulus B=χ−1v=187 GPa. These values are close to those still found for the pure (123) but disagree with other ones from the literature. The value 2.9±0.6 is found for the mean Gruneisen coefficient. It is abnormally high and far from the value 1.2 found for the bismuth cuprate (2212). The origin of this observed anomaly is discussed.