Cyrille Mercier

Surface alteration of zinc ultraphosphate glass in humid air at 140°C

A mechanism for the alteration of zinc ultraphosphate glass by humid air at 140°C is presented. The glass was prepared by melting a H 3 PO 4 -ZnO batch at 900°C for one hour, its composition is 54.6(±1.5)P 2 O 5 -34.2(±0.5)ZnO-11.2(±0.4)H 2 O. 1 H and 31 P nuclear magnetic resonance shows that water adsorption occurs and simultaneaously leads to the formation of monophosphoric (H 3 PO 4 ) and diphosphoric (H 4 P 2 O 7 ) acids. The surface conductivity data are consistent with the formation on the glass surface of an acidic solution of phosphates. The thermogravimetric data shows that this solution reaches equilibrium with the atmospheric water, that decreases the adsorption rate of water.

Crystal structure of alluaudite-type NaMg3(HPO4)2(PO4).

NaMg3(PO4)(HPO4)2 crystallizes in the alluaudite-type structure. Two types of [MgO6] octahedra, one [NaO10] polyhedron, one orthophosphate and one hydrogenphosphate tetrahedron form the structural set-up.

Synthesis and Characterization of Doped Bioactive Glasses

Abstract Bioactive glasses have been studied for several years. Hench has been the first to show their interest as bone substitutes. Bioglass 45S5 is the best known. This work reviews bioactive glasses of the SiO 2 , CaO, and Na 2 O domain. P, F, and N dopings are also presented. Mixture designs have been used to synthesize the best bioactive glass and to limit the essays. Structures have been studied by NMR analyses. Mechanic properties have been studied as a function of N ratios. Bioactivity has been determined by Fourier Transform Infrared (FTIR) spectroscopy in terms of time of HCA layer’s nucleation. The layer’s thickness has been estimated by Scanning Electron Microscopy coupled with Energy Dispersion Spectroscopy (SEM-EDS) analyses. The last part is about sol-gel synthesis and the Ag doping of an invert glass with 47% SiO 2 , 26.5% CaO, 21.5% Na 2 O, and 5% P 2 O 5 composition.

Mechanical properties, structure, bioactivity and cytotoxicity of bioactive Na-Ca-Si-P-O-(N) glasses

Bioactive glasses are able to bond to bone through formation of carbonated hydroxyapatite in body fluids. However, because of their poor strength their use is restricted to non-load-bearing applications. The effects of nitrogen addition on the physical and mechanical properties and structure of bioactive oxynitride glasses in the system Na-Ca-Si-P-O-N have been studied. Glasses with compositions (mol.%): 29Na2O-13.5CaO-2.5P2O5-(55 -3x)SiO2-xSi3N4 (x is the no. of moles of Si3N4) were synthesised with up to 1.5 at% P and 4.1 at% N. A novel 3-step process was used for addition of P and N and this proved successful in minimising weight losses and producing homogeneous glasses with such high SiO2 contents. The substitution of 4.12 at% N for oxygen results in linear increases in density (1.6%), glass transition temperature (6%), hardness (18%) and Youngs modulus (74%). Vickers Indentation Fracture (VIF) resistance (Kifr) was calculated from various relationships depending on the load, indent diagonal, crack lengths and Youngs modulus to hardness (E/H) ratio. Firstly, Meyers index n is calculated from the slope of the logarithmic plot of load versus indent diagonal. Then by comparing the experimental slopes of the logarithmic plots of crack lengths versus load it is concluded that the cracking mode is Radial Median type. The substitution of 4.12 at% N for oxygen results in an increase in Kifr of 40%. These increases in properties are consistent with the incorporation of N into the glass structure in three-fold coordination with silicon which results in extra cross-linking of the glass network. The structure of these bioactive oxynitride glasses was investigated by solid state nuclear magnetic resonance (MAS NMR) of 31P and 29Si. The structure reveals that all the N atoms are bonded to Si atoms with the formation of SiO3N, SiO2N2 and Q4 structural units with extra bridging anions at the expense of Q3 units. The bioactivity of the glasses has been evaluated by soaking them in simulated body fluid (SBF) and results confirm that all these oxynitride glasses are bioactive. Cytotoxicity tests based on different concentrations of these bioactive glass powders in a cell growth environment have also shown that they are not cytotoxic.

Bioactivity and Cytotoxicity of Oxynitride Glasses

Different kinds of bioactive materials are used as bone substitutes. In particular, bioglasses containing Si, Ca, Na and O, bind to host tissues with a stable chemical bond. The phenomenon of bioactivity is associated with the formation of a crystallized hydroxycarbonated apatite (HCA) layer on the bioglass surface when soaked in a simulated physiological fluid. This layer is similar to the mineral phase of bone. However, they do not have sufficient strength for use in load-bearing situations and therefore improving their mechanical properties would allow their use in more robust applications. Within the previously studies, we have shown that the density, glass transition temperature, hardness and elastic modulus have increased linearly with nitrogen content. The purpose of this work was to study the effects of nitrogen addition on the bioactivity in a simulated body fluid (SBF) and cytotoxicity tests have complemented the study.