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International audience; High-tech ceramics have always been associated to medical devices: they are used today as femoral heads and acetabular cups for total hip replacement, dental implants and restorations, bone fillers and scaffolds for tissue engineering. Here, we describe their current clinical use and propose a picture of their evolutions for the next 20 years. The need for tough, strong and stable bioinert ceramics should be met by either nano-structured, alumina and zirconia based ceramics and composites or by non-oxide ceramics. Nano-structured calcium phosphate ceramics and porous bioactive glasses, possibly combined with an organic phase should present the desired properties for bone substitution and tissue engineering. The position of ceramics in a gradual medical approach, from tissue regeneration to conventional implants, is discussed.

International audience; Deagglomeration of a nanocrystalline transition alumina performed using different techniques was first demonstrated to be active in the achievement of a better powder compaction ability under uniaxial pressing and consequently in the development of a highly dense and homogeneous microstructure during pressureless sintering. A major effect, however, was associated to the heating rate chosen during the densification cycle. In fact, the influence of different heating rates (10°C/min or 1°C/min) on phase and microstructural evolution during sintering was investigated in depth on the above best green bodies. A low-rate thermal cycle leads to a significant reduction of the α-Al2 O3 crystallization temperature and promotes a more effective particle rearrangement during phase transformation. As a consequence, in the low-rate treated material, it was possible to avoid the development of a vermicular structure as usually expected during the densification of a transition alumina and to yield a more homogenously fired microstructure.

International audience; Nanostructured plasma-sprayed chromium oxide ceramic coatings, with a higher wear resistance than coatings obtained using micrometric powder as starting material have been developed. The influence of the starting powder, i.e. Cr2O3 fused crushed powders and Cr2O3 nanopowders having grains size of 100 nm, has been investigated. The nanopowders are reconstituted into spherical micrometer sized granules by the spray-drying process before plasma spraying. It is shown that due to their specific microstructure the wear resistance of the nanostructured coatings is more than 20 times higher compared to the coatings obtained using micrometric powder

International audience; Doping of commercial alumina nanopowders by using aqueous solutions of metal salts was exploited to prepare alumina-based nanocomposites. The same procedure was applied to produce a composite made of immiscible phases, that is an alumina-zirconia material, by doping an α-alumina powder with a zirconium chloride solution, as well as to produce an alumina-YAG (yttrium aluminium garnet) system by doping alumina with a yttrium chloride solution and promoting YAG formation by solid-state reaction at high temperature. For this latter case, the difference in reactivity between two commercial powders, one made of transition alumina, the other of pure α-phase, was investigated in terms of phase evolution and purity. In all cases natural sintering was performed to develop dense bodies.

International audience; Resume_anglais A major constraint in improving the under-standing of the micromechanics of the fatigue failure process and, hence, in optimizing bone cement performance is found in the uncertainties associated with monitoring the evolution of the internal defects that are believed to dominate in vivo failure. The present study aimed to synthesize high resolution imaging with complementary damage monitoring/detection techniques. As a result, evidence of the chronology of failure has been obtained. The earliest stages of crack initiation have been captured and it is proposed that, in the presence of a pore, crack initiation may occur away from the pore due to the combined influence of pore morphology and the presence of defects within regions of stress concentration. Furthermore, experimental evidence shows that large agglomerations of BaS04 are subject to microcracking during fatigue, although in the majority of cases, these are not the primary cause of failure. It is proposed that cracks may then remain contained within the agglomerations because of the clamping effect of the matrix during volumetric shrinkage upon curing.

Graded bilayered glass–ceramic composite coatings on Ti6Al4V substrates were fabricated using an enameling technique. The layers consisted of a mixture of glasses in the CaO-MgO-Na2O-K2O-P2O5 system with different amounts of calcium phosphates (CPs). Optimum firing conditions have been determined for the fabrication of coatings having good adhesion to the metal, while avoiding deleterious reactions between the glass and the ceramic particles. The final coatings do not crack or delaminate. The use of high-silica layers (>60 wt % SiO2) in contact with the alloy promotes long-term stability of the coating; glass–metal adhesion is achieved through the formation of a nanostructured Ti5Si3 layer. A surface layer containing a mixture of a low-silica glass (∼53 wt % SiO2) and synthetic hydroxyapatite particles promotes the precipitation of new apatite during tests in vitro. The in vitro behavior of the coatings in simulated body fluid depends both on the composition of the glass matrix and the CP particles, and is strongly affected by the coating design and the firing conditions. © 2008 Wiley Periodicals, Inc. J Biomed Mater Res, 2009

Continuous and discrete approaches for forming simulations of textile performs both involve difficulties and drawbacks. The semi-discrete method is an alternative based on a meso-macro approach. It is based on specific finite elements made of a discrete number of the components of the textile at lower scale. Their strain energy in the interpolated displacement field leads to the nodal interior loads of the element. In this paper a new three node element is proposed. It is made up of warp and weft fibres, the tensile and in plane shear energy of which are considered. The directions of the warp and weft yarns are arbitrary with regard to the element sides. That is very important in case of simultaneous multiply draping simulations and when using remeshing. The determination of the material data necessary to the simulation from standard tensile and bias tests is straightforward. A set of elementary tests and mono and multi-ply draping shows the efficiency of the approach.

International audience; A provenance study of obsidians collected in the Jerf el Ahmar village dated from 9500 to 8700 BC cal (Middle Euphrates Valley, Syria) was made from geochemical analyses. The elementary composition of 44 obsidian artefacts and of 19 samples from potential obsidian volcanic sources was determined by inductively coupled plasma-atomic emission spectrometry and -mass spectrometry (ICP-AES/-MS) or particle induced X-ray emission (PIXE) and scanning electron microscope-energy dispersion of X-rays (SEM-EDX). We show that each of these approaches gives reliable source assignment. We found that 42 of the Jerf el Ahmar obsidians came from the Cappadocia (Göllü Dağ volcanic massif) and two from the Bingöl area in Eastern Anatolia. This information confirms the arrival in the Levant of obsidian from the latter sources during the end of the Pre-Pottery Neolithic A period, most probably in relation with the diffusion of the Neolithic process from the Middle Euphrates Valley towards the Northeast.

Two approaches are detailed for the determination of forming limit diagrams (FLDs). The first one is experimental: a correlation technique has been developed for the displacement field measurement on a sheet. The second approach is theoretical: a necking criterion based on the load-instability and plane strain localisation assumption is proposed. It includes the possibility to introduce the modified Gurson–Tvergaard damage model taking account the Hill’s or others anisotropic yield surfaces and the influence of triaxial stress state in the neck. The criterion is written in an intrinsic form and is as well applicable to linear strain paths as well as to non-linear strain paths. Finally, the FLDs for an aluminium alloy, a mild steel and a titanium alloy obtained by experimental and theoretical ways are compared.

Resume L'action de UF 4 sur ZrO 2 a permis de mettre en evidence, outre une phase zircone baddeleyite “dopee” par des traces de UF 4 , une phase MX 3.5 et une serie de microphases MX 3− y de symetrie orthorhombique. La phase MX 3.5 semble avoir une structure de type SmZrF 7 . L'etude par diffraction X et microscopie electronique, de la serie de microphases MX 3− y , revele l'existence systematique d'un sous-reseau UO 3 α deficitaire en anions. Un modele structural s'appuyant sur le principe de “maclage chimique” est propose. Il conduit a une serie M 3 n −4 X 8 n −10 ( n pair ⩾ 4) don les seuls termes simples isoles sont ( n → ∞) et ( n = 10). Toutes les autres phases mises en evidence resultent vraisemblablement de l'intercroissance ordonnee, monodimensionnelle des termes simples successifs n = 6, 8, 10, 12, ….

Bi 0.7 La 0.3 O 1.5 crystallizes with rhomboedral symmetry (space group R 3 m ) and hexagonal unit cell parameters: a = 0.4043(2) nm, c = 2.7557(7) nm, Z = 9. Its structure has been solved at room temperature by using both single-crystal X-ray diffraction and powder neutron diffraction techniques. It can be described as a regular repetition along the c axis of identical M 3 O 4.143 fluorite-like sheets. Each sheet comprises three close-packed cationic layers: one internal layer of Bi La atoms in distorted cubic eightfold coordination, surrounded by two external layers of Bi atoms in fourfold coordination. Extra anions partially occupy delocalized sites within vacant octahedra of the interlayer space. Relations with the fluorite type and possible diffusion pathways for anions are proposed.

International audience; The reaction of rare-earth nitrides with fluorides or the pyrolysis of these fluorides in gaseous ammonia atmosphere leads, in the case of lanthanum, cerium, and gadolinium, to nitride fluorides of general formula LnNxF3−3x. They crystallize with a fluorite-type structure which can be described in a consistent manner in terms of a Willis model. The magnetic properties of Gd3NF6 have been studied.

International audience; In a previous paper we have shown that at 740°C and under an oxygen pressure less than 1,3 torr the electrical conductance G of a NiO powder reaches rapidly an apparently stabilized signal Gi which sharply decreases after a sufficiently long time to a G0 value independent of PO2. From this observation we have studied the influence of the temperature successively on the electrical conductance Gi and G0. The Arrhenius law is only verified for the G0= f(T) curve. G0 appears as the representative value of the gas-solid equilibrium. // Dans un récent travail nous avons pu montrer qu'à 740°C et sous des pressions d'oxygène inférieures à 1.3 torr la conductance électrique G de l'oxyde de nickel atteignait rapidement un palier Gi et reprenait au bout d'un temps suffisamment long une valeur d'équilibre G0 indépendante de PO2. A partir de ces observations nous avons étudié l'influence de la température sur la conductance électrique en se plaçant successivement sur les paliers Gi fonction de Pi et sur G0. On constate que l'allure des deux courbes est très différente et que la loi d'Arrhenius est seulement vérifiée par la courbe G0= f(T) . G0 apparaît alors comme la valeur représentative de l'équilibre entre le solide et le gaz.