The effect of pH and the process of direct or inverse synthesis of silicon-Substituted hydroxyapatite prepared by hydrolysis in aqueous medium

Nanosized hydroxyapatite with silicon substitution Ca10(PO4)6−x(SiO4)x(OH)2−xâ–¡x (0 ≤ x ≤ 2)  of same silicon concentrations, variation of pH and the method of inverse and direct synthesis were successfully prepared first time by the theoretical maximum  of incorporation of Si into the hexagonal apatite structure   by   precipitation method aqueous. The effects        of the Si substitution on crystallite size, particle size and morphology of the powders were investigated. The crystalline phase, microstructure, morphology and particle size of hydroxyapatite and silicon substituted hydroxyapatites were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), EDX coupled with SEM and transmission electron microscopy (TEM).The samples were successfully synthesized as a single-phase apatite, and crystallization of apatite was enhanced during heating. The results obtained in this study show that the kinetics between different direct and inverse process showed different reactivities, in the presence of varying pH. Compared with the two methods, the inverse method have higher kinetic in the formation of hydroxyapatite silicate because of the difference in lattice parameters. The grain size of Si-HA samples is clearly finer than that of pure HA sample and this decreases with increasing Si content. The growth of HA nanorods with temperature can be described by “oriented attachmentâ€. According to this theory the adjacent HA crystallites would coalesce in one particular direction on the (1 1 0) high energy planes, creating templates                        to form elongated rod-like structure.  Fourier Transform Infrared Spectroscopy analysis reveals,  the silicon incorporation to hydroxyapatite lattice occurs via substitution of silicate groups for phosphate groups. Substitution of phosphate group    by silicate in the apatite structure results in a increase in the lattice parameters in both a-axis and c-axis of the unit cell

Elaboration of Novel NanoparticulateTiO2-P25@n-TiO2 Composite for Photocatalysis

A new mechanically stable TiO2-P25@n-TiO2 nanocoating was prepared after grafting of size-selected titanium-oxo-alkoxy particles on P25-TiO2 nanoparticles surface and their immobilization on a glass substrate followed by a thermal treatment. The 5-nm oxo-TiO2 particles were prepared in a sol-gel reactor with rapid reagents micromixing. The photocatalyst with 65% TiO2-P25 loading shows the highest activity towards ethylene degradation in a continuous-flow fixed-bed reactor. This material has a higher activity compared to that prepared by a conventional sol-gel method with strongly polydispersed titanium-oxo-alkoxy nanoparticles and clusters. The reaction conditions were explicitly analyzed along the reactor as a function of the ethylene concentration in framework of a kinetic model, which shows interplay between zero and first order processe

Optimisation of a diamond nitrogen vacancy centre magnetometer for sensing of biological signals

Sensing of signals from biological processes, such as action potential propagation in nerves, are essential for clinical diagnosis and basic understanding of physiology. Sensing can be performed electrically by placing sensor probes near or inside a living specimen or dissected tissue using well established electrophysiology techniques. However, these electrical probe techniques have poor spatial resolution and cannot easily access tissue deep within a living subject, in particular within the brain. An alternative approach is to detect the magnetic field induced by the passage of the electrical signal, giving the equivalent readout without direct electrical contact. Such measurements are performed today using bulky and expensive superconducting sensors with poor spatial resolution. An alternative is to use nitrogen vacancy (NV) centres in diamond that promise biocompatibilty and high sensitivity without cryogenic cooling. In this work we present advances in biomagnetometry using NV centres, demonstrating magnetic field sensitivity of approximately 100 pT/$\sqrt{Hz}$ in the DC/low frequency range using a setup designed for biological measurements. Biocompatibility of the setup with a living sample (mouse brain slice) is studied and optimized, and we show work toward sensitivity improvements using a pulsed magnetometry scheme. In addition to the bulk magnetometry study, systematic artifacts in NV-ensemble widefield fluorescence imaging are investigated

Optimisation of a diamond nitrogen vacancy centre magnetometer for sensing of biological signals

Sensing of signals from biological processes, such as action potential propagation in nerves, are essential for clinical diagnosis and basic understanding of physiology. Sensing can be performed electrically by placing sensor probes near or inside a living specimen or dissected tissue using well established electrophysiology techniques. However, these electrical probe techniques have poor spatial resolution and cannot easily access tissue deep within a living subject, in particular within the brain. An alternative approach is to detect the magnetic field induced by the passage of the electrical signal, giving the equivalent readout without direct electrical contact. Such measurements are performed today using bulky and expensive superconducting sensors with poor spatial resolution. An alternative is to use nitrogen vacancy (NV) centres in diamond that promise biocompatibilty and high sensitivity without cryogenic cooling. In this work we present advances in biomagnetometry using NV centres, demonstrating magnetic field sensitivity of approximately 100 pT/$\sqrt{Hz}$ in the DC/low frequency range using a setup designed for biological measurements. Biocompatibility of the setup with a living sample (mouse brain slice) is studied and optimized, and we show work toward sensitivity improvements using a pulsed magnetometry scheme. In addition to the bulk magnetometry study, systematic artifacts in NV-ensemble widefield fluorescence imaging are investigated

Optimization of a Diamond Nitrogen Vacancy Centre Magnetometer for Sensing of Biological Signals

Sensing of signals from biological processes, such as action potential propagation in nerves, are essential for clinical diagnosis and basic understanding of physiology. Sensing can be performed electrically by placing sensor probes near or inside a living specimen or dissected tissue using well-established electrophysiology techniques. However, these electrical probe techniques have poor spatial resolution and cannot easily access tissue deep within a living subject, in particular within the brain. An alternative approach is to detect the magnetic field induced by the passage of the electrical signal, giving the equivalent readout without direct electrical contact. Such measurements are performed today using bulky and expensive superconducting sensors with poor spatial resolution. An alternative is to use nitrogen vacancy (NV) centers in diamond that promise biocompatibilty and high sensitivity without cryogenic cooling. In this work we present advances in biomagnetometry using NV centers, demonstrating magnetic field sensitivity of ∼100 pT/√Hz in the DC/low frequency range using a setup designed for biological measurements. Biocompatibility of the setup with a living sample (mouse brain slice) is studied and optimized, and we show work toward sensitivity improvements using a pulsed magnetometry scheme. In addition to the bulk magnetometry study, systematic artifacts in NV-ensemble widefield fluorescence imaging are investigated

Stratégies pour la croissance de cristaux de diamant par CVD assisté par plasma micro-onde

L objectif de ce travail était d optimiser un procédé de croissance CVD de films de diamant monocristallin et de développer des outils permettant d établir des stratégies de croissance. Dans un premier temps, l observation de faces {113} à l état stationnaire sur nos cristaux de diamant, nous a incité à développer un modèle de croissance géométrique 3D dont les paramètres d entrée sont les vitesses de déplacement des plans {111}, {110} et {113} normalisées par rapport à celles du plan {100} (respectivement a, b et g). La validation de ce modèle par la détermination expérimentale des vitesses de croissance dans les différentes directions cristallographiques {100}, {111}, {110} et {113} en fonction des conditions de croissance a été démontrée. Un outil était alors disponible pour élaborer des stratégies de croissance en vue d obtenir une morphologie particulière ou d augmenter la surface des plateaux des cristaux en croissance. Le substrat de diamant utilisé jouant un rôle primordial sur la qualité de la croissance, une étude de son prétraitement et de sa provenance a été menée. Ainsi, il a été montré que pour l obtention de films épais de diamant CVD, même lorsqu une forte densité de puissance est utilisée, il est indispensable de faire subir préalablement au substrat un plasma d attaque en milieu H2/O2. Il a également été démontré que les substrats synthétiques HPHT Ib sont, bien que contenant une forte teneur en azote, très bien adaptés pour réaliser des films épais car ils présentent relativement peu de dislocations et des caractéristiques de polissage meilleures que les substrats CVD disponibles à l heure actuelle. Enfin, des solutions sont proposées pour limiter le coût de production de ce matériau qui est élevé. L une d elles consiste à utiliser une décharge pulsée permettant d augmenter les vitesses de dépôt de près de 25% tout en réduisant la puissance micro-onde moyenne injectée de 15%, et en conservant une qualité de matériau équivalente. La deuxième solution consiste à introduire de l azote en phase gazeuse, composant bien connu pour augmenter fortement les vitesses de croissance. Cette étude a mis en évidence que, à haute densité de puissance, un fort couplage entre la température de dépôt et la teneur en azote existe. En particulier, lorsque la concentration d azote est augmentée, le mode de croissance évolue d un mode de croissance par écoulement de marches vers un mode de croissance par germination bi-dimensionnelle.This study aims to optimize a CVD growth process for mono-crystalline diamond films and to develop tools suitable for the development of growth strategies. In a first stage, the observation of stabile {113} faces on our diamond crystals has motivated us to develop a 3D geometric growth model whose input parameters are the displacement speeds of {111}, {110} and {113} respectively, which are normalized to those of one the {100}faces ( denoted a, b and g respectively). The validation of the proposed model was demonstrated through the experimental measurement of the growth speeds of {100}, {111}, {110} and {113} crystallographic orientations respectively, which depend on the growth conditions. However, with this tool a particular growth strategy can be developed, in order to obtain a specific morphology, or to increase particular surface planes of the growing crystals. As the diamond substrate used played an important role in the growth quality, a study concerning its pre-treatment and origin was carried out. It has been demonstrated that in order to obtain thick CVD diamond films, using high microwave power density, it is essential that the substrate be etched by a H2/O2 plasma. Furthermore, it has been proven that synthetic HPHT Ib substrates, despite having a high concentration of nitrogen, are well-suited to obtaining thick films as they have relatively few dislocations, including theirpolishing characteristics which are better than the currently available CVD substrates. Finally, solutions are proposed to limit the production cost of this material which is quite high. The first refers to using a pulsed-discharge which allows an increased deposition speed by almost 25%, reducing at the same time the average injected microwave power by 15%, as well as preserving a material quality equivalent to that obtained before. The second solution refers to introducing nitrogen in the gas phase, a well-known component for its capacity to considerably increase the growth speed. Moreover, the highlight of this study is that, at a high power density, there is a strong link between the deposition temperature and the nitrogen concentration; when the nitrogen concentration is increased, the growth mode evolves from a step-flow to a bi-dimensional mode.PARIS13-BU Sciences (930792102) / SudocSudocFranceF

Vickers microhardness and indentation fracture toughness of tantalum sesquinitride, η-Ta2N3

International audienc

Analyse expérimentale de l'endommagement d'un composite à matrice ferritique Fe-TiB2 en chargement complexe

Les composites à matrice métallique présentent un intérêt considérable pour l’allègement des structures si l’amélioration de leur module spécifique s’accompagne d’un bon rapport résistance/ductilité. Le développement récent et prometteur de composites à matrice en acier ferritique renforcée par des particules céramiques fragiles nécessite l’analyse des mécanismes d’endommagement lors de différents chemins de chargements jusqu’à de grandes déformations plastiques pour une bonne compréhension de leur comportement mécanique afin d’optimiser leurs propriétés d’usage. La présente étude, soutenue par le projet ANR-09-MAPR-0001-05, porte sur l’analyse expérimentale de mécanismes d’endommagement statistiquement représentatifs de nouveaux composites à matrice ferritique renforcés par des particules TiB2 , lors d’essais de cisaillement simple monotone et inversé, et lors d’essais in-situ de flexion sous microscope électronique à balayage (MEB). Les évolutions microstructurales sont analysées par MEB et par diffraction des électrons rétrodiffusés (EBSD). L’analyse quantitative de l’endommagement est réalisée à l’aide d’outils numériques de traitement d’images développés sous Matlab©. A l’état initial, les textures morphologique et cristallographique des particules sont très marquées, avec une distribution hétérogène caractérisée par deux populations distinctes. Après quelques pourcents de déformation plastique, des marques d’endommagement sont visibles dans les particules, et augmente avec la déformation cumulée. L’endommagement se manifeste d’abord dans les grosses particules, et correspond essentiellement à des ruptures en mode d’ouverture de particules mono ou polycristallines. L’effet de taille de grain de la matrice et du type de chargement sur l’endommagement de ces composites est discuté, ainsi que la comparaison de leur rhéologie globale avec celle du matériau de base