Ti4+ to Ti3+ conversion of TiO2 uppermost layer by low-temperature vacuum annealing: interest for titanium biomedical applications.

Because of the Ti(3+) defects responsibility for dissociative adsorption of water onto TiO(2) surfaces and due to the hydroxyls influence on the biological behavior of titanium, controlling the Ti(3+) surface defects density by means of low-temperature vacuum annealing is proposed to improve the bone/implant interactions. Experiments have been carried out on Ti-6Al-4V alloys exhibiting a porous surface generated primarily by chemical treatment. XPS investigations have shown that low-temperature vacuum annealing can create a controlled number of Ti(3+) defects (up to 21% Ti(3+)/Ti(4+) at 573 K). High Ti(3+) defect concentration is linked to surface porosity. Such surfaces, exhibiting high hydrophilicity and microporosity, would confer to titanium biomaterials a great ability to interact with surrounding proteins and cells and hence would favor the bone anchorage of as-treated implants

Layered Li1+x(Ni0.425Mn0.425Co0.15)1–xO2 positive electrode materials for lithium-ion batteries

Layered Li1+x(Ni0..425Mn0..425Co0..15)1-xO2 materials (x = 0 and 0.12) were prepd. by copptn..

Investigation of the chromic phase transition of CuMo0.9W0.1O4 induced by surface protonation

CuMo0.9W0.1O4 oxide is known to exhibit two allotropic forms (α and γ forms) linked by a first-order phase transition that can be induced by pressure and/or temperature. In this work, we show that this α → γ phase transition (with a chromic effect from green to brown color) can also take place at 25 °C by a simple immersion of the powder in an aqueous solution with acidic pH. This chromic phase transition from the high-temperature/low pressure form into the low-temperature/high-pressure form is shown to be induced by surface protonation, whereas the copper-molybdate powder is dispersed in acidic solutions. Wettability measurements on both phases were performed in order to confirm the affinity of the α-form for protons in comparison with the γ-form. Then pH metric titration (addition step by step of an acid solution on the powder, controlling at each step the pH evolution) has allowed describing the kinetic aspects of the surface protonation (kinetic laws were approached and discussed). Finally, an interpretative model of the “halochromic” phenomenon based on the modification of the cations environment at the liquid−solid interface was proposed. For the first time, a superficial interaction between a solid oxide and a liquid medium, for which no partial dissolution−recrystallization sequence is occurring, is shown to be sufficient for producing a phase transition of the whole oxide bulk

Synthèse de revêtements Ti3SiC2 sur monolithes SiC à partir de sels fondus

International audienceCoatings with composition close to Ti3SiC2 were obtained on SiC substrates from Ti and Si powders with the molten NaCl method. In this work, the growth of coatings by reaction in the salt between monolithic SiC substrates and titanium powder is obtained between 1000 and 1200°C. At 1000°C, a coating of 8 µm thickness is formed in 10 hours whereas a thin coating of 0.5 µm has been grown in 2 hours. A lack in silicon was first found in the coatings prepared at 1100 and 1200°C. For these temperatures, the addition of silicon powder in the melt had a favorable effect on the final composition, which is found very close to the composition of Ti3SiC2. The reaction mechanism implies the formation of TiCx layers in direct contact with the SiC substrate and the presence of more or less important quantities of Ti3SiC2 and Ti5Si3Cx in the upper layers.Des revêtements de composition proche de Ti3SiC2 ont été obtenus sur des substrats SiC à partir de poudres Ti et Si par la méthode du NaCl fondu. Dans ce travail, la croissance de revêtements par réaction dans le sel entre des substrats monolithiques SiC et de la poudre de titane est obtenue entre 1000 et 1200°C. A 1000°C, un revêtement de 8 µm d'épaisseur est formé en 10 heures alors qu'un revêtement fin de 0,5 µm a été développé en 2 heures. Un manque de silicium a d'abord été trouvé dans les revêtements préparés à 1100 et 1200°C. Pour ces températures, l'ajout de poudre de silicium dans le bain a un effet favorable sur la composition finale qui se retrouve très proche de la composition de Ti3SiC2. Le mécanisme réactionnel implique la formation de couches de TiCx en contact direct avec le substrat SiC et la présence de quantités plus ou moins importantes de Ti3SiC2 et Ti5Si3Cx dans les couches supérieures

Structure And Nonlinear Optical Properties Of Sodium-Niobium Phosphate Glasses

The structural description of xNb2O5-(1 - x)(NaPO3) (0 ≤ x ≤ 0.40) glass network is reported through high-field (18.8 T) 17O and 93Nb nuclear magnetic resonance, O1s X-ray photoelectron spectroscopy and Raman spectroscopy. The different oxygen sites (POP, PONa, NbOP and NbONb) are resolved on the spectra, their relative proportion determined and compared to indirect calculations obtained from the decomposition of 31P NMR spectra. A good agreement is obtained, thus confirming the formation of the Nb(OP)6-y(ONb)y units with increasing y leading to the clusterization of NbO6 octahedra, mainly for x \u3e 0.2, which is related to the incomplete dissociation of Nb2O5 in the NaPO3 melt. The formation of these clusters is responsible for the large increase of the nonlinear optical properties, mainly due to the high polarizability of the Nb-O-Nb bond. © 2008 Elsevier B.V. All rights reserved

Low temperature Si doped ZnO thin films for transparent conducting oxides

Si doped zinc oxide (SZO, Si 3%) thin films are grown at low substrate temperature (T≤150 °C) under oxygen atmosphere, using pulsed laser deposition (PLD). Si addition leads to film amorphization and higher densification. Hall effect measurements indicate a resistivity of 7.9×10−4 Ω cm for SZO thin films deposited at 100 °C under optimized 1.0 Pa oxygen pressure. This value is in good agreement with optical resistivity simulated from the transmittance spectra. XPS measurements suggest more than one oxygen environment, and a Si oxidation state lying in between 2 and 3 only. As a matter of fact, the values of both measured and simulated carrier numbers are smaller than the ones expected, assuming that all Si cations in the ZnO matrix are at the 4+ oxidation state. Finally, the differences in the electrical and optical properties of SZO thin films deposited both on glass and PET substrates confirm the strong dependency of the electronic properties to the film crystallinity and stoichiometry in relationship with the substrate nature

Characteristics of the fluorocarbon surface film generated on carbon anode during F2 evolution in mollten KF-2HF

During the fluorine evolution reaction occurring in the electrolysis of molten KF-2HF, a thin, solid fluorocarbon layer is formed on the carbon anode. The high anodic overvoltage which characterized this process is mainly due to the presence of such a film which drastically changes the wettability of the electrode by the melt..

Switchable hydrophobic-hydrophilic layer obtained onto porous alumina by plasma-enhanced fluorination

Conventional lithographic printing processes using porous alumina for offset applications generally use “wet” routes. Recently “dry” processes have been developed which are based on a heat-induced hydrophilic/oleophilic conversion of one or more layers of the coating so that a stronger affinity to-wards ink or water fountain is created at the exposed areas with respect to the surface of the unex-posed coating. Treatments involving rf plasma-enhanced fluorination (PEF) constitute exceptional tools for modifying the surface properties of materials. Many advantages of these techniques can be indeed outlined, when compared to more conventional methods: room-temperature reactions, chemical modi-fications limited to surface only without changing the bulk properties, possible non-equilibrium reac-tions. The influence of PEF treatments on porous alumina layer used in printing plates has been tested with various fluorinated gases (CF4, C3F8 and C4F8) and characterized by XPS. The hydrophobic prop-erties of the fluorinated layer have been deduced from contact angle measurements. Using C4F8 rf-PEF treatment, the outmost surface of the hydrophilic alumina substrate used for lithographic printing is hydrophobized, or in other words, the hydrophilic substrate is converted into a support with hydro-phobic properties. Once being hydrophobized, the surface layer may be rendered hydrophilic using a heat pulse, thus giving rise to switchable hydrophobic-hydrophilic properties of the material

Study of the fluorination of carbon anode in molten KF-2HF by XPS and NMR investigations

During the electrolysis of molten KH-2HF, a solid CF film is formed on carbon anodes. The influence of the potential applied to the anode on the composition of the CF surface film was studied by XPS and NMR. Results obtained with carbon electrochemically passivated in molten KF-2HF have been compared with those obtained with carbon simply immersed in molten KF-2HF without any polarization. Whatever the potential, and even in the case of carbon sample immersed in molten KF-2HF without any polarization, the presence of covalent and semi-ionic C–F bonds has been pointed out both by XPS and NMR. For polarized samples, the higher the potential applied to the anode in KF-2HF, the higher the fluorination level. From investigations carried out with carbon activated at 40 V in molten KF-2HF, it was concluded that the electropolishing of the surface induced by this treatment allows enhancing drastically the fluorine evolution reaction

Study of the fluorination of carbon anode in molten KF-2HF by XPS and NMR investigations

During the electrolysis of molten KH-2HF, a solid CF film is formed on carbon anodes. The influence of the potential applied to the anode on the composition of the CF surface film was studied by XPS and NMR. Results obtained with carbon electrochemically passivated in molten KF-2HF have been compared with those obtained with carbon simply immersed in molten KF-2HF without any polarization. Whatever the potential, and even in the case of carbon sample immersed in molten KF-2HF without any polarization, the presence of covalent and semi-ionic C–F bonds has been pointed out both by XPS and NMR. For polarized samples, the higher the potential applied to the anode in KF-2HF, the higher the fluorination level. From investigations carried out with carbon activated at 40 V in molten KF-2HF, it was concluded that the electropolishing of the surface induced by this treatment allows enhancing drastically the fluorine evolution reaction