Synthesis by sol–gel route of oxyapatite powders for dense ceramics : applications as electrolytes for solid oxide fuel cells

Solid oxide fuel cells have considerable interest in recent years, because of their high efficiency and environmentally friendly nature. Such systems required oxygen-conducting electrolytes and now the most common electrolyte is yttria stabilized zirconia (YSZ). This compound exhibits high oxide ion conductivity at elevated temperatures (850–1000 °C). However, this high working temperature causes problems in terms of materials selection and lifetime. One solution is to develop new oxide ions conductors exhibiting high oxide ion conductivity at intermediary temperatures (700–800 °C). Recent work has identified Ln10−xSi6O26±z (Ln = rare earths) as a good fast oxide ion conductor. Undoped and doped Ln10−xB6O26±z (B = Si or Ge) oxides are currently prepared by solid-state methods. In that work, we propose a sol–gel process to synthesize powders of La9.33Si6O26 type-silicated apatites. The main advantage is to decrease the crystallization temperature in ,comparison to the conventional methods, allowing the synthesis of reactive powders with nanometric particles size. These oxides are synthesized using silicon alkoxide and lanthanum nitride as precursors. In the litterature, no study refers to the synthesis of mixed oxides with silicon alcoxides. However, there are several studies on sol–gel synthesis of glasses with this precursor. In this study, several processing parameters have been investigated (the hydrolysis ratio, the concentration of metallic precursors in the sol and the role of organic compounds) in order to synthesize pure phases after the decomposition of the sols. Pure powders of La9.33Si6O26 type-silicated apatites are obtained at 800 °C. These powders were used to prepare ceramics. Several processing parameters as morphology of powders (agglomeration, particle sizes) and, heating profiles have been studied on the densification. Dense ceramics (90–95%) have been prepared at temperatures around 1400 °C. The used of sol–gel powders allow the decrease of the sintering temperature of about 200 °C

New chemical route based on sol–gel process for the synthesis of oxyapatite La9.33Si6O26

New chemical route based on sol–gel process for the synthesis of oxyapatite La9.33Si6O2

Site-projected electronic structure of two-dimensional Ti 3 C 2 MXene: the role of the surface functionalization groups

International audienc

Synthesis by sol–gel route of oxyapatite powders for dense ceramics : applications as electrolytes for solid oxide fuel cells

International audienceSolid oxide fuel cells have considerable interest in recent years, because of their high efficiency and environmentally friendly nature. Such systems required oxygen-conducting electrolytes and now the most common electrolyte is yttria stabilized zirconia (YSZ). This compound exhibits high oxide ion conductivity at elevated temperatures (850–1000 °C). However, this high working temperature causes problems in terms of materials selection and lifetime. One solution is to develop new oxide ions conductors exhibiting high oxide ion conductivity at intermediary temperatures (700–800 °C). Recent work has identified Ln10−xSi6O26±z (Ln = rare earths) as a good fast oxide ion conductor. Undoped and doped Ln10−xB6O26±z (B = Si or Ge) oxides are currently prepared by solid-state methods. In that work, we propose a sol–gel process to synthesize powders of La9.33Si6O26 type-silicated apatites. The main advantage is to decrease the crystallization temperature in ,comparison to the conventional methods, allowing the synthesis of reactive powders with nanometric particles size. These oxides are synthesized using silicon alkoxide and lanthanum nitride as precursors. In the litterature, no study refers to the synthesis of mixed oxides with silicon alcoxides. However, there are several studies on sol–gel synthesis of glasses with this precursor. In this study, several processing parameters have been investigated (the hydrolysis ratio, the concentration of metallic precursors in the sol and the role of organic compounds) in order to synthesize pure phases after the decomposition of the sols. Pure powders of La9.33Si6O26 type-silicated apatites are obtained at 800 °C. These powders were used to prepare ceramics. Several processing parameters as morphology of powders (agglomeration, particle sizes) and, heating profiles have been studied on the densification. Dense ceramics (90–95%) have been prepared at temperatures around 1400 °C. The used of sol–gel powders allow the decrease of the sintering temperature of about 200 °C

Ion Implantation Enhanced Exfoliation Efficiency of V2AlC Single Crystals: Implications for Large V2CTz Nanosheet Production

International audienceMXenes are two-dimensional transition-metal carbides and nitrides with an attractive combination of physicochemical properties, gaining notable potential in many applications. Currently, MXene synthesis is mainly performed from powder precursors whose purity and grain size define the quality and flake size of 2D sheets, typically not exceeding 2–3 μm. In this work, we successfully synthesize macroscopic nanolayered V2CTz MXenes with lateral dimensions larger than 25 μm from a V2AlC single crystal by exploiting a new strategy based on ion implantation. Ne2+ ion implantation of the single-crystal precursor is applied to introduce defects in the crystal structure of V2AlC, which facilitates chemical etching and drastically reduces the etching time down to 8 h (∼10 times lower as compared to conventional synthesis from powder precursors). The quality and morphology of exfoliated macroscopic MXene multilayers have been comprehensively studied by performing detailed analyses based on different kinds of microscopies and spectroscopies. The obtained macroscopic flakes are ideal objects to study the intrinsic physical properties of V2CTz MXenes and explore their potential application, in particular, as membranes

Evaluation of command modes of an assistance robot for middle ear surgery

International audienceRobOtol is a micro-surgical tele operated system designed to assist middle ear surgery. A new prototype, with an improved controller system and mechanical enhancement is presented. Surgeons and engineers evaluated the robot by tasks specific to middle ear surgery with two command modes (position-velocity and position-position) and by questionnaires. There was no prevailing command mode. A human robot interface was developed to offer easy and fast intra operative adaptation of the command mode to surgeons' preferences and specific situations

Assessing the Surface Chemistry of 2D Transition Metal Carbides (MXenes): A Combined Experimental/Theoretical 13 C Solid State NMR Approach

International audienceThe surface functionalization of 2D transition metal carbides or nitrides, so-called MXenes, is one of the fundamental levers allowing to deeply modify their physicochemical properties. Beyond new approaches to control this pivotal parameter, the ability to unambiguously assess their surface chemistry is thus key to expand the application fields of this large class of 2D materials. Using a combination of experiments and state of the art density functional theory calculations, we show that the NMR signal of the carbon─the element common to all MXene carbides and corresponding MAX phase precursors─is extremely sensitive to the MXene functionalization, although carbon atoms are not directly bonded to the surface groups. The simulations include the orbital part to the NMR shielding and the contribution from the Knight shift, which is crucial to achieve good correlation with the experimental data, as demonstrated on a set of reference MXene precursors. Starting with the Ti3C2Tx MXene benchmark system, we confirm the high sensitivity of the 13C NMR shift to the exfoliation process. Developing a theoretical protocol to straightforwardly simulate different surface chemistries, we show that the 13C NMR shift variations can be quantitatively related to different surface compositions and number of surface chemistry variants induced by the different etching agents. In addition, we propose that the etching agent affects not only the nature of the surface groups but also their spatial distribution. The direct correlation between surface chemistry and 13C NMR shift is further confirmed on the V2CTx, Mo2CTx, and Nb2CTx MXenes

MXene-supported single-atom and nano catalysts for effective gas-phase hydrogenation reactions

International audienceTransition metal carbides are known as efficient catalysts or catalyst supports and two-dimensional carbides (MXenes) offer renewed possibilities to anchor metal atoms and promote catalytic performances. This paper first presents an in-depth study of the elaboration of Pt or Pd-loaded Ti3C2Tx MXenes and their unstacking for gas-phase catalysis investigations, along with step-by-step characterization by XRD, XPS, SEM and STEM. In particular, the influence of the MXene preparation method (HF vs. LiF-HCl etchants) on surface structure/composition and metal dispersion/oxidation state is disclosed. Second, the catalytic hydrogenation performances of these materials are reported, and reveal the interest of low-loaded Pt/MXene single-atom catalysts in terms of selectivity and resistance to sintering. They present an unusually high selectivity to 2-butene – without butane formation – in butadiene hydrogenation, a model reaction of applied interest for the petrochemical industry. Moreover, in CO2 reduction to CO (reverse water-gas shift reaction, relevant to greenhouse-gas valorization), these catalysts exhibit up to 99% selectivity and a superior Pt-molar activity with respect to oxide-supported references. This work may stimulate the elaboration and investigation of other MXene-based systems for thermal heterogeneous catalysis, which remains rarely addressed