In Situ Treatment of Thermal RF Plasma Processed Nanopowders to Control their Agglomeration and Dispersability

Titanium carbonitride nanoparticles have been produced in an inductively coupled thermal plasma and subsequently modified using a surfactant that has been deposited in situ on their surface in-flight. The surfactant was injected in the reactor while the nanoparticles are still dispersed in the gas phase, allowing the coating of primary particles instead of the corresponding agglomerates. In contrast to naked TiCN nanoparticles, the surfactant coated particles could be readily dispersed in water with a short ultrasonic treatment and built up no large agglomerates as proved by Photon Correlation Spectroscopy measurements. The investigated surfactants seem, however, to undergo a chemical modification and/or a thermal degradation at the surface of the TiCN nanoparticle

Controlled Synthesis of β-SiC Nanopowders with Variable Stoichiometry Using Inductively Coupled Plasma

In the growing field of nanomaterials, SiC nanoparticles arouse interest for numerous applications. The inductively coupled plasma (ICP) technique allows obtaining large amount of SiC nanopowders from cheap coarse SiC powders. In this paper, the effects on the SiC structure of the process pressure, the plasma gas composition, and the precursor nature are addressed. The powders were characterized by X-ray diffraction (XRD), Raman and fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM) and high resolution electron microscopy (HREM), chemical analyses, BET and photon correlation spectroscopy (PCS) measurements. Whatever the precursor (α- or β-SiC), the nanoparticles were crystallised in the cubic β-SiC phase, with average sizes in the 20-40nm range. Few residual grains of precursor were observed, and the decarburization due to the reductive Ar-H2 plasma lead to the appearance of Si nanograins. The stoichiometry of the final product was found to be controllable by the process pressure and the addition of methan

Silicon and Boron Containing Components by CVD and CVI for High Temperature Ceramic Composites

The potential large applications of ceramic composites require the preservation of their thermomechanical properties for long duration, in oxidative environments, under high temperature fatigue conditions and/or thermal cycling. This implies that the fibers and matrix properties, cracks deviation and load transfer at the fiber-matrix interface must be maintained. Different possibilities to progress in that way, that is to reduce the oxidation penetration in the parts or to improve the oxidation resistance at the fiber-matrix interface are examined. They include the use of protective external coatings, the development of new matrices or more oxidation resistant interphases. All components of the composite are examined successively. It appears that they are often composed of silicon and boron compounds, but more complex ternary or quaternary systems which include these two elements as compositional gradient materials or multilayered materials are developing. All these systems lead to some limitations of particular deposition or infiltration processes from the gas phase that are pointed out in view to some examples on the CVD and ICVI of ternary solids and multilayered materials, and on a comparison between CVD and ICVI processes for interphase elaboration. For each component of the composite, examples showing the improvement of the final properties are given. Finally we point out the domains where further research on deposition from the gas phase are needed

Improved plasma synthesis of Si-nanopowders by quenching

International audienceSilicon nanopowders are investigated intensively for application in microelectronics and energy among them.[1–3] However, for the moment the control of the product high quality and the processing costs are limiting their breakthrough. RF-thermal plasmas could respond to both criteria as it is a continuous process achieving high production volume while ensuring a good synthesis control from the gaseous phase. The absence of electrodes for igniting the plasma and the controlled process atmosphere of RF-plasmas are beneficial for producing high purity materials. Typically a supersaturated gaseous phase containing the precursor is condensed rapidly after nucleation took place. The nanoparticles grow then subsequently by coagulation and coalescence.[4] This rapid condensation is achieved either by natural thermal gradients in the plasma or by quenching using a cold source (gas or cold surface) or by using an expansion.[5–8] This paper addresses the development of a specific quenching nozzle design combining rapid cooling with an expansion for controlling the size of silicon nanopowders processed by an inductively coupled plasma (ICP). The design of the quenching device has been supported by computational fluid dynamic (CFD) calculations aiming at modelling the plasma properties like among them the temperature and the velocity of the powderfree plasma. The modelling has been validated by in-situ plasma characterization using an enthalpy-probe coupled to a mass spectrometer. The produced nanopowders were collected either on a filter membrane, or directly in the gas phase using an on-line and in-situ sampling system made of a TEM-grid fixed on a moveable support and then ex-situ characterized by XRD, Raman, microscopy and surface specific area measurement using the BET technique

In Situ Treatment of Thermal RF Plasma Processed Nanopowders to Control their Agglomeration and Dispersability

International audienceTitanium carbonitride nanoparticles have been produced in an inductively coupled thermal plasma and subsequently modified using a surfactant that has been deposited in situ on their surface in-flight. The surfactant was injected in the reactor while the nanoparticles are still dispersed in the gas phase, allowing the coating of primary particles instead of the corresponding agglomerates. In contrast to naked TiCN nanoparticles, the surfactant coated particles could be readily dispersed in water with a short ultrasonic treatment and built up no large agglomerates as proved by Photon Correlation Spectroscopy measurements. The investigated surfactants seem, however, to undergo a chemical modification and/or a thermal degradation at the surface of the TiCN nanoparticles

Numerical and Experimental Characterization of the Seismic Parameters of a Soft Soil Reinforced with Rigid Inclusions

International audienceThe characterization of the properties of soft soils reinforced with periodically placed cylindrical rigid inclusions is essential to improve the lifetime of railway tracks submitted to the critical speed issue. This work is about the use of numerical and experimental resources to characterize the velocity of surface waves of these reinforced media. The numerical approach is presented, using the spectral elements method (SEM3D) coupled with non-periodic homogenization. The homogenized medium is used to modify a discontinuous media into a medium with smoother contrasts of properties. Into the context of numerical simulations, it allows to suppress the sharp discontinuities, and thus reduces the cost of the computation linked to the mesh refinement. A cross-validation is made with a reduced scale experimental model, performed with the high-quality measurement bench MUSC. Two different configurations are studied, the first one with three inclusions is used to cross-validate the use of the homogenization method with the experimental measurements and the second is made on more complex case containing a high number of inclusions on the same type of resins

Controlled Synthesis of b-SiC Nanopowders with Variable Stoichiometry Using Inductively Coupled Plasma

International audienceIn the growing field of nanomaterials, SiC nanoparticles arouse interest for numerous applications. The inductively coupled plasma (ICP) technique allows obtaining large amount of SiC nanopowders from cheap coarse SiC powders. In this paper, the effects on the SiC structure of the process pressure, the plasma gas composition, and the precursor nature are addressed. The powders were characterized by X-ray diffraction (XRD), Raman and fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM) and high resolution electron microscopy (HREM), chemical analyses, BET and photon correlation spectroscopy (PCS) measurements. Whatever the precursor (α- or β-SiC), the nanoparticles were crystallised in the cubic β-SiC phase, with average sizes in the 20-40 nm range. Few residual grains of precursor were observed, and the decarburization due to the reductive Ar-H2 plasma lead to the appearance of Si nanograins. The stoichiometry of the final product was found to be controllable by the process pressure and the addition of methane

Assessment of physical properties of a sea dike using multichannel analysis of surface waves and 3D forward modeling

International audienceSeismic surface waves analysis methods have been widely developed and tested in the context of subsurface characterization and have demonstrated their effectiveness for sounding and monitoring purposes. Given their efficiency, surface waves methods have been used in a variety of contexts, including civil engineering applications. However, at this particular scale, many structures exhibit 3D geometries which drastically limit the efficiency of these methods since they are mostly developed under the assumption of a semi-infinite 1D layered medium without topography. Taking advantages of wave propagation modeling algorithm development and high-performance computing center accessibility, it is now possible to consider the use of a 3D elastic forward modeling algorithm for the inversion of surface wave dispersion. We use a parallelized 3D elastic modeling code based on the spectral element method which allows to obtain accurate synthetic data with very low numerical dispersion and a reasonable numerical cost. In this study, we choose a sea dike as a case example. We first show that their longitudinal geometry and structure may have a significant effect on dispersion diagrams of Rayleigh waves. Then, we investigate the sensitivity of the dispersion diagrams to small velocity and layer thickness perturbations, and show the limitations of the standard 1D surface wave methods approach. Finally, we demonstrate in this context the benefits of using both a 3D forward modeling engine and the whole dispersion diagram, instead of the dispersion curves only

Shared-Autonomy Control for Intuitive Bimanual Tele-Manipulation

Existing dual-arm teleoperation systems function on one-to-one coupling of the human and robotic arms to fully exploit the user's dexterity during bimanual tele-manipulation. While the individual coordination of the robot end-effectors can be necessary for complex and asymmetric tasks, it may result in a cumbersome user experience during symmetric bimanual tasks (e.g. manipulating and carrying objects). In this paper we propose a novel framework that includes the one-to-one direct control and a new shared autonomy strategy. The user can autonomously choose between the two, and if the new one is selected the robots move in a coordinated way, in which desired positions are extrapolated from the movements and gestures of just one users arm. These gesture commands are interpreted and handled by the control, with the purpose of unloading the users cognitive burden. Lastly, the tele-impedance paradigm, i.e., the remote control of robot impedance and position references, is applied to both controls, to improve remote physical interaction performances. The paper reports on the overall proposed architecture, its implementation and its preliminary validation trough a multi subject experimental campaign