[en] A coating process, carried out at moderate temperature, is presented for application more especially to cladding tubes for nuclear fuel rods: a surface pre-oxidation of the substrate (which temperature is lower than 500 C) is achieved with an oxidizing gas excited by a cold plasma. The pre-oxidized substrate is then coated with a metallic oxide prepared through heterogenous oxidation of a metallic halide by an oxidizing component containing gaseous mixture, activated by a cold plasma. The cold plasma is, more preferably, microwave generated

[en] Precipitation in the diffusion zone of Fe-1.62wt.%Mn and Fe-0.56wt.%V alloys nitrided at 843 K was studied by TEM and XRD analyses. Recent thermodynamic data have been used to interpret the different results in both systems. In the manganese containing alloy, the thermodynamically stable θ-Mn₆N₅ phase precipitates in the diffusion zone. Around the maximum hardness, in a narrow zone between 10 and 150 μm below the γ'/α interface, needle shaped precipitates are also present oriented along three mutually orthogonal directions. This phase, designated θ', belongs to one of the three space groupsP4m2c2c,P4n2n2corP4n2b2m.X-ray diffraction depth profiles show that the presence of theses precipitates is closely related to the macrostress in the diffusion layer. In the case of the vanadium containing alloy, nitriding simultaneously produces VN precipitates and a tweed structure which annealing experiments reveal to be metastable. EPMA studies show that excess nitrogen is present in the Fe-V alloy. Sidebands are observed only on the (200)_α peaks and are attributed to the microstrain gradient at a given nitrogen concentration, due to the periodicity of the tweed structure. The tweed contrast is due to a tetragonal distortion of the matrix, and not to a spinodal microstructure

[en] Micro-gap discharges created in heptane between two platinum pin-electrodes produce platinum particles embedded in an amorphous carbon matrix which exhibits a short-range order. The platinum particles can be sorted by size. The largest ones (>100 nm in diameter) are created by emission of droplets from the liquid pool formed when the discharge hits the electrode surface. They are submitted to high stress levels by fast thermal quenching. The smallest ones (<5 nm) are synthesized in the plasma. Nanoparticles with diameters ranging from 10 to 20 nm have structure defects and are synthesized in post-discharge where huge temperature gradients exist. The short-range order observed in carbon extends typically over 3 nm, and it is observed by high-resolution transmission electron microscopy. This ordered structure of carbon (and a fortiori sp³ bonds which are identified by FTIR analyses) is clearly visible around the smallest nanoparticles and it is likely formed at the same location, i.e. in the plasma. - Highlights: • We synthesized platinum nanoparticles in a carbon matrix by discharges in heptane. • Three size distributions of platinum nanoparticles are found. • Each distribution is associated to a specific growth mechanism. • The carbon matrix exhibit a short-range order

[en] Zr-B-O type coatings were obtained from magnetron cathode sputtering of ZrB₂ fritted targets in Ar-O₂ reactive plasmas. A low oxygen enrichment (<15 % at. O) of these coatings by bore substitution increases their amorphousness and greatly reduces the compressive internal stresses and microhardness of the films. The hardness stay higher than 10000 MPa as far as the coating has its metallic aspect. This effect is accompanied with a significant increase of the coating physical quality. For higher oxygen contents, these coatings are transparent amorphous oxides. (J.S.). 7 refs., 1 fig., 1 tab

[en] A collisional-radiative model is proposed to describe the behaviour of a helium plasma sustained in a resonant cavity at atmospheric pressure. A set of rate constants is proposed at 2450 K. Indeed, most of the available data in the literature are reliable below 500 K. It is shown that the time post-discharge is mainly controlled by ambipolar diffusion during the first ten μs, next by electron-assisted recombination of helium ions and finally by chemionization from the excited state. This post-discharge lasts for hundreds of μs. It is mainly due to the slow recombination of electrons together with chemionization. Then, at steady state in CW mode, the electron temperature is found to be lower than 1 eV since low reduced fields are needed to sustain the discharge

[en] Filamentation in an argon plasma is studied using a microwave cavity at atmospheric pressure. We show that the size and gas temperature of the filaments increase with the power absorbed by the plasma. The appearance of an additional filament occurs at specific values of the absorbed power. Each new filament appears with a smaller diameter than that of its parent filament but the sum of the diameters of all filaments evolves linearly with the absorbed power. A secondary filament emerges from a set of microfilaments created by a perturbation of the electric field (a slight increase in the incident power above a threshold value). This perturbation occurs over a larger radius than that of the parent filament. By resorting to modeling, we found that the filamentation process involves either a decrease in the effective frequency for momentum-transfer collisions, i.e., a lower electron temperature, or an increase in the electron density. We could show that a small change in the relative positions occupied by two filaments in the microwave cavity requires a strong variation in the electron temperature.

[en] Self-organization of SiO₂ nanodots is obtained by chemical vapor deposition out of hexamethyldisiloxane (HMDSO) and atmospheric pressure remote Ar-O₂ plasma operating at high temperature (1200-1600 K). The dewetting of the film being deposited when it is still thin enough (<500 nm) is found to be partly responsible for this self-organization. When the coating becomes thicker (∼1 μm), and for relatively high contents in HMDSO, SiO₂ walls forming hexagonal cells are obtained on a SiO₂ sublayer. For thicker coatings (>1 μm), droplet-shaped coatings with a Gaussian distribution in thickness over their width are deposited. The coatings are submitted to high compressive stress. When it is relaxed, 'nestlike structures' made of nanoribbons are synthesized.

[en] The new concept of surface texturing or surface patterning on austenitic stainless steel by plasma assisted diffusion treatment is presented in this paper. It allows the creation of uniform micro or nano relief with regularly shaped asperities or depressions. Plasma assisted diffusion treatments are based on the diffusion of nitrogen and/or carbon in a metallic material at moderate to elevated temperatures. Below 420 deg. C, a plasma assisted nitriding treatment of austenitic stainless steel produces a phase usually called expanded austenite. Expanded austenite is a metastable nitrogen supersaturated solid solution with a disordered fcc structure and a distorted lattice. The nitrided layer with the expanded austenite is highly enriched in nitrogen (from 10 to 35 at%) and submitted to high compressive residual stresses. From mechanical consideration, it is shown that the only possible deformation occurs in the direction perpendicular to the surface. Such an expansion of the layer from the initial surface of the substrate to the gas phase is used here for surface patterning of stainless steel parts. The surface patterning is performed by using masks (TEM grid) and multi-dipolar plasmas.

[en] Sonoluminescence (SL) spectroscopy is one of the very few ways to study the plasma formed in solutions submitted to ultrasound. Unfortunately, up to now only very limited emission bands were reported in SL spectra of aqueous solutions, moreover broad and badly resolved. It is shown here that by adding some N₂ and/or CO₂ in Ar, new molecular emissions (CN, N₂ and CO) can be observed and that for some of them rovibronic temperatures can be derived. The paramount importance of Stark broadening in these emissions is underlined, together with the need for data on Stark parameters for molecular emissions. (authors)

[en] Discharge–surface interaction in liquids includes many phenomena which are reviewed in this work. This is used to examine results in the area of nanoparticle synthesis and to propose a general sketch of formation mechanisms. (paper)