Synthesis of RuO 2 nanowires from Ru thin films by atmospheric pressure micro-post-discharge

International audienceOxidation by a micro-post-discharge at atmospheric pressure of thin films of ruthenium deposited on fused silica by pressure-modulated magnetron sputtering is studied. Single-crystalline RuO 2 nanowires are obtained for the first time with a diffusion process over large areas. Nanowires grow typically at temperatures below 550-600 K, provided the level of stress is high enough to fragment grains in sub-grains with sizes between 30 and 50 nm. Because of the alternation of dense and porous layers forming the coating, inward diffusion of vacancies leads to no patent Kirkendall's effect, pores being distributed over the whole coating thickness and not mainly at the interface with the substrate. The centre of the treatment being heated at temperatures higher than 900 K, gaseous RuO 4 is formed, leading to an evaporated area. At its edge, a ring of microcrystals is formed, likely by a CVD mechanism

Growth of ruthenium dioxide nanostructures by micro-afterglow oxidation at atmospheric pressure

International audienceVarious ruthenium dioxide nanostructures were grown locally by the oxidation of ruthenium samples with an Ar-O-2 microwave micro-afterglow operated at atmospheric pressure. A special attention was paid to the distribution of the surface temperature of the sample which evolves between 530 K and 820 K. Whatever the treatment time, the temperature and the gas composition set within the studied ranges, a general nanostructure, made of lamellae separated by 20-50 nm, is found. When the temperature rises, localized nano-sea urchins, nanotubes with square sections, nano-needles, and more complex structures are found spread over the surface. Treated surfaces were characterized by different surface diagnostics (SEM, XRD, SIMS, etc.) Finally, a growth mechanism is proposed emphasizing the role of emerging defects and stress on the appearance of localized nanostructures

Plasma chemical functionalisation of a Cameroonian kaolinite clay for a greater hydrophilicity

A Cameroonian kaolinite powder was treated with gliding arc plasma in order to increase the amount of hydroxyl functional groups present on its external surfaces. The functional changes that occurred were monitored by Fourier transform infrared spectroscopy. The crystalline changes were followed by the X-ray diffraction. The ionisation effect, acid effect, and water solubility of the treated samples were also evaluated. Results showed that there is breaking of the bonds in the Si–O–Si and Si–O–Al groups, followed by the formation of new aluminol (Al–OH) and silanol (Si–OH) groups at the external surface of kaolinite after exposing the clay to the gliding arc plasma. The increase in hydroxyl groups on the surface of kaolinite leads to the increase of its hydrophilicity. Moreover, new charges appear on its surfaces and no significant change in crystallinity has occurred. This study shows that clays in powder form being can effectively be functionalised by gliding arc plasma in spatial post discharge processing mode. Knowing that the treatment in spatial post discharge offers the possibility to process large amounts of clay, this work is of great interest to the industry

Gliding Arc Plasma Synthesis of MnO2 Nanorods for the Plasma-Catalytic Bleaching of Azoïc Amaranth Red Dye

Manganese (IV) oxide (MnO2) nanoparticles were synthesized, via a plasma-chemical route by using a gliding arc discharge at atmospheric pressure. α-MnO2 nanorods were obtained from the chemical reduction of KMnO4. The synthesis yield was 96.8% after 4.5 min of exposure of the solution to the plasma. Further increase of the exposure time induced a decrease of MnO2 yield because of its reductive transformation into Mn2+ ions. Particles were characterized by X-ray powder diffraction, scanning electron microscopy, Fourier Transform Infrared spectroscopy, and nitrogen physisorption. The plasma-catalytic properties of the synthesized material were tested in the bleaching of amaranth red (AR). AR bleaching efficiencies of 17 and 44% were respectively obtained when the plasma and plasma-catalyst processes were applied for 30 min with initial pH 10. The influence of the initial pH, and catalyst concentration were investigated: the AR bleaching efficiency increased linearly with the catalyst concentration and increased markedly when the pH of the solution decreased