Understanding coronal heating and solar wind acceleration: Case for in situ near‐Sun measurements

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94903/1/rog1641.pd

Emissivity of Boron Nitride and Metals for the Solar Probe Plus Mission

International audienc

Production of metallic nanopowders (Mg, Al) by solar carbothermal reduction of their oxides at low pressure

The carbothermal reduction of MgO and Al2O3 in argon flow at low pressure allows to lower the onset temperature of metal vapor formation. Thermodynamic calculations indicate that metal formation begins at 1400 and 1700 K for a primary vacuum (1000 Pa), respectively, for Mg and Al. In the experimental section, concentrated solar energy was used for the process heating in order to favor energy savings. The products of the reaction between MgO or Al2O3 and 2 varieties of carbon (graphite, carbon black) in flowing argon atmosphere at a total pressure of around 1000 to 1600 Pa were studied using X-ray diffraction, and microstructure observations revealed the formation of metallic nanopowders with some by-products. Metallic conversions close to 45 wt% and 52 wt%, respectively, for Mg and Al, were obtained. The low conversion yield of the carbothermal reduction of MgO can be attributed to a backward reaction reforming MgO powder and to a sintering process between oxide particles at high temperature. Aluminum production challenge is to avoid formation of undesired by-products: Al2O, Al4C3 and Al-oxycarbides. Advantages and weaknesses of the used process are described and some improvements are proposed to increase metallic yields

Study of carbon erosion under ion bombardment at high temperature: Application to the thermal protection system of Solar Probe+

International audienc

Experimental carbothermal reduction of MgO at low pressure using concentrated solar energy

International audienc

Experimental carbothermal reduction of MgO at low pressure using concentrated solar energy

The improved solar reactor Sol@rmet allows to investigate the reduction of MgO in presence of carbon using concentrated solar energy in low vacuum conditions close to 900 Pa. The influence of the carbon type was studied and it was shown that a carbon issued from a biomass source was a great candidate. A gradual increase of the temperature during experiment allowed to obtain promising results. Powders with a high Mg content up to 97 m% and a high yield rate up to 50% were collected. Short time experiments at fixed locations under the focus of the solar concentrator were performed in order to obtain information on the kinetics of the carbothermal reduction of MgO. Notably, these experiments have underlined the temperature effect on the CO emission. 50 to 80% of the CO emission mainly occurred in 100 s after the beginning of the experiments. The phase boundary reaction between MgO and C appeared to be the dominant process at the initial stage of the carbothermal reduction. Calculated activation energy of this process is around 260 kJ mol-1

Total hemispherical emissivity of sintered SiC up to 1850 K in high vacuum and in air at different pressures

International audienceThe total (0.6–40 μm) hemispherical emissivity of sintered silicon carbide samples was measured in different conditions of pressure and temperature, from high vacuum to atmospheric pressure in air and up to 1850 K using a direct method.Emissivity data are correlated to the presence of different thicknesses of the silica layer and material characterization using scanning electron microscopy, ellipsometry and 3D profilometry was carried out to complete the interpretation of the emissivity evolution with temperature and pressure according also to surface roughness