Search

The carbothermal reduction of MgO and Al 2 O 3 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 Al 2 O 3 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: Al 2 O, Al 4 C 3 and Al-oxycarbides. Advantages and weaknesses of the used process are described and some improvements are proposed to increase metallic yields.

In situ resource utilization (ISRU) refers to the in situ generation of consumables for autonomous or human activities from raw materials found on the Moon or other planetary bodies. The use of ISRU on the Moon may provide a means of reducing the cost and risk of human exploration of the Moon and beyond, and an impetus for commercial contributions to lunar exploration. Potential products include O2 and H2O for life support, H2 and O2 for fuel and propellant, and other elements and compounds for metallurgic and chemical production processes. If ISRU is to be applied successfully on the Moon, it is important that landing site selection, surface operations and suitable ISRU technologies are identified using knowledge of the availability and distribution of lunar resources and detailed understanding of the workings of the various processes available. Here, we review current knowledge of chemical and mineralogical resources on the Moon which can be used in the development of ISRU as a realistic component of future lunar exploration.

The study of the oxidation of SiC under CO 2 at high temperature and low pressure is achieved by means of theoretical and experimental determinations of the transition zone between the passive oxidation with formation of a protective silica layer and the active oxidation with major vaporization of SiO and etching of the SiC material. The theoretical determination is done using both models: a computer model “Solgasmix”, applied for a closed system at equilibrium and the other, our analytical model, which takes into account the mass transfer at the solid/gas interface. The comparison is done for these two models and then with the experimental results. XPS analyses are performed on “passive” and “active” samples to confirm the position of the transition line. Moreover, SEM micrographs complete the diagnostics.

During the atmospheric entry phase, the physico-chemical phenomena taking place on space shuttle walls can lead to an important excess of heating and damage of the protective materials. The aim of this work is the study of the catalytic recombination of atomic oxygen under plasma conditions chosen to simulate the atmospheric reentry. To do that, we have developed an experimental set-up MESOX (Moyen d'Essai Solaire d'OXydation), which associates a solar radiation concentrator and a microwave generator to reach high temperature, low enthalpy flow and low pressure plasma with an air gas flow. The study of atomic oxygen recombination on silicon- or aluminum-based ceramic materials, at high temperature (1000–1800 K) has been done for different pressures (200–2000 Pa) by a thermal and a chemical understanding. The results give a catalycity scale of materials (thermal recombination flux, qrec, and coefficient of atomic oxygen recombination, γ). The catalycity activity is weak for the sintered SiC target with atomic oxygen recombination flux reaching 35 kW/m2, however, for a target of sintered Al2O3, catalytic effect is obtained with energy fluxes between 90 to 180 kW/m2. The recombination coefficient γ confirms the catalycity scale of these ceramic materials.

The study of the physico-chemical behaviour of ceramic materials for space applications requires the implementation of specific simulation means. So, we have developed a testing bench named MESOX (Moyen d'Essai Solaire d'OXydation) for simulating the atmospheric reentry conditions of space planes, which associates a solar radiation concentrator to a microwave plasma generator. The theoretical oxidation is studied by a thermodynamical calculation particularly for the determination of the transition zone. Oxidation experiments are done under molecular and dissociated air on sintered ceramics (SiC, Si 3 N 4 , AlN).

Study of the physicochemical behaviour of ceramic materials for space applications requires the implementation of specific simulations. We have developed a testing bench, called MESOX, to simulate the atmospheric re-entry conditions of space planes, which associates a solar radiation concentrator with a microwave plasma generator. Oxidation experiments were done under molecular and dissociated air on sintered ceramics (SiC). The results were compared, and we found differences between the two environments in the conditions for the formation of a passive oxide layer.

For a chemical heat pump based on reversible solid-gas reactions, two criteria are very important to reach good performances i.e. the energetic density and power, both linked to the reactive medium implementation. An experimental optimization is done on the solid-gas pair CaCl2/CH3NH2 adding a filling material (expanded graphite) which improves the heat and mass transfer. The results obtained under fixed conditions of temperature and pressure present a maximum in the curve power vs packing density of the solid beyond 25% (in mass) of binding material. The interpretation of the behaviour that the reactive mixing of the solid-gas reactor undergoes could be explained by the theory of percolation.

Resume L'utilisation de reactions solid—gaz a ete envisagee en vue de realiser un refrigerateur solaire. Le couple choisi est LiCl/methylamine car il s'avere bien adapte a la production de glace dans des conditions de climat chaud. Apres avoir determine les conditions optimales de mise en oeuvre du solide reactionnel, nous avons teste la faisabilite physico-chimique d'un tel systeme sur une maquette de laboratoire. La reproductibilite des reactions ainsi que les performances obtenues sont satisfaisantes. Une production de 1 kg de glace par kg de solide reactif et un COP de 0,067 ont ete atteints.

Resume Une etude prealable a montre la faisabilite physico-chimique du systeme LiCl/CH3NH2 dans l'objectif de production de glace, avec une utilisation possible de capteur plan a surface non-selective, la temperature haute minimale necessaire a la decomposition etant de 80°C pour une temperature de condensation de 35°C. Les resultats positifs obtenus sur la maquette de laboratoire nous ont conduits a la conception et a la realisation d'un prototype de refrigerateur solaire destine a la conservation des vaccins. Les performances obtenues sur ce prototype sont actuellement une production quotidienne de 4,5 kg de glace soit 2,5 kg par m2 de capteur et un COP solaire de 0,053.