Thermodynamic Analysis on Lunar Soil Reduced by Hydrogen
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NTRODUCTION
OXYGEN and water are the most essential necessities for humankind to explore on the surface of moon. Oxygen is used for life support and also as a propellant for aircrafts. Water, apart from supporting human life, is a good source of oxygen. Hence, economically producing water and oxygen from lunar soil and rock are the primary concerns for future lunar activities. Fortunately, an abundance of oxygen, approximately 42 pct by weight, exists in the lunar lithosphere in the form of metal oxides of iron, magnesium, titanium, aluminum, and silicon, which makes it possible to extract oxygen directly on the moon. So far, more than 20 different processes have attempted to liberate oxygen from lunar materials.[1] For instance, Seboldt et al.[2] described an extraction process of oxygen from lunar soil and rocks using fluorine gas as a strong reagent, Steurer[3] extracted oxygen by vapor phase pyrolysis, and Cutler and Krag[4] designed a carbothermal scheme for the production of oxygen from lunar soil. Based on previous research work, Taylor and Carrier[5] overviewed and evaluated in detail all processes for oxygen production on the moon, which included methods, reactions, and flow process charts. Among these processes, the reduction of oxides in lunar soil and rocks using hydrogen gas is one of the simplest and best methods.[6] The process employs two steps to extract oxygen from the lunar soil. First, oxides in lunar soil are reduced by hydrogen and form water. In comparison with other reducing agents, such as CO, CH4, and carbon, the reduction reaction with hydrogen YUHAO LU, formerly Graduate Student, University of Alabama, Tuscaloosa, AL 35487, is now Postdoctoral Research Fellow, Department of Mechanical Engineering, University of Texas, Austin, TX 78712. DIVAKAR MANTHA, Research Engineer, and RAMANA G. REDDY, ACIPCO Endowed Chair Professor, are with the Department of Metallurgical and Materials Engineering, University of Alabama. Contact e-mail: [email protected] Manuscript submitted February 7, 2010. Article published online July 30, 2010. METALLURGICAL AND MATERIALS TRANSACTIONS B
requires the smallest activation energy and is the most feasible process on moon.[7,8] Second, the water is electrolyzed into hydrogen and oxygen. Theoretically, hydrogen produced from water can be recycled, which shows a high conversion efficiency. McKay and colleagues[6,9–12] carried out a series of experiments reducing lunar soil with hydrogen. Their experiments showed that oxygen yield from the regolith can be predicted from the total iron content. Yoshida et al.[13] and Watanabe et al.[14] investigated the kinetics of water production from lunar soil simulant and concluded that for particles under 75 lm, the optimal conditions for water production from lunar soil were 1273 K (1000 °C) and 10 to 15 minutes. The metallic iron was observed in scanning electron microscope pictures and energy-dispersive spectrometer spectra of the samples after reduction of lunar soil by hydrogen.[7,13] The extraction of oxygen and metals is concur
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