Combustion Synthesis of Ceramic Composites from Lunar Soil Simulant

Introduction: The extended human presence on the Moon will enable astronauts to develop new technologies and harness the Moon's abundant resources to allow manned exploration of more challenging environments [1]. Various approaches to establish permanent outposts on the Moon are being considered by major space agencies and construction companies from USA, Europe, Russia and China. Construction materials for such applications must be dense and strong, should be produced mostly from indigenous sources and able to protect crew members and equipment from the effects of radiation, meteoroid bombardment, and temperature extremes. Proposed materials for planetary outpost construction include concrete (cement or sulfurbased), sintered regolith, cast basalt ceramics, ice and Fe or Ti metals [2]. Construction of even simple infrastructures on planetary surfaces can greatly help to optimize operations and research activities, as well as the development of new missions through in-situ resource utilization. Lunar regolith is an easily accessible resource that consists mainly of silicon dioxide (47.3 wt %), aluminum oxide (17.8 wt %), iron oxide (10.5 wt %), calcium oxide (11.4 wt %), magnesium oxide (9.6 wt %) and others [3]. The lunar soil is very fine sand with particle size of ~100 μm [4]. The proposed method for synthesizing of lunar construction materials is calcination of a compacted lunar soil in a microwave furnace at temperature of up to 1500 °C for periods of about 2 h [5, 6]. An attractive advantage of this approach compared to others is the ability to utilize lunar soil to produce large, strong, crack-free sintered bricks. However, this process requires high energy consumption and use of complicated high-temperature equipments. In addition, long time calcination of lunar soil generates large particle agglomerates and hence reduces the degree of microstructural homogeneity lowering material mechanical properties. The process we propose overcomes some of the major disadvantages of that process. Novel approach: In this work, we are demonstrating the novel process for rapid production of dense ceramic composites from lunar soil simulant by using Self-propagating High-temperature Synthesis (SHS). SHS also referred to as combustion synthesis provided controllable morphology of synthesized products and decreased both power consumption and cost of hightemperature equipment. SHS has been successfully applied to the synthesis of a large variety of refractory and advanced ceramics. [7, 8]. In SHS the reactants to products conversion is accompanied by a large heat release 10-10 W/m. Under such conditions, a hightemperature combustion wave propagates through the reactants mixture, without requiring any additional energy supply. High temperatures, up to 4000 K, are reached at the combustion front, which propagates at a velocity of up to 25 cm/s. SHS processes are characterized by very high temperature gradients (up to 10 K/cm), and short reaction time (order of seconds). As a result, chemical conversion takes place under nonequilibrium conditions which favor the formation of metastable phases and unusual microstructures not attainable with conventional calcination in furnaces. Moreover, the volatile impurities adsorbed on reactant powders are removed during the high-temperature reaction, allowing for the synthesis of high purity materials. Major advantages of this process are the very low power consumption and use of simple equipment. Experimental: Our propose process for production of dense ceramic composites from lunar soil simulant (JSC-1) consists the following chemical reactions: