An Organic-Inorganic Nanohybrid Based on Lunar Soil Simulant

One of the long term goals of sending human beings to the Moon and the Mars is to stay there, for which temporary outposts and permanent bases must be constructed. Due to the tight constraint of space transportation capacity, it is highly desirable that the outposts and bases can be built by using locally harvestable resources, such as lunar soils. For instance, it is, theoretically, possible that as lunar soils of different chemical compositions are appropriately mixed together, through complicated heating and curing procedures “lunar cements”, materials that can react with water or other liquid agents to form load-bearing components, can be obtained. However, to achieve this, massive and energy-consuming “cement plants” must be built on the Moon, before the “lunar cements” are available. Even if this could be done, the “lunar cements”, as any other ordinary cementitious materials, are of low flexure strengths. Their long-term reliability, especially in the vacuum or high/low-temperature environments, is also problematic. Moreover, the availability of water or reactive chemicals necessary for the cementing process is quite limited. In view of these issues, over the years a few alternative techniques such as direct sintering of lunar soils, water-free sulfur cements, applications of lunar/planetary lava, and in-situ fabrication of glass or metals/alloys [9,10] have been proposed. The main issues related to these techniques include the lack of systematic testing data, the relatively high energy consumption, the relatively poor material properties, and/or the limited availability of resources. Therefore, they are still far from being directly useful for space construction. Recently, in a study on high-flexure-strength infrastructural materials, Qiao et al. developed polymer intercalation/exfoliation (PIE) cements. In a PIE cement, the binder is not formed through hydration. Rather, a small amount of polymer interphase reinforced by exfoliated silicate nanolayers and intercalated silicate layer stacks is employed to hold the inorganic particles together, forming a multiscale organic-inorganic structure. Due to the barrier effect of the nanolayers, the permeability of the PIE cement is low, resulting in the superior air/water-proofness. The flexure strength can be more than 100 MPa, larger than that of many aluminum alloys. The thermal stability is also superior. It is envisioned that, if the PIE technique can be extended to lunar soils; that is, if lunar soil grains can be strongly bonded by the nanointerphase, space infrastructural materials of high strength, low permeability, and high survivability can be developed. To produce these materials at the lunar surface, only the organic nanointerphases need to be prepared on and transported from the Earth, and the inorganic components can be harvested locally. The processing procedure is water free and quite straightforward, having great potential in building large-scale structures on the Moon as well as other planets or planetary satellites.