Theoretical Study on Thermal Release of Helium-3 in Lunar Ilmenite

Abstract

The in-situ utilization of lunar helium-3 resource is crucial to manned lunar landings and lunar base construction. Ilmenite was selected as the representative mineral which preserves most of the helium-3 in lunar soil. The implantation of helium-3 ions into ilmenite was simulated to figure out the concentration profile of helium-3 trapped in lunar ilmenite. Based on the obtained concentration profile, the thermal release model for molecular dynamics was established to investigate the diffusion and release of helium-3 in ilmenite. The optimal heating temperature, the diffusion coefficient, and the release rate of helium-3 were analyzed. The heating time of helium-3 in lunar ilmenite under actual lunar conditions was also studied using similitude analysis. The results show that after the implantation of helium-3 into lunar ilmenite, it is mainly trapped in vacancies and interstitials of ilmenite crystal and the corresponding concentration profile follows a Gaussian distribution. As the heating temperature rises, the cumulative amounts of released helium-3 increase rapidly at first and then tend to stabilize. The optimal heating temperature of helium-3 is about 1000 K and the corresponding cumulative release amount is about 74%. The diffusion coefficient and activation energy of helium-3 increase with the temperature. When the energy of helium-3 is higher than the binding energy of the ilmenite lattice, the helium-3 is released rapidly on the microscale. Furthermore, when the heating temperature increases, the heating time for thermal release of helium-3 under actual lunar conditions decreases. For the optimal heating temperature of 1000 K, the thermal release time of helium-3 is about 1 s. The research could provide a theoretical basis for in-situ helium-3 resources utilization on the moon.

Moon-Based Ground Penetrating Radar Derivation of the Helium-3 Reservoir in the Regolith at the Chang'E-3 Landing Site

“…The physical process of binding helium-3 to the lunar regolith is the implantation of the solar wind. The average speed of the solar wind on the lunar surface is ∼468 km/s [35], and the average energy of helium ions is ∼4 keV in the solar wind [36]. Although the thickness of the helium-3 implanted by the solar wind is ∼1 mm in the lunar regolith [37], the diffusion process of the helium-3 actually implanted into the lunar regolith takes a long time to reach equilibrium [36].…”

“…The average speed of the solar wind on the lunar surface is ∼468 km/s [35], and the average energy of helium ions is ∼4 keV in the solar wind [36]. Although the thickness of the helium-3 implanted by the solar wind is ∼1 mm in the lunar regolith [37], the diffusion process of the helium-3 actually implanted into the lunar regolith takes a long time to reach equilibrium [36]. Therefore, 209 the concentration distribution of helium-3 in the lunar regolith 210 is deeper than that of the solar wind implantation.…”

“…In addition, ilmenite has stronger adsorption on the 217 helium-3 compared with other lunar minerals (e.g., the content 218 of helium-3 in ilmenite is 10 to 100 times than that of other 219 minerals [38], [11]). The crystal of ilmenite has a hexagonal 220 close-packed structure, and its lattice spacing is similar to the 221 size of helium-3 atoms, so it is easy to capture the helium-222 3 atoms [36]. The majority of TiO 2 in the lunar regolith is 223 hosted by ilmenite, and the content of TiO 2 can be used as 224 an indicator of the helium-3 retention capacity of the lunar 225 regolith [11].…”

Taking advantage of glass: capturing and retaining the helium gas on the moon

“…A schematic illustration for the process to capture and retain the helium gas in ilmenite is shown in figure 4. The ilmenite lattice is more suitable for helium atoms to implant compared to other lunar regolith particles [36,37]. The high-speed ions in the solar wind implant into the lattice and are trapped in the vacancies and interstitials (figure 4(a)).…”

Research on Three-Phase Saturation Distribution Based on Microfluidic Visualization Experiment: A Case Study of Ling Xin Mining Area

“…All the fluid properties were obtained from or according to the Ling Xin mining area, China. e threephase porous flow conducted in this work could be considered as an incompressible two-dimensional flow [45][46][47][48][49].…”