4:30 PM - 4:45 PM
[PPS02-05] Triboelectric Charging of Lunar Regolith Simulant
Introduction
Lunar regolith is known to become charged due to the influence of cosmic radiation and solar plasma, with surface potentials of approximately 5-10 V on the dayside and around -50 to -200 V on the nightside [1]. Additionally, it has been suggested that the regolith may also be charged at depths of up to approximately 1 meter [2]. In such an environment, where electric fields are present, charged floating particles are expected to be influenced by these fields. In addition to the well-known levitating regolith dust, it is also conceivable that fine ice crystals, if charged, would also be affected by the electric field.
The triboelectric series is widely recognized as an indicator of the triboelectric charging properties of materials. This series ranks materials based on their tendency to acquire positive or negative charge when rubbed against another material. In previous studies, triboelectric series have primarily been presented as qualitative indicators for terrestrial minerals (mostly silicates, including feldspar) and organic materials. Recently, triboelectric series with quantitative indicators have been reported for various materials [3]. However, there has been no report on the triboelectric series of anorthosite and other abundant lunar minerals. Therefore, this study aims to clarify the triboelectric series of the mineral species constituting lunar regolith and to quantitatively measure the effect of particle size on triboelectric charging by evaluating the charging characteristics of various mineral powders.
Experiment
For this study, we used six types of minerals and rocks, including Anorthosite, Basalt, Ilmenite, Bronzite, and Olivine - common components of lunar regolith simulants - along with Laterite . These samples were sieved into four different particle size ranges: ~500, 500~250, 250~125, and 125~45 µm. The samples were thoroughly dried before measurements. In our experiment, we adopted a method in which mineral powders were charged by contact with the inner wall of a tube (inner diameters: 4 mm and 10 mm) as they passed through it. The powder inside the tube was transported by suction using an air pump, and the tube itself was placed inside a custom-made pass-through Faraday cage (1 m in length) for measurement. The charge accumulated on the tube was measured, while the powder that passed through the tube was directed into another Faraday cage at the exit, allowing for simultaneous measurement of the polarized positive and negative charges. Four different materials - Teflon, chemistry glass, nylon, and polyvinyl chloride - were used as tube materials to evaluate the relative triboelectric charging behavior of the mineral powders against each material. Based on these measurements, we compared the charging characteristics of the mineral powders and determined their triboelectric series.
Conclusion
It was observed that as the powder passed through the tube, the powder and tube became polarized, separating into positive and negative charges [Figure 1]. Furthermore, changing the tube material resulted in variations in the amount of charge acquired, indicating differences in charging tendencies. Notably, triboelectric charging with the Teflon tube produced more than ten times the charge compared to the other tubes for all mineral species [Figure 2]. These results allowed us to clarify the relative positions of the six mineral powders in the triboelectric series by comparing their interactions with Teflon, chemistry glass, and nylon.
The experimental setup developed in this study enables the quantitative evaluation of the charging characteristics of regolith powders. The findings are crucial for understanding the charging behavior of lunar regolith, contributing to more accurate predictions of charging phenomena and the development of charge mitigation strategies for lunar exploration.
[1] Phillips et al.,(2022).ICES [2] Jordan et al., (2015) .JGR Planets
[3] Zou et al.,(2020). Nature Communications
Lunar regolith is known to become charged due to the influence of cosmic radiation and solar plasma, with surface potentials of approximately 5-10 V on the dayside and around -50 to -200 V on the nightside [1]. Additionally, it has been suggested that the regolith may also be charged at depths of up to approximately 1 meter [2]. In such an environment, where electric fields are present, charged floating particles are expected to be influenced by these fields. In addition to the well-known levitating regolith dust, it is also conceivable that fine ice crystals, if charged, would also be affected by the electric field.
The triboelectric series is widely recognized as an indicator of the triboelectric charging properties of materials. This series ranks materials based on their tendency to acquire positive or negative charge when rubbed against another material. In previous studies, triboelectric series have primarily been presented as qualitative indicators for terrestrial minerals (mostly silicates, including feldspar) and organic materials. Recently, triboelectric series with quantitative indicators have been reported for various materials [3]. However, there has been no report on the triboelectric series of anorthosite and other abundant lunar minerals. Therefore, this study aims to clarify the triboelectric series of the mineral species constituting lunar regolith and to quantitatively measure the effect of particle size on triboelectric charging by evaluating the charging characteristics of various mineral powders.
Experiment
For this study, we used six types of minerals and rocks, including Anorthosite, Basalt, Ilmenite, Bronzite, and Olivine - common components of lunar regolith simulants - along with Laterite . These samples were sieved into four different particle size ranges: ~500, 500~250, 250~125, and 125~45 µm. The samples were thoroughly dried before measurements. In our experiment, we adopted a method in which mineral powders were charged by contact with the inner wall of a tube (inner diameters: 4 mm and 10 mm) as they passed through it. The powder inside the tube was transported by suction using an air pump, and the tube itself was placed inside a custom-made pass-through Faraday cage (1 m in length) for measurement. The charge accumulated on the tube was measured, while the powder that passed through the tube was directed into another Faraday cage at the exit, allowing for simultaneous measurement of the polarized positive and negative charges. Four different materials - Teflon, chemistry glass, nylon, and polyvinyl chloride - were used as tube materials to evaluate the relative triboelectric charging behavior of the mineral powders against each material. Based on these measurements, we compared the charging characteristics of the mineral powders and determined their triboelectric series.
Conclusion
It was observed that as the powder passed through the tube, the powder and tube became polarized, separating into positive and negative charges [Figure 1]. Furthermore, changing the tube material resulted in variations in the amount of charge acquired, indicating differences in charging tendencies. Notably, triboelectric charging with the Teflon tube produced more than ten times the charge compared to the other tubes for all mineral species [Figure 2]. These results allowed us to clarify the relative positions of the six mineral powders in the triboelectric series by comparing their interactions with Teflon, chemistry glass, and nylon.
The experimental setup developed in this study enables the quantitative evaluation of the charging characteristics of regolith powders. The findings are crucial for understanding the charging behavior of lunar regolith, contributing to more accurate predictions of charging phenomena and the development of charge mitigation strategies for lunar exploration.
[1] Phillips et al.,(2022).ICES [2] Jordan et al., (2015) .JGR Planets
[3] Zou et al.,(2020). Nature Communications