09:15 〜 09:30
[PPS04-07] An Examination of the Interactions Between Calcium Minerals and SO2 under A Simulated Venus Environment
キーワード：Venus, Geology, Experiments, Weathering, Minerals, SO2
Introduction: In situ probes and landers have been sent to explore Venus since the early 1960s [1], yet much of the surface environment remains a mystery. This includes both the surface chemistry, which was investigated by 7 landers for brief times, and the surface atmosphere, which is not well constrained [1-2]. For example, SO2 is thought to have an abundance between 130-180 ppmv [1,3-4], but this is based on limited data and more in situ measurements are required. Other laboratory experiments have identified SO2 is reactive with several elements, including Ca [5-7]. In this project we are exposing several Ca-bearing minerals to SO2 at simulated Venus conditions to ascertain the reaction rates. These minerals are from different mineral groups with different crystal structures and bonds, and we hope to understand the effects of crystal structure on kinetics of these reactions.
Methods: Venus simulation experiments are completed using a Thermogravimetric Analyzer (TGA). Four different Ca-bearing minerals [calcite (CaCO3), wollastonite (CaSiO3), anorthite (CaAl2Si2O8), and tremolite (Ca2Mg5Si8O22(OH)2] are hung in the TGA and exposed to Venus surface temperature (460°C) for 6-12 days in CO2/1.5% SO2. All experiments will also be completed at 700°C, to decrease the experiment time, and in 99.99% CO2, to use as a control.
The samples are being analyzed using several different methods. The surface chemistry of the samples is explored using X-ray Photoelectron Spectroscopy (XPS). The samples are milled using a Focused Ion Beam (FIB) to expose a cross section. The sample surface and cross section are then examined using a Scanning Electron Microscope (SEM) and Energy-Dispersive X-ray Spectroscopy (EDS) to observe the formation of secondary minerals and to determine any changes in chemistry. All samples were initially analyzed by X-Ray Diffraction (XRD) to confirm the mineralogy.
Results: At this time, calcite, tremolite, wollastonite, anorthite have all been tested in CO2/SO2 at 460°C for 6 days. Based on XPS results, calcite had 15.1 at% S at the surface in the form of a sulfate, which dropped to 10.6 at% after sputter removing 500Å of the surface. In addition, no carbonate peak was observed at the surface, indicating that sulfate had replaced the carbonate to form CaSO4. Anorthite had 5.9 at% S on the surface, which dropped to 0.2 at% after sputter removing 100Å. This indicates that S is only present at the surface and reactions between SO2 and anorthite are limited. This is likely due to the crystal structure, corroborated by other experiments with plagioclase under similar conditions which have found little to no reaction after exposure [5-6]. Tremolite was observed to be mottled after the experiment exhibiting patches of grey and white. The sample had sulfate on the surface, but more S was present on the grey regions than the white regions. The grey regions also contain higher abundances of Na and XRD indicates that it may be edenite (NaCa2Mg5Si7AlO22(OH)2). Future experiments for longer periods of time are planned to determine the reaction rates.
Acknowledgments: The PI was supported by an appointment to the NASA Postdoctoral Program at NASA GRC, administered by ORAU under contract with NASA. The authors would like to acknowledge Nathan S. Jacobson (NASA Glenn), John Setlock (Univ. of Toledo/NASA Glenn), and Peter Bonacuse (NASA Glenn) for their assistance in the lab.
References: [1] Johnson, N. M., and de Oliveira, M. R. R. (2019) Earth and Space Sci., 6,7 [2] Fegley, B., et al., (1997), Geochemistry of Surface-Atmosphere Interactions on Venus In: Venus II [3] Marcq, E. et al., (2017) Space Sci. Rev., 214, 10 [4] Fegley, B. (2014), Venus In: Treatise on Geochemistry 2nd Edition [5] Radoman-Shaw, B. et al., (2022) Meteorit. Planet. Sci., 57, 10, 1796-1819 [6] Santos, A. R. et al., (2023), JGR: Planets, Meteorit. Planet Sci., 57, 10 [7] Fegley, B. and Prinn, R. G. (1989) Nature, 337, 6202, 55-58
Methods: Venus simulation experiments are completed using a Thermogravimetric Analyzer (TGA). Four different Ca-bearing minerals [calcite (CaCO3), wollastonite (CaSiO3), anorthite (CaAl2Si2O8), and tremolite (Ca2Mg5Si8O22(OH)2] are hung in the TGA and exposed to Venus surface temperature (460°C) for 6-12 days in CO2/1.5% SO2. All experiments will also be completed at 700°C, to decrease the experiment time, and in 99.99% CO2, to use as a control.
The samples are being analyzed using several different methods. The surface chemistry of the samples is explored using X-ray Photoelectron Spectroscopy (XPS). The samples are milled using a Focused Ion Beam (FIB) to expose a cross section. The sample surface and cross section are then examined using a Scanning Electron Microscope (SEM) and Energy-Dispersive X-ray Spectroscopy (EDS) to observe the formation of secondary minerals and to determine any changes in chemistry. All samples were initially analyzed by X-Ray Diffraction (XRD) to confirm the mineralogy.
Results: At this time, calcite, tremolite, wollastonite, anorthite have all been tested in CO2/SO2 at 460°C for 6 days. Based on XPS results, calcite had 15.1 at% S at the surface in the form of a sulfate, which dropped to 10.6 at% after sputter removing 500Å of the surface. In addition, no carbonate peak was observed at the surface, indicating that sulfate had replaced the carbonate to form CaSO4. Anorthite had 5.9 at% S on the surface, which dropped to 0.2 at% after sputter removing 100Å. This indicates that S is only present at the surface and reactions between SO2 and anorthite are limited. This is likely due to the crystal structure, corroborated by other experiments with plagioclase under similar conditions which have found little to no reaction after exposure [5-6]. Tremolite was observed to be mottled after the experiment exhibiting patches of grey and white. The sample had sulfate on the surface, but more S was present on the grey regions than the white regions. The grey regions also contain higher abundances of Na and XRD indicates that it may be edenite (NaCa2Mg5Si7AlO22(OH)2). Future experiments for longer periods of time are planned to determine the reaction rates.
Acknowledgments: The PI was supported by an appointment to the NASA Postdoctoral Program at NASA GRC, administered by ORAU under contract with NASA. The authors would like to acknowledge Nathan S. Jacobson (NASA Glenn), John Setlock (Univ. of Toledo/NASA Glenn), and Peter Bonacuse (NASA Glenn) for their assistance in the lab.
References: [1] Johnson, N. M., and de Oliveira, M. R. R. (2019) Earth and Space Sci., 6,7 [2] Fegley, B., et al., (1997), Geochemistry of Surface-Atmosphere Interactions on Venus In: Venus II [3] Marcq, E. et al., (2017) Space Sci. Rev., 214, 10 [4] Fegley, B. (2014), Venus In: Treatise on Geochemistry 2nd Edition [5] Radoman-Shaw, B. et al., (2022) Meteorit. Planet. Sci., 57, 10, 1796-1819 [6] Santos, A. R. et al., (2023), JGR: Planets, Meteorit. Planet Sci., 57, 10 [7] Fegley, B. and Prinn, R. G. (1989) Nature, 337, 6202, 55-58