Synthesis and characterizations of defect-rich Martian regolith constituents

Abstract

Martian regolith draws intensive research attention for the future human settlement on Mars. Its defect-rich and highly concentrated amorphous features were present due to long-lasting space weathering by the solar wind radiation and mechanical impact from extraterrestrial objects. Within the frame of in-situ resource utilization, fundamental knowledge of the structures of the phase constituents and their defect variants are of critical importance. In contrast to naturally occurring minerals, the usage of laboratory synthesized samples has an advantage of providing pure, single-phase materials. This doctoral thesis focuses on the synthesis and characterization of olivines and plagioclase feldspars as representative major phases in Martian regolith. In addition, the impact of mechanical weathering using high-energy ball mill on selective synthesized phases are investigated here. Mechanochemical synthesis of the complete (Mg1-xFex)2SiO4 olivine solid solution was carried out (Chapter 3) to cover the wide range of olivine composition on Mars. Olivines with higher Fe content (x = 0.5 - 1) are likely to form larger crystallites (> 150 nm). Regression equations are demonstrated based on the X-ray reflection intensity and characteristic Raman modes for easy calculation of Mg/Fe-concentration in Martian olivines. Chapter 4 focuses on the structural differences between defect-rich and defect-poor forsterite (Mg2SiO4) endmember. DFT-PDF refinements indicate that post-processed forsterite contains Mg Frenkel-type and Mg2+ interstitial defects with concentrations of 23(3) and 10(3) wt.-%, respectively. A series of (Ca1-xNax)(Al2-xSi2+x)O8 plagioclase feldspars are synthesized using conventional solid-state method with subsequent calcination schemes (Chapter 5). The bulk chemical compositions obtained from EDX spectroscopy has been served for Al/Si ratio in the sample. Implementing PDF-Rietveld refinements on Mo X-ray data indicates disorder structure.