Microstructural Analysis of Calcium-Aluminum-Rich Inclusions

摘要

Refractory materials are among the building blocks of our solar system and their chemistry and structure hold clues to understanding our origins. In this thesis I present a multifaceted approach toward understanding the histories of refractory materials within calcium-aluminum rich inclusions (CAIs) in primitive meteorites. I apply high-spatial resolution techniques including electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), and scanning transmission X-ray microscopy (STXM) enabled by focused ion beam scanning electron microscopy (FIB-SEM) to investigate CAI components and the Wark Lovering Rims that surround them to obtain information on microstructure and crystal chemistry in meteorites with varied pre-terrestrial histories. These inclusions possess three-dimensional grain islands, which exhibit crystallographic preferred orientations. The islands formed by high-temperature condensation in the solar nebula in a process driven by surface energy minimization, as shown by density functional theory (DFT) calculations. I also report preliminary results from laboratory experiments designed to synthesize perovskite under controlled temperature and oxygen fugacity (fO₂) conditions. The goal of this project was to develop a calibrated barometer based on changes in the oxidation state of Ti and apply the barometer to measurements of meteoritic samples in order to infer the thermodynamic conditions under which meteoritic perovskite formed in CAIs.