INTERFACIAL REACTIONS · Atomic-scale investigation of structure, diffusions, and kinetics of Al2O3/MgO reaction interfaces during spinel growth

Atomic-scale investigation of structure, diffusions, and kinetics of Al2O3/MgO reaction interfaces during spinel growth

Much of our understanding of the evolution of the earth and other planets comes from the analysis of minerals and rocks, which contain abundant information about the formation conditions in their structure and composition. A typical case of mineral formation is reaction rim growth in which a new phase forms at the interface between two types of minerals, which is also referred to as solid-state reactions. Such a solid-state reaction not only happens during natural mineral evolution, but can also be applied to synthesize functional materials such as oxides and alloys. During the growth of the interlayers, the arrangement of atoms at the interfaces between the reactant and the product phases plays a crucial role. Typically the interface behaves differently during the initial and late growth stages. Therefore in order to figure out the fundamental mechanism of the interlayer growth, it is essential to understand the atomic structures of the reaction interfaces and their development during growth. In this research, the spinel forming reaction, MgO+Al2O3=MgAl2O4 is used as an ideal model system for studying solid-state reactions, as it is feasible for laboratorial growth, and the structure of these oxides can represent many other common metal oxides in nature and in functional application. MgAl2O4 layers with different thicknesses have been synthesized and the structure representing different growth stages have been selected for the microscopic study using a state-of-the-art aberration-corrected scanning transmission electron microscope (STEM) with sub-Å resolution. The main objective of this project is to understand the motion of interfaces during the growth of an MgAl2O4 interlayer between MgO and Al2O3 reactants. This has been fully achieved at the end of the project period. Furthermore, we have extended our research to natural volcanic rocks featuring an Mg(Fe)Al2O4 spinel rim around corundum (Al2O3), and obtained some preliminary results which might lead to further research.

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