Alumina (Al2O3) and Oxidation of Aluminium. A First-Principles Study

Doktorsavhandling, 1999

Aluminum oxides and oxidation mechanisms are topics for extensive research. One good reason for this is their wide range of applications. For instance, the .alfa. phase of Al2O3 is used in electronics, the .gamma. phase in catalysts, and the .kappa. phase for cutting tools. Other reasons are the abundance of these elements in the human environment and the roles of O and Al as prototype elements. In this thesis, theoretical calculations based on the density-functional theory (DFT) are used to determine the atomic structure of bulk .kappa.-Al2O3, to study surface structural properties of .kappa.- and .alfa.-Al2O3, and the initial stages of the oxidation process of aluminum are investigated in order to improve our understanding of this process. Concerning the method, we show that the current level of development of theoretical methods has made it possible to perform calculations that are able to investigate even structurally complex materials quantum-mechanically from first principles. In the search for the atomic structure of the metastable .kappa.-Al2O3, total energies for a large number of different structure models consistent with the crystallographic specifications are calculated. The calculations point out one candidate as the .kappa.-Al2O3 structure, which is cgrowth process. Further, the .kappa.-Al2O3 surface structure and properties such as electronic structure and bonding character are investigated. Despite the importance and the widely spread studies of the reaction between the O2 molecule and the Al(111) surface, the initial stages of this process are still a matter of discussion. Extensive calculations with DFT on this system have been carried out. The somewhat unexpected results for the potential-energy surface of O2 on Al(111) reveal a very complex system and may shed light on the confusing experimental data available. Further, chemisorption and diffusion of single O atom on the Al surface have been studied. The calculations on O/Al(111) corroborate earlier results.