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Adsorption of surface active elements on the iron (100) surface :A study based on ab initio calculations

by Cao, Weimin

Abstract (Summary)
In the present work, the structural, electronic properties, thermodynamic stability and adatom surface movements of oxygen and sulfur adsorption on the Fe surface were studied based on the ab initio method.Firstly, the oxygen adsorbed on the iron (100) surface is investigated at the three adsorption sites top, bridge and hollow sites, respectively. Adsorption energy, work function and surface geometries were calculated, the hollow site was found to be the most stable adsorption site, Which is in agreement with the experiments. In addition, the difference charge density of the different adsorption systems was calculated to analyze the interaction and bonding properties between Fe and O. It can be found out that the charge redistribution was related to the geometry relaxation.Secondly, the sulfur coverage is considered from a quarter of one monolayer (1ML) to a full monolayer. Our calculated results indicate that the most likely site for S adsorption is the hollow site on Fe (100). We find that the work function and its change Df increased with S coverage, in very good agreement with experiments. Due to a recent discussion regarding the influence of charge transfer on Df, we show that the increase in Df can be explained by the increasing surface dipole moment as a function of S coverage. In addition, the Fe-S bonding was analyzed. Finally, the thermodynamic stabilities of the different structures were evaluated as a function the sulfur chemical potential.Finally, a two dimensional (2D) gas model was proposed to simulate the surface active elements, oxygen and sulfur atoms, movement on the Fe (100) surface. The average velocity of oxygen and sulfur atoms was found out to be related to the vibration frequencies and energy barrier in the final expression developed. The calculated results were based on the density function and thermodynamics & statistical physics theories. In addition, this 2D gas model can be used to simulate and give an atomic view of the complex interfacial phenomena in the steelmaking refining process.
Bibliographical Information:

Advisor:

School:Kungliga Tekniska högskolan

School Location:Sweden

Source Type:Master's Thesis

Keywords:TECHNOLOGY; Materials science; sulfur; oxygen; surface adsorption; iron surface; ab initio calculations; adsorption energy; work function; difference charge density; thermodynamic stability; average velocity

ISBN:

Date of Publication:01/01/2009

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