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Calculation of Oxygen and Sulfur Average Velocity on the Iron Surface: A Two-dimensional Gas Model Study
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.ORCID iD: 0000-0001-7788-6127
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
2010 (English)In: Steel Research International, ISSN 1611-3683, Vol. 81, no 11, 949-952 p.Article in journal (Refereed) Published
Abstract [en]

In the present work, a two-dimensional (2D) gas model is derived and used to simulate the average velocity of individual atoms of the surface active elements oxygen and sulfur on the Fe(100) surface. The average velocity of oxygen and sulfur atoms was found to be related to the vibration frequencies and minimal energy barrier. The calculated results are based on data from density functional calculations combined with thermodynamics and statistical physics. The calculated average velocity of oxygen on the Fe (100) is lower than that of sulphur. This is because of the stronger interaction between oxygen and the first iron layer. We conclude that our simple 2D gas model may be useful for simulating and understanding the complex interfacial phenomena in the steelmaking refining process from an atomic point of view.

Place, publisher, year, edition, pages
2010. Vol. 81, no 11, 949-952 p.
Keyword [en]
average velocity, Oxygen and sulfur, iron surface, 2D gas model
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-26337DOI: 10.1002/srin.201000110ISI: 000284863500004Scopus ID: 2-s2.0-84859567855OAI: oai:DiVA.org:kth-26337DiVA: diva2:371867
Note
QC 20101123Available from: 2010-11-23 Created: 2010-11-23 Last updated: 2010-12-23Bibliographically approved
In thesis
1. Theoretical and experimental studies of surface and interfacial phenomena involving steel surfaces
Open this publication in new window or tab >>Theoretical and experimental studies of surface and interfacial phenomena involving steel surfaces
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The present work was initiated to investigate the surface- and interfacial phenomena for iron and slag/iron systems. The aim was to understand the mechanism of the effect of surface active elements on surface and interfacial properties. In the present work, the adsorption of oxygen and sulfur on iron surface as well as adatom surface movements were studied based on the ab initio method. BCC iron melting phenomena and sulfur diffusion in molten iron were investigated by Monte Carlo simulations. The impact of oxygen potential on interfacial mass transfer was carried out by X-ray sessile drop method.

Firstly, the structural, electronic and magnetic properties as well as thermodynamic stability were studied by Density functional theory (DFT). The hollow site was found to be the most stable adsorption site both for oxygen and sulfur adsorbed on iron (100) surface, which is in agreement with the experiment. The relaxation geometries and difference charge density of the different adsorption systems were calculated to analyze the interaction and bonding properties between Fe and O/S. It can be found that the charge redistribution was related to the geometry relaxation. In addition, the sulfur coverage is considered from a quarter of one monolayer (1ML) to a full monolayer. It was found that the work function and its change Δφ increased with S coverage, in very good agreement with experiment. Due to a recent discussion regarding the influence of charge transfer on Δφ, it is shown in the present work that the increase in Δφ can be explained by the increasing surface dipole moment as a function of S coverage. S strongly interacts with the surface Fe layer and decreases the surface magnetic moment as the S coverage increases.

Secondly, a two dimensional (2D) gas model based on density functional calculations combined with thermodynamics and statistical physics, was proposed to simulate the movement of the surface active elements, viz. oxygen and sulfur atoms on the Fe(100) surface. The average velocity of oxygen and sulfur atoms was found 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.

A distance dependent atomistic Monte Carlo model was developed for studying the iron melting phenomenon as well as effect of sulfur on molten iron surface. The effect of boundary conditions on the melting process of an ensemble of bcc iron atoms has been investigated using a Lennard-Jones distance dependent pair potential. The stability of melting process was energetically and spatially analyzed under fixed wall and free surface conditions and the effects of short and long-range interactions were discussed. The role of boundary conditions was significantly reduced when long-range interactions were used in the simulation. This model was further developed for investigating the effect of sulfur on molten iron surface. A combination of fixed wall and free surface boundary condition was found to well-represent the molten bath configuration while considering the second nearest neighbor interactions. Calculations concerning the diffusion of sulfur on molten surface were carried out as a function of temperature and sulfur concentration. Our results show that sulfur atoms tended to diffuse away from the surface into the liquid bulk and the diffusion rate increased by increasing temperature.

Finally, impact of oxygen potential on sulfur mass transfer at slag/metal interface, was carried out by X-ray sessile drop method. The movement of sulfur at the slag/metal interface was monitored in dynamic mode at temperature 1873 K under non-equilibrium conditions. The experiments were carried out with pure iron and CaO-SiO2-Al2O3-FeO slag (alumina saturated at the experimental temperature) contained in alumina crucibles with well-controlled partial pressures of oxygen and sulfur. As the partial pressure of oxygen increased, it was found that interfacial velocity as well as the oscillation amplitude increased. The thermo-physical and thermo-chemical properties of slag were also found to influence interfacial velocity.

 

Place, publisher, year, edition, pages
Stockholm: KTH, 2010. 56 p.
Keyword
Sulfur, Oxygen, Adsorption, Iron surface, ab initio calculations, Adsorption energy, Work function, Difference charge density, Magnetic properties, Thermodynamic stability, Average velocity, Monte Carlo simulation, X-ray sessile drop method, Mass transfer, Interfacial velocity
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-26194 (URN)978-91-7415-796-3 (ISBN)
Public defence
2010-12-08, Sal F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20101123Available from: 2010-11-23 Created: 2010-11-19 Last updated: 2010-11-23Bibliographically approved
2. Adsorption of surface active elements on the iron (100) surface: A study based on ab initio calculations
Open this publication in new window or tab >>Adsorption of surface active elements on the iron (100) surface: A study based on ab initio calculations
2009 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Stockholm: KTH, 2009. 40 p.
Keyword
sulfur, oxygen, surface adsorption, iron surface, ab initio calculations, adsorption energy, work function, difference charge density, thermodynamic stability, average velocity
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-11234 (URN)KTH/MSE--09/42--SE+THMETU/ART (ISRN)978-91-7415-438-2 (ISBN)
Presentation
Q21, Osquldasväg 6B, Kungliga Tekniska Högskolan (English)
Supervisors
Available from: 2009-10-09 Created: 2009-10-08 Last updated: 2010-12-23Bibliographically approved

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