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Theoretical and experimental studies of surface and interfacial phenomena involving steel surfaces
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
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 [en]
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: urn:nbn:se:kth:diva-26194ISBN: 978-91-7415-796-3 (print)OAI: oai:DiVA.org:kth-26194DiVA: diva2:371371
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
List of papers
1. Using and validation of the DFT method for oxygen adsorbed on the iron (100) surface
Open this publication in new window or tab >>Using and validation of the DFT method for oxygen adsorbed on the iron (100) surface
2010 (English)In: Transactions of the Institution of Mining and Metallurgy Section C - Mineral Processing and Extractive Metallurgy, ISSN 0371-9553, E-ISSN 1743-2855, Vol. 119, no 2, 67-70 p.Article in journal (Refereed) Published
Abstract [en]

Electronic and structural properties of atomic oxygen adsorbed on the iron (100) surface are examined using density functional theory calculations. 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 experiment. In addition, the difference charge density of the different adsorption system was calculated to analyse the interaction and bonding properties between Fe and O. It can be found out that the charge redistribution was related to the geometry relaxation. The calculated results are compared with the experimental and other theoretical results.

Keyword
IRON (100) SURFACE, DFT METHOD, OXYGEN ADSORPTION
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-26334 (URN)10.1179/037195510X12665949176373 (DOI)2-s2.0-77953785031 (Scopus ID)
Note

QC 20101123

Available from: 2010-11-23 Created: 2010-11-23 Last updated: 2017-12-12Bibliographically approved
2. Effect of electronic structure and magnetism on S adsorption on Fe (100) from first principles
Open this publication in new window or tab >>Effect of electronic structure and magnetism on S adsorption on Fe (100) from first principles
(English)In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215Article in journal (Other academic) Submitted
Identifiers
urn:nbn:se:kth:diva-26335 (URN)
Note
QC 20101123Available from: 2010-11-23 Created: 2010-11-23 Last updated: 2017-12-12Bibliographically approved
3. Calculation of Oxygen and Sulfur Average Velocity on the Iron Surface: A Two-dimensional Gas Model Study
Open this publication in new window or tab >>Calculation of Oxygen and Sulfur Average Velocity on the Iron Surface: A Two-dimensional Gas Model Study
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.

Keyword
average velocity, Oxygen and sulfur, iron surface, 2D gas model
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-26337 (URN)10.1002/srin.201000110 (DOI)000284863500004 ()2-s2.0-84859567855 (Scopus ID)
Note
QC 20101123Available from: 2010-11-23 Created: 2010-11-23 Last updated: 2010-12-23Bibliographically approved
4. An atomistic Monte Carlo investigation on the Solid-Liquid phasetransition in BCC iron: The role of boundary conditions
Open this publication in new window or tab >>An atomistic Monte Carlo investigation on the Solid-Liquid phasetransition in BCC iron: The role of boundary conditions
(English)In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801Article in journal (Other academic) Submitted
Identifiers
urn:nbn:se:kth:diva-26339 (URN)
Note
QS 20120328Available from: 2010-11-23 Created: 2010-11-23 Last updated: 2017-12-12Bibliographically approved
5. An atomistic Monte Carlo investigation on the influence of sulfur on molten iron surface at high temperature
Open this publication in new window or tab >>An atomistic Monte Carlo investigation on the influence of sulfur on molten iron surface at high temperature
(English)Article in journal (Other academic) Submitted
Identifiers
urn:nbn:se:kth:diva-26341 (URN)
Note
QC 20101123Available from: 2010-11-23 Created: 2010-11-23 Last updated: 2010-11-23Bibliographically approved
6. Sulfur Transfer at Slag/Metal Interface-Impact of Oxygen Potential
Open this publication in new window or tab >>Sulfur Transfer at Slag/Metal Interface-Impact of Oxygen Potential
2012 (English)In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 43, no 2, 363-369 p.Article in journal (Refereed) Published
Abstract [en]

In the present work, the interfacial movement resulting from sulfur mass transfer at the slag/metal interface was monitored by X-ray sessile drop method in dynamic mode at temperature 1873 K (1600 A degrees C) under nonequilibrium 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. The impact of oxygen potential on the droplet oscillation as sulfur from the gas phase reaches the metal drop through the intermediate slag phase was monitored. The interfacial velocity was investigated. It was found that the increases of interfacial velocity and the maximum oscillation time were mainly attributed to the partial pressure of oxygen increases. The experiment results were explained by previous ab initio calculations. The thermo-physical and thermo-chemical properties of slag were also found to influence interfacial velocity.

National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-26342 (URN)10.1007/s11663-011-9602-6 (DOI)000301778200015 ()2-s2.0-84861817169 (Scopus ID)
Funder
Swedish Research Council
Note
QC 20101123. Updated from submitted to published 20120424Available from: 2010-11-23 Created: 2010-11-23 Last updated: 2017-12-12Bibliographically approved

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