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Solubility of hydrogen in slags and its impact on ladle refining
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.ORCID iD: 0000-0003-0856-3417
2006 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

The aim of the present work was to clarify the mechanisms of hydrogen removal during vacuum degassing. The main reason for this was because the primary source of hydrogen pick-up in steel-making is the moisture in the furnace atmosphere and the raw material charged into the ladle furnace. Previous studies showed that the presence of hydroxyl ions in the ladle slag results in hydrogen transfer from the slag back into the steel bath. The main focus of this thesis was therefore to gain deeper knowledge of the ladle slag and its properties. For this purpose a number of slag compositions were examined in order to clarify whether these slags were single liquids at 1858 K. 14 out of 27 compositions in the Al2O3 CaO MgO SiO2 system was completely melted. These results were in disagreement with the existing phase diagrams.

Water solubility measurements were carried out by employing a thermo gravimetric technique. The temperature was found to have negligible effect on the water solubilities. The experimental results showed that the water capacity values varied between 1x103 and 2x103 in the majority of the composition range. However, for compositions close to CaO saturation the water capacity value could reach higher than 3x103. The experimental determined water capacity was further used to develop a water capacity model for the quaternary slag system Al2O3 CaO MgO SiO2. The model was constructed by considering the affects of the binary interactions between the cations in the slag on the capacity of capturing hydroxyl ions. The model calculations agreed well with the experimental results as well as with the literature data.

An attempt was made to develop a preliminary process model for dehydrogenation by using the results from CFD calculation. For this purpose industrial sampling was made during vacuum treatment. The hydrogen concentrations decreases fast in the initial stages of the degassing, but is slowed down in the final stage. The model calculations fit the initial stage of the dehydrogenation process well. In the final stage of the process the predicted values are somewhat lower than the plant data. The results from the model prediction showed that a dynamic process model could be satisfactorily constructed using the results from CFD calculation.

The present work aimed at determining how big impact hydroxyl ions in the slag have on the final hydrogen concentration in the liquid steel. It was found that the effect is of less importance regarding the final concentration of the metal after the degassing treatment.

Place, publisher, year, edition, pages
Stockholm: KTH , 2006. , x, 37 s. p.
Series
TRITA-ARK. Akademisk avhandling, ISSN 1402-7461
National Category
Other Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-4143ISBN: 91-7178-453-5 (print)OAI: oai:DiVA.org:kth-4143DiVA: diva2:10912
Presentation
2006-10-20, B2, Brinellvägen 23, Stockholm, 10:00
Opponent
Supervisors
Note

QC 20101110

Available from: 2006-10-10 Created: 2006-10-10 Last updated: 2015-08-25Bibliographically approved
List of papers
1. Characterization of melting of some slags in the Al2O3-CaO-MgO-SiO2 quaternary system
Open this publication in new window or tab >>Characterization of melting of some slags in the Al2O3-CaO-MgO-SiO2 quaternary system
2006 (English)In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 46, no 4, 614-616 p.Article in journal (Refereed) Published
Abstract [en]

A number of slag compositions in the Al2O 3-CaO-MgO-SiO2 quaternary system was investigated. The Al2O3, CaO, and SiO2 oxide powders were calcinated at 1073 K for 24 hours before being mixed in an agate mortar. The oxide mixtures were further pressed into small pellets and sealed in a glass bottle. A horizontal platinum furnace and platinum crucibles were used and each slag composition was investigated four times to confirm the reproductibility of the process. Efforts were made to carry out the experiments with identical quenching speed. The slags were quenched from 1793 K to examine the liquidity of the slag samples at lower temperatures. It was revealed that the quenched samples were multi-phase mixtures instead of melting at the experimental temperature under the influence of the phase diagrams.

Keyword
Calcination, Crucibles, Lime, Mixtures, Mortar, Ore pellets, Oxides, Platinum, Powders, Quenching
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-6248 (URN)10.2355/isijinternational.46.614 (DOI)000238231000022 ()2-s2.0-33745042993 (Scopus ID)
Note

QC 20101109

Available from: 2006-10-10 Created: 2006-10-10 Last updated: 2017-12-14Bibliographically approved
2. Water vapor solubility in ladle-refining slags
Open this publication in new window or tab >>Water vapor solubility in ladle-refining slags
2006 (English)In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 37, no 3, 389-393 p.Article in journal (Refereed) Published
Abstract [en]

A thermo-gravimetric technique was used to determine the hydrogen solubilities of some Al2O3-CaO-MgO-SiO2 quaternary slags. The focus of the work was to determine the water capacities in slags having lower SiO2 concentrations, which were relevant to industrial practices. The majority of the experiments were carried out in the temperature interval 1747 to 1827 K with water pressure of 157 mbar. The reliability of the experiments was confirmed using a quenching technique. The temperature was found to have a negligible effect on the water solubilities. The composition of the slag did not seem to significantly affect the water capacity. However, as the slag composition approached CaO saturation, a considerable increase of the solubility was noticed.

Keyword
Alumina, Lime, Silica, Solubility, Thermal effects, Thermogravimetric analysis
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-6249 (URN)10.1007/s11663-006-0023-x (DOI)000237948700007 ()2-s2.0-33845681523 (Scopus ID)
Note

QC 20101110

Available from: 2006-10-10 Created: 2006-10-10 Last updated: 2017-12-14Bibliographically approved
3. Water capacity model of Al2O3-CaO-MgO-SiO2 quaternary slag system
Open this publication in new window or tab >>Water capacity model of Al2O3-CaO-MgO-SiO2 quaternary slag system
2007 (English)In: Steel research, ISSN 0177-4832, Vol. 78, no 6, 460-464 p.Article in journal (Refereed) Published
Abstract [en]

The focus of the present work was to develop a water capacity model for the quaternary slag system Al2O3-CaO-MgO-SiO2. In the model, a silicate melt was considered to consist of two ion groupings, viz. cation grouping and oxygen ion. The water capacity of a melt is supposed to depend on the interactions between the cations in the presence of oxygen ions. These interactions were determined on the basis of the experimentally measured water solubility data. Only binary interactions were employed in the model. For the system CaO-SiO2, disagreement in the literature data was found. Since the interaction between Ca2+ and Si4+ would play an important role, experiments were carried out to determine the water capacities of some CaO-SiO2 slags. For this purpose a thermogravimetric method was employed. Iso-lines of water capacities at constant MgO contents were predicted by the model and compared with the experimental data from literature. The model calculations agreed well with the experimental results.

Keyword
Al2O 3-CaO-MgO-SiO2, Ladle slag, Model, Thermogravimetric method, Water capacity
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-6250 (URN)000248267600004 ()2-s2.0-34547250781 (Scopus ID)
Note

QC 20101110. Uppdaterad från In press till Published (20101110).

Available from: 2006-10-10 Created: 2006-10-10 Last updated: 2017-12-14Bibliographically approved
4. Process Model for Dehydrogenation during Vacuum Degassing
Open this publication in new window or tab >>Process Model for Dehydrogenation during Vacuum Degassing
(English)Manuscript (Other academic)
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-6251 (URN)
Note

QC 20101110

Available from: 2006-10-10 Created: 2006-10-10 Last updated: 2015-08-25Bibliographically approved

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