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Effect of Low Oxygen Partial Pressure on the Chromium Partition in CaO-MgO-SiO2-Cr2O3-Al2O3 Synthetic Slag at Elevated Temperatures
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, Materials Process Science.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
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2013 (English)In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 84, no 7, 670-679 p.Article in journal (Refereed) Published
Abstract [en]

The objective of the present work is to get an understanding of the impact of Al2O3 addition on the phase relationships in the CaO-MgO-Al2O3-SiO2-Cr2O3 slags at low oxygen partial pressures (P-O2 = 10(-4) Pa), with a view to control the precipitation of Cr-spinel in the slag. The equilibrium phases in CaO-MgO-Al2O3-SiO2-Cr2O3 slag system in the range on 1673-1873 K have been investigated. The compositions close to the industrial slag systems were chosen. The Cr2O3 content was fixed at 6 wt% and MgO at 8 wt%. Al2O3 contents in the slag were varied in the range of 3-12 wt%. The basicity (CaO/SiO2) of slag was set to 1.6. Gas/slag equilibrium technique was adopted. The samples were heated to 1873 K and soaked at this temperature for 24 h. The samples were then slow cooled to 1673 K and equilibrated for an additional 24 h. The oxygen partial pressure was kept at 10(-4) Pa. A gas mixture of CO/CO2 was used to control the oxygen partial pressure. After the equilibration, the samples were quenched in water. The chromium distribution and phase compositions in the quenched slags were studied using SEM-WDS and XRD techniques. The results were compared with the phase equilibrium calculations obtained from FACTSAGE software and the samples equilibrated in air. The size of spinel crystals increased drastically after slow cooling followed by annealing compared to samples being quenched after soaking at 1873 K. It was also found that low oxygen partial pressure had a strong impact on chromium partition. The amount of spinel phase increases with increased Al2O3 content.

Place, publisher, year, edition, pages
2013. Vol. 84, no 7, 670-679 p.
Keyword [en]
phase equilibrium, chromium partition, spinel, scanning electron microscope (SEM), low oxygen partial pressure
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-127508DOI: 10.1002/srin.201200214ISI: 000322366700006Scopus ID: 2-s2.0-84879877117OAI: oai:DiVA.org:kth-127508DiVA: diva2:644490
Funder
Mistra - The Swedish Foundation for Strategic Environmental Research, MISTRA-88035
Note

QC 20130830

Available from: 2013-08-30 Created: 2013-08-30 Last updated: 2017-12-06Bibliographically approved
In thesis
1. Abatement of Chromium Emissions from Steelmaking Slags - Cr Stabilization by Phase Separation
Open this publication in new window or tab >>Abatement of Chromium Emissions from Steelmaking Slags - Cr Stabilization by Phase Separation
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Chromium is an important alloying element in stainless steel but also environmentally harmful element. A number of mineralogical phases present in the slag matrix can contain chromium and lead to chromium leaching. Chromium in slag if not stabilized, could oxidize to the cancerogenic hexavalent state, and leach out if exposed to acidic and oxygen rich environment. Other environmental concerns are slag dusting and chromium escape to the atmosphere. Despite the fact that there is a certain risk of Cr-emission from slags at operating conditions, still very little is known regarding the emission of the oxides of chromium during the slag tapping. Spinel phase is known to be important for controlling the leaching properties of chromium from the slag. The objective of the present study was to get an understanding of the phase relationships and chromium partition in the chromium-containing industrial slags and synthetic slags with a view to control the chromium stabilization in spinel phase. The impact of slag basicity, heat treatment, oxygen partial pressure and Al2O3 addition, on the phase relationships and chromium partition has been determined. The experimental results were compared with the phase equilibrium calculations. It was found that the oxygen partial pressure in the gas phase had a strong impact on chromium partition. The experimental results show that the impact of the slag basicity on chromium partition at lower oxygen partial pressures was negligible in contrast to that in air. The amount of spinel phase was found to increase with increased Al2O3 content. Slow cooling of slag and soaking at low oxygen partial pressure would improve the spinel phase precipitation. This treatment will also lead to less Cr dissolved in the unstable matrix phases. Chromium oxide was found to be emitted when chromium containing slags were exposed to oxidizing atmosphere. The results indicate that chromium oxide evaporation increases with increase in temperature and oxygen partial pressure, but decreases with slag basicity and sample thickness.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. xi, 53 p.
Keyword
spinel; slag basicity; oxygen partial pressure; chromium oxide vaporization, шпинель; шлак; парциальное давление кислорода, испарение оксидa хрома, 尖晶石;炉渣碱度;氧分压;铬氧化物汽化, spinell, slaggbasicitet, syrepartialtryck, förångning av kromoxid
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-133480 (URN)978-91-7501-666-5 (ISBN)
Public defence
2013-12-06, B3, Brinellvägen 23, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Projects
Steel Eco-Cycle
Funder
Mistra - The Swedish Foundation for Strategic Environmental ResearchKnut and Alice Wallenberg Foundation
Note

QC 20131114

Available from: 2013-11-14 Created: 2013-11-05 Last updated: 2013-11-14Bibliographically approved

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