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Measurements of the thermodynamic activities of chromium  and vanadium oxides in CaO-MgO-Al2O3-SiO2 slags
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. (Materialens processvetenskap)
2009 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

In the present work, the thermodynamic activities of chromium and vanadium oxide in CaO-SiO2-MgO-Al2O3 slags were measured using gas-slag equilibration technique. The slag was equilibrated with a gas mixture of CO, CO2 and Ar gases enabling well-defined oxygen partial pressures in the gas mixture (PO2=10-3,10-4,10-5 Pa) at temperatures 1803, 1823K, 1873, 1923 K. The slags were kept in Pt crucibles during the equilibration and the duration of which was 20 h. From a knowledge of the thermodynamic activity of chromium and vanadium in Cr or V in Pt alloy, obtained from literature, and the oxygen partial pressure in the gas stream calculated by Thermo Calc software, the thermodynamic activity of chromium, vanadium oxide in the slags could be observed.An assessment of the experimental studies in earlier works reveal that, the activities of chromium at low chromium contents and vanadium in their respective alloys in platinum exhibits a strong negative deviation from ideality, the logarithms of activity coefficient of these elements were found to increase with increasing mole fractions of these metals in the Pt-alloys.Regarding the slag phase, all the chromium in the slags was assumed to be present in the divalent state in view of the low Cr contents and the low oxygen potentials employed in the present studies. Analogously, vanadium in the slag was assumed to be in the trivalent state in view of the low vanadium contents in the slag and the low oxygen partial pressure in the gas phase. Activity of chromium oxide, CrO decreases with increasing temperature and decreasing content of chromium oxide in slag and oxygen partial pressure in the gas phase. Activity of vanadium oxide, VO1.5 in slag phase shows a negative deviation from ideality. Activity coefficient of vanadium oxide shows a decrease with basicity of slag and the “break point” occurs at about slag basicity of 1 under the oxygen partial pressure of 10-3 Pa and temperature of 1873 K.A relationship for estimating the actual content of chromium, vanadium in slag as a function of activities of chromium or vanadium, temperature, oxygen partial pressure and slag basicity were developed from the present results, the agreement between the estimated and experimental values is satisfactory, especially at lower oxygen partial pressure.

Place, publisher, year, edition, pages
Stockholm: KTH , 2009. , x, 32 p.
Keyword [en]
thermodynamic activity, chromium oxide, vanadium oxide, equilibrium, slags, slag basicity, gas-equilibration technique
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-9940ISBN: 978-91-7415-212-8 (print)OAI: oai:DiVA.org:kth-9940DiVA: diva2:159971
Presentation
2009-01-14, Sal B3, KTH, Brinellvägen 23, Stockholm, 14:00 (English)
Opponent
Supervisors
Available from: 2009-02-11 Created: 2009-02-11 Last updated: 2010-10-14Bibliographically approved
List of papers
1. Behavior and Thermodynamics of Chromium, Vanadium and Their Oxides in Pt-alloys and Slags of Steelmaking Process
Open this publication in new window or tab >>Behavior and Thermodynamics of Chromium, Vanadium and Their Oxides in Pt-alloys and Slags of Steelmaking Process
(English)Article in journal (Other academic) Submitted
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-25281 (URN)
Note
QS 20120326Available from: 2010-10-14 Created: 2010-10-14 Last updated: 2012-03-26Bibliographically approved
2. Thermodynamic Activity of Chromium Oxide in CaO-SiO2-MgO-Al2O3-CrOx Melts
Open this publication in new window or tab >>Thermodynamic Activity of Chromium Oxide in CaO-SiO2-MgO-Al2O3-CrOx Melts
2009 (English)In: Steel Research International, ISSN 1611-3683, Vol. 80, no 3, 202-208 p.Article in journal (Refereed) Published
Abstract [en]

Thermodynamic activities of chromium oxide contained in CaO-SiO2-MgO-Al2O3 melts were measured in the present work using gas-slag equilibrium technique. The oxygen partial pressure was varied (10(-)3, 10(-4), 10(-5) Pa). Gas mixture of CO, CO2 and Ar were used and investigated at 1803, 1873 and 1923 K. The activities of CrO showed a strong positive deviation from ideality and a decrease with increasing temperature and oxygen partial pressure. A mathematical expression relating the amount of chromium oxide in the slag phase with the activity of Cr in the metal phase based on the present experimental results is presented.

Keyword
equilibrium, activity, chromium oxide, steel, melts, strongly reducing conditions, sulfide capacity, oxidation-state, phase-relations, 1500-degrees-c, system, equilibrium, slags
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-18349 (URN)10.2374/sri08sp124 (DOI)000265205000004 ()2-s2.0-64549130771 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2010-10-14Bibliographically approved
3. Activity of VO1.5 in CaO-SiO2-MgO-Al2O3 Slags at Low Vanadium Contents and Low Oxygen Pressures
Open this publication in new window or tab >>Activity of VO1.5 in CaO-SiO2-MgO-Al2O3 Slags at Low Vanadium Contents and Low Oxygen Pressures
2009 (English)In: Steel Research International, ISSN 1611-3683, Vol. 80, no 4, 251-255 p.Article in journal (Refereed) Published
Abstract [en]

In the present work, the gas-slag equilibration technique was employed for the measurement of the thermodynamic activity of vanadium oxide. The vanadium-containing slag kept in a platinum crucible was equilibrated with a gas mixture of CO, CO2 and Ar, with well-defined oxygen partial pressure at a pre-determined temperature. The slag sample was quenched and the composition of the final slag was determined by chemical analysis. From the value of the oxygen partial pressure, the thermodynamic activity of VO1.5 could be calculated using the value for the activity of vanadium in V-Pt alloy. The measurements were carried out in the temperature range 1823 similar to 1923K and the oxygen partial pressures employed were 10(-3), 10(-4), 10(-5) Pa. The present results show that the activity of vanadium(III) oxide in slag exhibits a negative deviation from ideality in the present composition range. With increasing basicity of the slag, the final content of vanadium oxide in the slag was found to show an initial increase followed by a constant content. The activities of vanadium(III) oxide did not exhibit any significant change with increasing temperature. The activity coefficient of vanadium(III) oxide decreased sharply with slag basicity approximately up to a basicity of 1, beyond which it showed a near-constant value. Increase in basicity was found to cause a change in the distribution of vanadium between the slag and the alloy phases even though this effect was less pronounced. From the present results, a mathematical relationship for estimating the vanadium content in slag for a given activity of vanadium in the molten metal phase was developed.

Keyword
equilibrium, activity, vanadium oxide, steel, melts, liquid-iron, melts, chromium
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-18382 (URN)10.2374/sri08sp138 (DOI)000265746700001 ()2-s2.0-67249117794 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2010-10-14Bibliographically approved

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