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Experimental and modelling studies of the thermophysical and thermochemical properties of some slag systems
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In order to optimize the metallurgical processes it is necessary to improve the understandings of the industrial slag properties, which include thermophysical and thermochemical properties. In the present study Mass Triangle Model was applied to predict these properties. According to the model formula, a program was developed in Visual C++ environment to calculate different properties in limited solubility ternary system. Successful applications of this model in predicting viscosity, surface tension, and density have been demonstrated in the case of a number of ternary slags in liquid state, as for example, RExOy-CaF2-SiO2 (RE refer to rare earth metal), MnO-TiO2-SiO2, CaO-Al2O3-SiO2, BaO-FeO-Fe2O3, CaO-MnO-SiO2 etc. In addition, the method has also been extended to predict electrical conductivities and sulphide capacities, which is first attempt to compute properties. Furthermore, an extension of this model has also been performed in the present study to obtain the corresponding properties in a homogeneous ternary system. Good agreement between model calculation and literature values had demonstrated that mass triangle model offers a powerful and efficient tool for estimations of various properties of molten system only based on limited experimental information.

Knowledge of the thermodynamic properties of chromium oxides-containing slags is of great importance to chromium retention in stainless steel production, in view of chromium impacts on economic costs and environmental protection. Thus, the oxidation states of chromium in slags as well as sulphide capacity of CrOx-containing slag have been studied. In the studies of oxidation state of chromium in slags, gas/slag equilibrium technique was used for CaO-SiO2-CrOx system and the ratio of Cr2+/Cr3+ in multicomponent slags was measured by X-ray absorption near edge spectra (XANES). High-temperature mass spectrometry method was also used to obtain the distribution of chromium oxides in CaO-MgO(-FeO)-Al2O3-SiO2-CrOx system. It is to be noted that the present work is probably the first to employ Knudsen cell-mass spectrometry as an effective way to estimate chromium valences through vapor species. Utilizing the data obtained in present study as well as those reported in literature, a mathematical correlation was established for estimating the ratio of Cr2+/Cr3+ as a function of temperature, partial pressure of oxygen and slag basicity. The comparison between experimental valence ratio values and estimated ones presents a satisfactory agreement.

The sulphide capacities of CaO-SiO2-CrOx pseudo-ternary slags were measured using the gas-slag equilibration technique in the temperature range 1823–1923 K under two different oxygen partial pressures 9.80×10-3 and 9.88×10-4 Pa. The results showed that log10Cs varied linearly with the reciprocal temperature, and the slope was higher than the corresponding value reported in the case of the binary CaO-SiO2 of corresponding composition. By using the equation developed as part of this project relating Cr2+/Cr3+ with basicity, oxygen partial pressure and temperature, it was possible to understand the effect of CrO on the sulphide capacities; viz. the sulphide capacity shows a decreasing trend as Cr2+ replaces Ca2+ in the slag. With further increase of Cr2+ content, there are indications of the occurrence of a minimum point beyond which the sulphide capacities show a slight increasing trend. The latter is attributed to the increasing extent of the polymerization reaction releasing oxygen ions for sulphide reactions in the metasilicate region. The behavior of CrO in the slag was found to be analogous to FeO.

Estimation of liquidus and solidus temperature of slag was also carried out in the present study. The results indicated that it is possible to get a reasonable idea of the solidus temperature from X-ray radiography while DSC would indicate the liquidus temperature of slag

Place, publisher, year, edition, pages
Stockholm: KTH , 2009. , viii, 50 p.
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-11232ISBN: 978-91-7415-440-5 (print)OAI: oai:DiVA.org:kth-11232DiVA: diva2:242351
Public defence
2009-10-30, Salongen, KTHB, Osquars Backe 31, stockholm, 10:00 (English)
Opponent
Supervisors
Projects
MISTRA
Note

QC 20100813

Available from: 2009-10-08 Created: 2009-10-07 Last updated: 2013-11-12Bibliographically approved
List of papers
1. A new method for evaluating some thermophysical properties for ternary system
Open this publication in new window or tab >>A new method for evaluating some thermophysical properties for ternary system
2008 (English)In: High Temperature Materials and Processes, ISSN 0334-6455, E-ISSN 2191-0324, Vol. 27, no 2, 119-126 p.Article in journal (Refereed) Published
Abstract [en]

In our earlier papers, we have presented a new method, named the mass triangle model, for calculating physicochemical properties in the ternary system within a limited solubility area. This model was shown to be superior to traditional geometrical models in the computation of ternary data from the known data for the corresponding binaries. In the present paper, the authors extend this method to a ternary system where the entire compositional area inside the ternary triangle is homogeneous. The successful application of this new method to the estimation of surface tension and density has been demonstrated in the case of the system Ni(3)S(2)-FeS-Cu(2)S at 1473K with mean square root error of +/- 1.83%, +/- 4.33% respectively, compared with the experimental results.

Keyword
geometrical models, thermophysical properties, ternary system
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-11226 (URN)000262259600006 ()2-s2.0-58049138879 (Scopus ID)
Note
QC 20100813Available from: 2009-10-08 Created: 2009-10-07 Last updated: 2017-12-13Bibliographically approved
2. A comparison of tradition geometrical models and mass triangle model in calculation the surface tensions of ternary sulphide melts
Open this publication in new window or tab >>A comparison of tradition geometrical models and mass triangle model in calculation the surface tensions of ternary sulphide melts
2008 (English)In: Calphad, ISSN 0364-5916, E-ISSN 1873-2984, Vol. 32, no 1, 49-55 p.Article in journal (Refereed) Published
Abstract [en]

Surface tension of the Ni3S2-FeS-Cu2S ternary mattes has been calculated using a mass triangle model as well as six traditional geometrical models based on the same calculation data to investigate the difference between mass triangle model and other kinds of geometrical models. From the calculated results, it might be seen that, the mass triangle model, irrespective of the method of selection of the binary data, would give the best results compared with other traditional geometrical models. The mean square root errors of the mass triangle method only range from 1.09% to 2.8%, which are almost within the experimental error of 2.5%.

Keyword
geometrical model, mass triangle model, surface tension, ternary, sulphide melts, thermodynamic properties, binary data, system, mixtures, density
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-11227 (URN)10.1016/j.calphad.2007.11.006 (DOI)000255096100006 ()2-s2.0-44249096358 (Scopus ID)
Note
QC 20100813Available from: 2009-10-08 Created: 2009-10-07 Last updated: 2017-12-13Bibliographically approved
3. Estimations of Electrical Conductivities in Molten Slag Systems
Open this publication in new window or tab >>Estimations of Electrical Conductivities in Molten Slag Systems
2009 (English)In: Journal of Iron and Steel Research International, ISSN 1006-706X, E-ISSN 2210-3988, Vol. 80, no 9, 680-685 p.Article in journal (Refereed) Published
Abstract [en]

In the present paper, the electrical conductivities of molten silicates systems, CaO-MgO-SiO2, Na2O-MgO-SiO2, CaO-FeO-SiO2 and CaO-MgO-MnO-SiO2 (SiO2 = 45wt %) were estimated by the mass triangle method developed earlier by Chou. The computed results are compared with other approaches found in the literature. The predictions show satisfactory agreement with experimental results reported in the literature. A correlation was also made between the cation-oxygen ion attraction parameter I and the electrical conductivities of slags. It was found that the electrical conductivity varies linearly with I when the content of transition metallic ions is less than 0.2 mole fraction. Beyond this, the effect of electronic conduction is expected to dominate. On the basis of the present approach, the electrical conductivities of higher order systems can be estimated. The approach suggested in the present paper offers a powerful tool to design slags for applications in metallurgical processes.

Keyword
electrical conductivity, molten slag, mass triangle model
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-11229 (URN)10.2374/SRI08SP165 (DOI)000269856200012 ()2-s2.0-70350389192 (Scopus ID)
Note
QC 20100813Available from: 2009-10-08 Created: 2009-10-07 Last updated: 2017-12-13Bibliographically approved
4. High-temperature mass spectrometric study of the vaporization process in the system CaO-MgO-Al2O3-Cr2O3-FeO-SiO2
Open this publication in new window or tab >>High-temperature mass spectrometric study of the vaporization process in the system CaO-MgO-Al2O3-Cr2O3-FeO-SiO2
2009 (English)In: Rapid Communications in Mass Spectrometry, ISSN 0951-4198, E-ISSN 1097-0231, Vol. 23, 2233-2239 p.Article in journal (Refereed) Published
Abstract [en]

Knudsen effusion mass spectrometry was used to study vaporization processes and thermodynamic properties of twenty samples of chromium-containing slags in the CaO-MgO-Al2O3-Cr2O3-FeO-SiO 2 system in the temperature range 1850-2750 K. Tungsten cells were used and Cr2O3 solid was used as a reference material. The system was calibrated using liquid gold. As FeO was the first emanating vapor species, monitoring of the chromium-containing species could be carried out only after the complete vaporization of FeO. This, however, was found to have very little impact on the concentration of the slags investigated. During the measurements, the ion current intensities of CrO+ and CrO +2 species in the mass spectra of the vapor over the CaO-MgO-Al2O3-Cr2O3-FeO-SiO 2 samples were monitored and compared with those corresponding to solid Cr2O3. Data on the partial pressures of vapor species as well as the activities of Cr2O3 as a function of temperature were obtained. The results are expected to be valuable in the optimization of slag composition in high alloy steelmaking processes.

Keyword
THERMODYNAMIC PROPERTIES; OXIDE MELTS; LIQUID; MIXTURES; CHROMIUM; CR2O3; FEO
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-11230 (URN)10.1002/rcm.4127 (DOI)000268003400015 ()2-s2.0-67650366930 (Scopus ID)
Note
QC 2010813Available from: 2009-10-08 Created: 2009-10-07 Last updated: 2017-12-13Bibliographically approved
5. Experimental Studies on the Oxidation States of Chromium Oxides in Slag Systems
Open this publication in new window or tab >>Experimental Studies on the Oxidation States of Chromium Oxides in Slag Systems
2010 (English)In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 41, no 5, 946-954 p.Article in journal (Refereed) Published
Abstract [en]

In view of the importance of the thermodynamic behavior of chromium in the slag phase as well as the serious discrepancies in the earlier reports on the valence state of chromium in slag melts, the oxidation state of chromium oxides in CaO-SiO2-CrOx and CaO-MgO-(FeO-) Al2O3-SiO2-CrOx were investigated experimentally in the present study using two different experimental techniques. The gas-slag equilibrium technique was adopted to study the CaO-SiO2-CrOx system between 1823 K (1550 °C) and 1923 K (1650 °C) and equilibrated with mixtures of CO-CO2-Ar gases corresponding to three different oxygen partial pressures (between 10-4 and 10-5 Pa). After equilibrating, the samples were quenched and subjected to analysis using the X-ray absorption near edge structure method to determine the distribution ratio of Cr2+/Cr3+ in the slags. The second technique examined the applicability of the high-temperature mass spectrometric method combined with the Knuden effusion cell for quantifying the valence states of Cr in the multicomponent system CaO-MgO-(FeO-) Al2O3-SiO2-CrOx up to a maximum temperature of 2000 K (1727 °C). The results showed that the Knudsen cell-mass spectrometric method could be used successfully to estimate the valence ratio for Cr in silicate melts. According to the present study, the Cr2+/Cr3+ ratio increased with increasing temperature and a decreasing slag basicity as well as the oxygen partial pressure prevailing in the system. A mathematical correlation of XCrO/XCrO1.5 as a function of temperature, oxygen partial pressure, and basicity was developed in the present work based on the present results as well as on those assessed from earlier data.

Keyword
strongly reducing conditions, silicate melts, 1500-degrees-c, xanes
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-24105 (URN)10.1007/s11663-010-9383-3 (DOI)000284333700004 ()2-s2.0-84860219095 (Scopus ID)
Note
Tidigare titel: Experimental studies on the oxidation states of chromium oxides in slag phase QC 20100813. Uppdaterad från submitted till published(20110104).Available from: 2010-08-13 Created: 2010-08-13 Last updated: 2017-12-12Bibliographically approved
6. Experimental Studies on the Sulfide Capacities of CaO-SiO2-CrOx Slags
Open this publication in new window or tab >>Experimental Studies on the Sulfide Capacities of CaO-SiO2-CrOx Slags
2010 (English)In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 41, no 2, 367-373 p.Article in journal (Refereed) Published
Abstract [en]

To understand the desulfurization process during the refining of Cr-containing steel grades, this work was initiated to study the reactions between Cr-sulfur and chromium-containing slags. The sulfide capacities of CaO-SiO2-CrOx pseudo-ternary slags were measured using the traditional gas-slag equilibration technique between 1823 K and 1923 K. Sixteen different slag compositions were examined, and two different equilibrium oxygen partial pressures were used to understand the impact of the varying valence of Cr on the sulfide capacities. The results showed that log(10) Cs varied linearly with the reciprocal T, and the slope was higher than the corresponding value reported for the binary CaO-SiO2 of corresponding composition. It was difficult to isolate the relative effects of the bi- and trivalent Cr in the slags because the Cr2+/Cr3+ ratio was influenced by the basicity of the slag. By using the equation developed by these authors earlier that related Cr2+/Cr3+ with basicity, oxygen partial pressure, and temperature, it was possible to obtain an approximate trend of the CrO effect on the sulfide capacities; viz. the sulfide shows a decreasing trend as Cr2+ replaces Ca2+ in the slag. With a continued increase of Cr2+ content, indications of the occurrence of a minimum point were observed; beyond which the sulfide capacities showed a slight increasing trend. The latter was attributed, based on slag-structure analysis by Gaskell et al., to the increasing extent of the polymerization reaction releasing oxygen ions for sulfide reactions.

Keyword
strongly reducing conditions, silicate melts, thermodynamic properties, cao-al2o3-sio2 slags, chromium-oxide, phase-diagrams, system, 1500-degrees-c, optimization, equilibria
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-19363 (URN)10.1007/s11663-009-9338-8 (DOI)000276235800011 ()2-s2.0-77951299236 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
7. Measurements of Solidus and Liquidus Temperatures of CaO-Al2O3-SiO2 and CaO-MgO-Al2O3-SiO2 Slags with MnO Additions
Open this publication in new window or tab >>Measurements of Solidus and Liquidus Temperatures of CaO-Al2O3-SiO2 and CaO-MgO-Al2O3-SiO2 Slags with MnO Additions
2012 (English)In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 83, no 2, 157-161 p.Article in journal (Refereed) Published
Abstract [en]

The present work was carried out with a view to re-examine the phase diagram aspects of CaO?Al2O3?SiO2 and CaO?MgO?Al2O3?SiO2 slags with MnO additions. The aim was to confirm the homogeneous liquid range necessitated for sulfide capacities measurements of the above-mentioned slags. The liquidus and solidus temperatures of these slags were measured by DSC and X-ray radiograph techniques. The experimental results were compared with the liquidus and solidus temperatures obtained from literature (Slag Atlas) and commercial softwares ThermoCalc and FactSage. The results indicate that there is good agreement between the experimental values and those retrieved from literature and the commercial software in the case of the ternary system CaO?Al2O3?SiO2. For the CaO?MgO?MnO?Al2O3?SiO2 system, significant deviations were observed between the different sources. The present observations indicate that X-ray radiography can be a very useful tool in estimating the solidus temperatures of slags while DSC would complement the information with respect to liquidus temperatures.

Place, publisher, year, edition, pages
Wiley-Blackwell, 2012
Keyword
solidus temperature, liquidus temperature, X-ray radiography, DSC
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-90901 (URN)10.1002/srin.201100191 (DOI)000299818400006 ()2-s2.0-84863058848 (Scopus ID)
Note

QC 20120307. Updated from "Submitted" to "Published" 131112

Available from: 2012-03-07 Created: 2012-03-05 Last updated: 2017-12-07Bibliographically approved

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