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Investigation of vanadium-containing oxide systems: CALPHAD and experiments
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics.
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Fundamental studies on thermodynamic properties of vanadium-containing oxides systems are essential to understand practical vanadium metallurgical process. The CALPHAD technique is here applied to the thermodynamic modelling of the V-O, Ca-V-O and Ti-V-O systems. The compound energy formalism is used for all the solution phases. All optimization processes and calculations are performed using the Thermo-Calc software package. The present work attempts to develop a self-consistent thermodynamic database of all phases in the studied systems. The obtained datasets can be used to calculate thermodynamic properties, stable as well as metastable phase equilibria and driving forces for oxidation etc.

Steelmaking slag is an important secondary source for vanadium extraction. The phase relationships and vanadium distribution in the CaO-SiO2-MgO-V2O3-Al2O3 synthetic slags, whose compositions were chosen based on the relevance to the steel producers, are also studied. Phase equilibria in the temperature range of 1773 to 1823 K at oxygen partial pressure of 10-10 bar and 0.21 bar were characterized.

An investigation of the volatilization of vanadium oxide was also carried out in the present work. Isothermal evaporation of vanadium pentoxide in the temperature range between 1723 and 1873 K was investigated by Thermogravimetric Analysis under different oxygen partial pressures, viz. oxygen, air or CO2. The Arrhenius activation energy for the evaporation reaction in various atmospheres was calculated from the experimental results. A mathematical model was developed to describe the kinetics of the evaporation process. Evaporation coefficients and enthalpies in various atmospheres were also estimated. The present results may have some implications in recovering vanadium from different vanadium-bearing sources.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2016. , p. 47
Keywords [en]
Calphad; thermodynamic modelling; compound energy formalism; evaporation kinetics, activation energy, TGA, activity
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-197292ISBN: 978-91-7729-169-5 (print)OAI: oai:DiVA.org:kth-197292DiVA, id: diva2:1051224
Public defence
2016-11-25, Sal F3, Lindstedtsvägen 26, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20161202

Available from: 2016-12-02 Created: 2016-12-01 Last updated: 2016-12-02Bibliographically approved
List of papers
1. Thermodynamic assessment of the V-O system
Open this publication in new window or tab >>Thermodynamic assessment of the V-O system
2015 (English)In: Calphad, ISSN 0364-5916, E-ISSN 1873-2984, Vol. 51, p. 144-160Article in journal (Refereed) Published
Abstract [en]

The V-O system was thermodynamically assessed using the CALPHAD method. The available experimental data on thermodynamic and thermochemical properties as well as phase diagram information were critically examined and a self-consistent set of thermodynamic parameters was obtained. In total 20 phases were included in this binary system. Five among them were treated as solid solution phases within the framework of the compound energy formalism. The halite phase was modeled as (V,V+2,V+3,Va)<inf>1</inf>(O-2,Va)<inf>1</inf> covering the solubility of both V and O. Thermodynamic descriptions of two different models for the corundum phase are presented, one of which is more complex to correctly take the defect mechanisms into account. The liquid phase was described by the ionic two-sublattice model with the formula (V+2)<inf>P</inf>(O-2,Va-Q, VO<inf>1.5</inf>,VO<inf>2</inf>, VO<inf>2.5</inf>)<inf>Q</inf>. The stoichiometric Magnéli phases V<inf>n</inf>O<inf>2n-1</inf> (n is an integer between 4 and 8) were modeled as (V+3)<inf>2</inf>(V+4)<inf>n-2</inf>(O-2)<inf>2n-1</inf>. Using the present thermodynamic description reliable experimental phase diagram, thermodynamic and thermochemical data were well reproduced.

Keywords
VANADIUM-OXYGEN SYSTEM, HIGH-TEMPERATURE THERMODYNAMICS, PHASE-EQUILIBRIA, N SYSTEM, 2-SUBLATTICE MODEL, V2O3-VO2 SYSTEM, SOLID-SOLUTIONS, DEGREES K, DEGREES-C, MONOXIDE
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-174578 (URN)10.1016/j.calphad.2015.08.003 (DOI)000366790500015 ()2-s2.0-84942099865 (Scopus ID)
Note

QC 20151208. QC 20160121

Available from: 2015-12-08 Created: 2015-10-07 Last updated: 2017-12-01Bibliographically approved
2. An assessment of the Ca-V-O system
Open this publication in new window or tab >>An assessment of the Ca-V-O system
2017 (English)In: Calphad, ISSN 0364-5916, E-ISSN 1873-2984, p. 29-40Article in journal (Refereed) Published
Abstract [en]

The Ca-V-O system is studied with an emphasis on the following oxide sub-systems: CaO-V2O5, CaO-V2O3, V2O5-CaV2O5 and CaO-V2O5-VO2. The aim of the present assessment is to obtain a thermodynamic description of the Ca-V-O system. The compound energy formalism was used to describe the liquid by applying the ionic two-sublattice model and the β-bronze phase CaxV2O5 (0.17≤x≤0.33) using a three-sublattice model. Phase equilibria and thermodynamic properties were critically evaluated using the CALPHAD approach and a consistent set of thermodynamic model parameters was obtained. Satisfactory agreement between calculated and experimental values is achieved.

Keywords
Bronze; Thermodynamic modelling; CALPHAD; V2O5-CaV2O5, CaO-V2O5-VO2
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-197325 (URN)10.1016/j.calphad.2016.11.005 (DOI)000397374900004 ()2-s2.0-84998995935 (Scopus ID)
Note

QC 20161202

Available from: 2016-12-02 Created: 2016-12-02 Last updated: 2019-10-09Bibliographically approved
3. An assessment of the Ti-V-O system
Open this publication in new window or tab >>An assessment of the Ti-V-O system
(English)Article in journal (Other academic) Submitted
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-197326 (URN)
Note

QC 20161202

Available from: 2016-12-02 Created: 2016-12-02 Last updated: 2016-12-02Bibliographically approved
4. Kinetic Studies on Evaporation of Liquid Vanadium Oxide, VO (x) (Where x=4 or 5)
Open this publication in new window or tab >>Kinetic Studies on Evaporation of Liquid Vanadium Oxide, VO (x) (Where x=4 or 5)
2012 (English)In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 43, no 6, p. 1684-1691Article in journal (Refereed) Published
Abstract [en]

As part of the Swedish National Eco-steel project, the present work was carried out with a view to study the evaporation of vanadium as V2O5 with a focus on the health hazards. The evaporation rate was followed by monitoring the mass loss from liquid V2O5 melts by thermogravimetric analysis (TGA) in the temperature range 1723 K to 1873 K (1450 A degrees C to 1600 A degrees C). The studies were carried out under three different oxygen partial pressures, viz, oxygen, air, or CO2. The experiments were carried out in the isothermal mode. The Arrhenius activation energies for the evaporation reaction in different atmospheres were calculated from the results. A mathematical model was developed in order to describe the kinetics of the evaporation process. Good agreement could be achieved between the mathematical model and the experimental results. Evaporation coefficients and enthalpies in different atmospheres were also estimated. The present results may also have implications in recovering vanadium values from different vanadium sources.

Keywords
Vapor-Pressure Curves, Melts, Oxidation, Thermogravimetry
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-110069 (URN)10.1007/s11663-012-9742-3 (DOI)000312342900042 ()
Note

QC 20130110

Available from: 2013-01-10 Created: 2013-01-10 Last updated: 2017-12-06Bibliographically approved
5. Experimental Study of Phase Equilibria in CaO-SiO2-MgO-Al2O3-V2O3 Slags
Open this publication in new window or tab >>Experimental Study of Phase Equilibria in CaO-SiO2-MgO-Al2O3-V2O3 Slags
2014 (English)In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 85, no 12, p. 1588-1596Article in journal (Refereed) Published
Abstract [en]

Thermodynamic data with regard to slags containing vanadium oxide are scarce and scattered. In the present study, the classic gas-slag equilibrium technique has been adopted to investigate the phase relationships in the CaO-SiO2-MgO-Al2O3-V2O3 slags. The phase equilibria in the slag systems in the temperature range of 1773-1823K (1500-1550 degrees C) at oxygen partial pressures of 10(-5) Pa and 0.21 x 10(5) Pa were characterized. CaVO3 was precipitated in samples with basicity 1.5 and 1.8 treated in air at 1773 K (1550 degrees C) while all vanadium was dissolved in equilibrium phases in samples treated at oxygen partial pressure of 10(-5) Pa. Vanadium distribution between the slags and solid Pt and phase compositions were analyzed using scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), and X-ray diffractomer (XRD) techniques. The effects of temperature, oxygen partial pressure, and slag basicity on the phase compositions in the slags are presented. Activities of VO1.5 were also calculated using the value of vanadium activity in the Pt-V alloy.

Keywords
vanadium oxide, phase equilibrium, activity, thermodynamics, steelmaking slags
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-158282 (URN)10.1002/srin.201400017 (DOI)000345832000002 ()2-s2.0-84913616789 (Scopus ID)
Note

QC 20150109

Available from: 2015-01-09 Created: 2015-01-07 Last updated: 2017-12-05Bibliographically approved

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