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MoO3 Evaporation Studies from Binary Systems towards Choice of Mo Precursors in EAF
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.
2010 (English)In: Steel Research International, ISSN 1611-3683, Vol. 81, no 9, 784-791 p.Article in journal (Refereed) Published
Abstract [en]

The evaporation rate of molybdenum oxide from mixtures with CaO or MgO was studied in the temperature range 300-1573 K. The investigations were carried out using high temperature X-ray diffraction and thermogravimetry. Further, additions of these precursors to molten steel in the laboratory scale and the Mo yield achieved were determined. The X-ray studies show that the calcium molybdate is formed from the oxide mixture in the temperature interval 773-873K, which precedes the beginning of evaporation of MoO3. Results of thermogravimetric studies with mixtures CaO and MgO with MoO3 as well as the compounds CaMoO4 and MgMoO4 confirm the above results. Addition of various molybdenum precursors, viz, the mixtures of carbon with pure MoO3, CaMoO4 and MgMoO4, as well as oxide mixtures (CaO + MoO3, MgO + MoO3) show that the highest yield was observed for CaMoO4 + C and MoO3 + C mixtures, while MgO + C + MoO3 mixture showed much lower yield.

Place, publisher, year, edition, pages
2010. Vol. 81, no 9, 784-791 p.
Keyword [en]
calcium and magnesium molybdates evaporation, steel alloying, Mo yields, calcium molybdate formation
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-24516DOI: 10.1002/srin.201000055ISI: 000281912200013Scopus ID: 2-s2.0-77956601719OAI: oai:DiVA.org:kth-24516DiVA: diva2:351251
Note
QC 20100913. Uppdaterad från in press till published (20101203).Available from: 2010-09-13 Created: 2010-09-13 Last updated: 2010-12-03Bibliographically approved
In thesis
1. Energy and environmental optimization of some aspects of EAF practice with novel process solutions
Open this publication in new window or tab >>Energy and environmental optimization of some aspects of EAF practice with novel process solutions
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The objective of the present thesis is to optimize the electric arc furnace (EAF) practice from an environmental view point. Two aspects that meet the requirements of the secondary steelmaking industries today, viz. Mo alloying with maximum retainment of the alloying element in molten steel and optimization of foaming by carbonate addition with a view to optimize the energy need of the process. Both these aspects would also have a significant impact on the process economy.

Iron molybdate (Fe2MoO4) has been synthesized from commercial grade materials and proposed as a new potential precursor for steel alloying with Mo. The thermal stabilities of different molybdates, viz. Fe2MoO4, CaMoO4 and MgMoO4, were studied using thermogravimetry analysis (TGA). It was found that Fe2MoO4 is the most stable one and doesn’t evaporate in Ar atmosphere when heating up to 1573 K.

The synthesis of Fe2MoO4 requires high temperature (1373 K) and long holding time (up to 16 hours). In a view of this, the possibilities for in-situ formation of Fe2MoO4 and CaMoO4 from their precursor mixtures were studied with the aid of high-temperature X-ray diffraction (XRD) and TGA analysis. Laboratory and industrial trials on steel alloying with Mo were conducted using precursor mixtures as sources of Mo. It was found that the mixture, which contains FeOx, MoO3 and C (Fe2MoO4 precursor), can provide the Mo yield up to 98 % at both the laboratory as well as industrial trials. The Mo yields even in the case of C+MoO3 and C+MoO3+CaO mixtures were around 93 % in these trials. The higher yield for the MoO3+C+FeOx mixture was attributed to the stabilization of Mo in the precursor (marked by the decrease in the Gibbs energy of Mo) and the readiness to dissolve in the steel bath.

The heat effect of the slag foaming with carbonates addition was studied at 1623 and 1673 K with the aid of thermal analysis technique with a new crucible design. Experiments were conducted by adding limestone and dolomite pieces of defined shapes (together with iron sinkers) in molten slag and monitoring the temperature changes accompanying the decomposition of carbonates. It was found that the decomposition energies for dolomite and limestone for the studied slag composition are in the range 56-79 % of theoretical values, which is linked to the energy saving effect of slag foaming. No influence of sample shape on decomposition energy was found both for limestone and dolomite.

The kinetics of slag foaming by limestone particles was studied at 1773 K with the aid of X-ray imaging system. A model was proposed to describe the decrease in foam height with time on the basis of CaO shell formation during decomposition reaction.

The energy impact of limestone and raw dolomite addition was examined in a 100-ton EAF. It was found that, in the case of addition of carbonates after the scrap is completely molten; the endothermic heat effects for limestone and dolomite (2255 and 2264 kJ/kg respectively) were only 70 % from theoretical values. This is indicative of the resistance to heat transfer due to increased foaming.

Place, publisher, year, edition, pages
Stockholm: KTH, 2010. viii, 53 p.
Keyword
Molybdates, slag foaming, steel alloying, EAF, carbonate decomposition
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-24486 (URN)978-91-7415-721-5 (ISBN)
Public defence
2010-10-08, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20100914Available from: 2010-09-14 Created: 2010-09-10 Last updated: 2010-12-03Bibliographically approved

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