| 1. |
- Brämming, Mats, et al.
(author)
-
BOS vessel vibration measurement for foam level detection
- 2011
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In: ISIJ International. - : Iron and Steel Institute of Japan. - 0915-1559 .- 1347-5460. ; 51:1, s. 71-79
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Journal article (peer-reviewed)abstract
- In the BOS process liquid slag together with dispersed metal droplets, solid particles and process gases form an expanding foam. Certain process conditions may lead to excessive foam growth, forcing foam out through the vessel mouth, an event commonly known as 'slopping'. Slopping results in loss of valuable metal, equipment damage and lost production time. In the early 1980s a system for foam level and slopping control was installed at SSAB's steel plant in Luleå, a system based on the correlation between BOS vessel vibration in a narrow low frequency band and foam development. The technique, in this case with an accelerometer mounted on the trunnion bearing housing, soon showed its usefulness, for example when adapting existing lance patterns to a change in oxygen lance design from a 3-hole to a 4-hole nozzle. Estimating the actual foam height in the BOS vessel was of great importance in the recently completed RFCS funded research project "IMPHOS" (Improving Phosphorus Refining). Based on the earlier positive experiences, it was decided to further develop the vessel vibration measurement technique. Trials on an industrial size BOS vessel type LD/LBE have been carried out, this time with a tri-axial accelerometer mounted on the vessel trunnion. FFT spectrum analysis has been used in order to find the frequency band with best correlation to the foam level development. The results show that there is a correlation between vessel vibration and foam height that can be used for dynamic foam level and slopping control. © 2011 ISIJ.
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| 2. |
- Kapilashrami, A., et al.
(author)
-
Bubble formation through reaction at liquid-liquid interfaces
- 2005
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In: Steel Research International. - : Wiley. - 1611-3683. ; 76:9, s. 616-623
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Journal article (peer-reviewed)abstract
- Slag foaming is an important phenomenon in steelmaking processes with both beneficial as well as negative effects. The present work is part of the wider project on the modelling of slag foaming, with special reference to dynamic conditions. Since bubble formation is the first step to foam formation, the present work was carried out in an attempt to simulate the bubble formation in slag/metal reactions in steelmaking processes by water-modelling experiments. The bubble formation due to the gas produced through chemical reaction at the interface between oleic acid and sodium bicarbonate solution was systematically monitored. The chemical reaction rate was varied by varying the concentration of sodium bicarbonate. The bubbles were observed to be generated in the heavier aqueous phase just below the water-oil interface. The bubbles penetrated the interface and escaped through the oil phase. The rate of the reaction was estimated from the volume of the gas that passed the water/oil interface. It was observed that the bubble formation and bubble growth mechanism were influenced by the reaction rate while the bubble size seemed to be unaffected by the reaction rate.
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| 3. |
- Kapilashrami, A., et al.
(author)
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Foaming of slags under dynamic conditions
- 2006
-
In: Metallurgical and materials transactions. B, process metallurgy and materials processing science. - : Springer Science and Business Media LLC. - 1073-5615 .- 1543-1916. ; 37:1, s. 109-117
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Journal article (peer-reviewed)abstract
- Slag foaming under dynamic conditions has been studied in laboratory scale to examine the influence of properties commonly used to describe the foaminess and foam stability of slags under steady-state conditions. Synthetically produced slags with compositions relevant to tool steel and stainless steel production were studied through X-ray equipment in measurements simulating the dynamic conditions found in real processes. It is found that the dynamic systems display a more complex behavior than systems Under steady state. Traditional theories for foaming do not seem to be valid for slag foaming under dynamic conditions. The foam displays a fluctuating behavior, which the presently available models are not able to take into account. The concept of a foaming index does not seem to be applicable, resulting in the need for alternative models.
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| 4. |
- Kapilashrami, A., et al.
(author)
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The fluctuations in slag foam under dynamic conditions
- 2006
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In: Metallurgical and materials transactions. B, process metallurgy and materials processing science. - : Springer Science and Business Media LLC. - 1073-5615 .- 1543-1916. ; 37:1, s. 145-148
-
Journal article (peer-reviewed)abstract
- ABHA KAPILASHRAMI, formerly with the Royal Institute of Technology, is with Corus Research, Development and Technology, 1970 CA IJmuiden, The Netherlands. ASHOK KUMAR LAHIRI, Professor, is with the Department of Metallurgy, Indian Institute of Science, Bangalore 560012, India. MARTEN GORNERUP and SESHADRI SEETHARAMAN, Professor, are with the Department of Material Science and Engineering, Royal Institute of Technology, 10044 Stockholm, Sweden. Contact c-mail: raman@ kth.se.
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| 5. |
- Kapilashrami, E., et al.
(author)
-
Studies of the wetting characteristics of liquid iron on dense alumina by the X-ray sessile drop technique
- 2003
-
In: Metallurgical and materials transactions. B, process metallurgy and materials processing science. - : Springer Science and Business Media LLC. - 1073-5615 .- 1543-1916. ; 34:2, s. 193-199
-
Journal article (peer-reviewed)abstract
- In the present work, the reaction between a molten iron drop and dense alumina was studied using the X-ray sessile-drop method under different oxygen partial pressures in the gas atmosphere. The changes in contact angles between the iron drop and the alumina substrate were followed as functions of temperature and varying partial pressures of oxygen in the temperature range 1823 to 1873 K both in static and dynamic modes. The results of the contact angle measurements with pure iron in contact with dense alumina in extremely well-purified argon as well as under different oxygen partial pressures in the gas atmosphere showed good agreement with earlier measurements reported in the literature. In the dynamic mode, when argon was replaced by a CO-CO2-Ar mixture with a well-defined PO, in the gas, the contact angle showed an initial decrease followed by a period of nearly constant contact angle. At the end of this period, the length of which was a function of the P-O2 imposed, a further steep decrease in the contact angle was noticed. An intermediate layer of FeAl2O4 was detected in the scanning electron microscope (SEM) analysis of the reacted substrates. An interesting observation in the present experiments is that the iron drop moved away from the site of the reaction once the product layer covered the interface. The results are analyzed on the basis of the various forces acting on the drop.
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| 6. |
- Kapilashrami, F., et al.
(author)
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Investigation of the reactions between oxygen-containing iron and SiO2 substrate by X-ray sessile-drop technique
- 2003
-
In: Metallurgical and materials transactions. B, process metallurgy and materials processing science. - 1073-5615 .- 1543-1916. ; 34:5, s. 647-652
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Journal article (peer-reviewed)abstract
- The X-ray sessile-drop method was employed in the present investigation to measure the contact angle between liquid iron and a silica substrate under argon as well as CO-CO2-Ar atmospheres in the temperature range of 1823 to 1833 K. In the latter case, the measurements were carried out in the dynamic mode, and the contact-angle changes were followed as a function of time as oxygen in the gas dissolved in the metal. The static measurements in argon showed that the contact angles in the experimental temperature range are of the order of 135 deg, similar to those observed in the case of the alumina substrate. In the dynamic mode, oxygen partial pressures varying between 9.9.10(-4) and 1.5.10(-2) Pa were imposed on the system. In these experiments, the contact angle decreased in two stages, with an intermediate steady-state region. Fayalite slag, formed due to the reaction between the metallic phase and the substrate, was found to accumulate around the drop. The results are of relevance in understanding the mechanism of corrosion of silica-containing refractories by molten iron.
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| 7. |
- Kataoka, T., et al.
(author)
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Ferromagnetism in ZnO co-doped with Mn and N studied by soft x-ray magnetic circular dichroism
- 2011
-
In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 99:13, s. 132508-
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Journal article (peer-reviewed)abstract
- We have investigated the electronic structure of ZnO:Mn and ZnO:Mn,N thin films using x-ray magnetic circular dichroism (XMCD) and resonance-photoemission spectroscopy. From the Mn 2p -> 3d XMCD results, it is shown that, while XMCD signals only due to paramagnetic Mn(2+) ions were observed in ZnO:Mn, nonmagnetic, paramagnetic, and ferromagnetic Mn(2+) ions coexist in ZnO:Mn,N. XMCD signals of ZnO:Mn,N revealed that the localized Mn(2+) ground state and Mn(2+) state hybridized with ligand hole coexisted, implying p-d exchange coupling. In the valence-band spectra, spectral weight near the Fermi level was suppressed, suggesting that interaction between magnetic moments in ZnO:Mn,N has localized nature.
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| 8. |
- Millman, M.S., et al.
(author)
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Observations on BOS refining
- 2013
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In: Transactions of the Indian Institute of Metals. - : Springer Science and Business Media LLC. - 0972-2815 .- 0975-1645. ; 66, s. 525-534
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Journal article (peer-reviewed)abstract
- Selected IMPHOS (IMproving PHOSphorus refining) heats ([1], [2]: Millman et al. in Proc. Scanmet 3, 2008; and Millman et al. in Ironmak Steelmak 38:499, 2011), have been used to make observations on decarburizing and dephosphorising performance characteristics during BOS refining. If it is assumed that decarburization takes place solely in the slag/metal emulsion then maximum metal residence time in the emulsion is just under 9 sec and at peak decarburisation time, the maximum amount of metal in the emulsion is ∼ 50 % of the total metal content in the converter. To evaluate the effects of changes in slag component chemistry on phosphorus refining it is necessary to account for changes in slag weight, which can change substantially throughout a heat and be significantly different heat-to-heat. Dephosphorising performance depends on the thermodynamic stability of slag phases that are able to take-up phosphorus and the distribution of phosphorus between these thermodynamically stable phases. The application of proprietary thermodynamic models such as MTDATA and FACTSage has helped to clarify such events. The stability of the foamy slag/metal emulsion changes over the period of the blow. Slag height increases with an increase in FeO (tot) wt% and decreases with a decrease in decarburisation rate and the collapse of the foamy slag. © 2013 Indian Institute of Metals.
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| 9. |
- Millman, M.S., et al.
(author)
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Some observations and insights on BOS refining
- 2013
-
In: Ironmaking & steelmaking. - 0301-9233 .- 1743-2812. ; 40:6, s. 460-469
-
Journal article (peer-reviewed)abstract
- Selected IMPHOS heats,1,2 have been used to make observations on decarburising and dephosphorising performance, scrap melting and slag foaming characteristics during BOS refining. If it is assumed that decarburisation takes place solely in the slag/metal emulsion then maximum metal residence time in the emulsion is just under 9 seconds and at peak decarburisation time, the maximum amount of metal in the emulsion is ∼50% of the total metal content in the converter. To evaluate the effects of changes in slag component chemistry on phosphorus refining it is necessary to account for changes in slag weight, which can change substantially throughout a heat and be significantly different heat-to-heat. Dephosphorising performance depends on the thermodynamic stability of slag phases that are able to take up phosphorus and the distribution of phosphorus between these thermodynamically stable phases. The application of proprietary thermodynamic models such as MTDATA and FACTSage has helped to clarify such events. Skull build-up on the scrap pile is at a maximum when the bulk bath temperature is ∼1460°C. At this time, the solid scrap and skull component of the bulk bath makes-up just over 60% of all the metal charged to the converter. All scrap and skull is melted out at a bulk bath temperature of ∼1610°C. The stability of the foamy slag/metal emulsion changes over the period of the blow. Slag height increases with an increase in FeO(tot)wt-% and decreases with a decrease in decarburisation rate and the collapse of the foamy slag. © 2013 Institute of Materials, Minerals and Mining.
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| 10. |
- Millman, M.S., et al.
(author)
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Study of refining performance in BOS converter
- 2011
-
In: Ironmaking & steelmaking. - 0301-9233 .- 1743-2812. ; 38:7, s. 499-509
-
Journal article (peer-reviewed)abstract
- A unique in blow sampling system has been applied to a blowing converter to retrieve simultaneously representative bulk metal bath and slag/metal emulsion samples from seven specified positions and every 2 min from start of blow. Full sample datasets from 20 heats have been grouped according to differences in the bulk bath phosphorus removal profiles and analysed with respect to relative refining ability of the slag/metal emulsion and the bulk metal bath. The complexity of the thermokinetic relationships behind the removal of carbon and the transfer of silicon, phosphorus, manganese and sulphur between the metal and slag is highlighted and the metal circulation rate in the emulsion is derived. © 2011 Institute of Materials, Minerals and Mining.
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| 11. |
- Araujo, C. Moysés, et al.
(author)
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Room temperature ferromagnetism in pristine MgO thin films
- 2010
-
In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 96:23
-
Journal article (peer-reviewed)abstract
- Robust ferromagnetic ordering at, and well above room temperature is observed in pure transparent MgO thin films (<170 nm thick) deposited by three different techniques. Careful study of the wide scan x-ray photoelectron spectroscopy rule out the possible presence of any magnetic contaminants. In the magnetron sputtered films, we observe magnetic phase transitions as a function of film thickness. The maximum saturation magnetization of 5.7 emu/cm(3) is measured on a 170 nm thick film. The films above 500 nm are found to be diamagnetic. Ab initio calculations suggest that the ferromagnetism is mediated by cation vacancies.
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| 12. |
- Arvanitidis, I., et al.
(author)
-
Intrinsic reduction kinetics of cobalt- and nickel-titanates by hydrogen
- 2000
-
In: Journal of Materials Research. - 0884-2914 .- 2044-5326. ; 15:2, s. 338-346
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Journal article (peer-reviewed)abstract
- The isothermal reduction of synthetic CoTiO3 and NiTiO3 in hydrogen (1 atm) was investigated using thermogravimetric analysis technique in the temperature range, 928-1287 K (CoTiO3) and 884-1387 K (NiTiO3). Shallow beds of fine titanate powders were reduced by hydrogen at a high flow rate. Quenched samples were analyzed by scanning electron microscopy. The rates of the reaction of the titanates with H-2 were very fast during the reduction of Co2+, Ni2+, or Fe2+ ions into metals. The reduction of the remaining titanium oxide was very slow. The activation energy for the reduction of CoTiO3 by hydrogen to Co and TiO2 was evaluated to be 151 +/- 1 kJ/mol, and the activation energy for the reduction of NiTiO3 by hydrogen to Ni and TiO2 was evaluated to be 153 +/- 1 kJ/mol. The study was complemented by hydrogen reduction of synthetic TiO2 (rutile). The results were also compared with the hydrogen reduction of FeTiO3.
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| 13. |
- Bora, D. K., et al.
(author)
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Influence of crystal structure, ligand environment and morphology on Co L-edge XAS spectral characteristics in cobalt compounds
- 2015
-
In: Journal of Synchrotron Radiation. - : International Union of Crystallography (IUCr). - 0909-0495 .- 1600-5775. ; 22, s. 1450-1458
-
Journal article (peer-reviewed)abstract
- The electronic structure of a material plays an important role in its functionality for different applications which can be probed using synchrotron-based spectroscopy techniques. Here, various cobalt-based compounds, differing in crystal structure, ligands surrounding the central metal ion and morphology, have been studied by soft X-ray absorption spectroscopy (XAS) at the Co L-edge in order to measure the effect of these parameters on the electronic structure. A careful qualitative analysis of the spectral branching ratio and relative intensities of the L 3 and L 2 peaks provide useful insight into the electronic properties of compounds such as CoO/Co(OH)2, CoCl2.6H2O/CoF2.4H2O, CoCl2/CoF2, Co3O4 (bulk/nano/micro). For further detailed analysis of the XAS spectra, quantitative analysis has been performed by fitting the spectral profile with simulated spectra for a number of cobalt compounds using crystal field atomic multiplet calculations.
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| 14. |
- Brämming, Mats, et al.
(author)
-
Comparison between vessel vibration and audiometry for slopping control in the top-blown BOS process
- 2011
-
In: Steel Research International. - : Wiley. - 1611-3683 .- 1869-344X. ; 82:6, s. 683-692
-
Journal article (peer-reviewed)abstract
- Excess slag foam growth is a frequent problem in the BOS process. In the worst case, foam is forced out of the vessel and this phenomenon, commonly called slopping, not only results in loss of valuable metal yield but also in equipment damage and lost production time. In order to minimize slopping, accurate estimation of the foam level inside the vessel is an important part of BOS process control. In the top blown BOS vessel, slopping control is achieved using both static and dynamic measures. The most common implemented technique for dynamic foam height estimation and slopping control is the audiometer system. An alternative method, vessel vibration monitoring, has been investigated as part of the work in a RFCS funded research project called IMPHOS. In order to judge the usefulness of this method, parallel vibration and audio measurements have been carried out on 130 tonne as well as on 300 tonne BOS vessels. The results show that during stable process conditions there is good agreement between the two methods with regard to foam height estimation and, as vessel vibration and audiometry are largely independent of each other, a combination of the two is likely to increase significantly the accuracy of slopping prediction. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
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| 15. |
- Kapilashrami, Abha, et al.
(author)
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Bubble formation and dynamic slag foaming phenomena
- 2006
-
In: 2006 TMS Fall Extraction and Processing Division: Sohn International Symposium. - 0873396332 - 9780873396332 ; , s. 233-245
-
Conference paper (peer-reviewed)abstract
- Slag foaming proves to be both blessing and curse for the process productivity, depending on where in the process it occurs. In pyrometallurgical processes, slag foaming is often a result of chemical reactions taking place in the slag. As the slag composition and reaction rates are changing, foaming occurs under dynamic conditions. In the present work, slag foaming was studied with XRF. The foam displayed a fluctuating behaviour, unaccountable by existing models. The concept of foaming index was found not to be satisfactory in describing the foam, resulting in the need for alternative theories. The rate of fluctuations was seen to be related to the difference between rate of gas generation and rate of gas escape from the system (Ug-Ue) as well as the bubble sizes. Thus, model development of dynamic foaming phenomenon has to take the effective chemical reaction rate as well as the bubble sizes into consideration. The first step in obtaining foam is to form bubbles. In the present work, gas bubbles were generated through chemical reaction at interface between two immiscible liquids and the bubble formation was studied optically. The gas bubble size was seen to be uninfluenced by the reaction rate. However, bubble formation was seen to take place in one of the phases and since the bubbles consequently traversed the interface under the influence of buoyancy, the viscosity of the first phase was found to influence the final bubble size where increased viscosity would yield a larger bubble size.
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| 16. |
- Kapilashrami, A, et al.
(author)
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Drying of oil-in-water emulsions on hydrophobic and hydrophilic substrates
- 2004
-
In: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 233, s. 155-161
-
Journal article (peer-reviewed)abstract
- We have investigated the effect of the hydrophobic/hydrophilic character of the substrates on the drying behaviour of dilute silicone oil-in-water (o/w) emulsions by light microscopy and ellipsometry. The poly(dimethylsiloxane) (PDMS) emulsion droplets, which are stabilised by a triblock PEO/PPO/PEO copolymer, form a close-packed structure containing domains of hexagonally packed droplets on the hydrophilic substrate. We find that the hydrophilic substrate does not destabilise the emulsion droplets; the close-packed structures are very stable and coalesce very slowly only when most of the water has evaporated. This is supported by ellipsometry measurements, which showed that the emulsion droplets do not adsorb to the hydrophilic substrate. The hydrophobic substrate, on the other hand, destabilises the emulsion and we observed a significant increase in the coalescence rate. Ellipsometry measurements suggest that destabilisation is promoted by the strong interaction between the emulsion droplets and the hydrophobic substrate. We also find that the emulsion undergoes dewetting followed by a release of oil and rewetting of the substrate when the o/w emulsion film reaches a critical thickness on the hydrophobic substrate
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| 17. |
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| 18. |
- Kapilashrami, A, et al.
(author)
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Ellipsometric studies of nonionic block copolymers adsorbed at the solid/water and oil/water interfaces
- 2003
-
In: Colloids ad Surfaces a-Physicochemical and Engineering Aspects. ; 225:1-3, s. 181-192
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Journal article (peer-reviewed)abstract
- We report on the interfacial behaviour of a series of nonionic diblock copolymers at solid hydrophobic and hydrophilic surfaces/water and silicone oil/water interfaces, studied by ellipsometry. The polymers consist of a hydrophobic C-18 chain linked to a hydrophilic poly(ethylene oxide) (PEO), block varying from 50 to 250 U. The adsorption of these copolymers at low bulk concentrations was found to be dominated by the PEO block at all interfaces. At higher concentration the copolymer forms surface aggregates at the silica surface whereas we observe a gradual increase in the adsorbed layer thickness with increased surface excess at the solid hydrophobic surface, indicating a transition from a flat conformation to brush-like layer structure. The results indicate a similar evolution in adsorbed amount with concentration at the silicone oil/water interface as at the hydrophobic silica surface. The influence of the rheological proper ies of the interface on the adsorption of the diblock copolymer was investigated by comparing results from two silicon oils with different viscosities. The copolymers were found to have stronger affinity to a low viscosity (990 mPa s) silicone oil than to a higher viscosity (12 800 mPa s) silicone oil and the hydrophobised silica surface. At the silicone oil/water interface the adsorption of a commercial nonionic triblock copolymer was furthermore investigated and compared with the diblock copolymers. (C) 2003 Elsevier B.V. All rights reserved.
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| 19. |
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| 20. |
- Kapilashrami, A., et al.
(author)
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Ellipsometric studies of nonionic copolymers adsorbed at the solid/water and oil/water interfaces
- 2003
-
In: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 225, s. 181-192
-
Journal article (peer-reviewed)abstract
- We report on the interfacial behaviour of a series of nonionic diblock copolymers at solid hydrophobic and hydrophilic surfaces/water and silicone oil/water interfaces, studied by ellipsometry. The polymers consist of a hydrophobic C18 chain linked to a hydrophilic poly(ethylene oxide) (PEO), block varying from 50 to 250 U. The adsorption of these copolymers at low bulk concentrations was found to be dominated by the PEO block at all interfaces. At higher concentration the copolymer forms surface aggregates at the silica surface whereas we observe a gradual increase in the adsorbed layer thickness with increased surface excess at the solid hydrophobic surface, indicating a transition from a flat conformation to brush-like layer structure. The results indicate a similar evolution in adsorbed amount with concentration at the silicone oil/water interface as at the hydrophobic silica surface. The influence of the rheological properties of the interface on the adsorption of the diblock copolymer was investigated by comparing results from two silicon oils with different viscosities. The copolymers were found to have stronger affinity to a low viscosity (990 mPa s) silicone oil than to a higher viscosity (12800 mPa s) silicone oil and the hydrophobised silica surface. At the silicone oil/water interface the adsorption of a commercial nonionic triblock copolymer was furthermore investigated and compared with the diblock copolymers
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