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  • 1.
    Ahmed, Hesham
    et al.
    Department of Materials Science and Engineering, Royal Institute of Technology.
    El-Geassy, Abdel Hady
    Central Metallurgical Research and Development Institute (CMRDI), Helwan, Cairo.
    Seetharaman, Seshadri
    Kungliga tekniska högskolan, KTH.
    Kinetics of Reduction of NiO–WO3 Mixtures by Hydrogen2010In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 41, no 1, p. 161-172Article in journal (Refereed)
    Abstract [en]

    The kinetics of reduction of the oxide mixtures of Ni-W with different Ni/(Ni-W) molar ratios within the range of 923 K to 1173 K in flowing hydrogen gas was investigated by means of thermogravimetric analysis under isothermal conditions. The products were examined by X-ray diffraction, scanning electron microscope (SEM), and electron dispersion spectroscopy (EDS) analyses. Five different oxide mixtures apart from the pure oxides were studied in the present work. The results indicate that the reduction reaction proceeds through three consecutive steps that are as follows:NiO-WO3→Ni-WO3→Ni-WO2→Ni-WFrom the experimental results, the Arrhenius activation energies of the three steps were evaluated for all of the studied compositions. The activation energy for the first step was calculated to be approximately 18 kJ/mol. For the second and third stages, the activation energy values varied from 62 to 38 kJ/mol for the second stage and 51 to 34 kJ/mol for the third stage depending on the Ni/(Ni + W) molar ratio in the precursors; the activation energy increased with increasing ratios. SEM images showed that the grain size of the final product was dependent on the Ni/(Ni + W) molar ratio; smaller grains were formed at higher nickel contents.

  • 2.
    Ahmed, Hesham
    et al.
    Department of Materials Science and Engineering, Royal Institute of Technology.
    Seetharaman, Seshadri
    Kungliga tekniska högskolan, KTH.
    Reduction-Carburization of NiO-WO3 Under Isothermal Conditions Using H2-CH4 Gas Mixture2010In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 41, no 1, p. 173-181Article in journal (Refereed)
    Abstract [en]

    Ni-W-C ternary carbides were synthesized by simultaneous reduction–carburization of NiO-WO3 oxide precursors using H2-CH4 gas mixtures in the temperature range of 973 to 1273 K. The kinetics of the gas–solid reaction were followed closely by monitoring the mass changes using the thermogravimetric method (TGA). As a thin bed of the precursors were used, each particle was in direct contact with the gas mixture. The results showed that the hydrogen reduction of the oxide mixture was complete before the carburization took place. The nascent particles of the metals formed by reduction could react with the gas mixture with well-defined carbon potential to form a uniform product of Ni-W-C. Consequently, the reaction rate could be conceived as being controlled by the chemical reaction. From the reaction rate, Arrhenius activation energies for reduction and carburization were evaluated. Characterization of the carbides produced was carried out using X-ray diffraction and a scanning electron microscope (SEM) combined with electron dispersion spectroscopy (SEM-EDS) analyses. The grain sizes also were determined. The process parameters, such as the temperature of the reduction–carburization reaction and the composition of the gas mixture, had a strong impact on the carbide composition as well as on the grain size. The results are discussed in light of the reduction kinetics of the oxides and the thermodynamic constraints.

  • 3.
    Albertsson, Galina Jelkina
    et al.
    Division of Materials Process Science, Royal Institute of Technology (KTH).
    Teng, Lidong
    Division of Materials Process Science, Royal Institute of Technology (KTH).
    Engström, Fredrik
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Seetharaman, Seshadri
    Division of Materials Process Science, Royal Institute of Technology (KTH).
    Effect of the heat treatment on the chromium partition in CaO-MgO-SiO2-Cr2O3 synthetic slags2013In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 44, no 6, p. 1586-1597Article in journal (Refereed)
    Abstract [en]

    Mg-spinel phase is known to be important for control of Cr leaching from Cr-containing slags. The objective of the present study is to get an understanding of the phase relationships in the CaO-MgO-SiO2-Cr2O3 system with a view to control the precipitation of Cr-spinel in the slag phase. The equilibrium phases in CaO-MgO-SiO2-Cr2O3 slag system in the range of 1673 K to 1873 K (1400 °C to 1600 °C) have been investigated experimentally and compared with the results from thermodynamic calculations. The slag compositions close to the industrial slag systems were chosen. The Cr2O3 and MgO contents in the slag were fixed to be 6 and 8 wt pct, respectively. The basicity (CaO/SiO2) of the slag was varied in the range of 1.0 to 2.0. The slags were synthesized at a pre-determined oxygen partial pressure (10-4) or air (2.13 × 104 Pa) at a temperature above the liquidus temperature. The samples were then soaked at targeted temperatures for 24 hours in controlled atmosphere in order to achieve the equilibrium state before quenching in water. Four different heat-treatment regimes (defined as Ia, Ib, II.a and II.b) in Section II-D) were used in the present experiments. The lower oxygen partial pressure was maintained by a suitable mixture of CO and CO2 gases. Phases present and their compositions in the quenched slags were studied using scanning electron microscopy coupled with energy-dispersive spectroscopy and X-ray diffraction techniques. The chromium content in the phases present was analyzed using wavelength-dispersive spectrometer. The experimental results obtained are compared with the calculation results from Factsage software. The size of spinel crystals increased drastically after slow-cooling from 1873 K (1600 °C) followed by annealing at 1673 K (1400 °C) for 24 hours (heating regimes II) compared to samples being quenched directly after soaking at 1873 K (1600 °C) (heating regime I.a). It was found that the amount of foreign elements in the spinel phase, and other phases decreased after soaking at oxygen partial pressure of 10-4 Pa resulting in phases with less defects and foreign oxide contents compared to those treated in air. The size of spinel crystals was found to be larger in samples with lower basicity

  • 4.
    Beskow, Kristina
    et al.
    Department of Materials Science and Engineering, Division of Metallurgy, Royal Institute of Technology.
    Nurni, Viswanathan
    Jonsson, Lage T.I.
    Department of Materials Science and Engineering, Division of Metallurgy, Royal Institute of Technology.
    Sichen, Du U.
    Department of Materials Science and Engineering, Division of Metallurgy, Royal Institute of Technology.
    Study of the deoxidation of steel with aluminum wire injection in a gas-stirred ladle2001In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 32, no 2, p. 319-328Article in journal (Refereed)
    Abstract [en]

    In the present work, the deoxidation of liquid steel with aluminum wire injection in a gas-stirred ladle was studied by mathematical modeling using a computational fluid dynamics (CFD) approach. This was complemented by an industrial trial study conducted at Uddeholm Tooling AB (Hagfors, Sweden). The results of the industrial trials were found to be in accordance with the results of the model calculation. In order to study the aspect of nucleation of alumina, emphasis was given to the initial period of deoxidation, when aluminum wire was injected into the bath. The concentration distributions of aluminum and oxygen were calculated both by considering and not considering the chemical reaction. Both calculations revealed that the driving force for the nucleation of Al2O3 was very high in the region near the upper surface of the bath and close to the wire injection. The estimated nucleation rate in the vicinity of the aluminum wire injection point was much higher than the recommended value for spontaneously homogeneous nucleation, 103 nuclei/(cm3/s). The results of the model calculation also showed that the alumina nuclei generated at the vicinity of the wire injection point are transported to other regions by the flow.

  • 5.
    Bustnes, J.A.
    et al.
    LKAB, Research & Development, 983 81 Malmberget.
    Nurni, Viswanathan
    Sichen, Du U.
    LKAB, Research & Development, 983 81 Malmberget.
    Seetharaman, Seshadri
    Division of Metallurgy, Department of Materials Science and Technology, Royal Institute of Technology.
    Investigation on reduction of CoAI2O4 by hydrogen gas using TGA2000In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 31, no 3, p. 540-542Article in journal (Refereed)
  • 6.
    Gedda, Hans
    et al.
    Luleå tekniska universitet.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Powell, John
    Melt-solid interactions in laser cladding and laser casting2005In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 36B, no 5, p. 683-689Article in journal (Refereed)
    Abstract [en]

    Experimental data in conjunction with mathematical models are used to explain various aspects of laser casting and laser cladding by the preplaced powder method. For increasing speed, the data can be distinguished between substrate melting, dilution-free clad bonding, bond-free casting, and poor contact breaking the melt track into spheres. Results include a thermodynamic explanation of the wide range of process parameters over which dilution-free clad deposits can be produced, as the process switches from heating of the insulating powder to additional cooling when the melt front reaches the substrate. Also, the interaction of the melt pool with the powder bed is analyzed to identify why laser castings have microscopically uneven surfaces and do not bind with the substrate. The advancement of the melt front through the powder layer is governed by heating, melting, and incorporation of each individual grain. Although most powder grains are in the small size range for the case studied, the few particles up to a factor 3 larger delay and therefore govern the front advancement due to much slower melting and surface tension driven incorporation, depending on the particle size in a nonlinear manner. [Substrate: mild steel; cladding material: Co-base alloy].

  • 7.
    Haapakangas, Juho
    et al.
    Process Metallurgy, University of Oulu.
    Suopajärvi, Hannu
    Process Metallurgy, University of Oulu.
    Iljana, Mikko
    Process Metallurgy, University of Oulu.
    Kemppainen, Antti
    Process Metallurgy, University of Oulu.
    Mattila, Olli
    SSAB Europe Oy, Rautaruukintie 155, P.O Box 93, 92101, Raahe.
    Heikkinen, Eetu-Pekka
    Process Metallurgy, University of Oulu.
    Samuelsson, Caisa
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Fabritius, Timo
    Process Metallurgy, University of Oulu.
    Coke Reactivity in Simulated Blast Furnace Shaft Conditions2016In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 47, no 4, p. 2357-2370Article in journal (Refereed)
    Abstract [en]

    Despite the fact that H2 and H2O are always present in the gas atmosphere of a blast furnace shaft, their role in the solution-loss reactions of coke has not been thoroughly examined. This study focuses on how H2 and H2O affect the reaction behavior and whether a strong correlation can be found between reactivity in the conditions of the CRI test (Coke Reactivity Index) and various simulated blast furnace shaft gas atmospheres. Partial replacement of CO/CO2 with H2/H2O was found to significantly increase the reactivity of all seven coke grades at 1373 K (1100 °C). H2 and H2O, however, did not have a significant effect on the threshold temperature of gasification. The reactivity increasing effect was found to be temperature dependent and clearly at its highest at 1373 K (1100 °C). Mathematical models were used to calculate activation energies for the gasification, which were notably lower for H2O gasification compared to CO2 indicating the higher reactivity of H2O. The reactivity results in gas atmospheres with CO2 as the sole gasifying component did not directly correlate with reactivity results in gases also including H2O, which suggests that the widely used CRI test is not entirely accurate for estimating coke reactivity in the blast furnace.

  • 8.
    Jakobsson, Anders
    et al.
    Division of Metallurgy, Department of Materials Science and Technology, Royal Institute of Technology.
    Nurni, Viswanathan
    Sichen, Du U.
    Division of Metallurgy, Department of Materials Science and Technology, Royal Institute of Technology.
    Seetharaman, Seshadri
    Division of Metallurgy, Department of Materials Science and Technology, Royal Institute of Technology.
    Interfacial phenomena in some slag-metal reactions2000In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 31, no 5, p. 973-980Article in journal (Refereed)
    Abstract [en]

    In the present work, the change of the interfacial tension at the slag-metal interface for sulfur transfer between molten iron, slag, and gas phases was monitored by X-ray sessile drop method in dynamic mode in the temperature range of 1830 to 1891 K. The experiments were carried out with pure iron samples immersed partly or fully in the slag phase. The slag consisted of 30 wt pct CaO, 50 wt pct Al2O3, and 20 wt pct SiO2 (alumina saturated at the experimental temperatures) with additions of FeO. Metal and slag samples contained in alumina crucibles were exposed to a CO-CO2-SO2-Ar gas mixture with defined oxygen and sulfur partial pressures, and the change of the shape of the metal drop was determined as a function of time. The equipment and the technique were calibrated by measurements of the surface tensions of the pure Cu, Ni, and Fe containing two different amounts of dissolved oxygen. A theoretical model was developed to determine the sulfur content of the metal as a function of time on the basis of sulfur diffusion in the slag and metal phases as well as surface tension-induced flow on the metal drop surface. Attempts were made to compute the interfacial tensions on the basis of force balance.

  • 9.
    Kanari, N.
    et al.
    Centre National de la Recherche Scientifique, Mineral Processing Environmental Engineering Team.
    Gaballah, I.
    National de la Recherche Scientifique, Mineral Processing Environmental Engineering Team.
    Allain, E.
    Center of Pyrometallurgy, Department of Metallurgical Engineering, University of Missouri Rolla.
    Menad, Nourreddine
    Chlorination of chalcopyrite concentrates1999In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 30B, no 4, p. 567-576Article in journal (Refereed)
    Abstract [en]

    The chlorination behaviors of two chalcopyrite concentrates and their pure constituents in Cl^sub 2^ + N^sub 2^ were investigated by thermogravimetric analysis (TGA) in nonisothermal conditions up to 1000 deg C. The effect of temperature on the reaction of chlorine with both concentrates was studied between 170 deg C and 300 deg C under isothermal conditions. The effects of gas flow rate, chlorine content of the gas mixture, and reaction time on the reaction rate were also investigated. The reaction products were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Results showed that the kinetics of chlorination of chalcopyrite concentrates generating chlorides of Cu, Pb, Zn, Fe, and S was rapid at about 300 deg C. The iron and sulfur chlorides were volatilized, leading to a residue containing valuable metal chlorides.

  • 10.
    Kiamehr, Saeed
    et al.
    Royal Institute of Technology (KTH).
    Ahmed, Hesham
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Nurni, Viswanathan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Seetharaman, Seshadri
    Division of Materials Process Science, KTH-Royal Institute of Technology .
    Changes in Effective Thermal Conductivity During the Carbothermic Reduction of Magnetite Using Graphite2017In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 48, no 3, p. 1502-1513Article in journal (Refereed)
    Abstract [en]

    Knowledge of the effective thermal diffusivity changes of systems undergoing reactions where heat transfer plays an important role in the reaction kinetics is essential for process understanding and control. Carbothermic reduction process of magnetite containing composites is a typical example of such systems. The reduction process in this case is highly endothermic and hence, the overall rate of the reaction is greatly influenced by the heat transfer through composite compact. Using Laser-Flash method, the change of effective thermal diffusivity of magnetite-graphite composite pellet was monitored in the dynamic mode over a pre-defined thermal cycle (heating at the rate of 7 K/min to 1423 K (1150 °C), holding the sample for 270 minutes at this temperature and then cooling it down to the room temperature at the same rate as heating). These measurements were supplemented by Thermogravimetric Analysis under comparable experimental conditions as well as quenching tests of the samples in order to combine the impact of various factors such as sample dilatations and changes in apparent density on the progress of the reaction. The present results show that monitoring thermal diffusivity changes during the course of reduction would be a very useful tool in a total understanding of the underlying physicochemical phenomena. At the end, effort is made to estimate the apparent thermal conductivity values based on the measured thermal diffusivity and dilatations.

  • 11.
    Kumar, TK Sandeep
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Nurni, Viswanathan
    Indian Institute of Technology Bombay.
    Ahmed, Hesham
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering. Central Metallurgical Research& Development Institute (CMRDI).
    Andersson, Charlotte
    LKAB, Research & Development.
    Björkman, Bo
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Erratum to: Estimation of Sintering Kinetics of Magnetite Pellet Using Optical Dilatometer2017In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 48, no 1, p. 743-745Article in journal (Refereed)
    Abstract [en]

    Authors have used a new way for measuring bulk volume based on the image (pixel) analysis named as Light Table Imaging (LTI), and subsequently bulk densities and porosities. Authors lately found that there was a slight error in calibrating the scale (known distance) to pixel measurement and understand the need to communicate the error and subsequent corrections.  

  • 12.
    Kumar, TK Sandeep
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Nurni, Viswanathan
    Indian Institute of Technology Bombay.
    Ahmed, Hesham
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Andersson, Charlotte
    LKAB, Research & Development.
    Björkman, Bo
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Erratum to: Estimation of Sintering Kinetics of Oxidized Magnetite Pellet Using Optical Dilatometer2017In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 48, no 1, p. 746-748Article in journal (Refereed)
    Abstract [en]

    Authors have used a new way for measuring bulk volume based on the image (pixel) analysis named as Light Table Imaging (LTI), and subsequently bulk densities and porosities. Authors lately found that there was a slight error in calibrating the scale (known distance) to pixel measurement and understand the need to communicate the error and subsequent corrections.  

  • 13.
    Kumar, TK Sandeep
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Nurni, Viswanathan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Ahmed, Hesham
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Andersson, Charlotte
    LKAB, Research & Development, 983 81 Malmberget.
    Björkman, Bo
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Estimation of Sintering Kinetics of Oxidized Magnetite Pellet Using Optical Dilatometer2015In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 46, no 2, p. 635-643Article in journal (Refereed)
    Abstract [en]

    The quality of magnetite pellet is primarily determined by the physico-chemical changes thepellet undergoes as it makes excursion through the gaseous and thermal environment in theinduration furnace. Among these physico-chemical processes, the oxidation of magnetite phaseand the sintering of oxidized magnetite (hematite) and magnetite (non-oxidized) phases are vital.Rates of these processes not only depend on the thermal and gaseous environment the pellet getsexposed in the induration reactor but also interdependent on each other. Therefore, a systematicstudy should involve understanding these processes in isolation to the extent possible andquantify them seeking the physics. With this motivation, the present paper focusses on investigatingthe sintering kinetics of oxidized magnetite pellet. For the current investigation, sinteringexperiments were carried out on pellets containing more than 95 pct magnetiteconcentrate from LKAB’s mine, dried and oxidized to completion at sufficiently low temperatureto avoid sintering. The sintering behavior of this oxidized pellet is quantified throughshrinkage captured by Optical Dilatometer. The extent of sintering characterized by sinteringratio found to follow a power law with time i.e., Ktn. The rate constant K for sintering wasdetermined for different temperatures from isothermal experiments. The rate constant, K, varieswith temperature as lnTKð1=nÞ ¼ lnK0 QRT ; and the activation energy (Q) and reaction rateconstant (K¢) are estimated. Further, the sintering kinetic equation was also extended to a nonisothermalenvironment and validated using laboratory experiments.

  • 14.
    Kumar, TK Sandeep
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Nurni, Viswanathan
    Indian Institute of Technology Bombay.
    Ahmed, Hesham
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Andersson, Charlotte
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Dahlin, Anders
    LKAB.
    Björkman, Bo
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Investigation of Magnetite Oxidation Kinetics at the Particle Scale2019In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 50, no 1, p. 150-161Article in journal (Refereed)
    Abstract [en]

    The induration of magnetite pellets is a complex physico-chemical process that involves oxidation, sintering, and heat transfer. The thermal- and gas-composition profile that is experienced by the pellet in an induration reactor could result in the formation of a homogenous or heterogeneous pellet structure, which could affect the pellet quality. The oxidation kinetics of magnetite pellets from sintering studies have been studied at two levels, namely, the pellet scale and at the particle scale, and the findings of the latter are presented here. The rate of oxidation of the magnetite concentrate depends primarily on temperature, oxygen content in the oxidizing gas, and particle size. These factors are investigated in this study. It was found that the oxidation of the magnetite concentrate is comprised of two distinct stages, a primary stage with high rates followed by a secondary stage where rates decrease significantly. The isothermal oxidation behavior as analyzed by the Avrami kinetic model was found to fit better than the shrinking-core model. The partially oxidized particles were examined microstructurally to supplement the experimental and model results. The Avrami kinetic model for isothermal oxidation was extended to non-isothermal profiles using the superposition principle, and the model was validated experimentally.

  • 15.
    Kumar, TK Sandeep
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Nurni, Viswanathan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering. Department of Metallurgical Engineering & Materials ScienceIndian Institute of Technology Bombay (IITB).
    Ahmed, Hesham M.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering. Central Metallurgical Research & Development Institute (CMRDI).
    Andersson, Charlotte
    LKAB, Research & Development, 983 81 Malmberget.
    Björkman, Bo
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Estimation of Sintering Kinetics of Magnetite Pellet Using Optical Dilatometer2016In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 47, no 1, p. 309-319Article in journal (Refereed)
    Abstract [en]

    During induration of magnetite pellets, oxidation of magnetite followed by sintering of the oxidized magnetite (hematite) is desirable. Sintering of magnetite which hampers the oxidation of magnetite is aimed to be kept as low as possible. In succession to our earlier study on sintering behavior of oxidized magnetite (hematite), this paper focusses on the sintering behavior of magnetite phase in isolation with an objective to estimate their kinetic parameters. The pellets prepared from the concentrate of LKAB’s mine, which majorly contains (>95 pct) magnetite, are used for the sintering studies. Optical Dilatometer is used to capture the sintering behavior of the magnetite pellet and determine their isothermal kinetics by deducing the three parameters, namely—activation energy (Q), pre-exponential factor (K′), and time exponent (n) with the help of power law and Arrhenius equation. It is interesting to find that the time exponent (n) is decreasing with the increase in sintering temperature. It is also interesting to note that the activation energy for sintering of magnetite pellet shows no single value. From the present investigation, two activation energies—477 kJ/mole [1173 K to 1373 K (900 °C to 1100 °C)] and 148 kJ/mole [1373 K to 1623 K (1100 °C to 1350 °C)]—were deduced for sintering of magnetite, suggesting two different mechanisms operating at lower and other at higher temperatures. The estimated kinetic parameters were used to predict the non-isothermal sintering behavior of magnetite using the sintering kinetic model. Predicted results were validated using experimental data.

  • 16.
    Kumar, TK Sandeep
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Viswanathan, N. N
    Indian Institute of Technology Bombay (IITB)MumbaiIndia.
    Ahmed, Hesham
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering. Center of Metallurgical Research and Development InstituteCairoEgypt.
    Dahlin, A.
    Luossavaara-Kiirunavara Aktiebolag (LKAB)MalmbergetSweden.
    Andersson, Charlotte
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Björkman, Bo
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Developing the Oxidation Kinetic Model for Magnetite Pellet2019In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 50, no 1, p. 162-172Article in journal (Refereed)
    Abstract [en]

    Oxidation is a vital phenomenon for magnetite pellets in their excursion through the furnace during induration. One of the pre-requisites for magnetite pellets to achieve homogeneously structured good quality pellets is to have complete oxidation before sintering begins. Partially oxidized magnetite pellets, upon sintering, might result in inhomogeneous structured pellets which could be detrimental to pellet quality. It is necessary to understand the mechanisms responsible for magnetite oxidation, and hence, it is intended in this study to investigate experimentally as well as develop a mathematical model based on oxidation kinetics. Oxidation of pellets is largely influenced by the oxidation kinetics of particles and hence should be studied at particle as well as at pellet scale. The principles of the Grain Model have been adopted to develop the Oxidation Model at pellet scale, whereas the particles’ oxidation follows the Avrami Kinetic Model. Isothermal oxidation experiments performed Thermogravimetric Analyzer showed that oxidation rate of magnetite at pellet scale contained two peaks. They were complemented well by oxidation rates predicted from the model. Further, the pellet was investigated microstructurally at pellet and particle scale to substantiate the findings from the experiments and the model. The oxidation model developed is used to predict the progression of oxidation in the magnetite pellet with respect to the reaction time at three different temperatures (873 K, 973 K, and 1073 K (600 °C, 700 °C, and 800 °C)) and at four levels of oxygen (0.21, 0.30, 0.60, and 1.00 atm) in the oxidizing gas.

  • 17.
    Lehner, Theo
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Kho, T.S.
    School of Civil and Chemical Engineering, RMIT University, Melbourne.
    Swinbourne, D.R.
    School of Civil and Chemical Engineering, RMIT University, Melbourne.
    Cobalt distribution during copper matte smelting2006In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 37, no 2, p. 209-214Article in journal (Refereed)
    Abstract [en]

    Many smelter operators subscribe to the "precautionary principle" and wish to understand the behavior of the metals and impurities during smelting, especially how they distribute between product and waste phases and whether these phases lead to environmental, health, or safety issues. In copper smelting, copper and other elements are partitioned between copper matte, iron silicate slag, and possibly the waste gas. Many copper concentrates contain small amounts of cobalt, a metal of considerable value but also of some environmental interest. In this work, the matte/slag distribution ratio (weight percent) of cobalt between copper matte (55 wt pet) and iron silicate slag was thermodynamically modeled and predicted to be approximately 5. Experiments were performed using synthetic matte and slag at 1250 °C under a low oxygen partial pressure and the distribution ratio was found to be 4.3, while between industrial matte and slag, the ratio was found to be 1.8. Both values are acceptably close to each other and to the predicted value, given the errors inherent in such measurements. The implications of these results for increasingly sustainable copper production are discussed

  • 18.
    Lundgren, Maria
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering.
    Khanna, Rita N.
    SMaRT Centre, School of Materials Science and Engineering, The University of New South Wales.
    Ökvist, Lena Sundqvist
    Swerea MEFOS AB.
    Sahajwalla, Veena
    SMaRT Centre, School of Materials Science and Engineering, The University of New South Wales.
    Björkman, Bo
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    The Evolution of Structural Order as a Measure of Thermal History of Coke in the Blast Furnace2014In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 45, no 2, p. 603-616Article in journal (Refereed)
    Abstract [en]

    Investigations were carried out on cokes heat treated in the laboratory and on cokes extracted from the experimental blast furnace (EBF) raceway and hearth. X-ray diffraction (XRD) measurements were performed to investigate changes in structural order (Lc), chemical transformations in coke ash along with comparative thermodynamic equilibrium studies and the influence of melt. Three data processing approaches were used to compute Lc values as a function of temperature and time and linear correlations were established between Lc and heat treatment temperatures during laboratory investigations. These were used to estimate temperatures experienced by coke in various regions of EBF and estimated raceway temperatures were seen to follow the profile of combustion peak. The MgAl2O4 spinel was observed in coke submerged in slag during laboratory studies and in cokes found further into the raceway. Coke in contact with hot metal showed XRD peaks corresponding to presence of Fe3Si. The intensity of SiO2 peak in coke ash was seen to decrease with increasing temperature and disappeared at around 1770 K (1500 °C) due to the formation of SiC. This study has shown that the evolution of structural order and chemical transformations in coke could be used to estimate its thermal history in blast furnaces.

  • 19.
    Muhmood, Luckman
    et al.
    Division of Materials Process Science, Department of Materials Science and Engineering, Royal Institute of Technology.
    Nurni, Viswanathan
    Iwase, Masanori
    Thermochemistry Group, Department of Energy Science and Technology, Kyoto University.
    Seetharaman, Seshadri
    Division of Materials Process Science, Department of Materials Science and Engineering, Royal Institute of Technology.
    Evaluating the diffusion coefficient of sulfur in low-silica CaO-SiO 2-Al 2O 3 slag2011In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 42, no 2, p. 274-280Article in journal (Refereed)
    Abstract [en]

    The chemical diffusion coefficient of sulfur in the ternary slag of composition 51.5 pct CaO-9.6 pct SiO 2-38.9 pct Al 2O 3 slag was measured at 1680 K, 1700 K, and 1723 K (1403 °C, 1427 °C, and 1450 °C) using the experimental method proposed earlier by the authors. The P S2 and P O2 pressures were calculated from the Gibbs energy of the equilibrium reaction between CaO in the slag and solid CaS. The density of the slag was obtained from earlier experiments. Initially, the order of magnitude for the diffusion coefficient was taken from the works of Saito and Kawai but later was modified so that the concentration curve for sulfur obtained from the program was in good fit with the experimental results. The diffusion coefficient of sulfur in 51.5 pct CaO-9.6 pct SiO 2-38.9 pct Al 2O 3 slag was estimated to be in the range 3.98 to 4.14 × 10 -6cm 2/s for the temperature range 1680 K to 1723 K (1403 °C to 1450 °C), which is in good agreement with the results available in literature

  • 20.
    Muhmood, Luckman
    et al.
    Division of Materials Process Science, Department of Materials Science and Engineering, Royal Institute of Technology.
    Nurni, Viswanathan
    Seetharaman, Seshadri
    Division of Materials Process Science, Department of Materials Science and Engineering, Royal Institute of Technology.
    A proposal for a novel method to measure the diffusivity of species in slag2011In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 42, no 2, p. 393-399Article in journal (Refereed)
    Abstract [en]

    The rate of reactions involved in steel-refining operations largely depend on the transport of species through the slag or metal phase at steel refining temperatures; the intrinsic reaction rates are expected to be high. Therefore, the study of diffusivity of species in slag is of great importance. The present work proposes a new methodology, in which experiments can be designed to determine the diffusivity of species in liquid slag. In this article, a mathematical description for the methodology is formulated and subsequently solved using numerical methods. This exercise will help in identifying appropriate bounds for experimental parameters for a desired accuracy. The proposed methodology is generic for any species in the liquid slag phase. However, diffusion of sulfur through slag has been illustrated as a case study. The order of magnitude for the diffusion coefficient for sulfur was taken from the classic works of Saito and Kawai, the sulfide capacity and sulfur partition ratio were retrieved from the works of Taniguchi et al., and the slag density was retrieved from earlier experimental results of the present authors. The slag density was obtained from earlier experimental results from the present group. The Henrian activity coefficients were retrieved from literature. Subsequent to the present work, the design of experiments and measurements carried out using the proposed methodology and the results obtained are presented as the second article on this subject.

  • 21.
    Muhmood, Luckman
    et al.
    Department of Materials Science and Engineering, Division of Materials Process Science, Royal Institute of Technology.
    Nurni, Viswanathan
    Seetharaman, Seshadri
    Department of Materials Science and Engineering, Division of Materials Process Science, Royal Institute of Technology.
    Some investigations into the dynamic mass transfer at the slag-metal interface using sulfur: Concept of interfacial velocity2011In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 42, no 3, p. 460-470Article in journal (Refereed)
    Abstract [en]

    In the current work, dynamic studies of mass transfer of sulfur from the gas phase to the metal phase of pure iron through CaO-SiO2-Al 2O3-FeO quaternary slag were carried out. X-ray videos were taken that were later processed to identify the oscillation of the metal drop occurring during the mass transfer. It was observed that the metal drop had hybrid oscillations. Each of these oscillations could be identified as composed of a symmetric and an asymmetric element, which was attributed to the changes in the shape of the droplet. The latter (asymmetric part) could be identified by the deviation of the left and right contact angles from the stable configuration. The symmetric oscillations were traced to the surface movement of sulfur at the interface, which created an instantaneous area change at the slag-metal interface. This area change was due to the combined effect of Marangoni flow and interface dilatation. The velocity of sulfur at the interface was calculated from the area change and had a maximum order of magnitude as 10-4 m/s. It was also observed that the interfacial velocity increased with increase in temperature

  • 22.
    Wang, L.J.
    et al.
    Collaborative Innovation Center of Steel Technology, University of Science and Technology Beijing.
    Nurni, Viswanathan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Muhmood, Luckman
    Department of Materials Science and Engineering, Division of Materials Process Science, Royal Institute of Technology, Aditya Birla Science and Technology Company Ltd, Navi Mumbai, KJ Somaiya College of Engineering, Mumbai.
    Kapilashrami, E.
    SSAB Oxelösund AB.
    Seetharaman, Seshadri
    Division of Materials Process Science, Department of Materials Science and Engineering, Royal Institute of Technology, Kungliga tekniska högskolan, KTH, Department of Metallurgy, Royal Institute of Technology, Stockholm, Division of Metallurgy, Department of Materials Science and Technology, Royal Institute of Technology.
    Some Aspects of Interfacial Phenomena in Steelmaking and Refining2016In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 47, no 4, p. 2107-2113Article in journal (Refereed)
    Abstract [en]

    Unique experiments were designed to study the surface phenomena in steelmaking reactions. The concept of surface sulfide capacities and an understanding of the surface accumulation of surface-active species, based on experimental results, are presented. In order to understand the flow phenomenon at slag/metal interface, experiments were designed to measure the interfacial velocity of S on the surface of an iron drop immersed in an aluminosilicate slag using the X-ray sessile drop method. The oscillation of the iron drop in the slag due to the change in the surface concentration of sulfur at the slag–metal interface was monitored by X-ray imaging. From the observations, the interfacial velocity of sulfur was evaluated. Similar experiments were performed to measure the interfacial velocity of oxygen at the interface as well as the impact of oxygen potential on the interfacial velocity of sulfur. The interfacial shear viscosity and the dilatational modulus were also evaluated. In a study of the wetting of alumina base by iron drop at constant oxygen pressure under isothermal condition, the contact angle was found to be decreased with the progress of the reaction leading to the formation of hercynite as an intermediate layer creating non-wetting conditions. In the case of silica substrate, an intermediate liquid fayalite layer was formed

1 - 22 of 22
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