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  • 101.
    Tomé Torquemada, Silvia
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Sichen, Du
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Experimental study on the activity of calcium in liquid silicon2019In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916Article in journal (Other academic)
  • 102.
    Tomé Torquemada, Silvia
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Vickerfält, Amanda
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Sichen, Du
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Experimental study on the activities of Sr, Al and Zr in liquid silicon2019In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916Article in journal (Other academic)
    Abstract [en]

    Experiments were carried out to determine the activities of Sr, Al and Zr in liquid silicon at temperatures between 1723K and 1873K (1450°C and 1600°C). Different oxide pellets, made of a SrSiO3-Sr2SiO4 mixture, an Al2O3-Al6Si2O13 mixture and a ZrSiO4-SiO2 mixture (for the Sr-Si system, Al-Si system and Zr-Si system respectively), were equilibrated with liquid silicon in a closed system. The activities of the metals in the silicon were calculated based on the contents of the element dissolved in the silicon. The temperature had negligible effect on the activity coefficients for the Sr and Al in the liquid silicon at the temperature range studied, while the activity coefficient of Zr in liquid silicon increased with temperature.

  • 103. Tripathi, N.
    et al.
    Sichen, Du
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Chemical characterisation of non-metallic inclusions during casting of hot work die steel2006In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 33, no 3, p. 213-222Article in journal (Refereed)
    Abstract [en]

    A chemical characterisation of the non-metallic inclusions in the aluminium killed tool steels during the casting process has been performed. The steel samples taken during the mould fillings, after casting and from the final products have been studied. The chemical compositions of the different phases in the inclusions have been analysed using SEM/EDX. Three types of inclusions, namely, type 6 ( spinel surrounded by the calcium-aluminate oxide solution), type 7 ( calcium-aluminate oxide solution) and type 9 ( alumina based inclusions) have been found in the steel samples during the mould filling. Type 9 inclusions originate from the erosion of the nozzles and the closing gates during the mould fillings. The steel samples after casting contain four types of inclusions namely, types 6, 7, 9, 10 ( alumina-silicate oxide solution) and 11 ( spinel phase with calcium sulphide). The types of inclusions vary with the position in the ingot. In the steel samples from the final products three types of inclusions were detected, namely types 6, 7 and 11. The investigation have revealed that the increase in the sulphur activity of the steel melt during the casting is the cause of the formation of oxide sulphide and calcium sulphide phases in the inclusions detected after casting and in the final products.

  • 104. Viswanathan, N
    et al.
    Ji, F.-Z.
    Sichen, Du
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Dynamic Viscosity Measurements on Fayalite Slag2001In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 41, p. 722-727Article in journal (Refereed)
  • 105. Wang, Daya
    et al.
    Yan, Baijun
    Du, Sichen
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Reply to the "Discussion of Determination of Activities of Niobium in Cu-Nb Melts Containing Dilute Nb"2015In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 46, no 5, p. 2019-2019Article in journal (Other academic)
    Abstract [en]

    Daya Wang, Baijun Yan, and Du Sichen replied to the observations made by Professor Jacob on their study on the determination of activities of niobium in Cu-Nb Melts containing dilute Nb. The authors compared the observations and findings of Professor Jacob with their own data using pure liquid as standard state. The authors stated that in their experiments, the solid powder that had equilibrated with liquid copper in the lowest and highest oxygen partial pressures at all experimental temperatures was identified by XRD.

  • 106. Wang, Daya
    et al.
    Yan, Baijun
    Sichen, Du
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Determination of Activities of Niobium in Cu-Nb Melts Containing Dilute Nb2015In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 46, no 2, p. 533-536Article in journal (Refereed)
    Abstract [en]

    The activity coefficients of niobium in Cu-Nb melts were measured by equilibrating solid NbO2 with liquid copper under controlled oxygen potentials in the temperature range of 1773 K to 1898 K (1500 degrees C to 1625 degrees C). Either CO-CO2 gas mixture or H-2-CO2 gas mixture was employed to obtain the desired oxygen partial pressures. Cu-Nb system was found to follow Henry's law in the composition range studied. The temperature dependence of Henry's constant in the Cu-Nb melts could be expressed as follows: log gamma(0)(Nb(l)) = 3305/T + 0.72. The partial molar excess Gibbs energy change of niobium in Cu-Nb melts can be expressed as follows: Delta(G) over bar (ex)(Nb) = 63,280 + 13.2T(J/mol)

  • 107. Wang, Hui
    et al.
    Li, Fan
    Sichen, Du
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Development of an Analytical Technique to Determine the Fractions of Vanadium Cations with Different Valences in Slag2011In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 42, no 1, p. 9-12Article in journal (Refereed)
    Abstract [en]

    The current work aimed to develop a reliable method to analyze the amounts of different vanadium cations in metallurgical slag. The application of the technique to the samples of supercooled slag showed its applicability and reliability.

  • 108.
    Wang, Hui
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Xiao, Yiwu
    Jiang, Kaixi
    Sichen, Du
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Development of an analytical technique to quantify Cr2+ and Cr3+ in metallurgical slags2008In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 39, no 2, p. 390-393Article in journal (Refereed)
    Abstract [en]

    Knowledge of thermodynamic properties of chromium oxides in molten slags is very important for the optimization of the steel making processes of stainless and high-alloying steels as well as the processes of chromium ores. Despite this importance, the thermodynamic data for chromium oxides at steel making temperatures are still too scarce to meet the demand. Only a few experimental studies are found in the literature.[1-5] Chromium exists in the form of ions, namely, Cr2+, Cr3+, and even Cr6+ in oxide solutions. The fractions of these irons depend not only on temperature but also on the chemical potentials of chromium and oxygen in the system. In the slags of steel making, chromium would mostly take the form of Cr(2+)and Cr3+. The difficulties associated with maintaining the fractions of these ions and accurate determination of the same are among the main reasons for the scarcity of thermodynamic data. For example, Cr2+ easily reacts with lixiviating impregnant and forms intermediates in wet chemical analysis due to its unstable nature.

  • 109.
    Wang, Huijun
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    A Study on the Reaction between MgO Based Refractories and Slag-Towards the Development of Carbon-free Lining Material2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In present thesis, the fundamental studies on the reaction between MgO based refractories and slag were undertaken for the development of a carbon-free bonding MgO lining material. Alumina was selected as a potential binder material. Due to MgO-Al2O3 chemical reaction, the developed refractory was bonded by MgO·Al2O3 spinel phase. To begin with, an investigation of the dissolution process of dense MgO and MgO·Al2O3 spinel in liquid slag was carried out. To obtain reliable information for dissolution study, a new experimental method was therefore developed. In this method, a cylinder was rotating centrally in a special designed container with a quatrefoil profile. This method also showed a good reliability in revealing the dissolution mechanism by quenching the whole reaction system. The experimental results showed that the dissolution process of MgO and spinel was controlled by both mass transfer and chemical reaction. It was found that the rapid dissolution of spinel was mainly because of its larger driving force. To improve the resistance against slag penetration, two aspects were studied to develop carbon-free MgO refractory. First, colloidal alumina was used and the effect of its addition into MgO matrix was investigated. The use of colloidal alumina was to form bonding products in the grain boundary of MgO. The results showed that the alumina addition greatly improved the resistance of MgO based refractory against slag penetration in comparison with the decarburized MgO-carbon refractory. It was found that the improvement of resistance was mainly related to the spinel-slag reaction products of CaO·Al2O3 and CaO·MgO·Al2O3 solid phases at the grain boundaries. Second, the effect of particle size distribution on the penetration resistance of MgO was investigated. The most profound improvement against the slag penetration was obtained by using a proper particle size distribution. The results highlighted the importance of considering the refractory structure. Experiments were undertaken to investigate the dissolution mechanism of different types of MgO based refractories in liquid slag. It was observed that the dissolution of spinel bonded MgO refractory was much slower than the decarburized MgO-carbon refractory. The primary dissolution in spinel bonded MgO refractory occurred at the slag-penetrated layer, and the removal of this layer by peeling off enhanced the dissolution rate rapidly.

  • 110.
    Wang, Huijun
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Du, Sichen
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Dissolution of MgO·Al2O3 spinel and MgO in CaO-Al2O3-MgO-SiO2 slag under forcedconvectionManuscript (preprint) (Other academic)
    Abstract [en]

    In this work, the dissolution mechanism of dense MgO·Al2O3 spinel and MgO rod into molten CaO-Al2O3-MgO-SiO2 slag was investigated at 1873 K with forced convection. The dissolutionexperiments were carried out by employing a newly developed rotating cylinder method. The effect of rotation speed and reaction time on the dissolution rate was studied. The measured dissolution rates of both spinel and MgO were dependent on the rotation speed, indicating that mass transfer in the slag phase to one of the rate-limiting steps. It was also found that the dissolution rate of spinel in slag was enhanced more rapidly than that of MgO with the increasing reaction time and rotation speed. It was also found that the composition of the slag at the interface was far from equilibrium value between the slag and solid. The results implied that the chemical reaction at the solid-slag interface should be the other important step that jointly controlling the dissolution process.

  • 111.
    Wang, Huijun
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Du, Sichen
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    White, Jesse Franklin
    Elkem AS, Technology.
    A New Experimental Design to Study the Kinetics of Solid Dissolution into Liquids at Elevated Temperature2017In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916Article in journal (Other academic)
    Abstract [en]

    A new method was developed to study the dissolution of solid cylinder in liquid under forcedconvection at elevated temperature. In the new design, a rotating cylinder was placedconcentrically in a container fabricated by boring four holes into a blank materials for creatingan internal volume with a quatrefoil profile. A strong flow in radial direction in the liquid wascreated, which was evidently shown by computational fluid dynamic (CFD) calculations andexperiments at both room temperature and elevated temperature. The new setup was able tofreeze the sample as it was at experimental temperature especially the interface between thesolid and the liquid. This freezing was necessary to obtain reliable information forunderstanding the reaction mechanism. This was exemplified by the study of dissolution ofrefractory in liquid slag. The absence of flow in radial direction in the traditional setup using asymmetrical cylinder was also discussed. The difference in the findings by different worksusing the symmetrical cylinder was found to be mostly due to the extent of misalignment of therod in the cylinder.

  • 112.
    Wang, Huijun
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Glaser, Bjoern
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Sichen, Du
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Improvement of Resistance of MgO-Based Refractory to Slag Penetration by In Situ Spinel Formation2015In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 46, no 2, p. 749-757Article in journal (Refereed)
    Abstract [en]

    MgO-in situ spinel substrate was prepared at 1773 K (1500 degrees C) using colloidal alumina suspension and coarse MgO as raw materials. While the addition of 10 mass pct colloidal alumina had limited effect, addition of 20 mass pct colloidal alumina into the MgO matrix improved greatly the resistance of the substrate against the slag penetration at 1873 K (1600 degrees C). The improvement was found to be mainly related to the formation of solid phases, CaO center dot Al2O3 and CaO center dot MgO center dot Al2O3 at the grain boundaries due to slag-spinel reaction. Putting the reacted substrate into contact again with new slag revealed no appreciable new slag penetration. The results showed a potential solution to improve the resistance of MgO-based refractory to slag penetration and to improve steel cleanness.

  • 113.
    Wang, Huijun
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Sichen, Du
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Caballero, Roberto
    Department of R&D, INSERTEC.
    Dissolution of MgO Based Refractories in CaO-Al2O3-MgO-SiO2 SlagIn: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619XArticle in journal (Other academic)
    Abstract [en]

    Dissolution of different types of MgO based refractories into molten CaO-Al2O3-MgO-SiOslag was studied at 1873 K. The prepared refractory cubes were dissolved in both stagnant slagand slag stirred with different speeds. Even in a stagnant slag, the decarbonized commercial MgO-carbon refractory dissolved very fast. Formation of micro spinel particles by addition of either colloidal alumina or micro alumina powder in the MgO matrix efficiently reduced the dissolution. The dissolution of MgO refractories into slag was found to be controlled by the slag penetration into the MgO matrix. In the case of stagnant slag, the slag penetration would lead to the final dissociation of the decarbonized commercial MgO-carbon cube in less than 6 minutes. A slag penetrated layer was formed in the cubes with spinel particles formed in situ.The major dissolution took place between the MgO grains and the liquid in this penetrated layer. The increase of the thickness would slow down the dissolution process. In the case of forced convection, the slag penetrated layer was removed at high stirring speeds and partially removed at lower stirring speeds. The removal of the penetrated layer would enhance the dissolution process.

  • 114. White, Jesse F.
    et al.
    Allertz, Carl
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Du, Sichen
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Boron partitioning between SiO2-CaO-MgO slags and liquid silicon at controlled nitrogen potential2013In: International Journal of Materials Research - Zeitschrift für Metallkunde, ISSN 1862-5282, E-ISSN 2195-8556, Vol. 104, no 7, p. 650-656Article in journal (Refereed)
    Abstract [en]

    During refining of silicon using slag treatment, boron dissolved in the silicon is extracted to a liquid oxide (slag) phase. In this investigation the partitioning of boron between SiO2-CaO-MgO slags and liquid silicon was examined at 1873 K over a range of slag compositions and CO-N-2 gas mixtures. It was found that the distribution of boron is strongly dependent on the nitrogen partial pressure as well as the slag composition. The greatest partition ratios were achieved at 0.6 atm CO/0.4 atm N-2 with low silica content in the slag. The concentration of MgO in the slag seems to have little or no impact on the boron partition ratio.

  • 115. White, Jesse F.
    et al.
    Allertz, Carl
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Du, Sichen
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    The thermodynamics of boron extraction from liquid silicon using SiO2-CaO-MgO stag treatment2013In: International Journal of Materials Research - Zeitschrift für Metallkunde, ISSN 1862-5282, E-ISSN 2195-8556, Vol. 104, no 3, p. 229-234Article in journal (Refereed)
    Abstract [en]

    In the refining of solar-grade silicon using slag treatment, boron dissolved in the silicon is oxidized and rejected to a liquid oxide (slag) phase. In this study the partitioning of boron between liquid silicon and SiO2-CaO-MgO slags was examined at 1 873 K over a range of slag compositions and oxygen partial pressures. It was found that the distribution of boron is indeed dependent on both the slag composition and the oxygen partial pressure. The concentration of MgO seems to have little impact on the partition ratio.

  • 116. White, Jesse F.
    et al.
    Du, Sichen
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Mass Transfer in Slag Refining of Silicon with Mechanical Stirring: Transient Kinetics of Ca and B Transfer2015In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 46, no 1, p. 135-144Article in journal (Refereed)
    Abstract [en]

    Mechanical stirring was demonstrated to be a potent means to increase the mass transfer rates of B and Ca in slag refining of silicon, and optimal stirring conditions were attained with only a modest kinetic energy input into the melt. Experiments were undertaken to measure mass transfer rates between liquid silicon and CaO-SiO2 slags at 1823 K (1550 degrees C) with varying stirring speed and slag composition. A remarkable feature of this system is the extreme fluctuation in interfacial area-these changes occur very rapidly and are difficult to capture. As little as 50 rpm stirring speed promotes, significant transient increases in interfacial area. At stirring speeds above 100 rpm, the rates of mass transfer do not increase significantly, so it is evident that above this threshold mass transfer in the bulk phases and interfacial area generation are already maximized. With a sufficiently high content of CaO in the slag, interfacial phenomena induced by the mass flux of calcium facilitate emulsification, and this is explained from a thermodynamic standpoint. It is likely that the calcium transfer enhances boron transfer by increasing the available interfacial area.

  • 117.
    White, Jesse Franklin
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Equilibrium and Kinetic Considerations in Refining of Silicon2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The purity requirements for photovoltaic-grade (PV) silicon are very stringent. In PV applications, purified silicon is either doped with boron or phosphorous, so the levels of these particular elements have to be tightly controlled. An alternative process route to photovoltaic-grade silicon that has been successfully implemented on an industrial scale is a multi-step process comprising carbothermic reduction, slag refining, hydrometallurgical extraction, and finally directional solidification. There are many fundamental aspects of the process that are not fully understood and need to be defined.

     

    In the refining of silicon using slag treatment, boron dissolved in the silicon is oxidized and rejected to a liquid oxide (slag) phase. The partitioning of boron between liquid silicon and SiO2–CaO–MgO slags was examined at 1873. It was found that the distribution of boron is strongly dependent on the oxygen partial pressure and nitrogen partial pressure, as well as the slag composition. The concentration of MgO seems to have little impact on the partition ratio. The greatest partition ratios were achieved at 0.6 atm CO / 0.4 atm N2 with low silica content in the slag.

     

    Experiments were carried out to study mass transfer rates between liquid silicon and CaO–SiO2 slag using mechanical stirring at 1823 K. The evidence suggests that the reduction of calcium oxide at the interface leads to a rapid, temporary drop in the apparent interfacial tension. At low apparent interfacial tension, mechanical agitation facilitates the dispersion of metal into the slag phase, which dramatically increases the interfacial area; here it has been estimated to increase by at least one order of magnitude. As the reaction rate slows down, the apparent interfacial tension increases and the metal re-coalesces. The rates of mass transfer of both Ca and B were found to increase by agitating the melt, which shows that without forced convection, the overall kinetic rates are mass-transfer controlled. From a reactor design perspective, this is ideal since it should be simpler to achieve optimal mixing conditions with less kinetic energy input into the melt.

     

    The infiltration of silicon into graphite was found to be highly dependent on the internal structure of the graphite substrate. It was confirmed that the heating history of silicon in contact with a graphite substrate strongly influences the melting behavior, which is likely attributed to a gas-solid reaction that forms SiC below the liquidus temperature of silicon and alters the surface properties of the graphite. It was also observed that a partial pressure of CO greater than 0.05 atm in the inlet gas leads to SiC formation on the surface of the silicon and severely hinders proper melting. 

  • 118.
    White, Jesse Franklin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Du, Sichen
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Mass Transfer in Slag Refining of Silicon with Mechanical Stirring: Rates of Ca and B TransfeManuscript (preprint) (Other academic)
  • 119.
    White, Jesse Franklin
    et al.
    Elkem AS, Technology, Kristiansand, Norway .
    Du, Sichen
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Mass Transfer in Slag Refining of Silicon with Mechanical Stirring: Transient Interfacial Phenomena2014In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 45, no 1, p. 96-105Article in journal (Refereed)
    Abstract [en]

    Experiments have been carried out to study the rates of mass transfer between liquid silicon and CaO-SiO2 slag with impeller stirring at 1823 K (1550 A degrees C). The occurrence of transient interfacial phenomena related to the mass transfer of calcium has been observed; the evidence suggests that the reduction of calcium oxide at the interface leads to a rapid, temporary drop in the apparent interfacial tension. At low apparent interfacial tension, mechanical agitation facilitates the dispersion of metal into the slag phase, which dramatically increases the interfacial area; here, it has been estimated to increase by at least one order of magnitude. As the reaction rate slows down, the apparent interfacial tension increases and the metal recoalesces. The incidental transfer of calcium very likely promotes the transfer of boron by increasing the interfacial area. Mechanical mixing appears to be an extremely effective means to increase the reaction rate of boron extraction and could feasibly be implemented in the industrial slag refining of silicon to improve reaction rates.

  • 120.
    White, Jesse Franklin
    et al.
    Elkem AS, Technology, Kristiansand, Norway .
    Ma, Luyao
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Forwald, Karl
    Du, Sichen
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Reactions Between Silicon and Graphite Substrates at High Temperature: In Situ Observations2014In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 45, no 1, p. 150-160Article in journal (Refereed)
    Abstract [en]

    Graphite as a refractory material has found wide application in many process steps to produce photovoltaic silicon. In the current study, the melting behavior of silicon in contact with different grades of graphite was investigated. The infiltration of silicon into graphite was found to be highly dependent on the internal structure of the graphite substrate. It was confirmed that the heating history of silicon in contact with a graphite substrate strongly influences the melting behavior, which is likely attributed to a gas-solid reaction that forms SiC at less than the liquidus temperature of silicon and alters the surface properties of the graphite. It was also observed that a concentration of CO greater than 5 pct in the inlet gas leads to SiC formation on the surface of the silicon and severely hinders melting.

  • 121.
    Wu, Liushun
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Study on some phenomena of slag in steelmaking process2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The present work is to study slag phenomena in steelmaking process. In order to attain thegoal, a number of high temperature experiments and simulation experiments were carried out.

    Four master slags were used to study the effect of CaF2 on slag viscosity. Experimentalresults indicated the effect of CaF2 on slag viscosity depended strongly on the composition ofmaster slag. For high basicity slags, CaF2 mainly suppressed the precipitation of solid phasesat lower temperatures, leading to a lower viscosity compared to CaF2-free slags. For slagswith higher SiO2 contents, CaF2 both lowered the viscosity of the liquid phase and suppressedthe precipitation of solid phases.

    The viscosities of solid-liquid mixtures were experimentally determined for silicon oilparaffinsystem at room temperature and solid-liquid oxide mixture at steelmakingtemperature. The results of both measurements indicated that the increasing trend of mixturesviscosity with particle fraction can be described by Einstein-Roscoe equation.Silicone oils of different viscosities were used to simulate slag foaming. The experimentalresults showed, at a constant viscosity, the foaming height increased first with superficialvelocity before reaching a maximum value. Thereafter, the foaming height decreased with thefurther increase of the superficial velocity. Similar, a maximum foaming height was observedat an optimum viscosity when a constant superficial gas velocity was applied. Based on theexperimental data, a semi-empirical equation of foaming height was developed. Thepredictions of the model agreed well with experiment data. The model could also reasonablywell explain the industrial pilot trial experiments.

    Water-silicon oils model and liquid alloy (Ga-In-Sn)- 12% HCl acid model were employed tosimulate the formation of open-eyes in a gas stirred ladle. The experimental results indicatedthat the viscosity of the top liquid and the interfacial tension between the two liquids had onlylittle effect on the open-eye size. A semi-empirical model was developed to describe the sizeof open-eye as functions of the gas flow rate, bath height and slag height. The two sets ofparameters obtained for the water and Ga-In-Sn models were very different. Industrial trialswere also conducted to examine the applicability of the models. Liquid alloy model couldwell predict the formation of an open-eye during ladle treatment.

    Two cold models, sodium tungstate-oil model and water-oil model, were carried out tosimulate the formation of droplets in a gas stirred ladle. The experimental results showed thatthe gas flow rate and interfacial tension had strong impact on the size of droplets. A semiempiricalmodel was developed to describe the size of droplets for water model. Meanwhile,the parameter obtained for water model can be used for sodium tungstate-silicone oil system.The results indicate the model has strong compatibility.

  • 122.
    Wu, Liushun
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Gran, Jimmy
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Du, Sichen
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    The effect of calcium fluoride on slag viscosity2011In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 42, no 5, p. 928-931Article in journal (Refereed)
    Abstract [en]

    The effect of CaF(2) on the viscosity of high-basicity Al(2)O(3)-CaO-MgO-SiO(2) (-CaF(2)) slags for secondary steelmaking was studied using a Brookfield digital viscometer. The addition of approximately 3 mass pct CaF(2) could decrease the liquidus temperature substantially in the case of high CaO containing slags, leading to good flowability of the slag at the temperature of the ladle treatment. The addition of CaF(2) had the strongest effect on the viscosity of liquid slag with high SiO(2) content.

  • 123.
    Wu, Liushun
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Valentin, P.
    Sichen, Du
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Study of Open Eye Formation in an Argon Stirred Ladle2010In: STEEL RES INT, ISSN 1611-3683, Vol. 81, no 7, p. 508-515Article in journal (Refereed)
    Abstract [en]

    Two cold models were employed to simulate the formation of open-eyes in a gas stirred ladle. In the first model, water and silicon oils were employed to simulate liquid steel and slag respectively. In the second one, liquid Ga-In-Sn alloy was used to simulate liquid steel, while 12% hydrochloric acid simulated the top slag. The experimental results indicated that the gas flow rate, height of the lower liquid and height of the top liquid has a strong impact on the open-eye size. On the other hand, the viscosity of the top liquid and the interfacial tension between the two liquids had only little effect on the open-eye size. A semi-empirical model was developed to describe the size of open-eye as a function of the heights of the two adults and the gas flow rate. The two sets of parameters obtained for the the water and Ga-In-Sn models were very different Industrial trials were also conducted to examine the applicability of the models. The model developed based on the Ga-In-Sn model could well predict the formation of an open-eye during ladle treatment. The model could be adopted by the industry to estimate the real gas flow rate by measuring the size of the open-eye online. On the other hand, the mathematical model based on water model experiments was unsatisfactory when applied to the industrial ladle process.

  • 124. Zhu, M-Y
    et al.
    Jones, T
    Sichen, Du
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Modelling study of slag foaming by chemical reactio2001In: Scandinavian journal of metallurgy, ISSN 0371-0459, E-ISSN 1600-0692, Vol. 30, p. 51-56Article in journal (Refereed)
123 101 - 124 of 124
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