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Träfflista för sökning "(WFRF:(Seshadri S)) srt2:(2000-2004)"

Sökning: (WFRF:(Seshadri S)) > (2000-2004)

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1.
  • Seetharaman, Seshadri, et al. (författare)
  • Estimation of liquidus temperatures for multicomponent silicates from activation energies for viscous flow
  • 2000
  • Ingår i: Metallurgical and Materials Transactions. A. - 1073-5623 .- 1543-1940. ; 31:1, s. 111-119
  • Tidskriftsartikel (refereegranskat)abstract
    • This article considers the viscous-flow phenomenon in molten silicate melts in the vicinity of their liquidus temperatures. An agglomeration of ionic species occurs in the liquid slag with decreasing temperatures and results in an increase in the viscosity and the activation energy for viscous flow. The latter was found to be nonlinear, increasing rapidly as the temperature is approached wherein a solid phase is likely to separate from the liquid. The second derivative of the activation energy for viscous flow with respect to temperature was found to show a discontinuity in the vicinity of the liquidus temperature. This has been verified in the case of viscous flow for both pure water and CaO-SiO2 melts. Experimental data for the viscosities, of complex silicate melts and mold fluxes have also demonstrated the occurrence of a discontinuity in the second-derivative function, which is in accordance with the liquidus temperature as determined by differential thermal analysis (DTA). Thus, the second derivative offers a useful way of estimating the liquidus temperatures of multicomponent silicates, which are often difficult to determine due to supercooling effects.
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2.
  • Sridhar, S., et al. (författare)
  • Abating environmentally harmful waste gases
  • 2002
  • Ingår i: JOM. - 1047-4838 .- 1543-1851. ; 54:5, s. 30-33
  • Tidskriftsartikel (refereegranskat)abstract
    • A gas-purification method, based on the condensation of nitrogen, sulfur, and carbon-containing environmentally hazardous gases produced from industrial processes, is proposed in this article. The method, which utilizes the cooling capacity of waste nitrogen in the oxygen plant to condense the hazardous gases, is capable of removing hazardous impurities up to 99.98%. Theoretical calculations underlying the condensation process are presented employing gases produced in a blast furnace and coke oven in an integrated steel plant. The cooling power required for, the condensation process is calculated using the waste nitrogen generated from an oxygen plant that generates captive oxygen for the steel plant. Design modifications that need to be made to the oxygen plant in order to utilize the cooling power of the waste nitrogen gas are also presented. As a case study, the advantages of the method are illustrated with purification of coke-oven gas. The economic impact and the investment aspects are also discussed.
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3.
  • Sridhar, S., et al. (författare)
  • Viscosity estimation models for ternary slags
  • 2001
  • Ingår i: Steel research. - : Wiley. - 0177-4832. ; 72:1, s. 3-10
  • Tidskriftsartikel (refereegranskat)abstract
    • Five models to estimate slag viscosity have been compared with the experimental data obtained using the rotating cylinder method. The comparison was made for four ternary silicate systems, viz. FeO-MgO-SiO2, CaO-MnO-SiO2, FeO-MnO-SiO2 and CaO-Feo-SiO2. The KTH model and the model using the Gibbs energy of mixing have been found successful in estimating the slag viscosity. On the other hand, the comparisons of the experimental results with the calculated viscosity using the Riboud, Urbain and NPL models have shown poor agreement. While the limited number of the data points used for parameter optimisation would be one of the reasons for the failure of the Riboud and NPL models when applied for these ternary systems, the description of the slag composition in Urbain's approach could probably explain the disagreement between the estimated and experimental viscosity. Further studies are needed for the KTH model to accommodate fluorides in the model structure.
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4.
  • Arvanitidis, I., et al. (författare)
  • Intrinsic reduction kinetics of cobalt- and nickel-titanates by hydrogen
  • 2000
  • Ingår i: Journal of Materials Research. - 0884-2914 .- 2044-5326. ; 15:2, s. 338-346
  • Tidskriftsartikel (refereegranskat)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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5.
  • Bjorkvall, J., et al. (författare)
  • A model description of the thermochemical properties of multicomponent slags and its application to slag viscosities
  • 2001
  • Ingår i: Glass Physics and Chemistry. - 1087-6596 .- 1608-313X. ; 27:2, s. 132-147
  • Tidskriftsartikel (refereegranskat)abstract
    • In view of the urgent need for an extrapolation of the thermochemical and thermophysical properties of multicomponent metallurgical slags, a semiempirical slag model has been developed at the Department of Metallurgy, Royal Institute of Technology, Stockholm. In this model, Temkin's description of ionic melts is coupled with Lumsden's total dissociation of polymerized silicate and aluminate species. The excess Gibbs energies are described by means of Redlich-Kister polynomials. The model parameters that correspond to binary silicate systems are generated from available experimental data and used consequently to describe systems of higher order. The model is successful in extrapolating the thermodynamic data for a number of ternary and higher-order silicate systems. in view of the uncertainties in the literature data in the case of the Al2O3-SiO2 system. Knudsen cell mass spectrometric measurements are conducted and the model parameters are assigned on the basis of these results. This enables reasonable predictions of the thermodynamic properties of multicomponent aluminosilicate slags. The model description is also used in linking thermodynamic data with slag Viscosities. The viscosities of ternary silicates could be predicted from the binary viscosities and the thermodynamic data.
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6.
  • Bjorkvall, J., et al. (författare)
  • Thermodynamic description of Al2O3-CaO-MnO and Al2O3-FeO-MnO melts - a model approach
  • 2000
  • Ingår i: Calphad. - 0364-5916 .- 1873-2984. ; 24:3, s. 353-376
  • Tidskriftsartikel (refereegranskat)abstract
    • Assessments for the binary systems. Al2O3-CaO, Al2O3-FeO and Al2O3-MnO were carried out using a slag model developed at the present department. Calculations of the oxide activities in the homogenous liquid phase have been performed for the Al2O3-CaO-MnO and Al2O3-FeO-MnO systems, The activities in the ternary systems were calculated using the parameters obtained from the binary subsystems. Comparison between experimental data and the model calculations demonstrates the ability of the model to describe the thermodynamics of ternary systems using only information ti-om the binary systems. In the case of the Al2O3-CaO-MnO system, the comparison between model calculations and the results of the only available experimental measurements is less satisfactory. This could partly be attributed to the non availability of experimental data for the subsystem CaO-MnO. Future experimentation in the Al2O3-CaO-MnO system is strongly recommended.
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7.
  • Bjorkvall, J., et al. (författare)
  • Thermodynamic description of 'FeO'-MgO-SiO2 and 'FeO'-MnO-SiO2 melts - a model approach
  • 2000
  • Ingår i: High Temperature Materials and Processes. - 0334-6455 .- 2191-0324. ; 19:1, s. 49-59
  • Tidskriftsartikel (refereegranskat)abstract
    • Activities of the oxide components in the 'FeO'-MgO-SiO2 and 'FeO'-MnO-SiO2 systems have been predicted based on the information of binary systems using a thermodynamic model. The model considers the ionic melt as an oxygen-ion matrix with the cations including Si4+ distributed in it. The interactions between different cations in the presence of O2- are considered as functions of both composition and temperature. The activities predicted by the model are in good agreement with the experimental data available in the literature.
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8.
  • Bjorkvall, J., et al. (författare)
  • Thermodynamic model calculations in multicomponent liquid silicate systems
  • 2001
  • Ingår i: Ironmaking & steelmaking. - : Informa UK Limited. - 0301-9233 .- 1743-2812. ; 28:3, s. 250-257
  • Tidskriftsartikel (refereegranskat)abstract
    • A thermodynamic model developed earlier in the present laboratory for oxidic melts was applied to some multicomponent systems, namely CaO-FeO-MgO-SiO2, Al2O3-CaO-MgO-SiO2, Al2O3-FeO-MnO-SiO2, and Al2O3-CaO-FeO-MgO-MnO-SiO2. Model calculations were carried out using only the parameters corresponding to the binary systems, which, in turn, were based on the available thermodynamic information for these systems. The predicted thermodynamic activities of the component oxides in higher order systems were compared with the experimental data published in the literature. In general, the agreement between the model predictions and the experimental values was found to be satisfactory within the limits of experimental uncertainties and limitations of the model calculations. Examples of model predictions for some typical slag compositions, relevant to the Swedish steel industry and used in the blast furnace, electric arc furnace, and ladle furnace are also presented.
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9.
  • Bustnes, J. A., et al. (författare)
  • Investigation of the reduction of ZnWO4 by hydrogen gas
  • 2000
  • Ingår i: Zeitschrift für Metallkunde. - 0044-3093. ; 91:6, s. 500-503
  • Tidskriftsartikel (refereegranskat)abstract
    • The reduction of zinc tungstate by hydrogen gas was studied using a thermogravimetric method in the temperature range 823 to 1073 K. The experiments were carried out isothermally. A new W to Zn binary phase was found in the samples reduced at 873 K. This discovery is in disagreement with the earlier information on Zn-W phase equilibria that Zn and W do not form alloys. The favorable kinetic conditions would be of help for the formation of this phase. On the other hand, this phase was not observed in the sample reduced at 1073 K. The evaporation of zinc during the reduction was found to play an important role. The apparent activation energy for the reduction of ZnWO4 by hydrogen was evaluated to be 90 kJ/mole using the initial reaction rates.
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10.
  • Jakobsson, A., et al. (författare)
  • Interfacial phenomena in some slag-metal reactions
  • 2000
  • Ingår i: Metallurgical and materials transactions. B, process metallurgy and materials processing science. - : Springer Science and Business Media LLC. - 1073-5615 .- 1543-1916. ; 31:5, s. 973-980
  • Tidskriftsartikel (refereegranskat)abstract
    • 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 pet CaO, 50 wt pet Al2O3, and 20 wt pet 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.
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