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Title: Decarburization of iron-carbon alloys with oxidising slags
Author: Luna, Oscar Miguel Ojeda
Awarding Body: Sheffield City Polytechnic
Current Institution: Sheffield Hallam University
Date of Award: 1977
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Reactions which are generated from slag-metal-gas systems, such as those found in Oxygen Steelmaking, have been studied in the present research. A system has been developed whereby one gram iron-carbon alloys have been decarburized by synthetic slags. Fayalite slags were initially used for decarburization after which lime bearing slags from the CaO-FeO-SiO₂ ternary followed. The slags, although highly reactive, were found to be contained adequately in iron crucibles. By protecting the iron crucibles with a zirconia film the iron crucibles can be safely used up to 1400°C. The experimental technique has been well established. The data obtained from the decarburization experiments indicated an increase in rate of decarburization with increasing lime content up to a certain composition. For slags containing about 26 % CaO the rates for decarburization commence to decrease. The range of temperatures under which reactions were studied (1240°C to 1600°C) indicated that the decarburization takes place more rapidly by the presence of a more fluid and consequently more turbulent system. Gas lancing was used to change the hydrodynamic state of the system. The increase in turbulence caused a more rapid decarburization of the iron-carbon alloys as compared to those when no gas lancing was used. Little effect was found on the rate of decarburization when the oxygen potentials of the gas were changed. There is clear evidence that the overall rates of the decarburization process are not controlled by the rate of chemical reaction itself. Experimental observation from X-ray analysis and scanning electron microscopy, have established that internal heterogeneous nucleation takes place in the metal phase. The nucleation sites are extremely small particles of entrapped slag. Mass Transfer Coefficients have been calculated for the various iron-carbon/slag reactions. For fayalite slag, values of the mass transfer coefficient were found to be from 3.20 x 10⁻⁴ cm/sec to 11.40 x 10⁻⁴ cm/sec for 1240 and 1400°C respectively. Maximum values for the mass transfer coefficient in lime bearing slags were found to be in the range of 12.75 x 10⁻⁴ cm/sec at 1300°C to 19.95 x 10⁻⁴ cm/sec at 1400°C. It has not been possible to establish a precise correlation for the mass transfer coefficients with the simple models for mass transfer proposed by other authors. The generation of carbon monoxide gives rise to a situation which is very complex to describe in terms of mathematical models. Nevertheless the experimental kinetics have been discussed in relationship to the classical film theory for mass transfer across an interface between two phases. This has allowed conclusions to be drawn about the rate controlling step of the overall mechanism of transfer, some agreement between experimental data and the model has allowed estimates to be made of relative velocity between slag and metal, Sh, Gr and Re numbers. In addition, the penetration theory has also been examined, and analysis indicated that it has some potential applicability to this type of system. Finally, the discussion suggests that Danckwerst surface renewal adaptation of the penetration theory is worthy of future examination.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available