A Mossbauer study of electric steelmaking basic slags
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THE slags formed during the manufacture
of steel in the basic electric furnace are of a very complex composition and constitution. These slags are only partly derived from the fusion of the nonmetallic materials present in the scrap; they derive far more from the lime and silica added in order to enable the formation of a slag with opportune physicochemical characteristics. The metal-slag-gas processes that take place during steel making have been amply studied with thermodynamic methods. ~-3 These present us with indications for choosing the most favorable range of slag composition for the fulfilment of metallurgical requirements. However, the thermodynamic approach always refers to conditions of equilibrium, and gives no indication about the course of the processes in different situations, as occurs very often in industrial practice. With regard to this a deeper knowledge of the constitution of the slags is necessary, so as to be able to correlate it with their physicochemical properties and with their behavior. As it is somewhat difficult to examine directly the slags in the molten state, generally this type of study is performed on solid samples obtained via quenching from the molten state. Examinations of mineralogical type upon such samples have produced evidence that the slags can be made up of an ensamble of heterogeneous phases. 4,5 In order to describe the reactivity and behavior of these slags, one has had to resort to semiempirical parameters such as the "basicity", the "base-excess ''6,7 and the "free oxygen mole n u m b e r " of the ionic theory, s From the technological point of view, perhaps the most interesting characteristic of the slags is their oxidizing power expressed by the "activity of the F e O " ; the influence of the composition on such a parameter is represented in well known ternary diagrams where the slag is described as belonging to the simplified system (CaO-MgO)-(SiO2 + AI203)-"FeO". 9 These diagrams bring to light how the "activity of the F e O " is strongly dependent upon the composition of the slag, since evidently, if this is
E. RAMOUS, Professor, G. PRINCIPI, M. MAGRINI, and A. TIZIANI, Associate Professors, are with lstituto di Chimica Industriale, Universit~t di Padova, Padova, Italy. Manuscript submitted July 18, 1980. METALLURGICAL TRANSACTIONS B
varied, the structural situation can change notably and hence the behavior of the iron ions can change remarkably. In order to clarify this problem the following aspects remain to be looked at more closely: a) the type of iron ion effectively present and the influence of the composition and of the degree of oxidation on the Fe2+/Fe 3+ ratio; b) the structural situation of the different iron ions: whether associated with " a c i d " components (silica) and with what coordination, or with " b a s i c " components (lime, magnesium oxide, and so forth). For this type of investigation to be carried out on samples obtained by quenching, we applied MOssbauer Effect Spectroscopy (MES) which is able to supply detailed information directl
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