The dissolution rate of Al 2 O 3 into the CaO-SiO 2 -Al 2 O 3 slag system was investigated at 1 873 K by employing a novel experimental method which involved continual measurement of the torque variation on a rotating alumina rod dipped into a molten slag. Measured torque variation was successfully related to the dissolution rate of the rod. The dissolution rate of alumina was found affected by a number of factors: the rate increased with increasing temperature, the rotating speed of the rod, the CaO content in the slag, and the Al 2 O 3 content in the slag for a fixed CaO content. It was found that the dissolution rate was highly dependent on the viscosity and the diffusivity of slags. The activation energy obtained from an Arrhenius type analysis was in the range of 84 kJ mol Ϫ1. It was concluded that the dissolution of Al 2 O 3 into the CaO-SiO 2 -Al 2 O 3 slag system was controlled by the mass transfer in the slag phase. An iso-dissolution rate diagram was constructed for the dissolution of Al 2 O 3 into the CaO-SiO 2 -Al 2 O 3 slag system at 1 873 K.

A sensorless algorithm is developed on the basis of a rotor flux observer in the stationary frame. In particular, it involves a parameter adaptive algorithm for an initial rotor flux like the observer, which was recently proposed by Bobtsov et al. (Automatica, vol 61, Nov, 2015). In the proposed method, the flux observer is linked to the parameter estimator via a compensating term which results from parameter error. This method has a robust property against dc bias errors, i.e., it cures the inherent weakness of the pure integrator (flux observer) to dc offsets which frequently occur in current measurements and voltage estimates. The robust performance is demonstrated through simulations and experimental results. Index terms: Sensorless, nonlinear observer, flux estimator, linear regression form, position observer, voltage offset. NOMENCLATURE α − β Stationary axis reference frame quantities. d − q Synchronous axis reference frame quantities. v, i Stator voltage and current. λ Stator flux. x Rotor flux. η Initial rotor flux. q Subtracted value initial rotor flux from rotor flux. R, L Resistance and inductance of stator winding. ψ m PM flux linkage constant.

The wetting behavior of solid Al 2 O 3 with molten CaO-Al 2 O 3 -SiO 2 was investigated at 1 873 K using the sessile drop method. A new model was developed to represent the time dependence of the contact angle, i.e., the spreading behavior of a liquid drop on a solid substrate. The model takes into consideration chemical interactions which continually take place at the interface between the solid Al 2 O 3 and molten CaOAl 2 O 3 -SiO 2 . By applying the model to the experimental results of the present study the equilibrium contact angle between the liquid slag and solid alumina was determined for a number of different slag compositions, and an iso-contact angle diagram was constructed. The equilibrium contact angle was greatly affected by the slag composition, and it was found that the interfacial tension was the major factor governing the equilibrium contact angle. In the region of low SiO 2 content, the slag with higher CaO content exhibits a smaller contact angle, i.e., better wettability with alumina. For slag with a given CaO/SiO 2 ratio, an increase in Al 2 O 3 results in a corresponding increase in the contact angle, i.e., decrease in wettability. For a given CaO/Al 2 O 3 ratio, the variation of the contact angle with SiO 2 content shows a minimum. The contact angle decreases by increasing the surface roughness of the alumina substrate.

Desulfurization kinetics of molten pig iron were studied using CaO-SiO 2 -Al 2 O 3 -Na 2 O quaternary slag systems at 1 350°C. The concentration of Na 2 O in slag decreases with time due to evaporation. The rate of desulfurization increases by increasing the Na 2 O content in slag, decreasing Al 2 O 3 content, increasing the slag basicity, i.e., the ratio of CaO to SiO 2 , and increasing the temperature. A mathematical model has been developed which enables the effect of decrease in Na 2 O content over time to be taken into consideration. The model provides a rate equation that can represent all conceivable rate controlling steps, such as interfacial chemical reaction, mass transport in the metal phase, and in the slag phase. The apparent rate coefficient-a parameter employed in the model-was dependent on temperature and slag composition, especially Na 2 O content. An equation is suggested which relates the coefficient to the sulfide capacity of slag. The activation energy of the apparent rate coefficient was found to be 127 kJ mol Ϫ1 . It was concluded that the desulfurization of molten pig iron using the present slag system is controlled either by the interfacial chemical reaction or slag phase mass transfer.KEY WORDS: desulfurization; pig iron; kinetics; rate; Na 2 O; slag. cible, along with the reaction crucibles filled with the samples was preheated by holding it above the hot zone using a molybdenum wire. It was then lowered to the zone for reaction, and placed on the support. As soon as the crucible assembly (holding crucibleϩreaction crucibles) was placed on the support, one of the reaction crucibles was taken out from the furnace by using a specially designed tong, which was taken as the starting point for kinetic study. The reaction crucibles were taken out of the furnace one at a time according to a predetermined time schedule. These samples were then subjected to chemical analysis. ResultsEffects of basicity (CaO/SiO 2 ), Na 2 O, Al 2 O 3 and temperature were examined, and experimental results are summarized in Table 2. Figure 2 shows the effect of Na 2 O in slag on the rate of sulfur transfer from metal to slag at 1 350°C. In the experiments the basicity of CaO/SiO 2 in mass% was fixed at unity, and the Al 2 O 3 content was adjusted so as to maintain the ratio of Al 2 O 3 to CaOϩSiO 2 ϩAl 2 O 3 in mass% at 0.18. It is clear that Na 2 O greatly enhances the rate of desulfurization. It is also seen that the desulfurization reaction is ISIJ International, Vol. 41 (2001) completed in about 20 min and thereafter a decrease in sulfur is hardly seen. The efficiency of desulfurization was calculated by taking the ratio of the amount of sulfur removed from the metal in 60 min to the initial amount of sulfur, and the results are given in Fig. 3. The efficiency increases along with increasing the Na 2 O content in the slag, and reaches 90 % with 20 mass% Na 2 O. Figure 4 shows the effect of Al 2 O 3 in the slag on the rate of sulfur transfer from metal to slag at 1 350°C. In the experiments the basicity of C...

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Composition evolution and number density of oxide inclusions in austenitic stainless steel were investigated by analyzing inclusions in a commercial austenitic stainless steel slab. The composition of inclusions was observed to be strongly dependent on size of the inclusion and location in the slab, both, where the inclusions were found. The number density of inclusions increased as the inclusions were found at deeper location from the slab surface. The basicity (%CaO/%SiO 2 ) of the inclusions decreased with decreasing the inclusion size, while the manganese oxide content (%MnO) increased with decreasing the inclusion size. As the inclusions were located deeper from the slab surface, the basicity (%CaO/%SiO 2 ) was found decreased but (%MnO) increased. Such composition changes along with the position in the slab was attributed to the combination of pre-existing inclusions which were entrapped from the argon oxygen decaburization slag and inclusions precipitated during solidification due to decrease in solubility limit of concerned elements. A theoretical model was developed in order to represent the inclusion composition in the austenitic stainless steel during continuous casting, as a function of the size and location of the inclusion. The model predictions for the composition of inclusion, such as (%CaO/%SiO 2 ), (%MnO), and Al 2 O 3 content, were in good agreement with the measured data.

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The surface tension of CaO-SiO 2 -Al 2 O 3 system at 1 873 K was computed using a modified Butler's equation, and by making use of critically evaluated ionic surface distances of pure oxides involved in the system. For CaO-SiO 2 and CaO-Al 2 O 3 binary systems, the computed results are in good agreement with the experimental results reported by other researchers. For CaO-SiO 2 -Al 2 O 3 ternary system, the surface tension in a wide range of liquid compositional range was computed and the results were favorably compared with the experimental results reported in the literature. It was found that the surface tension increases with decreasing SiO 2 , and with increasing CaO or Al 2 O 3 . For a given SiO 2 content, the surface tension was relatively independent of the CaO/Al 2 O 3 ratio. An iso-surface tension diagram has been suggested for liquid CaO Excess Free Energy of the SurfaceFor the alkali-halide system, Lumsden 8) calculated the heat of mixing of binary alkali-halide mixtures, and the heat of mixing was found to be proportional to the potential energy of mixing due to the non-polar London force and the polarization energy. Provided that the excess Gibbs free energy is mainly determined by the electric field arising from the polarization which is generated by the different ions having the same or different charge sign, the excess free energy can be obtained by partial differentiation of the heat of mixing and have the following proportionality with ionic distances. According to Lumsden,8) . (5) where k is the proportionality factor, the polarizability, Z coordination number, and z i valency of cation of i.Therefore the excess Gibbs free energy of i in the bulk phase can be expressed by Eq. (6).... (6) If the excess Gibbs free energy in the surface has the same function of temperature and compositions as that in the bulk, the excess Gibbs free energy of i in the surface phase can be expressed in a similar way. (7) where (Z S )Ј is the apparent coordination number in the surface under consideration of surface relaxation and z i is the ratio of the ionic distance in the surface phase to that in the bulk phase () represents the excess free energy if the bulk concentration of B had a value of N B S . Then the ratio of) can be then expressed as follows:.......... (8) whereIf the surface relaxation is not considered in the coordination number and ionic distance, the calculated results on the surface tension of molten ionic solutions including molten slags did not agree with the experimental values. 1) Therefore the surface relaxation structure as well as the coordination number should be considered in order to evaluate the surface tension of molten slag. This was pointed out by Tanaka et al. and almost the same relations in Eqs. (5)- (7) was applied to express the effect of the surface relaxation structure on the excess Gibbs energy in the surface. 1,2) The ratio (b) has the relationship with the heat of evaporation and the surface tension for the pure substance i as seen by Eq. (9). 4)Tanaka et al. 4) found tha...