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Kim, Jong Bae,Sohn, Il Minerals, Metals & Materials Society 2018 Metallurgical and materials transactions. B, Proce Vol.49 No.1
<P>The effect of the initial FeO content and CaO:SiO2 ratio (CaO mass pct/SiO2 mass pct) on the reduction smelting of FeO with carbon flake addition is investigated in the CaO-MgOsatd.-SiO2-FeO slag system at 1823 K (1550 A degrees C). Carbon rapidly reacted with FeO in the molten slag, causing both foaming and compositional changes in the slag. As FeO is reduced, the MgO saturation is modified, and solid precipitants, including MgO and other complex oxides, were observed, which significantly affected the slag properties, including the viscosity and foaming behavior. The solid-phase fraction and viscosity were estimated from changes in the measured FeO content over time using the thermochemical software FactSage. The iron recovery, which is distinguished from the amount of reduced Fe droplets, showed opposite behavior to the measured maximum foaming height and modified foaming index. According to the FeO mass transfer coefficient considering slag foaming at various initial FeO contents and CaO:SiO2 ratios, the reduction rate was optimal at higher initial FeO contents and a CaO:SiO2 ratio of 2.0, which did not correspond to the optimal iron recovery at an initial FeO content of 44 mass pct and above and a CaO:SiO2 ratio of 1.2. The results showed that slag foaming may increase the reduction kinetics, but the slag composition needs to be optimized for greater iron recovery. (C) The Minerals, Metals & Materials Society and ASM International 2017</P>
Yang, J. G.,Park, J. H. Minerals, Metals & Materials Society 2017 Metallurgical and materials transactions. B, Proce Vol.48 No.4
<P>The equilibrium reaction between Ni alloys and CaO-Al2O3-CaF2-TiO2 system electroslag remelting (ESR) slags was investigated in the temperature range of 1773 K to 1873 K (1500 A degrees C to 1600 A degrees C) at p(O-2) = 10(-16) atm in order to obtain the optimized composition of the slags for producing Ni alloys with various Al and Ti ratios. In addition, the temperature dependence of the reaction equilibria between the ESR slags and Ni alloys was also evaluated. The stable ionic species of titanium in the ESR slag under the present experimental conditions was experimentally confirmed to be mainly Ti4+ (i.e., TiO2) by X-ray photoelectron spectroscopy analysis of the quenched samples. The activity-composition relationship of TiO2 and Al2O3 in the ESR slag was determined as a function of the Al/Ti ratio of the alloys and the CaF2 content of the slags in conjunction with the activity ratio of Al to Ti in the alloys calculated from the FactSage(TM) 7.0 software. The temperature dependence of the activity-composition relationship of TiO2 and Al2O3 in the slag showed good linear correlations, and the equilibrium content ratio of TiO2 to Al2O3 at a fixed activity ratio increased with increasing temperature, which was expected based on the standard enthalpy change of the reaction. Thus, higher amounts of TiO2 should be added at higher operation temperatures in the ESR process. A 120 kg scale pilot ESR test (2000 A and 16 V) was performed to produce a commercial grade Ni-based superalloy based on the activity-composition relationship of the slag components obtained in the present study. Consequently, the contents of Al and Ti in the solidified ESR ingot were nearly the same as that of the original electrode throughout the entire length (280 mm) after the ESR process. (C) The Minerals, Metals & Materials Society and ASM International 2017</P>
Relationship Between Sulfide Capacity and Structure of MnO-SiO2-Al2O3-Ce2O3 System
Jeong, S. J.,Kim, T. S.,Park, J. H. Minerals, Metals & Materials Society 2017 Metallurgical and materials transactions. B, Proce Vol.48 No.1
<P>Sulfide capacity of the MnO-SiO2-Al2O3-Ce2O3 system was measured at 1873 K (1600 A degrees C), and the structural analysis was carried out using micro-Raman spectroscopy to understand the role of Ce2O3 in the sulfur dissolution behavior. Sulfide capacity of the basic melts (MnO/SiO2 = 2.2(+/- 0.14)) decreased with increasing content of Ce2O3 to approx. 4 mol pct, beyond which it increased. Sulfide capacity continuously decreased in the less basic system (MnO/SiO2 = 1.0(+/- 0.15)), whereas it was hardly affected by Ce2O3 in the relatively acidic composition (MnO/SiO2 = 0.3(+/- 0.05)). There was a significant increase in the intensity of Raman band at 600 cm(-1) by Ce2O3 addition in high MnO/SiO2 (=2.2) system, which originated from the transition from [(Al,Mn-0.5)O-4]-tetrahedron to [(Al,Ce)O-6]-octahedron due to strong attraction between Al2O3 and Ce2O3. Combining thermodynamic and structural information, the effect of Ce2O3 on the sulfide capacity of Mn-aluminosilicate melts can be explained by the following factors: (1) Activity of MnO in the melts decreased by addition of Ce2O3; (2) Free oxygen was consumed in the structure modification from [(Al,Mn-0.5)O-4] to [(Al,Ce)O-6] unit by addition of Ce2O3; and 3) When the Ce3+ content was greater than critical value (approx. 4 mol pct) in high MnO/SiO2 (=2.54) melts, excess Ce3+ and Mn2+ ions competitively reacted with S2- ions, resulting in an increase of sulfide capacity. (C) The Minerals, Metals & Materials Society and ASM International 2016</P>