Carbon Solubility in the CaO-SiO 2 -3MgO-CaF 2 Slag System
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The dominant carbon dissolution mechanisms in slags have been well-known to be the incorporated carbide or free carbide mechanisms depending on the composition and in particular the extended basicity (basic oxides/ acidic oxides).[1–6] And when sufficient nitrogen is present in some slag systems, cyanide (–CN) has also been known to form with the incorporated and free carbide to significantly increase the carbon and nitrogen content of the slag compared to nitrogen-free reacting systems, as verified by the present authors in the CaO-10SiO2-Al2O3CaF2 slag system.[1,4] The relative contents of slag constituents are provided in wt pct in the present paper. In this study, the carbon solubility in the CaO-SiO2MgO-CaF2 slag system has been investigated. The effect of the extended basicity [(CaO + MgO)/SiO2] and CaF2
JUN-YONG PARK, Graduate Student, and IL SOHN, Associate Professor, are with Materials Science and Engineering, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 120-749, Korea. Contact e-mail: [email protected] SUNG-MO JUNG, Professor, is with the Graduate Institute of Ferrous Technology, POSTECH, San31, Hyoja-dong, Nam-gu, Pohang, Gyeongbuk 790-784, Korea. Manuscript submitted August 27, 2013. Article published online March 5, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS B
content on the carbon solubility has been provided. In addition, the carbon solubility of the slag was correlated to the melt structure using Fourier transformed infrared (FT-IR) and Raman spectroscopy of as-quenched slags from 1773 K (1500 C). Reagent grade chemicals (Junsei; Tokyo, Japan) of CaCO3 (99.5 pct), SiO2 (99.5 pct), MgO (98 pct), and CaF2 (99 pct) were used. A total of 4 g was pre-melted in a Pt-10Rh crucible for 5 hours at 1773 K (1500 C) with Ar gas flowing at 4.2 cm3/s. The post-experimental chemical compositions were analyzed using X-ray fluorescence spectroscopy (XRF; S4 Explorer; Bruker AXS GmbH, Karlsruhe, Germany), as provided in Table I. There are slight changes in the composition of the slags and the postexperimental compositions were used in subsequent results. In past work by Kor and Richardson,[7] it was inferred that the CaF2 and H2O could react to form CaO and HF, which could affect not only the partial pressure of H2O, but also the activity of O2 in the slag as CaO is increased. Changes in the activity of O2 can have a significant effect on the carbon solubility.[4,6] However, in the present work, ultra high purity grade gases (99.9999 pct) were passed through columns of drierite and soda lime to remove impurities such as H2O and CO2 that may be present in the gases and there is likely negligible amount of moisture to react with the CaF2 in the slag. Thus, the very slight change in the weighed and postexperimental chemical analysis of the slag, if any, is likely due to the formation of SiF4 according to earlier work by Mitchell[8] expressed in Eq. [1]. ðSiO2 Þ þ 2ðCaF2 Þ ¼ 2ðCaOÞ þ SiF4 :
½1
The CaF2 and SiO2 loss decreases with increasing CaO and seems to agree with the findings of Mitchell and Kumar et al.[
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