Thermodynamic behavior of Na 2 O-B 2 O 3 melt
- PDF / 184,122 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 47 Downloads / 195 Views
CTION
SINCE B2O3 was reported to be a potential substitute for CaF2 as a flux, thermodynamic studies on B2O3-bearing slags have been extensively reported.[1–7] Also, the effect of Na2O on the removal of sulfur and phosphorus from molten steel has also been a subject of interest for a long time.[8,9,10] Richardson estimated the activities of the components in the CaO-B2O3 slag,[1] and Min measured the activity of BaO in the BaO-B2O3 slag by using a thermochemical equilibration technique.[2] Mu¨ller and Demirok discussed the enthalpy changes of mixing of the CaO-B2O3 and BaO-B2O3 melts based on the glass-structural viewpoint.[3] The results of these studies indicate that the thermodynamic characteristics of both systems are very similar due to the similarity of the phase diagrams in each slag system. Rao and Gaskell measured the thermodynamic properties of the MnO-B2O3, MnO-SiO2-B2O3, and MnO-TiO2-B2O3 slags,[4] and Huang et al. measured the activities of the components of the MgOB2O3, SiO2-B2O3, and MgO-SiO2-B2O3 slags.[5,6] An electrochemical technique was used by Fujiwara et al. for the activity of FexO in the FexO-B2O3 melt.[7] The authors in these studies suggested that the activities of slag components in the B2O3-bearing slags could be affected by the interaction between the cations of basic oxides and the borate polyanionic groups. However, because most of these studies are limited to only their experimental slag systems, an integrated comparison for the interactions between each component in the B2O3-bearing slags is not available in the current literature. In the present study, the activity of Na2O in a Na2O-B2O3 melt was measured by using a thermochemical equilibration technique throughout the entire slag composition, although the activities of the components in this slag system, where the experimental composition was limited to the narrow JOO HYUN PARK, Graduate Student, and DONG JOON MIN, Associate Professor, are with the Department of Metallurgical Engineering, Yonsei University, Seoul 120-749, Korea. Manuscript submitted April 6, 2000. METALLURGICAL AND MATERIALS TRANSACTIONS B
liquid region (i.e., less than 33 (mol pct) Na2O), are available in the research literature.[11] Thereafter, the thermodynamic behavior of MgO, CaO, BaO, and Na2O in the B2O3-bearing slags and the influence of acidic oxides such as SiO2 and P2O5 on the stability of Na2O in the Na2O-bearing slags were discussed. In addition, the molar Gibbs free energy of mixing and the heats of formation of solid compounds were introduced in order to compare the interactions between slag components in various binary slag systems. II. EXPERIMENTAL A. Experimental Principles The equilibrium reaction between Na2O in the slag and Na in the molten silver is as follows:[14] 2NaAg ⫹
1 O2 (g) ⫽ Na2O (l) 2
[1]
⌬G⬚ ⫽ ⫺374,000 ⫹ 107T (J/mol) K[1] ⫽
aNa2O a2Na ⭈ pO1/22
aNa2O ⫽ ␥2Na ⭈ X 2Na ⭈ K[1] ⭈ pO1/22
[2] [3]
where K[1], ai , pO2, ␥Na, and XNa are, respectively, the equilibrium constant of Eq. [1], the activity of i, the oxygen partial pressure,
Data Loading...
