Activity of chromium oxide and phase relations for the CaO‐SiO₂‐CrO_X system at 1873 K under moderately reducing conditions

Abstract

In order to optimize the slag composition operated in the decarburization process of stainless steel production, activity of chromium oxide, aCrOy, and phase relations for the CaO-Si02-CrOy system have been investigated under moderately reducing conditions, Ib 2 =7.04 010-6 Pa at 1873 K. Activity coefficients of chromium oxides show strong dependencies on XCaOIXSi02, an index of basicity, and chromium content of the slag. Solubility of chromium oxide in the slag system drastically decreases with increasing XCaOIXSi02, which is consistent with increase in activity coefficients of chromium oxides. The optimal CaO-Si02-CrOx slag for a practical decarburization process has been recommended to be doubly saturated with crOl.5 and CaCrz04, namely XCaOlXSi02 =1.47 at 1873 K, which may not be significantly affected by operating temperatures. Aktlvltlit von Chromoxld und Phasenbezlehungen 1m System CaO-SIOz-CrOx bel 1873 K unter schwach reduzlerenden Bedlngungen. Zur Optimierung der Schlackenzusammensetzung bei der Entkohlung nichtrostender Stahle wurden die Aktivitat von Chromoxid aCrO, und die Phasenbeziehungen im Systems CaO-Si02-CrOy unter schwach reduzierenden Bedingungen ( P02 = 7.04 010-6 Pal bei 1873 K untersuchl. Die Aktivitatskoeffizienten der Chromoxide hang en stark von der Basizitat, dargestellt durch XCaOIXSi02, und dem Chromgehalt der Schlacke abo Die Loslichkeit der Chromoxide im Schlackensystem sinkt drastisch mit steigendem Verhaltnis steel research 70 (1999) No. 8+9

Manganese and Chromium Distribution between CaO–SiO2–MgOsat.–CrO1.5–MnO Slags and Fe–Cr–Mn Stainless Steel

“…21,23,24,42) With respect to g CrO , the basicity effect reported by these authors is consistent: they all found that g CrO increases with increasing slag basicity. This behavior is similar to that of other divalent transition metal oxides, such as FeO, MnO and NiO.…”

“…For example, Pretorius and Muan 23) found that g CrO 1.5 decreases sharply in acid melts with increasing slag basicity and levels off at a mass% CaO/mass% SiO 2 ratio of around 0.7 in the CaO-SiO 2 -CrO x -Al 2 O 3 system at 1 783 K and at 10 Ϫ9.56 atmϽp O 2 Ͻ 10 Ϫ12.5 atm. On the other hand, for the CaO-SiO 2 -CrO x system at p O 2 ϭ6.95 · 10 Ϫ11 atm and at 1 873 K, Morita et al 21) observed a continuous increase of g CrO 1.5 in a C/S ratio (X CaO /X SiO 2 ) range between 0.6 and 1.5. Also Pei et al 24) investigated a CrOx in the CaO-SiO 2 -Al 2 O 3 -MgO sat.…”

“…The thermodynamic behavior of CrO x was intensively investigated in the CaO-SiO 2 -CrO x 20,21) ternary, in the CaOSiO 2 -Al 2 O 3 -CrO x quaternary 22,23) and in the CaO-SiO 2 -Al 2 O 3 -MgO-CrO x 22,24,25) and the CaO-SiO 2 -Al 2 O 3 -FeOCrO x 26) quinaries, under different oxygen partial pressures and at temperatures ranging from 1 783 to 1 923 K. In these studies, the activities of CrO x and the oxidation state of Cr in the molten slag were discussed as a function of slag composition, temperature and oxygen partial pressure.…”

“…Mn and Cr losses can be minimized by the use of slags with high MnO and CrO x activities at low concentrations of MnO and CrO x . Many studies have been reported on the thermodynamics of the individual Mn [7][8][9][10][11][12][13][14][15][16][17][18][19] and Cr [20][21][22][23][24][25][26] equilibria. There are many data available on the MnO activity in the MnO-SiO 2 7) and the MnO-FeO 8,9) binaries, in the CaOSiO 2 -MnO 10,11) and the FeO-MnO-MO x (MO x ϭSiO 2 , Al 2 O 3 ) [12][13][14] ternaries, in the FeO-MnO-MgO-SiO 2 , 15) MnO-CaO-MgO-SiO 2 16) and MnO-SiO 2 -CaO-Al 2 O 3 17) quaternaries, in multi-component steelmaking slags (CaOSiO 2 -MnO-Fe t O-P 2 O 5 -MgO sat.…”

Standard Gibbs Free Energy of Formation of MnO-saturated MnO Cr2O3 Solid Solution at 1873K.

“…)-Gas system, using the thermodynamic properties of manganese and chromium in molten copper [9][10][11][12][13][14][15] summarized in Table 1(b), the standard Gibbs free energy change of the Reaction (2) in case of MϭCu, DG°2 ,MϭCu , and DG°f , MnO · Cr 2 O 3 were determined from the experimental results for this system. In case of this system, the dissolved chromium, oxygen and carbon in copper phase are so dilute that the terms of their interaction can be neglected.…”