The rate constant of C02 dissociation on the surfaces of CaO-Si02' CaO-Al203' CaO-Si02-CaF2and CaO-Si02-Fe.Oslags was measuredby means of a 13C02-CO isotope exchangetechnique as functions of slag basicity, iron content, temperature and imposed equilibrium C02/CO ratio, It was shown that CaOSi02-Fe*O slags with low iron content and those with high iron content had different rate determining steps, According to those rate determining steps, the apparent rate constant, k., was ca]culated for each slag. Consequently, we obtained the equations: k. =k(1 -~iei) and k.=k(1 -~iei) ( If weassume that the dissociation of adsorbed C02 on the surface of slag controls an overall reaction, with the adsorption equilibrium for C02and CO, reactions (4) and (6) that the reverse rate of reaction (7) may be negligible.Therefore, the measurement of the forward rate of reaction (7) mol~1)) is the gas constant. AP*3c0= and (P*3co)*q are the partial pressure decrease of P*=c02 by reaction (7) and the partial pressure of P*3co when the complete isotope exchangeequilibrium was achieved, respectively. Hereafter, the left hand side of Eq. (9) will be represented by k* as the apparent forward rate constant.2.2. Experimental ArrangementThe experimentai arrangement is shown in Fig. l Fig. 8.

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

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