Thermodynamic evaluation of spinel containing refractory castables corrosion by secondary metallurgy slag A.P. Luz a, * , A.G. Tomba Martinez b , M.A.L. Braulio a , V.C. Pandolfelli a a Federal University of Sa ˜o Carlos – Materials Engineering Department, Rod. Washington Luiz, km 235, Sa ˜o Carlos – SP, C.P. 676, CEP 13565-905, Brazil b Materials Science and Technology Research Institute (INTEMA), Ceramics Division, Av. Juan B. Justo 4302, (7600) Mar del Plata, Argentina Received 24 July 2010; received in revised form 23 October 2010; accepted 28 November 2010 Available online 21 January 2011 Abstract This work addresses the thermodynamic evaluation of different spinel-containing refractory castable compositions in contact with a basic steel ladle slag (CaO/SiO 2  9). The main differences among the castable compositions were the amount of silica fume (0 or 1 wt%), the binder source (calcium aluminate cement or hydratable alumina) and the spinel incorporation route (in situ or pre-formed). The interaction of the liquid slag with the refractory was carried out with the help of thermodynamic software (FactSage) and the applied methodology considered the changes in the slag composition due to the interaction with the castable. The theoretical results were compared with the experimental data attained by corrosion cup- tests, pointing out that the thermodynamic calculations were suitable for predicting various aspects observed in the corroded samples by SEM. Therefore, the equilibrium simulations led to parameters that indicated the corrosion resistance trends, complementing the experimental evaluation and reducing further experimental testing. # 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Keywords: C. Corrosion; Spinel containing castables; Thermodynamic simulation; Spinel 1. Introduction Corrosion of spinel containing castables has been exten- sively studied [1–6]. Nevertheless, although work has been reported on the dissolution of Al 2 O 3 into lime–alumina–silica slags [7–9], information regarding the reaction mechanisms and the characterization of the formed phases in the refractories microstructure at high temperatures is rather limited. Al 2 O 3 –MgAl 2 O 4 refractory castables present higher resis- tance to structural spalling than high alumina or basic castables due to their lower slag penetration. Refractory compositions in this system can be designed based on adding [9,10]: (a) coarse pre-formed spinel grains as aggregates, (b) fine pre-formed spinel as one of the constituents of the castable matrix, and (c) MgO and Al 2 O 3 fines in order to generate the in situ spinel phase. Some authors [1,5] stated that fine spinel, formed in situ by the reaction of MgO and Al 2 O 3 in the castable matrix, increases the slag penetration resistance when compared to pre- formed spinel containing ones. The positive effect of the in situ spinel formation on the refractory corrosion performance is still under discussion in the scientific literature. Sarpoolaky et al. [9] consider that the corrosion resistance of the spinel containing castables is mainly associated with the extensive interlocking between calcium hexaluminate (CaO6Al 2 O 3 – formed due to the transformations and reactions of the calcium aluminate cement used as the bonding additive) and corundum or spinel grains in the matrix of the castables. On the other hand, because the slag is the most reactive component in the melt, its composition has a critical effect on the corrosion mechanism of the Al 2 O 3 –MgAl 2 O 4 refractories [1,10]. The current knowledge and understanding of the reaction sequences involved in the dissolution of alumina and spinel in the molten slags, particularly the nature of the various formed phases at the slag/castable interface and their stability regarding the slag composition and heat treatment temperature, are far from being complete [7,11]. Due to these aspects, an alternative to understand the reaction and corrosion mechanisms of the spinel containing castables and to predict their phase evolution at a high temperature is the thermodynamic calculations. The FactSage www.elsevier.com/locate/ceramint Available online at www.sciencedirect.com Ceramics International 37 (2011) 1191–1201 * Corresponding author. Tel.: +55 16 33518253; fax: +55 16 33615404. E-mail address: anapaula.light@gmail.com (A.P. Luz). 0272-8842/$36.00 # 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved. doi:10.1016/j.ceramint.2010.11.043