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Luz A.P.,Federal University of Sao Carlos | Martinez A.G.T.,Materials Science and Technology Research Institute INTEMA | Braulio M.A.L.,Federal University of Sao Carlos | Pandolfelli V.C.,Federal University of Sao Carlos
Ceramics International | Year: 2011

This work addresses the thermodynamic evaluation of different spinel-containing refractory castable compositions in contact with a basic steel ladle slag (CaO/SiO2 ∼ 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.


Luz A.P.,Federal University of Sao Carlos | Braulio M.A.L.,Federal University of Sao Carlos | Martinez A.G.T.,Materials Science and Technology Research Institute INTEMA | Pandolfelli V.C.,Federal University of Sao Carlos
Ceramics International | Year: 2011

The chemical corrosion of two Al2O3-MgO castables (containing distinct binder sources: hydratable alumina or calcium aluminate cement) were evaluated in this work via thermodynamic calculations. Two simulation models were proposed according to the following procedures: (1) firstly the matrix and later the aggregates of the castables were placed, separately, in contact with an industrial basic slag, and (2) the overall chemical composition of the design castables was directly reacted with the molten slag. The theoretical results were further compared with experimental data collected after corrosion cup tests. Although the thermodynamic evaluation of the overall castable compositions was able to identify the phase transformations correctly, a two-step analysis of the matrix components and aggregates particles seems to be the best alternative to evaluate the binder source effect on the corrosion performance of the two Al2O 3-MgO refractory materials. © 2011 Elsevier Ltd and Techna Group S.r.l.


Tomba Martinez A.G.,Materials Science and Technology Research Institute INTEMA | Luz A.P.,Federal University of Sao Carlos | Braulio M.A.L.,Federal University of Sao Carlos | Pandolfelli V.C.,Federal University of Sao Carlos
Ceramics International | Year: 2015

This work focuses on the evaluation of the corrosion behavior of Al2O3-MgO cement-bonded castables based on thermodynamic calculations, in order to understand the reaction steps and some scientific and technological issues that still need to be better explained when such materials come into contact with basic industrial slags at high temperatures. Special attention was given to analyzing the role played by the calcium hexaluminate phase (CA6) during the first heating stage of the samples and their further chemical attack. Experimental measurements (cup tests at 1500 °C) and thermodynamic simulations were carried out considering a basic slag (CaO/SiO2=4.2) and four refractory castables with different spinel (MgAl2O4) sources (pre-formed or in situ) and with or without silica fume (0 or 1 wt%). Considering the attained results, a novel corrosion mechanism is proposed pointing out that a suitable design of the castable compositions can induce the formation of CA6 at the border of the coarse aggregates, preventing their further dissolution and increasing the overall wear resistance of these refractories. In Addition, incorporating optimized contents of silica fume and cement to the spinel-containing castables helps to master the generation of the CA6 and CA2 protective layers, resulting in a lower chemical attack at high temperatures. © 2014 Elsevier Ltd and Techna Group S.r.l.


Martinez A.G.T.,Materials Science and Technology Research Institute INTEMA | Luz A.P.,Federal University of Sao Carlos | Braulio M.A.L.,Federal University of Sao Carlos | Pandolfelli V.C.,Federal University of Sao Carlos
Ceramics International | Year: 2012

Alumina-magnesia refractory castables usually present silica fume in their compositions, due to their ability to induce better flowability and to compensate the expansion related to the in situ spinel formation. In this paper, four compositions containing distinct silica fume content (0-1 wt%) were designed and analyzed by creep resistance and hot mechanical strength. The θ-projection concept coupled with the thermodynamic simulations were used in order to predict the creep behavior and to identify the main mechanism leading to the deformation of the samples. Based on the collected results, a linear correlation between the creep parameters (θi) and the silica fume content was attained by analyzing the experimental data, resulting in reliable data and the likelihood to simulate the performance of other compositions in the same system. Moreover, particle sliding assisted by viscous flow was suggested as the dominant creep mechanism in the studied castables. © 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved.


Luz A.P.,Federal University of Sao Carlos | Braulio M.A.L.,Federal University of Sao Carlos | Tomba Martinez A.G.,Materials Science and Technology Research Institute INTEMA | Pandolfelli V.C.,Federal University of Sao Carlos
Ceramics International | Year: 2012

Although the in situ spinel formation in alumina-magnesia refractory castables induces an expansive behavior, many investigations highlight its positive role in the corrosion resistance of such materials. Thus, this work addresses the slag attack evaluation of four designed in situ spinel-containing castables (containing hydratable alumina or calcium aluminate cement as a binder source and 0 or 1 wt% of silica fume) when in contact with a Fe xO rich industrial slag. Corrosion cup-tests, microstructural characterization and a two-step thermodynamic simulation model were used in order to investigate the reactions taking place during the slag-refractory interactions. According to the attained results, hydratable alumina seems to be a suitable binder to improve the corrosion resistance of such castables, as it induces densification and the formation of an alumina-rich spinel phase at the slag-matrix interface. Moreover, the thermodynamic calculations matched to the experimental observations, attesting the efficiency of the proposed simulation model for the evaluation of the in situ spinel-containing castable corrosion behavior. © 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

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