Materials Science and Technology Research Institute INTEMA

San Justo, Argentina

Materials Science and Technology Research Institute INTEMA

San Justo, Argentina
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Tomba Martinez A.G.,Materials Science and Technology Research Institute INTEMA | Luz A.P.,Federal University of São Carlos | Braulio M.A.L.,Federal University of São Carlos | Sako E.Y.,Saint - Gobain | Pandolfelli V.C.,Federal University of São Carlos
Journal of the European Ceramic Society | Year: 2017

This work revisits the proposed mechanisms presented in the literature for CA6 formation in Al2O3-MgO and Al2O3-MgAl2O4 castables bonded with calcium aluminate cement. New experimental tests, thermodynamic simulations and re-evaluation of the chemical composition and microstructural aspects observed for samples fired in the temperature range of 1150°C to 1500°C were carried out. Based on these data, a new interpretation of the CA6 generation process, as well as the features which influence the location and morphology of this phase were proposed. CA6 formation via solid and liquid states are suggested to take place in all evaluated compositions, where the former (solid-state) is the main reaction predicted for the silica-free refractories (AM0MS and AS0MS), whereas the liquid-state one prevails in the AM1MS and AS1MS materials. The CA6 crystal morphology should be affected by these different reaction mechanisms. According to the experimental results, it was also discussed the role of the calcium hexaluminate features in the overall corrosion behavior of the designed refractories when they were placed in contact with molten slag at high temperatures. Such aspects have not been previously reported in published papers related to this subject. © 2017 Elsevier Ltd.


Luz A.P.,Federal University of São Carlos | Martinez A.G.T.,Materials Science and Technology Research Institute INTEMA | Braulio M.A.L.,Federal University of São Carlos | Pandolfelli V.C.,Federal University of São 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.


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

The better performance of spinel-containing refractory castables when in contact with basic slag is mainly associated with their higher corrosion resistance. Although the literature has shown various studies related to this subject, only few of them evaluated the overall microstructural effect on the corrosion resistance. Considering this aspect, four different compositions were produced, in order to evaluate the binder source influence (calcium aluminate cement or hydratable alumina), the silica fume addition and spinel incorporation method (in situ or pre-formed) effects. Based on the physical properties (apparent porosity, linear thermal expansion and pore size diameter distribution) and also on the phases generated (detected by SEM, before and after corrosion), a basic slag corrosion mechanism, for the set conditions, is proposed. The results pointed out that lower penetration can be attained by reducing the pore size diameters, whereas chemical corrosion resistance is a consequence of higher content of fine alumina, lower amount of calcium aluminates and the lack of liquid phase in the castable matrix. This study stresses that the castable formulation design and the proper raw material selection are of utmost importance to understand and master the performance of this class of refractory castables. © 2011 Elsevier Ltd and Techna Group S.r.l.


Luz A.P.,Federal University of São Carlos | Braulio M.A.L.,Federal University of São Carlos | Martinez A.G.T.,Materials Science and Technology Research Institute INTEMA | Pandolfelli V.C.,Federal University of São 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.


Luz A.P.,Federal University of São Carlos | Braulio M.A.L.,Federal University of São Carlos | Tomba Martinez A.G.,Materials Science and Technology Research Institute INTEMA | Pandolfelli V.C.,Federal University of São 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.


Martinez A.G.T.,Materials Science and Technology Research Institute INTEMA | Luz A.P.,Federal University of São Carlos | Braulio M.A.L.,Federal University of São Carlos | Pandolfelli V.C.,Federal University of São 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.


Tomba Martinez A.G.,Materials Science and Technology Research Institute INTEMA | Luz A.P.,Federal University of São Carlos | Braulio M.A.L.,Federal University of São Carlos | Pandolfelli V.C.,Federal University of São 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.


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

Abstract This work addresses the main aspects related to the use of alternative binders [hydratable (HA) or colloidal alumina (ColAlu)] in castables containing different spinel sources (pre-formed or in situ generated), in order to point out: (i) the features that control the corrosion behavior of these materials, and (ii) the key factors to better select a refractory composition. Thermodynamic calculations, corrosion cup-test and SEM analyses were carried out in order to evaluate the slag attack of the designed refractory compositions. According to the attained results, the alumina-based binders (HA or ColAlu) induced a more effective sintering process due to their high specific surface area, improving the physical properties and the binding level of the generated microstructure. The spinel grain size also played an important role in the corrosion behavior of these refractories, as the finer the particles, the greater their dissolution was into the molten liquid, leading to further precipitation of spinel in the solid-liquid interface as a continuous and thick layer. Among the evaluated compositions and considering the presence of silica fume, the most suitable formulation with optimized corrosion resistance was the one with in situ spinel generation and HA as a binder. © 2015 Elsevier Ltd and Techna Group S.r.l.

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