In cement production, which involves the production of cement clinker in rotary kilns, the main refractories used are magnesia-spinel bricks. These bricks may suffer infiltration by the clinker liquid phase, resulting in the corrosion of the spinel and the formation of low refractoriness mineralogical phases, such as the Q phase (C 20 A 13 M 3 S 3 ), which compromises refractory performance. Thus, the aim of this work is to correlate the infiltration resistance of magnesia-spinel bricks made from different grades of magnesia by clinker collected in three different cement plants (A, B and C). The purity of magnesia, besides its physical properties, strongly influences the properties and the infiltration resistance of magnesia-spinel bricks; as such the use of high grade magnesia is essential for producing high performance refractories.

ResumoRefratários MgO-C encontram-se entre os mais adequados para o uso na linha de escória de panelas para aço líquido. Seu comportamento, nesta aplicação, depende de fatores termodinâmicos e cinéticos. Métodos de cálculo termodinâmico para avaliar o potencial de degradação de refratários MgO-C por escórias e pela atmosfera são revistos brevemente. Tais métodos envolvem, em geral, premissas importantes sobre a quantidade de materiais envolvidos. Para avaliar um método mais simples, foram escolhidos dois tijolos MgO-C e duas escórias típicas do processo da CSN. Estes tijolos e escórias foram caraterizados, neste trabalho. O método apresentado consiste na realização de cálculos de equilíbrio em que a principal variável é a fração de escória em uma mistura hipotética com o refratário. Para a composição do refratário foram empregadas (a) composição média e (b) composição da matriz do tijolo. Os resultados indicam que é possível realizar previsões iniciais quanto à reatividade do refratário e determinada escória de forma simples. Os cálculos, evidentemente, não substituem testes cinéticos e testes em escala industrial, em vista da complexidade dos sistemas em questão. Palavras-chave: Refratários; Escória; MgO-C, Panelas de aço. A THERMODYNAMIC APPROACH TO THE EVALUATION OF THE BEHAVIOR OF MGO-C REFRACTORIES IN THE SLAG LINE OF STEEL LADLES AbstractMgO-C refractories are some of the most adequate for the use in the slag line of steel ladles. The behavior of these refractories in this application depend both on thermodynamic and kinetic aspects. The most common thermodynamic calculation approaches used to study this interaction are briefly reviewed. These methods depend, in general, on important assumptions about the amount of materials interacting. In order to evaluate a simpler method, two MgO-C bricks and two slags typical of CSN process were used. These bricks and slags were characterized in the present work. The thermodynamic method in question involves equilibrium calculations in which the main variable is the fraction of slag in a hypothetical mixture with the refractory. For the refractory composition, two different values were considered: the average composition and the matrix composition. The results indicate that it is possible to make preliminary predictions concerning the refractory reactivity when exposed to a given slag. These calculations, evidently, will not substitute kinetic and industrial tests, in view of the complexity of the systems in question.