Engineered Expansion Routes for Alumina-Magnesia Castables

摘要

Alumina-magnesia refractory castables are well known for their expansive behavior which is usually associated to the in-situ spinel formation at temperatures in the range of 1000 and 1500℃. This reaction is affected by chemical and microstructural parameters such as the microsilica content and the magnesia grain size. As this class of castables is commonly bonded with calcium aluminate cement (CAC), expansive reactions involving CA{sub}2 (calcium dialuminate) and CA{sub}6 (calcium hexaluminate) must also be taken into account in the engineering expansion design. Additionally, as these reactions are mostly carried out using small particle size reactants, various studies in the literature draw attention only to the castables' matrices. Nevertheless, as the refractory aggregates comprise mostly of a castable formulation, it is also important to consider their effect on the volumetric stability of in-situ spinel castables. Considering these aspects, this work addresses an overall analysis concerning the effect of raw materials on the expansion behavior of in-situ spinel castables bond with calcium aluminate cement, in order to attain a designed expansion based on previously engineered microstructure. One route to achieve this aim was to evaluate the effect of the CAC content, which affected the CA{sub}6 formation. Furthermore, as microsilica influences spinel, CA{sub}2 and CA{sub}6 formation, its amount was another way to forecast castable expansion. Changing the magnesia grain size was an additional possibility for the engineered expansion control, as its particle size reduction resulted in a lower overall expansion. The results also pointed out that refractory aggregates can be active partners in the castables' reaction and hence must be considered when analyzing the expansive behavior. Finally, various expansion routes were attained and presented, resulting a greater flexibility design and optimization of the thermal-mechanical benefits when in-situ spinels are applied to steel ladles. Castables with a higher performance would lead to cleaner steel and a longer lining working life.