Novel Insights Regarding the CA_6 Formation in Cement-Bonded Spinel Refractory Castables

摘要

Previous microstructural development during sintering is barely considered when studying the different corrosion mechanisms of cement-bonded castables containing in situ or pre-formed spinels (MgAl_2O_4), as it is assumed to be the same regardless of the spinel incorporation route. Calcium hexaluminate (CaO.6Al_2O-3 - CA_6), for instance, is usually associated as the straightforward product reaction between alumina and CA_2 (CaO.2Al_2O_3). However, additional CA_6 formation routes involving CMA (CaO-MgO-Al_2O_3) phases [CaMg_2Al_(16)O_(27) (CM_2A_8) and Ca_2Mg_2Al_(28)O_(46) (C_2M_2A_(14)] were reported in the literature, but were never evaluated in the refractory field. In order to better understand the role of spinel in the CA_6 development in cement-bonded castables, the present work addresses an in-depth microstructural evolution analysis of high-alumina castables containing in situ or pre-formed spinels. According to the results, CA_6 formation takes place by the decomposition reaction of CM_2A_8 and, consequently, its distribution throughout the microstructure after the thermal treatment was fully affected by the previous spinel grain location. This different route plays a key role in the slag resistance behavior, pointing out the importance of understanding the correct microstructural evolution.