With the aim of studying the wear mechanism of alumina-spinel castables, a post-mortem study was carried out on samples taken from a used electric arc furnace roof including optical microscopy (phase distribution), SEM observations (for phases not easily appreciated optically), EDAX analysis, and X-ray diffraction. Microstructural analysis confirmed the reaction of the refractory to external agents, even though there was no direct contact with liquid steel and slag. The presence of calcium oxide as fine parties on the surface of the modified castable is the most important factor regarding the degradation of the material as it causes higher reactivity on the concrete. CaO reacts with alumina and precipitates low-melting CA_2 and CA_6 products near the hot side of the roof. CA_2 reacts with silica, thereby forming gehlenite (C_2AS). A strict control of the proportion and size distribution of the spinel phase can improve the behaviour of the refractory material in service, as the addition of fine particles increases resistance to corrosion and the addition of larger particles increases resistance to thermal spalling.
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