Infiltration characteristics of industrial coal slag into alumina (Al2O3) refractory material with a temperature gradient induced along the slag's penetration direction are compared to those obtained under near-isothermal conditions. Experiments were conducted with a hot-face temperature of 1450 degrees C and a CO/CO2 ratio of 1.8, which corresponds to an oxygen partial pressure of similar to 10(-8) atm. The refractory under the near-isothermal temperature profile, with higher average temperatures, demonstrated a greater penetration depth than its counterpart that was under the steeper temperature gradient. Slag that did not infiltrate into the refractory due to the induced temperature gradient, pooled and solidified on the top of the sample. Within the pool, a conglomerated mass of troilite (FeS) formed separately from the surrounding slag. Microscopy of the cross-sectioned infiltrated refractories revealed that the slag preferentially corroded the matrix regions closer to the top surface. Furthermore, the formation of a thick layer of hercynite (FeAl2O4) at the top of refractory/slag interface significantly depleted the slag of its iron-oxide content with respect to its virgin composition. A qualitative description of the penetration process is provided in this article.