Synthetic slags with compositions representative of carbonaceous feedstock derived from coal and petroleum coke were infiltrated into 90% Cr2O3-10% Al2O3 refractory material with a temperature gradient induced along the penetration direction of the slag. Experiments were conducted with a hot-face temperature of 1723 K (1450 degrees C) in a CO/CO2 gas mixture with a ratio of 1.8, which corresponded to an approximate oxygen partial pressure of 10 (8) atm. Interactions between the slags and the refractory produced solid-solution spinel layers on the top interfaces of the refractory samples, whose chemistries reflected the compositions of major constituents of the starting slags. FeCr2O4 formed when samples were infiltrated with slag composition rich in FeO, which was typical for coals derived from eastern USA. (Mg, Fe)Cr2O4 formed when samples were infiltrated with slags, containing considerable concentrations of both MgO and FeO that were common in western US coals. In slags resulted from substituting 50% (by weight) of the coal feedstock by petcoke, similar solid solution phases formed as the pure coal counterparts, but with addition of V2O3, which originated from the petcoke feedstock. The chromium spinel layers, to a reasonable extent, limited infiltration by hindering the slag from flowing into the porous microstructure of the refractory and the formation mechanisms of the product layers were discussed. The Fe(Cr,V)(2)O-4 layer that formed in the presence of petcoke ash exhibited an uneven morphology. As compared to the FeO rich slags, MgO rich slags penetrated further beyond the protective layers and into the refractory. Both of these phenomena could lead to increased refractory spallation rates in actual gasification conditions. (C) 2013 Elsevier Ltd. All rights reserved.