Densification of porous alumina by CrO3 infiltration was investigated on model composites containing a sapphire interface. Gas-solid deposition of Cr2O3 from CrO3 source on sapphire and glass at 600 degrees C was also investigated. The deposited Cr2O3 layers were characterized using X-ray diffraction and transmission electron microscopy. It was found that similar to gas-phase deposition on sapphire, in CrO3-infiltrated porous alumina Cr2O3 grows epitaxially on adjacent alumina surfaces, suggesting a gas-solid condensation mechanism. The deposition rate and morphology of the Cr2O3 film deposited on alumina depend strongly on the crystallographic orientation.