The reaction of lanthanum nitrate with metallic oxides that can be present in the oxide scales formed at elevated temperatures on the surface of stainless steel has been investigated as model systems of the processes occurring during the oxidation of lanthanum coated stainless steel. X-ray diffraction (XRD) experiments have shown that LaCrO3 and LaFeO3 are the most stable compounds. XRD, chemical analysis and thermogravimetric experiments have demonstrated that in the case of Cr2O3, nitrate anions are able to oxidize Cr(III) to Cr(VI) resulting in a precursor phase of perovskite structure that influences the corrosion inhibition of stainless steel at high temperatures.