Characterization of FeNi3 alloy in Fe–Ni–O system synthesized by citric acid combustion method

Fe–Ni–O samples, with Fe/Ni ratio ranging from 2 to 1/3, were synthesized. Samples synthesized with and without citric acid in the precursor were compared and it was found that the addition of citric acid is the necessary condition for FeNi3 formation; it was found that FeNi3 alloys were formed in these samples even when calcined in an air atmosphere. X-ray diffraction and X-ray photoelectron spectroscopy measurements were used to characterize the samples. Because of the existence of FeNi3 alloys, Fe–Ni–O samples showed strong reactivity to NO and NO + O2 but were inert to O2 alone.