Growth of γ′-Fe₄N and γ-Fe ultrafine powders synthesized by laser-induced pyrolysis of mixtures of Fe(CO)₅and NH₃

With iron pentacarbonyl (Fe(CO)₅) and ammonia (NH₃) as precursors, the growth of ultrafine particles of γ′-Fe₄N (size 10-30 nm) and γ-Fe (size 30-100 nm) occurred in the high-temperature reaction zone induced by a cw CO₂ laser. The prepared particles were characterized by transmission electron microscopy, Mössbauer spectroscopy and X-ray diffraction. It was found that a lower synthesis temperature was favorable to the formation of fcc γ′-Fe₄N, and a higher temperature favored the formation of γ-Fe. In addition, the synthesis temperature has a strong effect on the structures and morphologies of y-Fe and γ′-Fe₄N particles. The growth mechanisms of γ′-Fe₄N and γ-Fe particles are discussed.