Nanocrystalline α–Fe, Fe₃C, and Fe₇C₃ produced by CO₂ laser pyrolysis

Abstract

Nanocrystalline α–Fe, Fe3C, and Fe7C3, particles with narrow size distributions were produced by CO2 laser pyrolysis of vapor mixtures of Fe(CO)5 and C2H4. Details of the synthesis procedure are discussed. Mossbauer spectroscopy and x-ray diffraction were used to identify the structural phases and the former was used also to study the magnetism of the nanoparticles. All the nanoparticles were observed to be ferromagnetic in this size range. If excess C2H4 appears in the reactant gas mixture, several monolayers of pyrolytic carbon were observed to form on the particle surface, as deduced from transmission electron microscopy and Raman scattering studies. Results of thermo-gravimetric analysis/mass spectroscopy studies of this carbon coating indicate it is gasified in hydrogen at temperatures T ∼ 250 °C.

Impact of Fe Content in Laboratory-Produced Soot Aerosol on its Composition, Structure, and Thermo-Chemical Properties

“…Cementite Fe 3 C is one of the most abundant Fe carbides and would exhibit a signal at ∼708.3 eV, which could interfere with the signals of Fe (III) (Shabanova and Trapeznikov 1975;Bonnet et al 2002). It is known, that Fe 3 C forms by CO 2 laser pyrolysis of Fe(CO) 5 and C 2 H 4 (Bi et al 1993). The low energy shoulder of the Fe2p 3/2 peak in the spectrum of the soot type with 53% (m/m) Fe even extends to 707-706 eV and thus, minor amounts of metallic Fe (0) cannot be ruled out completely (srdata.nist.gov/xps).…”

Structural, electronic, and magnetic properties of iron carbideFe7C3phases from first-principles theory

“…On the other hand, h structure ͑or a pseudohexagonal lattice͒ was often observed in the crystallization of amorphous alloys [1][2][3] and carburization of iron. [9][10][11][12][13] It is well known that complex processes such as nucleation and growth of a carbide in amorphous alloys, carburization, and precipitation in steels depend on many factors, such as chemical composition, thermal history, temperature, and interface interactions with the other phases. Our calculations show that the o-Fe 7 C 3 has a more stable Fe sublattice and may contain carbon ͑vacancy͒ defects.…”

“…27 On the other hand, it has been reported that carburization of ferrite will produce mainly nanosized particles of h-Fe 7 C 3 from chemically produced C clusters. [9][10][11][12][13] For the nanocrystals obtained by methods such as carburization of iron, the defects causing the formation of different Fe 7 C 3 lattices may not be observed by methods such as x-ray diffraction. Audier and co-workers obtained microcrystals of o-Fe 7 C 3 by disproportioning CO on Fe at 500°C, 14 suggesting that the h phase transformed into the o phase ͑through stacking fault generation͒ as the nanoparticles increase in size.…”

“…6 Fe 7 C 3 forms also as nanoparticles by means of high-pressure techniques [7][8][9] or by carburization of ferrite. [10][11][12][13] Audier and co-workers obtained Fe 7 C 3 microcrystals by disproportioning CO on Fe at 500°C.…”

Temperature dependence of FMR spectrum of Fe3C magnetic agglomerates

“…Temperature dependence of FMR spectrum of Fe 3 C magnetic agglomerates 1. Introduction Nanocrystalline iron carbide Fe 3 C (cementite) is a very important compound for potential applications in catalysis, gas sensors and in possible reduction of the cost required to produce bulk quantities of metallurgical materials [1][2][3][4][5].…”