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2 Materials Science Poland

2 2005

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Carburisation of nanocrystalline iron with ethylene

100%

Narkiewicz U. , Kucharewicz I. , Arabczyk W. , Lenart S.

tom Vol. 23, No. 4

939--946

The carburisation of nanocrystalline iron with ethylene has been studied. The carburisation processes were carried out under atmospheric pressure, under the flow of pure ethylene or ethylene-hydrogen mixture at a constant temperature in the range of 310-550 °C. The process was controlled using a spring thermobalance and cathetometer, with the accuracy of 0,1 mg. The phase composition of the samples after carburisation was determined by means of X-ray diffraction (XRD). As a result of the carburisation of nanocrystalline iron with ethylene, the formation of iron carbide Fe3C occurs, followed by the formation of carbon deposits. Under a C2H4/H2 gas mixture, these two reaction steps can be separated, while under pure ethylene the reactions are much faster and the simultaneous formation of iron carbide and carbon deposits is observed. Depending on temperature and on the carburisation degree, various forms of carbon deposits can be observed using TEM: spherical, helicoidal, and nanotubes. The diameter of these carbon forms is below 100 nm.

FMR study of agglomerated nanoparticles in a Fe3C/C system

75%

Guskos N. , Typek J. , Maryniak M. , Narkiewicz U. , Kucharewicz I. , Wróbel R.

tom Vol. 23, No. 4

1001--1008

Three samples with various Fe3C/C ratios have been prepared by the carburisation of iron with ethylene or an ethylene-hydrogen mixture. Carburisation was controlled with thermogravimetry. After carburisation, the samples were characterized using XRD and scanning electron microscopy. XRD measurements have shown the presence of the Fe3C (cementite) phase only. The mean size of cementite crystallites estimated using Scherrer's equation was in the range of 40-46 nm. Ferromagnetic resonance (FMR) absorption signals were investigated at room temperature. In all samples an asymmetric, very broad, and intense FMR line shifted toward low magnetic field was recorded. The linewidth, intensity, and position of the resonance field depended strongly on carbon concentration. With increasing carbon concentration the linewidth and integrated intensities of the FMR spectra decreased, and the resonance line shifted towards higher magnetic fields. The separation of granules from each other by carbon could drastically influence the FMR absorption spectrum due to decreasing intergranular interaction with increasing carbon concentration.