The carburisation of iron is known as a method to improve the hardness of steel. The iron carbide itself can be applied for example for the production of sensors or magnets. It is also an intermediate product in the formation of carbon deposit obtained in the reaction of hydrocarbons with iron.
The aim of this study is to investigate the carburisation mechanism in the interval of carbon concentration below that corresponding to the iron carbide formation.
The nanocrystalline iron (mean size of crystallite-17 nm) iron promoted with small amount of oxides (Al2O3, CaO, K2O) was used in the experiments. The grain fraction of 1,2~1,5 mm was taken. The decomposition of methane has been studied in the temperature range of 400 to 5500C under atmospheric pressure. The mass change of the sample was measured using spring thermobalance and cathetometer, with the accuracy of 0,0001g. The phase composition after carburisation process was characterized using X-ray diffraction and Moessbauer spectroscopy.
At the beginning of the carburisation process the measured increase of the sample mass does not correspond to the determined iron carbide content. The formation of the thin carbon layer on the iron surface is suggested for this area, connected with diffusion of iron atoms to this layer to form on intercalated iron~graphite compounds.