Formation mechanism of connected polycrystalline iron fibres by pyrolysis of iron carbonyl in magnetic field

Abstract

Polycrystalline iron fibres (PIFs) can be prepared by pyrolysis of iron carbonyl in a magnetic field, but some of them usually combine. In the present work, the formation mechanism of connected PIFs has been studied by varying magnetic field intensity, feed volume and feed rate. The results reveal that the weight percentage of connected PIFs can be reduced by increasing the magnetic field intensity, increasing the feed rate and, especially, decreasing the feed volume. This is because the process is one of 'space confined growth', and only when the feed volume is reduced below a threshold can the concentration of connected fibres be markedly suppressed. In addition, this threshold increases with increasing magnetic field intensity, because this change preferentially aids the growth of original or new single fibres. The average diameter of single PIFs also decreases greatly with a reduction in percentage of connected fibres. An average diameter of 0·40 μm can be obtained with the amount of connected fibres reduced below 2·0 wt-%.