The manufacture and characterisation of single phase magnetite and haematite aligned fibres from an aqueous sol-gel process

A stable iron(III)hydroxide sol was produced, spun as a gel fibre and collected as an aligned tow blanket. The alignment of the fibre was found to be 88.8% within ±20° of the axis of alignment, comparable to that of some commercially developed ceramic fibres. Heating in air at a temperature of 250°C for 1 hour yielded single phase haematite fibres, and these were characterised by X-ray diffraction and electron microscopy. Upon reduction of the gel fibre in 5% H2 in N2 at 350°C for 1 hour, single phase magnetite was obtained and characterised by X-ray diffraction, infrared and Mössbauer spectroscopy. The morphology of the fibre was studied, and it was found that the transformation to magnetite was accomplished with no compromise of integrity of the fibre or its alignment, although there was an accompanying change in microstructure. The strain to break of the magnetite fibres was measured to be of a least 0.6%, and this compares well with some commercial fibres. © 1998 Kluwer Academic Publishers.