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

A stable iron(lll)hydroxide sol was produced, spun as a gel fibre and colle cted as an aligned tow blanket. The alignment of the fibre was found to be 88.8% within +/-20 degrees of the axis of alignment, comparable to that of some commercially developed ceramic fibres. Heating in air at a temperature of 250 degrees C for 1 hour yielded single phase haematite fibres, and the se were characterised by X-ray diffraction and electron microscopy. Upon re duction of the gel fibre in 5% H-2 in N-2 at 350 degrees C for 1 hour, sing le phase magnetite was obtained and characterised by X-ray diffraction, inf rared and Mossbauer 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 w as an accompanying change in microstructure. The strain to break of the mag netite fibres was measured to be of a least 0.6%, and this compares well wi th some commercial fibres. (C) 1998 Kluwer Academic Publishers.