Decomposition, shrinkage and evolution with temperature of aligned hexagonal ferrite fibres

The decomposition, shrinkage and evolution of aligned gel fibres with the stoichiometric compositions for BaM, SrM and Co2Z were investigated over a range of temperatures. SrM and BaM began to form by 750 and 800°C respectively, giving pure SrM and BaM phases at 900 and 1000°C. The Z phase formed at 1250°C, and only after the full crystallisation of the M and Y phases at 1000°C. Pure phase fibres of all ferrites were produced from stoichiometric mixes, unlike standard ceramic preparations. The fibres shrank by up to 22-23% at 1200°C, with no loss of alignment, and were appeared sintered (∼97%) by this point. The formation of the M ferrite phases seemed to occur at unexpectedly high temperatures compared to previous work on bulk sol-gel M ferrites. Halides were retained in the fibre over 800°C, and ferrite formation was delayed until the halides were lost. © 2001 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.