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 CO(2)Z were investigated over a range of temperatures. SrM and Ba-M began to form by 750 and 800 degreesC respectively, giving pure SrM and BaM phases at 900 and 1000 degreesC. The Z phase formed at 1250 degreesC, and only after the full crystallisation of the M and Y phases at 1000 degreesC. 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 degreesC, with no loss of alignment, and were appeared sintered (similar to 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 degreesC, and ferrite formation was delayed until the halides were lost. (C) 2001 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.