Production of rare-earth orthoferrite ceramic fibres by aqueous sol-gel blow spinning process

Rare-earth orthoferrite, LnFeO3 (Ln=La, Sm, Gd, Dy, Er and Yb) ceramic fibres were produced by aqueous sol-gel blow spinning process at low-temperatures. Stable, charge stabilised, colloidal precursor sols of orthoferrites were prepared by room temperature processing of inexpensive and commercially available metal salts. The average diameter (Zav) of the colloidal sol particles was in the range 4–7 nm and had a narrow size distribution. The sols were concentrated, combined with spinning aids, and processed further to a viscous ‘spinning solution’. The gel fibres of about 6 μm diameter were blow spun, collected as random fibres, dried and heated to increasingly higher temperatures at a rate of 50 °C/h. The gel fibres converted to flexible ceramic fibres, and single-phase perovskite structure crystallised directly for all the LnFeO3 (Ln=La, Sm, Gd, Dy, Er and Yb ) fibres on heating them to 700 °C. The ceramic fibres had mean diameter of about 3–4 μm, and consisted of randomly oriented submicron sized grains.