Effect of formic-acid-to-acetic-acid ratio on the structure and spinnability of aqueous aluminium sol of alumina fibre

Abstract The structure and spinnability of sol are essential for obtaining high-performance continuous alumina-based fibres. Herein, the surface electrostatic potential analysis and conventional experimental methods (X-ray diffraction, Fourier-transform infrared spectroscopy, 27Al nuclear magnetic resonance solution spectra and rheological methods) were combined to investigate and discuss the relationship between the structure and spinnability of aluminium carboxylate sols with different formic-acid-to-acetic-acid molar ratios. The results showed that the aluminium carboxylate sol structure changed with the formic-acid-to-acetic-acid molar ratio and greatly affected the sol's spinnability. The tetramer (AlO6 oligomer) products comprising two effective active carboxylate groups in the sol increased with the formic acid content, which helped form linear long-chain polymers. However, excess formic acid content led to a large increase of AlO6 monomer products that were unable to form linear long-chain polymers, which decreased the sol's spinnability. When the formic-acid-to-acetic-acid molar ratio was 1.15:0.85, the sol containing more AlO6 oligomer products had the best spinnability. Furthermore, α-Al2O3 ceramic fibres with good morphology, small grains and uniform diameter distribution were obtained after calcination at 1200 °C.