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Due to the lack of relevant in situ characterization techniques, the investigation of aluminum sol–gel progress is lacking. In this study, combined with molecular dynamics simulation and conventional experimental methods, the microstructures, rheological properties, and gelation process of the carboxylic aluminum sol system were studied. The experimental results showed that, with the increase in solid content, the microstructure of the colloid developed from a loose and porous framework to a homogeneous and compact structure. The viscosity of aluminum sol decreased significantly with the increase in temperature, and a temperature above 318 k was more conducive to improving the fluidity. The simulation results show that the increase in free volume and the connectivity of pores in colloidal framework structure were the key factors to improve fluidity. In addition, free water molecules had a higher migration rate, which could assist the rotation and rearrangement of macromolecular chains and also played an essential role in improving fluidity. The Molecular dynamics simulation (MD) results were consistent with experimental results and broaden the scope of experimental research, providing necessary theoretical guidance for enhancing the spinning properties of aluminum sol. [ABSTRACT FROM AUTHOR]

In‐depth studies of the structure of precursor sols is very important for understanding the subsequent sol to gel transition. Here, density functional theory was applied to study the reaction of Al powder with formic and acetic acid in aqueous solution to find the structure of Al(III) complex in precursor sols. The Al3+ ion obtained by dissolving Al powder in aqueous solution of formic and acetic acid would preferentially coordinate with water molecules to form aluminum hydrates. As the reaction energy barrier of aluminum hydrates with CH3COO− and HCOO− was comparable, both aluminum formoacetate and other aluminum carboxylate monomers could be obtained. Most Al(III) complexes formed by other carboxylate monomers were similar to that prepared from aluminum formoacetate. However, some Al(III) monomers and Al(III) dimer with different structural characteristics might be detrimental to the formation of linear polymers. The formation of other aluminum carboxylate monomers had great influence on the structure of precursor sols. [ABSTRACT FROM AUTHOR]

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-Al 2 O 3 ceramic fibres with good morphology, small grains and uniform diameter distribution were obtained after calcination at 1200 °C. [ABSTRACT FROM AUTHOR]

Abstract In this work, we reported the synthesis of monophasic boron-containing mullite (MBM) fibers using basic aluminum acetate (BAA) and tetraethyl orthosilicate (TEOS) as starting materials and performed a comparative study between our newly synthesized MBM and commercial Nextel™ 312 fibers. The morphology and the tensile strength are investigated for the new MBM fibers. Continuous and uniform green fibers with a smooth surface were produced via hand drawing method. After the pyrolysis process, amorphous inorganic MBM fibers with a tensile strength of 1.18 ± 0.17 GPa were obtained. After various heat treatment processes (1000–1400 °C for 1.5 h), we found the mullite formation temperature is within the temperature range from 1050 to 1075 °C for both MBM and Nextel™ 312 fibers. However, the results show that the MBM fibers fabricated in this study have a better thermal stability than Nextel™ 312 fibers despite the fact both have the same chemical composition. The improved stability of our MBM fibers is owing to their higher Al 4 B 2 O 9 formation temperature and lower Al 18 B 4 O 33 decomposition rate in comparison to those of Nextel™ 312 fibers. Moreover, the newly synthesized MBM fibers have more stable microstructure and less loss in tensile strength at elevated temperatures. [ABSTRACT FROM AUTHOR]